The title of the talk Derek Wise is scheduled to give on Tuesday (in 5 days from now) has been posted. Here's the current ILQGS schedule as it stands so far.
Code:
DATE Seminar Title Speaker Institution
Sep 03 [B]Multiymplectic effective General Boundary Field Theory[/B] J.Zapata Morelia
Sep 17 [B]Thermality of spherical causal domains–entanglement spectrum[/B] H.Haggard Marseille
Oct 01 [B]BH entropy from LQG: higher dim. and gen. theories[/B] N.Bodendorfer PennState
Oct 15 [B]Holographic SR: observer space from conformal geometry[/B] Derek Wise Erlangen
Oct 29 TBA Asieh Karami Morelia
Nov 12 [B]What can we learn from shape dynamics?[/B] Tim Koslowski NewBrunswick
Nov 26 TBA Johannes Thürigen PotsdamAEI
Dec 10 TBA Saeed Rastgoo Morelia
http://arxiv.org/abs/1305.3258
Holographic Special Relativity
Derek K. Wise
(Submitted on 14 May 2013)
We reinterpret special relativity, or more precisely its de Sitter deformation, in terms of 3d conformal geometry, as opposed to (3+1)d spacetime geometry. ...
... We conjecture a relationship between this kind of "holographic relativity" and the "shape dynamics" proposal of Barbour and collaborators, in which conformal space takes the place of spacetime in general relativity. We also briefly survey related pictures of observer space, including the AdS analog and a representation related to twistor theory.
17 pages, 5 illustrations
Interesting find! Here is the poster, with an elaborate drawing by Penrose illustrating his CCC idea:
http://www.claymath.org/workshops/CCC/CCCposter.jpg
You can click on it to enlarge it, making it more legible.
I see that among those on the discussion panel and/or giving talks were Kris Meissner (Warsaw), George Ellis (Capetown), Ted Newman (Pittsburg). Meissner posted a paper in July presenting new statistical evidence of circular ripples in the CMB that might have emanated from events in prior aeon, thus supporting the CCC conjecture. The site has abstracts for some of the talks. Here is a partial list of titles:
9:00 Roger Penrose On CCC's motivations, equations, observational implications, and future research
10:00 Vahe Gurzadyan Positive lambda, the 2nd law and observations
11:30 Krzysztof Meissner
2:00 Paul Tod The equations of CCC
3:00 Michael Eastwood Twistors, tractors, and conformally invariant operators
4:30 Rod Gover Klein, Poincaré, and geometry at infinity
9:00 Gabriele Veneziano A bouncing cosmology from string theory's new symmetries?
10:00 Kostas Skenderis Holography and the very early universe
11:30 Tsou Sheung Tsun A theory of Fermion masses and mixing
2:00 Helmut Friedrich Existence and asymptotic behaviour of space-time with positive lambda
3:00 Lars Andersson
4:30 Tim Adamo Gravity in twistor space
9:00 Claude LeBrun
10:00 Jörg Frauendiener
11:30 Laszlo Szabados On the total mass of closed universes with positive cosmological constant
2:00 Neil Turok
3:00 George Ellis Indications that gravity is essentially a conformal theory
This semester's schedule for the International LQG Seminar was posted today.
To follow the ILQGS series, go here: http://relativity.phys.lsu.edu/ilqgs/
Links to audio and to slides PDF usually appear there around the time that the online seminar is scheduled to be given. Get the slides on a separate window before you start the audio, so you will be able to scroll through the slides along with the speaker.
==quote==
ILQGS SEMINAR SCHEDULE
SPRING 2014
Code:
1/21 [B]Matter matters in asymptotically safe quantum gravity[/B] P. Dona (Sissa)
2/4 TBA B. Dittrich (Perimeter)
2/18 TBA S. Steinhaus (Perimeter)
3/4 [B]Simplicity constraints in spin foam models[/B] M. Geiller, S. Speziale (PSU,Marseille)
3/18 [B]S-matrices for General Boundary QFT on Anti de Sitter spacetime[/B] M. Dohse (Morelia)
4/1 [B]Continuum limit and renormalization[/B] L. Freidel (Perimeter)
4/15 [B] Linking canonical and covariant LQG[/B] A. Zipfel (Erlangen)
4/29 [B]LQC and the very early universe[/B] I.Agullo, A.Barrau, G.Mena (LSU, Grenoble, Madrid)
5/13 [B]Hawking radiation in LQG[/B] J. Pullin (LSU)
1/21 [B]Matter matters in asymptotically safe quantum gravity[/B] P. Dona (Sissa)
2/4 [B]A new vacuum for loop quantum gravity[/B] B. Dittrich (Perimeter)
2/18 [B]Quantum group spin nets:refinement & relation to spin foam[/B] S. Steinhaus (Perimeter)
3/4 [B]Simplicity constraints in spin foam models[/B] M. Geiller, S. Speziale (PSU,Marseille)
3/18 [B]S-matrices for General Boundary QFT on Anti de Sitter spacetime[/B] M. Dohse (Morelia)
4/1 [B]Continuum limit and renormalization[/B] L. Freidel (Perimeter)
4/15 [B] Linking canonical and covariant LQG[/B] A. Zipfel (Erlangen)
4/29 [B]LQC and the very early universe[/B] I.Agullo, A.Barrau, G.Mena (LSU, Grenoble, Madrid)
5/13 [B]Hawking radiation in LQG[/B] J. Pullin (LSU)
Hopefully the slides PDF for the 4 Feb talk by Bianca Dittrich will be posted well in advance of the talk so one can get an idea of the topic A new vacuum for loop quantum gravity ahead of time. If and when that happens, the link might be: http://relativity.phys.lsu.edu/ilqgs/dittrich020414.pdf
The June 1-6 SIGRAV school, "Gravity and the Quantum", at a villa on the Lago di Como in Northern Italy sounds nice. Here are the introductory/survey courses being offered
QUANTUM COSMOLOGY Abhay Ashtekar
NON-COMMUTATIVE GEOMETRY AND QUANTUM GRAVITY John Barrett
BLACK HOLES Eugenio Bianchi
QUANTUM SPACE Laurent Freidel
ASYMPTOTIC SAFETY Roberto Percacci
COVARIANT LOOP QUANTUM GRAVITY Carlo Rovelli
Here are some photos of the Villa del Grumello where it is being held and the Lake Como surroundings: http://www.villadelgrumello.it
Princeton IAS will hold a one-week school focused on String Theory the week of June 16-20. This is part of the PiTP (Prospects in Theoretical Physics) annual series, aimed primarily at advanced graduate students and postdocs.
Here is the PiTP 2014 home page: https://pitp2014.ias.edu
A partial list of topics to be covered:
"Application of AdS/CFT" (Steven Gubser, Princeton University)
"Introduction to Higher Spins" (Simone Giombi, Princeton University)
"Introduction to Topological String Theory" (Hirosi Ooguri, California Institute of Technology)
"String Compactification" (To Be Announced)
"Super-Symmetric Quantum Field Theories" (Nathan Seiberg, Institute for Advanced Study)
Other lecturers will be: Nima Arkani-Hamed (Institute for Advanced Study), Igor Klebanov (Princeton University), Juan Maldacena (Institute for Advanced Study), Alexander Polyakov (Princeton University), Herman Verlinde (Princeton University), and Edward Witten (Institute for Advanced Study).
What I see at the ESQG workshop website is a list of confirmed speakers different from what just MTd2 posted:
==quote==
Talks
Confirmed speakers
Name--------- Institution
Giovanni Amelino-Camelia Sapienza, Rome
Massimo Cerdonio INFN, Padua
John Donoghue University of Massachusetts, Amherst
Astrid Eichhorn Perimeter Institute, Waterloo
Jonathan Granot Open University of Israel
John Kelley IMAPP, Radboud University, Nijmegen
Jerzy Kowalski-Glickman University of Wroclaw
Joao Magueijo Imperial College, London
David Mattingly University of New Hampshire
Jakub Mielczarek Jagiellonian University, Crakow
Igor Pikovski Vienna Center for Quantum Science and Technology
Floyd Stecker NASA - Goddard Space Flight Center
==endquote==
The fourth workshop on the Experimental Search for Quantum Gravity (ESQG) will be held in Trieste on 1-5 September http://www.sissa.it/app/esqg2014/
Since it's still 3 months off, titles of talks have not yet been announced. Here's the list of invited speakers:
Code:
Stephon Alexander Dartmouth
Giovanni Amelino-Camelia Sapienza, Rome
Massimo Cerdonio INFN - Padua
Astrid Eichhorn Perimeter Institute, Waterloo
Agnes Ferte Institut d'Astrophysique Spatiale
Julien Grain Institut d'Astrophysique Spatiale
Jonathan Granot Open University of Israel
Giulia Gubitosi Sapienza, University of Rome
Brian Keating University of California, San Diego
John Kelley IMAPP, Radboud University, Nijmegen
Jerzy Kowalski-Glikman University of Wroclaw
Joao Magueijo Imperial College, London
David Mattingly University of New Hampshire
Jakub Mielczarek Jagiellonian University, Crakow
Jonathan Miller Universidad Tecnica Federico Santa Maria
Daniele Oriti Albert Einstein Institute
Igor Pikovski Vienna Center for Quantum Science and Technology
Carlo Rovelli Aix-Marseille University
Floyd Stecker NASA - Goddard Space Flight Center
The purpose of the workshop is to bring together experimentalists, theoreticians, and phenomenologists interested in possible tests probing the quantum/discrete structure of spacetime. There will be a number of rather focussed talks discussing possible phenomenological tests of quantum gravity and proposing some new ideas in this direction.
===============
Strings 2014 is scheduled for 23-27 June at Princeton http://physics.princeton.edu/strings2014/Invited_speakers.shtml
The list of invited speakers has 74 names.
The titles of the talks have not been posted as yet.
================
The 2014 SIGRAV school "Gravity and the Quantum" was just held 1-6 June at Villa Grumello on Lake Como in Italy.
http://www.centrovolta.it/sigrav2014
Here's a list of the six courses given at the school:
QUANTUM COSMOLOGY Abhay Ashtekar
NON-COMMUTATIVE GEOMETRY AND QUANTUM GRAVITY John Barrett
BLACK HOLES Eugenio Bianchi
QUANTUM SPACE Laurent Freidel
ASYMPTOTIC SAFETY Roberto Percacci
COVARIANT LOOP QUANTUM GRAVITY Carlo Rovelli
I understand each course consisted of a series of lectures given on different days. Ashtekar's was a series of five. Links to slides for some of the talks have been posted.
=================
Anderson Hidden geometry in heterotic string and F-theory compactifications
Basso Scattering amplitudes at strong coupling beyond the area paradigm
Baumann B-modes and the Nature of Inflation
Bizon Gravitational turbulent instability of AdS5
de Boer The entropy of a hole in space-time
Bousso A Proof of the Covariant Bound
Cachazo Scattering Equations
Casini Entropy and Energy on null surfaces
Cheng Umbral Moonshine and String Theory
Chesler A holographic perspective on the Kibble-Zurek mechanism
Conlon Moduli, 0.1-1 keV Cosmic Axion Background and the Galaxy Cluster Soft Excess
Cordova Toda CFT from Six Dimensions
Cremonini Probing the structure of quantum phases of matter with holography
Dabholkar Quantum Black Holes and Quantum Holography
Dolan Amplitudes and the Scattering Equations, Proofs and Polynomials
Erdmenger Applications of AdS/CFT to high energy and condensed matter physics*
Esole Singularities and Gauge Theory Phases
Freedman Precision Tests of the AdS/CFT Correspondence
Gaiotto Topological order in N=1 Super Yang Mills theory
Gauntlett Holographic Lattices, Metals and Insulators
Gomis Sphere Partition Functions, the Zamolodchikov Metric and Surface Operators
Gopakumar From Higher Spins to Strings
Graham New methods for discovering light fields
Green Visionary
Gromov Quantum spectral curve and AdS/CFT spectral problem
Gross Visionary
Guica A toy model for the Kerr/CFT correspondence
Hanada Monte Carlo approach to string/M-theory
Hellerman String Theory of the Regge Intercept
Hubeny Holographic Entanglement
Kachru Mock Modular Moonshine for M22 and M23
Klevers Recent Progress on the Abelian Sector of F-theory
Komargodski A Cardy-like formula in four dimensions
Kovac Detection of B-mode Polarization at Degree Angular Scales with BICEP2
Kutasov ADE N=1 SUSY Dynamics
Lee,Sungjay New Exact Results on D-branes and Orientifolds in Calabi Yau Spaces
Lee,Sangmin Scattering amplitudes in three dimensions
Leigh The Exact are normalization Group and Higher Spin Holography
Liu Entanglement Tsunami
Mafra The closed-string 3-loop amplitude
Maldacena Visionary
Marchesano F-term axion monodromy inflation
Marino Non-perturbative effects in M-theory
Minahan Three-point correlators from string theory amplitudes
Moore Visionary
Murugan Meromorphic functions and the topology of giants
Neitzke A smooth R3 index for N=2 theories in four dimensions
Nekrasov Nonperturbative Dyson-Schwinger identities in gauge theories and sigma models
Papadodimas The black hole interior in AdS/CFT
Polchinski Black Hole Information: Spacetime versus Quantum Mechanics*
van Raamsdonk Gravitation from Entanglement
Raju State dependent operators and the information paradox
Rastelli The Superconformal Bootstrap
Sen Mass renormalization and vacuum shift in string theory
Silverstein The powers of monodromy
Simmons-Duffin Bootstrapping the 3d Ising Model
Staudacher N=4 Scattering Amplitudes and the Regularized Graßmannian
Steinhardt TBA
Stieberger Unity of tree–level superstring amplitudes
Strominger Visionary
Sundrum BTZ/CFT
Tachikawa Recent advances in SUSY*
Takayanagi Quantum Entanglement and Local Operators
Tomasiello New gravity duals for higher-dimensional superconformal theories
Tonni Entanglement negativity in conformal field theory
Trnka Four-point scattering from Amplituhedron
Tseytlin Strings in AdS and their deformations
Vafa On 6d SCFT's
Vasiliev Higher-rank fields and currents
Warner Resolving Black Holes via Microstate Geometries
Witten Opening Remarks
Weigand Mordell-Weil torsion and matter spectra in F-theory
Zaldarriaga The dawn of B-mode cosmology
The five "vision/outlook" talks come at the end. Green Gross Maldacena Moore Strominger. Here's the entire schedule if anyone is interested: http://physics.princeton.edu/strings2014/Scientific_Program.shtml
All the talks have 30 minute slots, except that the opening remarks get 15 minutes and three review talks get an hour each (Polchinski, Erdenmenger, Tachikawa on BH info, nonstring AdS/CFT apps, Susy status)
Plenary talks will be broadcast at http://www.princeton.edu/WebMedia/
Note: to distinguish between the two speakers named Lee, here is Sungjay Lee's profile: http://inspirehep.net/author/profile/Sungjay.Lee.1
and for Sangmin Lee:
http://inspirehep.net/author/profile/S.Lee.61
Steinhardt: "What has been learned from BICEP2?"
apparently download from menu http://physics.princeton.edu/strings2014/Talk_titles.shtml
My computer cannot open the file which is labeled "Steinhardt.pptx" and has size 28 MB.
It seems to be asking for "Office" or "OpenOffice". You may be better prepared than I, to view the slides.
Andy Strominger gave one of the 4 "vision" talks at the end of Strings 2014. His slides are online: http://physics.princeton.edu/strings2014/slides/Strominger.pdf
He lists here 74 research questions (some with hints) that he collected from colleagues who proposed them as ones which might be answered in the next 5-10 years. Plus he put in his own favorite such question: explain why S = A/(4[STRIKE]h[/STRIKE]G)
So a list of 75 including some inspiring/challenging ones. Not all are specific to Superstring/M theory and so some could be of general interest. E.g. see question #30 from Nathan Seiberg, or for that matter Strominger's own "question zero".
Peter Woit reports planned locations of future conferences: Strings 2015 will be in Bangalore, Strings 2016 in Tsinghua, Strings 2017 in Israel, Strings 2018 in Japan and Strings 2019 in Belgium.
Videos for some talks are now online.
Here's link to an excellent talk by Paul Steinhardt:
http://physics.princeton.edu/strings2014/videos/talk1h.mp4
Last edited by a moderator:
#66
Rexcirus
3
1
I want to report this:
Sapienza University of Rome 8 -12 september 2014
Conceptual and Technical Challenges for Quantum Gravity 2014
This conference will provide an opportunity for an encounter between different approaches and different perspectives on the quantum-gravity problem. Its main goal is to contribute to a higher level of shared knowledge among the quantum-gravity communities pursuing each specific research program.
We plan to have plenary talks on many different approaches, including in particular string theory, loop quantum gravity, spacetime noncommutativity, causal dynamical triangulations, asymptotic safety and causal sets. We shall also welcome contributions from the perspective of philosophy of science.
...
Sapienza University of Rome 8 -12 september 2014
Conceptual and Technical Challenges for Quantum Gravity 2014
...
We plan to have plenary talks on many different approaches, including in particular string theory, loop quantum gravity, spacetime noncommutativity, causal dynamical triangulations, asymptotic safety and causal sets. We shall also welcome contributions from the perspective of philosophy of science... http://ctcqg2014.relativerest.org/
Thanks! I saw this earlier but neglected to post it. It comes right on the heels of the Experimental Search for Quantum Gravity conference at ISAS Trieste. Here is the list of plenary speakers so far.
Eric A. Bergshoeff, University of Groningen (NL)
Massimo Bianchi, Università di Roma “Tor Vergata” (IT)
Jeremy Butterfield, Trinity College, University of Cambridge (UK)
Fay Dowker, Imperial College (London, UK)
Laurent Freidel, Perimeter Institute for Theoretical Physics (Waterloo, CA)
Jerzy Kowalski-Glikman, University of Wrocław (PL)
Helge Kragh, Aarhus University (DK)
Stefano Liberati, SISSA (Trieste, IT)
Daniel Litim, University of Sussex (Brighton, UK)
Renate Loll, Radboud University (Nijmegen, NL)
João Magueijo, Imperial College (London, UK)
Shahn Majid, Queen Mary, University of London (UK)
Daniele Oriti, Max Planck Institute for Gravitational Physics (Postdam-Golm, DE)
Carlo Rovelli, Centre de Physique Théorique de Luminy (Marseille, FR)
It's an interesting lineup: speakers from lines of research like AsymSafeQG, CDT, NCG, Group Field Theory, QG Phenomenology, Causal Sets, Covariant LQG,...
Sep 2 [B]Casimir effect on a quantum geometry[/B] Javier Olmedo LSU
Sep 16 [B]Cov LQG: classical action, phase space & gauge symmetries[/B] Wolfgang Wieland PSU
Sep 30 TBA Brajesh Gupt PSU
Oct 14 [B]White holes[/B] Carlo Rovelli CNRS Marseille
Oct 28 [B]New applications for LQG[/B] Jerzy Lewandowski University of Warszaw
Nov 11 [B]Lorentz transformations from abstract quantum theory[/B] Philip Hoehn PI
Nov 25 TBA Derek Wise FAU Erlangen
Dec 9 [B]Invariance of Connections and Measures in LQC[/B] Maximilian Hanusch Uni Paderborn
The fourth workshop on the Experimental Search for Quantum Gravity (ESQG) will be held in Trieste on 1-5 September http://www.sissa.it/app/esqg2014/
... Here's the list of invited speakers:
Code:
Stephon Alexander Dartmouth
Giovanni Amelino-Camelia Sapienza, Rome
Massimo Cerdonio INFN - Padua
Astrid Eichhorn Perimeter Institute, Waterloo
Agnes Ferte Institut d'Astrophysique Spatiale
Julien Grain Institut d'Astrophysique Spatiale
Jonathan Granot Open University of Israel
Giulia Gubitosi Sapienza, University of Rome
Brian Keating University of California, San Diego
John Kelley IMAPP, Radboud University, Nijmegen
Jerzy Kowalski-Glikman University of Wroclaw
Joao Magueijo Imperial College, London
David Mattingly University of New Hampshire
Jakub Mielczarek Jagiellonian University, Crakow
Jonathan Miller Universidad Tecnica Federico Santa Maria
Daniele Oriti Albert Einstein Institute
Igor Pikovski Vienna Center for Quantum Science and Technology
Carlo Rovelli Aix-Marseille University
Floyd Stecker NASA - Goddard Space Flight Center
The purpose of the workshop is to bring together experimentalists, theoreticians, and phenomenologists interested in possible tests probing the quantum/discrete structure of spacetime. There will be a number of rather focussed talks discussing possible phenomenological tests of quantum gravity and proposing some new ideas in this direction.
...
The schedule of ESQG talks has been posted. http://www.sissa.it/app/esqg2014/schedule.php
Some titles and abstracts are still TBA, here are those that have been posted so far:
Astrid Eichhorn (Perimeter Institute, Waterloo) Testing asymptotically safe quantum gravity through coupling to dynamical matter
I will discuss the main idea of asymptotically safe quantum gravity. I will then focus on the effect of dynamical matter degrees of freedom, and discuss the evidence for the consistency of the asymptotic safety scenario for gravity with the Standard Model. Further, I will explain why only some models of "New Physics" seem to be compatible with asymptotic safety, thus providing a possibility to experimentally rule out asymptotic safety at the LHC or future colliders.
Igor Pikovski (Vienna Center for Quantum Science and Technology) Exploring gravitational phenomena in low-energy quantum theory
We discuss how the ability to manipulate and to control quantum systems to very high precision opens the route for new experiments on the interplay between quantum theory and general relativity. It is shown how quantum optical systems can be used for testing low energy quantum mechanics on a fixed background space-time and quantum gravity phenomenology. We consider gravitational time dilation in low-energy quantum theory and derive the resulting decoherence of composite quantum systems [1]. We also show how pulsed opto-mechanical systems can provide a means to probe possible quantum gravitational modifications of the center-of-mass canonical commutator [2]. The results demonstrate that the interplay between quantum theory and general relativity can affect even low-energy quantum systems and that it offers novel phenomena which can be probed in experiments. [1] I. Pikovski, M. Zych, F. Costa, and C. Brukner, Universal decoherence due to gravitational time dilation, arXiv:1311.1095 (2013). [2] I. Pikovski, M. R. Vanner, M. Aspelmeyer, M. Kim, and C. Brukner, Probing Planck-scale physics with quantum optics, Nature Physics 8, 393 (2012).
Jose Manuel Carmona (Universidad de Zaragoza) Thresholds in the presence of Lorentz violating kinematics including modified conservation laws
We discuss the leading Lorentz violations in the kinematics of particle processes with modified dispersion relations and modified composition law of momenta and some phenomenological implications on thresholds in different reactions.
Giampiero Esposito (INFN, Sezione di Napoli) Three-body problem in effective field theories of gravity
The quantum corrections to the Newtonian potential obtained in effective field theories of gravity are shown to produce tiny but nonnegligible effects. For example, in the restricted problem of 3 bodies, the coordinates of Lagrangian points are slightly modified, and the planetoid is no longer at equal distance from the two bodies of large mass in the configuration of stable equilibrium. The equations of the full 3-body problem are also under investigation in the presence of quantum corrections.
Brian Keating (University of California, San Diego ) The Discovery of B-mode Polarization by the BICEP2 Experiment
BICEP2 is a Cosmic Microwave Background (CMB) polarimeter designed to search for the signal of gravitational waves from inflation in B-mode polarization at large angular scales. BICEP2 observed from the South Pole for three seasons from 2010-2012 and recently published results showing an excess of B-modes in the range 30 < ell < 150 with >5 sigma significance. We find that this excess can not be explained by instrumental systematics or foreground models; it is confirmed in cross-correlation with BICEP1 (at 100 and 150 GHz) and preliminary data from the Keck Array. The observed B-mode power spectrum is well fit by a lensed-LCDM cosmological model with the addition of primordial tensor fluctuations with tensor-to-scalar ratio r=0.20^{+0.07}_{-0.05}. I will discuss the BICEP2 experiment, observations, and data analysis, as well as current and planned efforts to follow up this detection
Giulio Fabbian (SISSA) POLARBEAR experiment: results from the first observational campaign and the prospects
I will present the POLARBEAR experiment, an ongoing ground-based CMB polarization experiment located in northern Chile. I will review its latest results obtained from the analysis of the data collected during the first observational campaign and discuss their implication for cosmology and fundamental physics.
Stephon Alexander (Dartmouth) Parity Violating Gravitational Waves and the Standard Model
I show how parity violating gravitational waves can simultaneously generate the observed baryon asymmetry and provide a natural period of parametric resonance of preheating at the end of inflation . I discuss how this signal of parity violation may also be observable in other sectors in theories beyond the standard model.
Julien Grain (Institut d'Astrophysique Spatiale) A brief overview of loop quantum cosmology and its potential observational signatures
Loop quantum cosmology (a symmetry-reduced quantum model of the Universe inspired by loop quantum gravity) extends the inflationary paradigm to the Planck era: the big bang singularity is replaced by a quantum bounce naturally followed by inflation. Testing for these models requires to compute the amount of cosmological perturbations produced in this quantum background and subsequently derives their footprints on the cosmic microwave background. I propose to review two theoretical approaches treating for cosmological perturbations in a quantum background (see Barrau et al. 2014 and Agullo et al. 2013), making their respective assumptions and methodology as explicit as possible. I will then show the observational consequences of those treatments focusing on the specific case of the cosmic microwave background anisotropies as a probe of the primordial Universe.
Agnes Ferte (Institut d'Astrophysique Spatiale) Constraints on chiral gravity through the CMB polarization
If parity invariance is broken in the primordial universe, the cosmic microwave background TB and EB cross-correlations, usually vanishing, become non zero. Their detection would then constrain the level of parity violation. I propose to present forecasts on the detection of this parameter by realistically estimating the uncertainties on the TB and EB spectra via the pure pseudo spectrum method, which efficiency has been shown. I will present the results of this forecast in the case of two typical experimental setups: a small-scale experiment and a large scale survey. Our results show that no constraints can be put on the level of parity violation in the former case. However a range of model would be accessible with a future CMB satellite-like mission: for instance, a parity violation of at least 50% with r = 0.2 could be detected.
Mercedes Martin-Benito (Radboud University Nijmegen) Echoes of the early Universe
By applying quantum informational and optical tools to quantum gravity theories in the very early universe, we show that the fluctuations of quantum fields as seen by late comoving observers are significantly influenced by the history of the early universe, transmitting information about the nature of the universe in timescales when quantum gravitational effects where non-negligible. This might be observable even nowadays thus used to build falsifiability tests of quantum gravity theories.
Jonathan Granot (Open University of Israel) Experimental Bounds on Quantum Gravity from Fermi Observations of GRBs
I will discuss recent searches for quantum gravity signatures using high-energy photons from gamma-ray bursts (GRBs), focusing on the search for Lorentz Invariance Violation (LIV) in the form of a dependence of the photon propagation speed on its energy. Fermi gamma-ray space telescope observations of ~8 keV to ~30 GeV photons from the short (< 1 s) GRB 090510 at a cosmological distance (z = 0.903), enabled for the first time to put a direct time of flight limit on a possible linear variation of the speed of light with photon energy that is beyond the Planck scale. Parameterizing |v/c-1| = E/E_{QG}, for deterministic LIV our most conservative limits are E_{QG}/E_{Planck} > 1.2, while less conservative limits are up to 1-2 orders of magnitude stricter. Using the same data, we have now also set Planck-scale limits on stochastic (or fuzzy) LIV - the first of this kind. I will finish by briefly outlining the prospects for future GRB observations by the Cherenkov Telescope Array (CTA) - the next generation ground based very high energy (from ~20-30 GeV to ~300 TeV) observatory.
Carlo Rovelli (Aix-Marseille University) Planck Stars
I describe a new suggestion for measurable quantum gravity effects: the bounce of a primordial Planck star.
Anupam Mazumdar (Lancaster University) Resolution of Cosmological and Blackhole Singularities
I will discuss how non-local action of higher derivative extension of Einstein's gravity could yield ghost free and devoid of any space or time like singularities.
Francesco Cianfrani (University of Wroclaw) Quantum Reduced Loop Gravity: status and perspectives.
I will present the status and the perspectives of Quantum Reduced Loop Gravity. Instead of discussing in details all the technical issues, I will focus on the relevance of this approach for grounding Loop Quantum Cosmology and for inferring a proper phenomenology for the early Universe.
Tomasz Trzesniewski (University of Wroclaw) Dimensional Flow in kappa-Minkowski Spacetime
Running of the spacetime dimension in small scales is predicted by many different approaches to Quantum Gravity, usually using a notion of the spectral dimension. This is also the case for the kappa-Minkowski spacetime, which appears in the Deformed Special Relativity and Relative Locality. The spectral dimension can easily be calculated in the (Euclidean) momentum space representation. Meanwhile, kappa-Minkowski momenta belong to the group AN(n), which can be represented as half of the de Sitter space. A novel prescription shows it can also be mapped to (half of) the Euclidean anti-de Sitter space, which gives the Euclidean version of momentum space. This allows us to calculate the kappa-Minkowski spectral dimension for different possible Laplacians, extending the known results and providing us with a possible hint for the choice of a physical Laplacian.
Goffredo Chirco (CPT, Universite' Aix-Marseille) Thermally correlated states of Loop Quantum Gravity
We define a class of states of LQG characterized by thermal correlations at the ultralocal level, which may reproduce the structure of correlations known for the perturbative quantum gravity states, in the appropriate limit. We show that these states have a consistent semiclassical interpretation, being peacked on classical values of the intrinsic geometry; and we study how these correlations propagate non-locally on the spin network. We propose these states as the fundamental quantum bricks defining the architecture of spacetime at the non perturbative level and we elaborate on the possible relevance of this proposal in the definition of a continuum limit for LQG.
Jonathan Miller (Universidad Tecnica Federico Santa Maria) The effect of Quantum Gravity on astrophysical neutrino flavor observables.
At the quantum level, an interaction of a neutrino with a graviton may trigger the collapse of the neutrino flavor eigenstate to a neutrino mass eigenstate. I will present that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to the relatively large scattering cross section of relativistic neutrinos off massive sources of gravitational fields (the case of gravitational Bethe-Heitler scattering). This results in a new technique for the indirect detection of gravitons by measuring the flavor composition of astrophysical neutrinos.
Jerzy Kowalski-Glikman (University of Wroclaw) Relative locality in 2+1 dimensions
The relative locality framework is based on two general premises: nontrivial geometry of momentum space and deformed momentum conservation rule. In my talk I will show how these premises take a concrete shape in the case of particles coupled to 2+1 gravity. Then I will briefly discuss the relevance of this construction to the case of physical 3+1 dimensions.
Giulia Gubitosi (Sapienza, University of Rome) Dimensional Reduction in the Early Universe
Giacomo Rosati (ITP, University of Wroclaw) Deformed Lorentz Symmetry and relative locality in FRW spacetime
An opportunity to test Planck-scale modifications of Lorentz symmetry is represented by propagation of particles from cosmological distances (as from GRBs). DSR has been investigated so far only for flat (Minkowskian) spacetimes, providing no room for interplay with cosmological redshift. Only recently a generalization to deSitter spacetime has been proposed (Phys.Rev.D86(2012)124035), relying on the recent understanding of relativity of locality in DSR. I here propose a formulation of DSR in FRW spacetimes, discussing some of the differences with the most studied scenario for broken Lorentz symmetries.
Niccolo' Loret (Perimeter Institute, Waterloo) Finsler geometry and deSitter momentum space
Finsler geometry provides a well studied generalization of Riemannian geometry which allows to account for possibly non-trivial structure of the space of con?gurations of a massive relativistic particle. Another recently developed framework for the description of modi?ed relativistic particle kinematics relies on the description of the particle momentum-space as a curved (pseudo-Riemannian) manifold. We will show that in some cases these two frameworks give equivalent descriptions of the physical properties of a relativistic particle, when its momentum-space is characterized by a deSitter metric and the spacetime is ?at. The generalization of this result could provide a useful mathematical tool to formalize Deformed Special Relativity phenomenology to curved spacetimes.
Gianluca Castignani (SISSA) Gamma-ray bursts as laboratories for quantum effects of gravity
Gamma-ray bursts (GRBs) are the most powerful explosions in the Universe. Most GRBs detected by the Fermi Gamma-ray Space Telescope exhibit a possible delay of up to about 10 seconds between the trigger time of the hard X-ray signal as measured by the Fermi Gamma-ray Burst Monitor (GBM) and the onset of the MeV-GeV counterpart detected by the Fermi Large Area Telescope (LAT). This delay may hint at important physics, whether it is due to the intrinsic variability of the inner engine or related to quantum dispersion effects (e.g. modified dispersion relations) in the velocity of light propagation from the sources to the observer. We searched for the presence of time lags between the LAT and GBM light curves for the five brightest GRBs of the 1st Fermi-LAT Catalog by means of cross correlation analysis. Time lags that are significantly different from zero and consistent with those reported in the literature are found for all the GRBs in our sample by mean of cross correlation analysis. Our analysis reveals the complexity of the time behavior of the GBM and LAT light curves and suggests that the delays should be ascribed to intrinsic physical mechanisms. Better sensitivity and a larger sample might put constraints on a possible origin of the delays in the context of modified dispersion relations and will allow to assess whether time lags are universally present in the early GRB emission.
John Kelley (Univ. of Wisconsin, Madison) Observation of High-energy Astrophysical Neutrinos with the IceCube Detector
The IceCube Neutrino Observatory is a cubic-kilometer-scale neutrino detector built into the ice sheet at the geographic South Pole. IceCube has recently observed a diffuse flux of high-energy astrophysical neutrinos with deposited energies up to 2 PeV. The detection of neutrinos at such energies, as well as features of their energy spectrum and flavor ratios, can be used to constrain potential phenomenological effects of quantum gravity. I will discuss the latest measurements from IceCube of these high-energy neutrinos and the implications for such constraints.
David Mattingly (University of New Hampshire) Lorentz violating effective field theories
Sabine Hossenfelder (Nordita) Space-time Defects
One of the most important questions in quantum gravity is whether or not space-time is fundamentally discrete or continuous. However, directly finding evidence for space-time discreteness has turned out to be difficult if not impossible. In my talk I will discuss the possibility to look for defects in the discrete structure rather than the discrete structure itself. Interestingly, these space-time defects can be modeled without violating Lorentz-invariance, and they can become observable by affecting the propagation of particles.
Daniele Oriti (Albert Einstein Institute) The universe as a quantum gravity condensate
We discuss the geometrogenesis scenario in quantum gravity and the role it may play in the context of loop quantum gravity and group field theory. We also emphasise the connection with other ideas of emergent space-time and with analogue gravity models. We report on recent results, in the group field theory formalism, aiming at realising this scenario and in particular at the derivation of effective cosmological dynamics from group field theory condensates. In light of these results, we suggest several directions to explore to extract testable consequences of this picture of the early universe.
Stephon Alexander Dartmouth
Dionigi Benincasa SISSA
Pawel Bielewicz SISSA
Jose Manuel Carmona* Universidad de Zaragoza
Gianluca Castignani SISSA
Goffredo Chirco CPT, Universite' Aix-Marseille
Francesco Cianfrani University of Wroclaw
Paolo Creminelli* ICTP, Trieste
Astrid Eichhorn* Perimeter Institute, Waterloo
Giampiero Esposito* INFN, Sezione di Napoli
Giulio Fabbian SISSA
Agnes Ferte* Institut d'Astrophysique Spatiale
Julien Grain* Institut d'Astrophysique Spatiale
Jonathan Granot Open University of Israel
Giulia Gubitosi Sapienza, University of Rome
Sabine Hossenfelder Nordita
Brian Keating* University of California, San Diego
John Kelley Univ. of Wisconsin, Madison
Jerzy Kowalski-Glikman University of Wroclaw
Niccolo' Loret Perimeter Institute, Waterloo
Joao Magueijo Imperial College, London
Francesco Marin* Universita' di Firenze and INFN
Mercedes Martin-Benito* Radboud University Nijmegen
David Mattingly University of New Hampshire
Anupam Mazumdar Lancaster University
Jakub Mielczarek Jagiellonian University, Crakow
Jonathan Miller Universidad Tecnica Federico Santa Maria
Daniele Oriti Albert Einstein Institute
Igor Pikovski Vienna Center for Quantum Science and Technology
Giacomo Rosati ITP, University of Wroclaw
Carlo Rovelli Aix-Marseille University
Floyd Stecker NASA - Goddard Space Flight Center
Tomasz Trzesniewski University of Wroclaw
Francesca Vidotto Radboud University Nijmegen
I've gathered the titles and abstracts of ESQG talks for which the slides have already been posted. Hopefully more links will show up tomorrow, as the workshop proceeds.
Links to the slides PDF are included alongside the speaker's name in the schedule, here: http://www.sissa.it/app/esqg2014/schedule.php
Jose Manuel Carmona (Universidad de Zaragoza) (slides)
16:30, Mon 1st Sep 2014 Thresholds in the presence of Lorentz violating kinematics including modified conservation laws
We discuss the leading Lorentz violations in the kinematics of particle processes with modified dispersion relations and modified composition law of momenta and some phenomenological implications on thresholds in different reactions.
Paolo Creminelli (ICTP, Trieste) (slides)
11:15, Tue 2nd Sep 2014 B-mode cosmology
The experimental sensitivity to B-modes is now in an interesting regime for primordial tensor modes. I will review the robustness of the tensor mode prediction in inflation and speculate about what we can learn if tensor modes are detected.
Astrid Eichhorn (Perimeter Institute, Waterloo) (slides)
10:45, Mon 1st Sep 2014 Testing asymptotically safe quantum gravity through coupling to dynamical matter
I will discuss the main idea of asymptotically safe quantum gravity. I will then focus on the effect of dynamical matter degrees of freedom, and discuss the evidence for the consistency of the asymptotic safety scenario for gravity with the Standard Model. Further, I will explain why only some models of "New Physics" seem to be compatible with asymptotic safety, thus providing a possibility to experimentally rule out asymptotic safety at the LHC or future colliders.
Giampiero Esposito (INFN, Sezione di Napoli) (slides)
17:00, Mon 1st Sep 2014 Three-body problem in effective field theories of gravity
The quantum corrections to the Newtonian potential obtained in effective field theories of gravity are shown to produce tiny but nonnegligible effects. For example, in the restricted problem of 3 bodies, the coordinates of Lagrangian points are slightly modified, and the planetoid is no longer at equal distance from the two bodies of large mass in the configuration of stable equilibrium. The equations of the full 3-body problem are also under investigation in the presence of quantum corrections.
Agnes Ferte (Institut d'Astrophysique Spatiale) (slides)
17:00, Tue 2nd Sep 2014 Constraints on chiral gravity through the CMB polarization
If parity invariance is broken in the primordial universe, the cosmic microwave background TB and EB cross-correlations, usually vanishing, become non zero. Their detection would then constrain the level of parity violation. I propose to present forecasts on the detection of this parameter by realistically estimating the uncertainties on the TB and EB spectra via the pure pseudo spectrum method, which efficiency has been shown. I will present the results of this forecast in the case of two typical experimental setups: a small-scale experiment and a large scale survey. Our results show that no constraints can be put on the level of parity violation in the former case. However a range of model would be accessible with a future CMB satellite-like mission: for instance, a parity violation of at least 50% with r = 0.2 could be detected.
Julien Grain (Institut d'Astrophysique Spatiale) (slides)
16:30, Tue 2nd Sep 2014 A brief overview of loop quantum cosmology and its potential observational signatures
Loop quantum cosmology (a symmetry-reduced quantum model of the Universe inspired by loop quantum gravity) extends the inflationary paradigm to the Planck era: the big bang singularity is replaced by a quantum bounce naturally followed by inflation. Testing for these models requires to compute the amount of cosmological perturbations produced in this quantum background and subsequently derives their footprints on the cosmic microwave background. I propose to review two theoretical approaches treating for cosmological perturbations in a quantum background (see Barrau et al. 2014 and Agullo et al. 2013), making their respective assumptions and methodology as explicit as possible. I will then show the observational consequences of those treatments focusing on the specific case of the cosmic microwave background anisotropies as a probe of the primordial Universe.
Brian Keating (University of California, San Diego ) (slides)
9:00, Tue 2nd Sep 2014 The discovery of primordial B-mode polarization
The era of Cosmic Microwave Background B-mode polarization cosmology has recently begun. The BICEP2 telescope observed from the South Pole for three seasons (2010�2012) and released results showing an excess of B-modes in the range 30 < ell < 150 with >5 sigma significance. We find that this excess can not be explained by instrumental systematics or foregrounds. The signal was confirmed in cross-correlation with BICEP1 (at 100 and 150 GHz) and preliminary data from the Keck Array. The observed B-mode power spectrum is well-fit by a lensed-LCDM cosmological model with the addition of primordial tensor fluctuations with tensor-to-scalar ratio r=0.20^{+0.07}_{-0.05}. I will discuss the BICEP2 experiment, observations, and data analysis, as well as current and planned efforts to follow up this detection.
Francesco Marin (Universita' di Firenze and INFN) (slides)
14:30, Mon 1st Sep 2014 Tests of quantum gravity with macroscopic mechanical oscillators
General relativity and quantum physics are expected to merge at the Planck scale, defined by distances of the order of 1.6x10^-35 m and/or extremely high energies of the order of 1.2x10^19 GeV. Since the study of particles collisions around the Planck energy is well beyond the possibilities of current and foreseeable accelerators, high-energy astronomical events (e.g. gamma-ray bursts) have been considered as the privileged natural system to unveil quantum gravitational effects. This common view has been enriched in the last years thanks to a number of studies proposing that signatures of the Planck-scale physics could manifest also at low energies. It is indeed widely accepted that, when gravity is taken into account, deviations from standard quantum mechanics are expected. In particular, we have recently shown that the very low mechanical energy achieved and measured in a vibration mode of a massive object can set an upper limit to possible modifications of the Heisenberg uncertainty principle, that are expected as an effect of gravity. We have indeed exploited the sub- millikelvin cooling of the normal modes of the ton-scale gravitational wave detector AURIGA at this purpose [1]. Here we will discuss some possible interpretations of our results, including possible consequences on deformed commutators, and an upper limit on the length scale at which quantum fluctuations of the space- time geometry should come into play[2]. We will also describe the preliminary results of a series of experiments devoted to investigate possible modifications to the dynamics of micro-oscillators, due to modified Heisenberg relations. [1] F. Marin et al., "Gravitational bar detectors set limits to Planck-scale physics on macroscopic variables", Nature Phys. 9, 71 (2013) [2] F. Marin et al., "Investigation of Planck scale physics by the AURIGA gravitational bar detector", to be published on New J. Phys.
Mercedes Martin-Benito (Radboud University Nijmegen) (slides)
17:30, Tue 2nd Sep 2014 Echoes of the early Universe
By applying quantum informational and optical tools to quantum gravity theories in the very early universe, we show that the fluctuations of quantum fields as seen by late comoving observers are significantly influenced by the history of the early universe, transmitting information about the nature of the universe in timescales when quantum gravitational effects where non-negligible. This might be observable even nowadays thus used to build falsifiability tests of quantum gravity theories.
Pawel Bielewicz (SISSA) (slides)
10:30, Tue 2nd Sep 2014 Planck 2013 cosmological results
I will present the Planck experiment and review the first cosmological results released in 2013. I will also briefly discuss prospects for the planned this year next release of the cosmological data.
Giulio Fabbian (SISSA) (slides)
14:30, Tue 2nd Sep 2014 POLARBEAR experiment: results from the first observational campaign and the prospects
I will present the POLARBEAR experiment, an ongoing ground-based CMB polarization experiment located in northern Chile. I will review its latest results obtained from the analysis of the data collected during the first observational campaign and discuss their implication for cosmology and fundamental physics.
Jerzy Kowalski-Glikman (University of Wroclaw) (slides)
11:15, Thu 4th Sep 2014 Relative locality in 2+1 dimensions
The relative locality framework is based on two general premises: nontrivial geometry of momentum space and deformed momentum conservation rule. In my talk I will show how these premises take a concrete shape in the case of particles coupled to 2+1 gravity. Then I will briefly discuss the relevance of this construction to the case of physical 3+1 dimensions.
Anupam Mazumdar (Lancaster University) (slides)
15:15, Wed 3rd Sep 2014 Resolution of Cosmological and Blackhole Singularities
I will discuss how non-local action of higher derivative extension of Einstein's gravity could yield ghost free and devoid of any space or time like singularities.
Jonathan Miller (Universidad Tecnica Federico Santa Maria) (slides)
9:00, Thu 4th Sep 2014 The effect of Quantum Gravity on astrophysical neutrino flavor observables.
At the quantum level, an interaction of a neutrino with a graviton may trigger the collapse of the neutrino flavor eigenstate to a neutrino mass eigenstate. I will present that such an essentially quantum gravity effect may have strong consequences for neutrino oscillation phenomena in astrophysics due to the relatively large scattering cross section of relativistic neutrinos off massive sources of gravitational fields (the case of gravitational Bethe-Heitler scattering). This results in a new technique for the indirect detection of gravitons by measuring the flavor composition of astrophysical neutrinos.
Tomasz Trzesniewski (University of Wroclaw) (slides)
17:00, Wed 3rd Sep 2014 Dimensional Flow in kappa-Minkowski Spacetime
Running of the spacetime dimension in small scales is predicted by many different approaches to Quantum Gravity, usually using a notion of the spectral dimension. This is also the case for the kappa-Minkowski spacetime, which appears in the Deformed Special Relativity and Relative Locality. The spectral dimension can easily be calculated in the (Euclidean) momentum space representation. Meanwhile, kappa-Minkowski momenta belong to the group AN(n), which can be represented as half of the de Sitter space. A novel prescription shows it can also be mapped to (half of) the Euclidean anti-de Sitter space, which gives the Euclidean version of momentum space. This allows us to calculate the kappa-Minkowski spectral dimension for different possible Laplacians, extending the known results and providing us with a possible hint for the choice of a physical Laplacian.
Francesca Vidotto (Radboud University Nijmegen) (slides)
14:30, Wed 3rd Sep 2014 What can we learn from Loop Quantum Cosmology? The case of Planck Stars
Loop Quantum Cosmology suggests that cosmological singularities are generically resolved by quantum effects. This can be understood at the effective level as the appearance of a repulsive force in the deep quantum-gravity regime. A similar mechanism should take place in the interior of black holes, whose singularity would then be replaced by a core of Planckian energy density. Such Planck Star provides a remnant which can help avoid the information paradox. Furthermore, if the evaporation ends with an explosive event, the Planck star could provide a precise astrophysical signal. Using the current models for primordial black holes and the bounds given by dark-matter abundance, this signal could be compatible with a specific kind of gamma rays, that we have already observed. http://www.sissa.it/app/esqg2014/slides/Vidotto_Trieste_2014.pdf
Sep 2 Casimir effect on a quantum geometry Javier Olmedo LSU
Sep 16 Cov LQG: classical action, phase space & gauge symmetries Wolfgang Wieland PSU
Sep 30 Phenomenological consequences of quantum geometries in LQC Brajesh Gupt PSU
Oct 14 White holes Carlo Rovelli CNRS Marseille
Oct 28 New applications for LQG Jerzy Lewandowski University of Warszaw
Nov 11 Lorentz transformations from abstract quantum theory Philip Hoehn PI
Nov 25 SL(2,C)Chern-Simons&Spinfoam Gravity w Cosm.Const Hal Haggard, Aldo Riello Bard/PI
Dec 9 Invariance of Connections and Measures in LQC Maximilian Hanusch Uni Paderborn
Third EFI Winter Conference on QG
Monday February 16 to Friday February 20 2015 Tux, Austria
General Information
The conference aims to bring together experts on canonical and covariant loop quantum gravity and related topics, in the scenic village of Tux, in the Austrian alps.
Hintertux Glacier
Topics covered by the conference include
Jerzy Lewandowski <Jerzy.Lewandowski_at_fuw.edu.pl>
Hanno Sahlmann <hanno.sahlmann_at_gravity.fau.de>
Universytet Warszawski
Friedrich-Alexander Universität Erlangen-Nürnberg
The schedule will keep the mornings free for work, skiing or hiking. Talks will start around 13:00 and may run till 19:00 or 20:00. Participants
... Here is a partial list that will be updated from time to time:
Ivan Agullo, Louisiana State University
Martin Ammon University of Jena
Mehdi Assanioussi, Warsaw University
Norbert Bodendorfer, Warsaw University
Goffredo Chirco University Aix-Marseille
Andrea Dapor, Warsaw University
Andrzej Dragan, Warsaw University
Maciej Dunajski, Cambridge University
Maite Dupuis, University of Waterloo
Beatriz Elizaga Complutense University of Madrid
Christian Fleischhack, University Paderborn
Marc Geiller, Pennsylvania State University
Florian Girelli, University of Waterloo
Muxin Han, University Erlangen-Nürnberg
Maximilian Hanusch, University Paderborn
Jeff Hnybida Perimeter Institute
Stefan Hollands*, Leipzig University
Marcin Kisielowski, University Erlangen-Nürnberg
Kamil Lacina*, Jagiellonian University Krakow
Miklos Långvik, Helsinki University
Jerzy Lewandowski, Warsaw University
Ilkka Maekinen, Warsaw University
Mercedes Martin-Benito Radboud University Nijmegen
Guillermo Mena Marugan, Instituto de Estructura de la Materia - CSIC
Loops '15 (Erlangen July 6-10):
http://www.gravity.physik.fau.de/events/loops15/loops15.shtml
MarcelGrossmann meeting (Rome July 12-18): http://www.icra.it/mg/mg14/
The triennial MG meetings cover a wide range of topics (astrophysics, observational cosmology, classical gravity etc etc.) Abhay Ashtekar is one of the invited speakers. Some 70 parallel sessions are planned, of which 4 will be devoted to string topics and 3 to QG. Here are the topics and chairpersons of the latter: Quantum Gravity
QG1 Loop Quantum Gravity, Quantum Geometry, Spin Foams (Jerzy Lewandowski) QG2 Quantum Gravity Phenomenology (Giovanni Amelino-Camelia) QG3 Loop quantum gravity: cosmology and black holes (Jorge Pullin, Parampreet Singh)
As a sample, here is Jerzy Lewandowski's brief statement about what's to be covered in session QG1:
==quote== Jerzy LEWANDOWSKI Parallel Session: QG1 - Loop Quantum Gravity, Quantum Geometry, Spin Foams Description: Loop Quantum Gravity (LQG), a framework suited to quantize general relativity, has seen rapid progress in the last three years. The results achieved strongly suggest that the goal of finding a working and predictive quantum theory of gravity is within reach. For specific kinds of matter couplings, a way to drastically simplify the dynamics and its physical interpretation has been discovered. It gives rise to a set of examples of theories of gravity coupled to the fields in which the canonical quantization scheme can be completed. Independently, there have been important breakthroughs in the path integral formulation of the theory related to the so called Spin Foam Models. The session will review the results of canonical Loop Quantum Gravity and Spin Foam Models with the emphasis on the models admitting local degrees of freedom without the symmetry (or any other) reduction. Related approaches to quantum gravity will be also welcome. The common theme is the background independent quantization of Einstein's gravity and the occurrence of quantum geometry.
==endquote==
http://www.gravity.physik.fau.de/events/cosmo2015/cosmo2015.shtml First Erlangen Workshop on Cosmology and Quantum Gravity
Quantum gravity effects are expected to play a prominent role in the early universe as for example in the context of primordial gravitational waves or are expected to manifest in finger prints in the cosmic microwave background. After the expected publications of the new Planck data by the end of 2014 this workshop aims to bring together researchers from quantum gravity as well as from cosmology with links to current experiments, which are interesting also from the quantum gravity perspective.
The workshop will be held at the FAU-Erlangen-Nürnberg from 9th to 13th of February and participants will be experts equally distributed from both research areas. The workshop will be comprised of introductory talks of quantum gravity and comsomology with a particular focus on topics interesting for both communities as well as specialized talks and ample time for discussion, to stimulate interaction between the participants.
Invited Speakers
Niayesh Afshordi (University of Waterloo
Ivan Agullo (Louisiana State University)
Abhay Ashtekar (Pennsylvania State University)
Tessa Baker (Oxford University)
Camille Francois Bonvin (CERN)
Latham Boyle (Perimeter Institute)
Edmund Copeland (University of Nottingham)
Raphael Flauger (Princeton University)
Ghazal Geshnizjani (University of Waterloo
Steffen Gielen (Imperial College London)
Jean-Luc Lehners (Albert Einstein Institute Golm)
Lucas Lombriser (University of Edinburgh)
Oriol Pojolas (IFAE and Universitat Autonoma de Barcelona)
Tehseen Rug (LMU Munich)
Angnis Schmidt-May (ETH)
Thomas Thiemann (University of Erlangen-Nürnberg)
Edward Wilson-Ewing (Albert Einstein Institute Golm)
Local organizing Committee
Kristina Giesel (University of Erlangen-Nürnberg)
Stefan Hofmann (LMU Munich)
Jochen Weller (LMU Munich)
Program
The workshop will start on Monday 9th of February at 3 pm and will end on Friday 13th of February at 1 pm. The detailed program will be available on the homepage soon.
======================
My comment: invited speakers with Loop involvement are Agullo, Ashtekar, Gielen, Thiemann, Wilson-Ewing. Likewise one of the organizers, Giesel.
It makes sense for some Loop researchers to become increasingly interested in cosmology because that is where QG has the greatest contact with observation.
AFAICS recovering classical GR was accomplished in the CHRR paper (Chirco, Haggard, Riello, Rovelli) showing that GR can simply be the equation of state of QG degrees of freedom, after Jacobson 1995.
So one has at least one valid QG theory---the next important order of business is to test theory by confronting it with early universe observations.
There can be several versions of Loop QG all of which recover GR as EoS. One wants to test them to see which best fits observations of ancient light.
A representative paper along these lines is the "LambdaCDM bounce" paper by Cai and Wilson-Ewing. [to get it simply google LambdaCDM bounce]. Notice that Wilson-Ewing is one of the speakers at the workshop. The C&W-E paper puts the standard cosmic model LCDM together with the loop cosmology bounce and gets constraints on some observable numbers.
DATE Seminar Title Speaker Institution
J27 Rainbows from quantum gravity Andrea Dapor University of Warszaw
F10 No firewalls in quantum gravity Alejandro Perez CNRS Marseille
F24 Cosmology with group field theory condensates Steffen Gielen Imperial College
M10 TBA Muxin Han Florida Atlantic University
M24 Information loss Matteo Smerlak Perimeter Institute
A7 Explicit computation of the evaporation of a quantum BH Jorge Pullin LSU
A21 Separability and quantum mechanics Fernando Barbero CSIC, Madrid
My5 Generalized GFT condensates and Cosmology Lorenzo Sindoni AEI
Mohsen Alishahiha
Holographic entanglement entropy for singular surfaces in hyperscaling violating geometry
Benjamin Basso
Structure Constants and Integrable Bootstrap in N=4 SYM Theory
Sayantani Bhattacharyya
A membrane paradigm at large D
Jacob Bourjaily
The On-Shell Analytic S-Matrix
Alejandra Castro
Wilson lines in AdS3/CFT2
Bartek Czech
Integral geometry: from tensor networks to holography
Justin David
Higher spin corrections to entanglement entropy
Roberto Emparan
Black holes in the 1/D expansion
Matthias Gaberdiel
Strings from a Higher Spin Perspective
Abhijit Gadde
Aspects of 2d (0,2) theories
Simone Giombi
Generalized F-theorem and the epsilon expansion
Daniel Harlow
Bulk Locality and Quantum Error Correction in AdS/CFT
Yasuyuki Hatsuda
Large N Non-Perturbative Effects in ABJM Theory
Jonathan Heckman
Geometry of 6D SCFTs
Kentaro Hori
The Grade Restriction Rule
Min-Xin Huang
Topological String on elliptic CY 3-folds and the ring of Jacobi forms
Ken Intriligator
Anomalies, RG flows, and the a-theorem in six-dimensional (1,0) theories
Romuald Janik
String Field Theory vertex from integrability
Robert de Mello Koch
Anomalous Dimensions of Heavy Operators from Magnon Energies
Charlotte Kristjansen
One-point Functions in dCFT and Integrability
Dieter Luest
Large N Graviton Scattering and Black Hole Production
Juan Maldacena
Some speculations on the black hole interior
Gautam Mandal
Thermalization in 2D field theories and holography
Sameer Murthy
Functional determinants and index theorems for exact quantum black hole entropy
Vasilis Niarchos
Exact correlation functions in 4d N=2 superconformal field theories
João Penedones
Mellin amplitudes: the scattering amplitudes of AdS/CFT
Eric Perlmutter
Holographic Duals of Conformal Blocks
Ramadevi Pichai
Knot polynomials, homological invariants and topological strings
David Poland
Conformal Bootstrap Review
Fernando Quevedo
Low energy SUSY and String Compactifications: The Last Attempts?
Loganayagam Ramalingam
A topological gauge theory for the entropy current
Mukund Rangamani
Brownian branes, emergent symmetries, and hydrodynamics
Balt van Rees
Bootstrapping the six-dimensional (2,0) theories
Daniel Roberts
The butterfly effect in spin chains and 2d CFT
Sudipta Sarkar
Holographic entanglement entropy and second law for black holes
John Schwarz
AdS5 X S5 Superspace Geometry
Ashoke Sen
Surviving in a metastable de Sitter space-time
Masaki Shigemori
Habemus Superstratum
Eva M Silverstein
String spreading and S-matrix data
Aninda Sinha
Some analytic results from conformal bootstrap
Marcus Spradlin
Cluster Algebras and Scattering Amplitudes
Douglas Stanford
A bound on chaos
Andrew Strominger
Memory, Soft Theorems and Symmetries
Sandip Trivedi
Constraints From Conformal Invariance on Inflationary Correlators
Angel M. Uranga
Trans-planckian axion field ranges and string theory
Cumrun Vafa
6d (1,0) Supersymmetric Theories and Their Compactifications
Edward Witten
An Overview Of Worldsheet and Brane Anomalies
Alberto Zaffaroni
A topologically twisted index for three-dimensional supersymmetric theories
Alexander Zhiboedov
Conformal Bootstrap With Slightly Broken Higher Spin Symmetry
++++++++++
Earlier yesterday (12 June) I checked and found 2 talk titles have been posted, by later in the day. there were 11. They were starting to put the titles on line. Now it's 50, not yet the full roster since 67 "confirmed invited speakers" are listed here: https://strings2015.icts.res.in/invitedSpeakers.php
There are so far around 270 participants registered. https://strings2015.icts.res.in/participants.php
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Monday, 14:30 - 16:00, Room: Seminar Room 5
Chair: Muxin Han Foundations of spin foam models: a report from the front
14:30 - 15:00, Daniele Oriti (Albert Einstein Institute, Germany)
We outline the main issues in establishing the foundations of spin foam models as quantum gravity models. We identify them in: 1) the complete (formal) definition of the covariant theory; 2) the relation with the canonical formulation; 3) the problem of quantisation (and construction) ambiguities; 4) the definition of the continuum limit; 5) the extraction of effective continuum physics. Then, we report on recent technical results aimed at addressing each of them. Duality between the 2D Ising model and 3D Spinfoams
15:00 - 15:30, Etera Livine (ENS Lyon (CNRS), France)
We present a duality between the 3D quantum gravity amplitude, given by spin network evaluations on the boundary, and the 2D Ising model. We show how it is realized through a supersymmetry, with the Ising spins representing the fermionic degrees of freedom. Finally we discuss the relation between the Ising critical points and the stationary points of the spin network generating function. Coupling Yang-Mills to Spin foams - a toy model
15:30 - 16:00, Sebastian Steinhaus (University of Hamburg, Germany)
The universal coupling of matter and gravity is one of the most important features of general relativity, allowing (precise) experimental tests. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics are hardly explored. This is related to the definition of matter and gravity on the discretisation; on top of the difficulties in pure gravity, as broken diffeomorphism invariance and non-uniqueness, we face similar issues for the matter part and, moreover, its coupling to gravity. To lift these issues, one eventually has to renormalize these theories, e.g. via coarse graining.
Due to a structure similar to spin foams, pure (lattice) Yang-Mills theory is a natural candidate to study these questions further. We propose a coupling to spin foams by choosing a 'local' coupling constant, which depends on the geometric data of the spin foam. To demonstrate the scope of this idea and the effect of different couplings on both matter and geometry, we coarse grain a simple toy model: We study Z_2 Ising spins coupled to a dynamical 2D (quantum group SU(2)_k) background and present the model's phase diagram(s).
Parallel Session: Foundations of Canonical LQG
Monday, 14:30 - 16:00, Room: Lecture Hall
Chair: Alok Laddha Quantization of scalar fields coupled to point masses
14:30 - 15:00, Fernando Barbero (Instituto de Estructura de la Materia, CSIC, Spain)
We will discuss the Fock quantization of a compound classical system consisting of point masses coupled to a scalar field in one dimension (a string attached to point masses). This toy model is useful to understand basic features of physical systems for which some relevant degrees of freedom may be associated with boundaries (such as black holes in LQG). A rigorous Hamiltonian description is used to characterize in a precise way the real Hilbert space of classical solutions to the equations of motion and construct the Fock space. The quantization procedure that we follow can be seen as a generalization of standard QFT in curved spacetimes and, hence, may be of interest beyond the simple model that we discuss. The space of states that we find displays some interesting features, the most striking one being the impossibility of factoring it as a tensor product of Hilbert spaces naturally associated with the point masses and the field. Some consequences of this fact will be discussed both within the context of QFT and quantum mechanics. Quantization of Plane Gravitational Waves: Kinematic and dynamic considerations
15:00 - 15:30, Seth Major (Hamilton College, USA)
Aspects of the quantization of a (1+1)-dimensional midi-superspace model for gravitational plane waves will be discussed. These aspects include a flat space-time condition, the algebra of constraints, regularization of the constraints and the role of geometric quantities, a class of kinematic states, and initial forays into the quantization of the
Hamiltonian constraint. On the Hamiltonian Constraint for plane gravitational waves
15:30 - 16:00, Franz Hinterleitner (Masaryk University, Brno, Czech Republic)
The Hamiltonian constraint for an effectively 1+1 dimensional midi-superspace model for plane gravitational waves is analyzed. Different versions of the operator are compared. Among others, the resulting possibilities of spatial inhomogeneity propagation serves as a test. Conditions for a solution modeling flat space are formulated.
Parallel Session: Asymptotic Safety and Renormalisation Techniques (in Spin Foams)
Monday, 14:30 - 16:00, Room: Seminar Room 3
Chair: Roberto Percacci Towards coarse-graining of spin foams in three dimensions
14:30 - 14:55, Sebastian Mizera (University of Cambridge, United Kingdom)
Understanding of the continuum limit constitutes a major outstanding problem in Loop Quantum Gravity. Encouraged by the early numerical results in the dimensionally reduced models, we introduce a new self-consistent coarse graining scheme in three dimensions. Here the effective building blocks take the form of a tensor network decorated by the original variables of the system, which explicitly preserves the gauge invariance at each step of the RG flow. This technique allows for the efficient computation of observables in the generalized lattice gauge theories, such as spin foam models. Joint work with B. Dittrich and S. Steinhaus (gr-qc/1409.2407). Coarse-graining of 3D spin foam models with finite non-abelian structure groups
14:55 - 15:20, Clement Delcamp (Perimeter Institute, Canada)
One of the most pressing issues of spin foam models is the construction of the large scale limit. We will discuss in this talk first results of coarse-graining for 3D spin foam models with finite non-abelian structure groups.
Physical states of the theory can be constructed via a coarse-graining procedure which iteratively improves the amplitude in the path integral. Tensor network renormalization techniques allow a concrete realization of this coarse-graining scheme. The procedure based on a gluing of cubical building blocks successfully deals with the large redundancy of degrees of freedom. Furthermore, our structure allows the implementation of simplicity constraints which converts topological BF models to spin foam models. We should therefore be able to address the question of the fate of the constraints throughout the coarse-graining procedure as well as investigating the existence of additional phases. Gauge and parametrization dependence in Quantum Gravity
15:20 - 15:40, Benjamin Knorr (FSU Jena, Germany)
We critically examine the gauge- and field-parametrization-scheme-dependence of renormalization group flows in the vicinity of non-Gaussian fixed points in quantum gravity. While physical observables are independent of such calculational specifications, the construction of quantum gravity field theories typically relies on off-shell quantities such as beta-functions and generating functionals and thus faces potential stability issues with regard to such generalized parametrizations. We analyze a two-parameter class of covariant gauge conditions and a one-parameter class of field parametrizations. The principle of minimum sensitivity is used to identify stationary points in this parametrization space. Matter renormalization: perfect fluid coupled to asymptotically safe gravity
15:40 - 16:00, Vadim Belov (University of Hamburg, Germany)
Asymptotic safety program is based on the existence of the UV fixed point of RG flow. In applications to astrophysical and cosmological problems, one usually tries to incorporate the emerging running of the couplings with appropriately chosen scale. We point towards the fact that renormalization in the matter sector might as well contribute on a par with gravity. Motivated by these applications we perform a first step towards the incorporation of the effective perfect fluid description into the picture of the flows. By coupling it with ADM-decomposed gravity we study how the renormalization of the latter may impact on the running of effective of hydrodynamical parameters. The corresponding flow equation is derived in addition to its gravitational counterparts.
Parallel Session: Other Related Topics including NCG, CDT, Causal Sets
Monday, 14:30 - 16:00, Room: Seminar Room 4
Chair: Astrid Eichhorn Aspects of the Bosonic Spectral Action
14:30 - 15:00, Mairi Sakellariadou (King's College London, UK)
I will first introduce the bosonic (cutoff based) spectral action and highlight some of its cosmological and high energy physics consequences. I will then propose a novel definition of the bosonic spectral action using zeta function regularization, in order to address the issues of renormalizability and spectral dimensions. Spontaneous emergent geometry
15:00 - 15:30, Pierre Martinetti (Università di Trieste, Italy)
Recent developments in noncommutative geometry, following the discovery of the Higgs boson, open some ways to physics beyond the Standard Model. The Higgs mass is below the threshold of stability of the electroweak vacuum, which might be the sign of the existence of an extra-scalar field. Noncommutative geometry allows to interprets this extra-field as the relic of a pre-geometric phase which spontaneously breaks to the standard model. We will present a model based on a mixing of the spinorial and gauge degrees of freedom, together with a twisted version of Connes spectral triple. Quantum non-commutative geometry
15:30 - 16:00, John Barrett (University of Nottingham, UK)
The talk will describe aspects of a project devoted to defining and investigating quantum gravity as a functional integral over non-commutative geometries. This approach also gives the coupling of quantum gravity to matter fields, the particles appearing as defects in a topological state sum model.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Monday, 16:30 - 18:00, Room: Seminar Room 5
Chair: Muxin Han What is renormalization useful for in Spin Foams?
16:30 - 17:00, Sylvain Carrozza (Aix-Marseille University, France)
My aim will be to critically review the conceptual and technical arguments which support the use of renormalization theory in spin foams. I will in particular argue that it is necessary to: 1) consistently complete the definition of the theory at the fundamental level; 2) understand its effective low-energy limit. By means of simple toy-models, I will finally illustrate why the GFT formalism is well suited to the task. Resumming Spin Foams
17:00 - 17:30, Jeff Hnybida (Radboud University, Netherlands)
We show how to resum spin foam amplitudes, and general SU(2) lattice gauge theory amplitudes in terms of spinors. We show how this allows for an explicit reduction to twisted geometry variables. Pachner moves in a 4d Riemannian holomorphic Spin Foam model
17:30 - 18:00, Lin-Qing Chen (Perimeter Institute, Canada)
In this work we study a Spin Foam model for 4d Riemannian gravity, and propose a new way of imposing the simplicity constraints that uses the recently developed holomorphic representation. Using the power of the holomorphic integration techniques, and with the introduction of two new tools: the homogeneity map and the loop identity, for the first time we give the analytic expressions for the behavior of the Spin Foam amplitudes under 4-dimensional Pachner moves. It turns out that this behavior is controlled by an insertion of nonlocal mixing operators. In the case of the 5-1 move, the expression governing the change of the amplitude can be interpreted as a vertex renormalisation equation. We find a natural truncation scheme that allows us to get an invariance up to an overall factor for the 4-2 and 5-1 moves, but not for the 3-3 move. The study of the divergences shows that there is a range of parameter space for which the 4-2 move is finite while the 5-1 move diverges. This opens up the possibility to recover diffeomorphism invariance in the continuum limit of Spin Foam models for 4D Quantum Gravity.
Parallel Session: Foundations of Canonical LQG
Monday, 16:30 - 18:00, Room: Lecture Hall
Chair: Alok Laddha A quantum kinematics for asymptotically flat gravity
16:30 - 17:00, Miguel Campiglia (Universidad de la República, Uruguay)
Aside from cosmology, most physically relevant problems in gravity are modeled with asymptotically flat boundary conditions at infinity. It is thus of interest to explore how one may impose such conditions at the quantum level. In this talk I present a proposal for such conditions, in the context of the so-called Koslowski-Sahlmann representation. Based on work with M. Varadarajan. Fractal Coherent States
17:00 - 17:30, Suzanne Lanéry (FAU Erlangen, Germany)
Motivated by obstructions to the construction of semi-classical states on the holonomy-flux algebra, i will discuss how a discrete subalgebra can be extracted while preserving universality and diffeomorphism invariance. This paves the way for the construction of states whose semi-classicality is enforced step by step, starting from collective, macroscopic degrees of freedom and going down progressively toward smaller and smaller scales. Constraint quantization and chaos
17:30 - 18:00, Philipp Hoehn (Perimeter Institute, Canada)
There is strong evidence that a generic general relativistic spacetime features chaotic dynamics. This has severe (and often ignored) repercussions for the quantization and interpretation of the dynamics as a chaotic (Hamiltonian) constrained system generally does not give rise to a Poisson algebra of Dirac observables. Nevertheless, in certain cases one can explicitly quantize such systems. By means of toy models, I will discuss general challenges and some surprising consequences for the quantum theory of chaotic constrained systems which presumably will also appear in canonical quantum gravity.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Monday, 16:30 - 18:00, Room: Seminar Room 3
Chair: Emanuele Alesci The geometry of relative locality
16:30 - 17:00, Laurent Freidel (Perimeter institute, Canada)
Relative locality is the principle that spacetime is an entity which is probe dependent. By opposition absolute locality is the hypothesis that spacetime is an absolute entity, this hypothesis permeate all of physics. I would review many recent development in which we understood how this new principle forces a formulation of physics in phase space, and how gravity and the quantum naturally equip phase space with several natural geometrical structure. One is a metric that descend from the probability measure of quantum mechanics. The other one is another metric that come from spacetime localization. Absolute locality results in the requirement that the localization metric is flat. Relaxing this condition we promote this localization metric to a new dynamical entity. This allow to put together gravity and the quantum on equal footing. We will also present the first example known, modular spacetime that incorporate these principles. We will also show for the first time the generalization of Einstein equation that naturally follow from demanding compatibility between gravity and the quantum. Quantum black hole in the full theory
17:00 - 17:30, Daniele Pranzetti (FAU Erlangen, Germany)
I present the construction of a spherically symmetric quantum black hole within the full theory by means of a generalized class of quantum gravity condensate states. The construction relies on the group field theory formalism, which provides a second quantized version of loop quantum gravity. The black hole condensate is defined by an infinite superposition of graph-based states encoding in a precise way the topology of the spatial manifold. I impose the isolated horizon boundary condition and show how the entropy calculation can be performed. Loop gravity with non-zero cosmological constant
17:30 - 18:00, Jonathan Ziprick (University of New Brunswick, Canada)
We propose a new way to include a cosmological constant in loop gravity. Starting from the continuous Ashtekar variables, we take the curvature of the connection to be piecewise-constant and develop a symplectomorphism between such geometries and a spin network phase space. This data is suitable for the study of (anti) de Sitter cosmology, as well as non-homogenous models.
Parallel Session: Other Related Topics including NCG, CDT, Causal Sets
Monday, 16:30 - 18:00, Room: Seminar Room 4
Chair: Astrid Eichhorn Exploring fuzzy space through Monte Carlo Methods
16:30 - 16:55, Lisa Glaser (Nottingham University, Great Britain)
A spectral triple is the collection of a fermion space and a Dirac operator.
The collection of all Dirac operators for a given fermion space defines its space of geometries.
Fuzzy spaces are a special case of spectral triples with simple matrix algebras.
They are cases of matrix geometries and have a simple representation.
These simple repesentations allow us to explore the space of geometries using Markov Chain Monte Carlo methods.
In attempting to explore the space of geometries we have to face many open questions:
- Which action should we use?
- What observables can we measure in it?
In this talk I will present our answers to these questions and show some of the data generated. Towards (3+1) gravity through Drinfel'd doubles with cosmological constant
16:55 - 17:15, Pedro Naranjo (University of Burgos, Spain)
We present the generalisation to (3+1) dimensions of a quantum deformation of the (2+1) (Anti)-de Sitter and Poincar\'e Lie algebras that is compatible with the conditions imposed by the Chern-Simons formulation of (2+1) gravity. Since such compatibility is automatically fulfilled by deformations coming from Drinfel'd double structures, we believe said structures are worth being analysed also in the (3+1) scenario as a possible guiding principle towards the description of (3+1) gravity. To this aim, a canonical classical r-matrix arising from a Drinfel'd double structure for the three (3+1) Lorentzian algebras is obtained. This r-matrix turns out to be a twisted version of the one corresponding to the (3+1) κ-deformation, and the main properties of its associated noncommutative spacetime are analysed. In particular, it is shown that this new quantum spacetime is not isomorphic to the κ-Minkowski one, and that the isotropy of the quantum space coordinates can be preserved through a suitable change of basis of the quantum algebra generators. Throughout the paper the cosmological constant appears as an explicit parameter, thus allowing the (flat) Poincar\'e limit to be straightforwardly obtained. (Re)constructing Spacetime Geometry from Quantum Dynamics
17:15 - 17:40, Matti Raasakka (Independent researcher, Finland)
I will present some encouraging recent results in extracting effective spatiotemporal notions such as locality and duration directly from quantum dynamics. The most concrete results concern for now quantum systems with finite-dimensional observable algebras, but should generalize at least to hyperfinite algebras (such as in QFT). I will also discuss a background-independent algebraic framework for quantum physics, where these methods are directly applicable. Semiclassical Field Theory
17:40 - 18:00, Eugene Kur (University of California, Berkeley, USA)
Recent developments in multisymplectic geometry have clarified how to apply the Hamiltonian formalism of field theory to arbitrary spacetime slicings. This allows us to use various semiclassical approaches (such as the WKB approximation of the path integral) in a much more general context. I will discuss applications of these semiclassical ideas to the Unruh effect and black hole entropy, as well as describe the modifications to the symplectic structure and Hamilton's principle function that come from looking at general spacetime slicings and general spacetime boundaries.
Tuesday parallel sessions (7 July) Loops 2015 Parallel Session: Foundations of Covariant LQG (Spin Foams)
Tuesday, 14:30 - 16:00, Room: Lecture Hall
Chair: Muxin Han The cosmological constant in the Loop Quantum Gravity framework.
14:30 - 15:00, Maite Dupuis (University of Waterloo, Canada)
The Loop Quantum Gravity framework has been mostly studied in the case of a zero vanishing cosmological constant. A Loop Quantum Gravity model with a cosmological constant is not well understood even in the 3d toy model case. For the 3d case, several approaches to define a model of quantum gravity exist and in the case of a non-vanishing cosmological constant, the models such as the Turaev-Viro spin foam model or the Chern-Simons model are written in terms of a quantum group. To reconcile the Loop Quantum Gravity approach with these models, we deform the Loop Quantum Gravity framework using quantum groups or Poisson-Lie groups. Following this line, a topological model with a Hamiltonian constraint for 3d gravity with a cosmological constant has been defined. The Hamiltonian constraint can be solved and the solutions can be related to the Turaev-Viro spin foam amplitude. Moreover, geometric observables for quantum hyperbolic geometries have been defined.
I am going to present an overview of this program consisting in introducing a cosmological constant in the 3d Loop Quantum gravity framework and will comment the 4d case. 3d loop gravity and the cosmological constant.
15:00 - 15:30, florian Girelli (University of Waterloo, Canada)
Using inspiration from Chern-Simons theory, I will explain how one can use Poisson Lie groups to deform the classical phase space of loop quantum gravity to introduce a cosmological constant. I will focus on the 3d case and present the geometric details behind the construction. This model is quantizable and solvable and I will highlight some of these steps if time permits. Encoding Curved Tetrahedra in Face Holonomies
15:30 - 16:00, Hal Haggard (Bard College, USA)
I will present a generalization of Minkowski’s classic theorem on the reconstruction of tetrahedra from algebraic data to homogeneously curved spaces. Euclidean notions such as the normal vector to a face are replaced by Levi-Civita holonomies around each of the tetrahedron’s faces. This new approach allows the reconstruction of both spherical and hyperbolic tetrahedra within a unified framework. Several interesting mathematical structures arise in setting up a phase space for these curved tetrahedra such as group-valued moment maps and quasi-Poisson spaces. Curved tetrahedra also provide a natural starting point for thinking about discrete and quantum gravity in spacetimes with a cosmological constant.
Parallel Session: Foundations of Canonical LQG
Tuesday, 14:30 - 16:00, Room: Seminar Room 5
Chair: Wojciech Kaminski New applications for canonical LQG
14:30 - 15:00, Jerzy Lewandowski (Uniwersytet Warszawski, Polen)
I will outline several new findings in canonical LQG. New perspectives for canonical LQG dynamics
15:00 - 15:30, Mehdi Assanioussi (University of Warsaw, Poland)
This talk is about the implementation of a new scalar constraint operator for canonical LQG. I will briefly present the regularization procedure and I will discuss the quantum algebra and the possible construction of a symmetric quantum operator. I will conclude with a qualitative description of the physical states and few remarks about the physical Hamiltonian, in case of gravity coupled to a free scalar field, obtained with a similar regularization. Symmetry Reduction and Quantum Configuration Spaces
15:30 - 16:00, Christian Fleischhack (Paderborn University, Germany)
First, we review the C*-algebraic foundations of loop quantization, focusing on configuration spaces and symmetry implementation. Then, we apply these findings to loop quantum cosmology. In particular, we derive an embeddability criterion for the configuration spaces and review the Hanusch results on non-commutativity of quantization and symmetry reduction.
Parallel Session: Other Related Topics including NCG, CDT, Causal Sets
Tuesday, 14:30 - 16:00, Room: Seminar Room 3
Chair: Karim Noui Null canonical gravity, integrability and quantization
14:30 - 15:00, Michael Reisenberger (Universidad de la Republica, Uruguay)
The talk will focus on issues connected with the quantization of initial data for vacuum general relativity on null hypersurfaces. After a brief review of a classical canonical formulation of general relativity in terms of unconstrained null data, I will present recent joint work with Andreas Fuchs bearing on the quantization of the main null initial data. We note that the Poisson brackets of these data are almost the same in cylindrically symmetric gravity as in the full theory, and we use a non-linear and non-local change of variables to transform the Poisson brackets in the cylindrically symmetric case into a form that has a known quantization. Note that the talk deals with putting the classical theory in a quantizable form. Very little will be said about the quantum theory itself. Shape Dynamics: A Progress Report
15:00 - 15:30, Sean Gryb (Radboud University, Netherlands)
There exists a particularly useful foliation for General Relativity where the local gauge-invariant degrees of freedom are conformally invariant. Shape Dynamics is an approach to gravity where this observation is taken seriously to motivate an ontological shift from a spacetime picture to a picture of evolving conformal 3-geometry. Several exciting things arise if one embraces such an ontology: different possibilities exist for what happens behind the horizons of black holes, new insights are gained about the arrow of time, and, perhaps most promising, new scenarios arise for describing a UV completion of General Relativity. In this talk, I will review the basic formalism for Shape Dynamics, discuss some recent results and speculate about the implications for the quantum theory. Parity Horizons in Shape Dynamics
15:30 - 16:00, Gabriel Herczeg (University of California, Davis, United States)
Recent work has shown that the black hole solutions of shape dynamics are physically different than general relativistic black holes at and within their event horizons. The physical difference arises as a result of an inversion or reflection symmetry about the horizon of a shape dynamic black hole. I define the notion of a parity horizon and show that not only event horizons, but also Cauchy horizons and observer-dependent horizons belong to this class. I also show that this notion of parity endows charged shape dynamic black holes with CPT invariance, and discuss the implications for chronology protection.
Parallel Session: Classical and/or Quantum non-LQG Cosmology: theory and/or experiment
Tuesday, 14:30 - 16:00, Room: Seminar Room 4
Chair: Anna Ijjas GFT states for homogeneous cosmologies
14:30 - 15:00, Lorenzo Sindoni (Albert Einstein Institute, Potsdam, Germany)
I will present recent work in the construction of kinematical states, belonging to the GFT
Fock space, that can be used to describe cosmological spacetimes.
The construction, based on suitably defined refinement moves, follows closely the idea of condensate states, introduced in previous work. The new states encode the geometric and topological information of homogeneous cosmologies, while realizing, at the same
time, a form of coarse graining in terms of sum over a family of connected graphs. Cosmological perturbations in GFT condensates
15:00 - 15:20, Steffen Gielen (Imperial College London, UK)
Quantum cosmology can be viewed as an effective hydrodynamic approximation to quantum gravity, in which one describes the universe as a 'condensate' of quanta of geometry. This idea has been made concrete in group field theory (GFT) where these quanta correspond to tetrahedra or open spin network vertices. In the mean-field approximation of the condensate, one obtains a semiclassical description in terms of a statistical distribution of quanta over minisuperspace. I will review the basic ideas behind the formalism and show how one can extract information about the homogeneous mode and about cosmological inhomogeneities from this distribution. I will also discuss some interesting general consequences for cosmology, especially in the connection to CMB observations. Time and unitarity around a cosmological bounce
15:20 - 15:40, Antonin Coutant (Albert Einstein Insitute, Potsdam, Germany)
I will discuss the notion of time and unitarity in the vicinity of a bounce in quantum cosmology, that is, a turning point for the scale factor. It has been obtained in several approaches that a proper notion of time and evolution emerges form the Hamiltonian constraint of quantum cosmology if at least one degree of freedom is semiclassical enough. In particular, WKB solutions provide a key tool to analyze the possible interpretations of the wave function. Unfortunately, WKB methods fail drastically near a turning point. To address this issue, I developed a semiclassical framework in the momentum representation. I will then discuss the physics of matter degrees of freedom, when that momentum plays the role of time. The regime at hands goes beyond the Born-Oppenheimer approximation, and no classical background exists. I will show this by considering first an adiabatic evolution and then quantum transitions (i.e. particle creation). A Noncommutative Extension of Effective Loop Quantum Cosmology
15:40 - 16:00, Abraham Espinoza García (University of Guanajuato, Mexico)
A noncommutative modification of the Loop Quantum Cosmology effective scheme of the open FLRW model in the presence of a standard scalar field is proposed. We start from the holonomized Hamiltonian and implement a canonical noncommutativity (theta deformation) among the matter degree of freedom and the holonomy variable (volume representation) by performing a shift in such configuration variables, thus obtaining an effective noncommutative Hamiltonian. We also obtain a noncommutative extension of the modified Friedmann equation for a particular case of the theta deformation. It remains to be tackled the physical interpretation of such extension.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Tuesday, 16:30 - 18:00, Room: Lecture Hall
Chair: Muxin Han From a curved-space reconstruction theorem to a 4d Spinfoam model with a Cosmological Constant
16:30 - 17:00, Aldo Riello (Perimeter Institute, Canada)
I will discuss the first steps towards a definition of a spinfoam model for 4d gravity with a cosmological constant, via complex Chern-Simons theory with defects. The proposal hinges on a reconstruction theorem assessing the correspondence between a class of flat connections on a S3 graph complement (related to the 4-simplex 1-skeleton) and the geometries of a constant-curvature Lorentzian 4-simplex. The main result consists in showing that in the semiclassical approximation of the vertex amplitude the Regge action of simplicial general relativity correctly appears. This construction borrows ingredients from the EPRL/FK model and adapts them to the curved case. Time allowing I will also comment on the phase space structure of the boundary states of the model. Compactification of LQG phase space
17:00 - 17:30, Francesca Vidotto (Radboud University Nijmegen, Netehrlands)
In order to introduce the cosmological constant in a simplicial geometry, simplex faces should be taken of constant curvature. This yields a compactification of the phase space and the finiteness of the Hilbert space for each link. Not only the intrinsic, but also the extrinsic geometry turns out to be discrete, pointing to discreetness of time, in addition to space. Turaev-Viro amplitudes from a Hamiltonian constraint with positive cosmological constant
17:30 - 18:00, Julian Rennert (University of Waterloo, Canada)
I will give an update on the current status of the relation between the Turaev-Viro spinfoam model and a canonical quantum theory of q-deformed spin-networks. Building on the recent work of Girelli, Dupuis, Livine and Bonzom on hyperbolic discrete geometries and their quantization with a real deformation parameter I will focus on the quantum theory with q being a root of unity. This case is associated with a positive cosmological constant and indeed we find the expected spherical geometries from generalized length and angle operators. What's more, one finds that q-deformed spin-networks that solve a certain Hamiltonian constraint have q-deformed 6j-symbols as their amplitudes, which are the building blocks of the Turaev-Viro model. Hence, we have a promising model of 3D loop quantum gravity with positive cosmological constant.
Parallel Session: Foundations of Canonical LQG
Tuesday, 16:30 - 18:00, Room: Seminar Room 5
Chair: Wojciech Kaminski New Hamiltonian constraint operator for loop quantum gravity
16:30 - 16:55, Yongge Ma (Beijing Normal University, China)
A new symmetric Hamiltonian constraint operator is proposed for loop quantum gravity. On one hand, it inherits the advantage of the original regularization method of Thiemann, so that its regulated version in the kinematical Hilbert space is diffeomorphism covariant and creates new vertices to the spin networks. On the other hand, it overcomes the problem in the original treatment, so that there is no ambiguity in its construction and its quantum algebra is anomaly-free in a suitable sense. The regularization procedure for the Hamiltonian constraint operator can also be applied to the symmetric model of loop quantum cosmology, which leads to a new quantum dynamics of the cosmological model. Conformal symmetry in LQG
16:55 - 17:20, Miklos Långvik (Helsinki university & CPT Marseille, Finland)
Conformal symmetry plays a key role in modern quantum field theory and many authors have suggested that it could be relevant to understand quantum qravity non-perturbatively. As a first step towards exploring this idea within loop quantum gravity, we present some results on the action of the Minkowskian $\mathfrak{su}$(2,2) conformal symmetry on spin networks. Somewhat counterintuitively, the action of the generator of dilatations changes the discrete extrinsic curvature while keeping the areas and 3d volumes intact. We also construct a possible semi-classical picture for conformal spin networks in terms of twistors, which points towards a certain self-dual octahedron in complexified Minkowski space. The Conformal Nature of the Barbero-Immirzi Parameter
17:20 - 17:40, Patrick Wong (University of Cologne, Germany)
The Barbero-Immirzi parameter of loop quantum gravity is a one parameter ambiguity of the theory whose physical significance is as-of-yet unknown. It is an inherent characteristic of the quantum theory since it appears in the spectra of geometric operators. The parameter's appearance in the area and volume spectra imply that it plays a role in determining the fundamental length scale of space. This appearance as a rescaling of lengths motivates a possible conformal interpretation. Presented here is an analysis of the conformal scaling of the triad formalism and the revelation that the Barbero-Immirzi parameter precisely corresponds to the conformal scale factor. Furthermore, at the kinematical level the conformal scale factor materializes as a scalar field coupled to gravity. The development of this conformal scalar field to the quantum sector of the theory is sketched. Real Change in Hamiltonian GR Observables from Equivalence to the Lagrangian
17:40 - 18:00, J. Brian Pitts (University of Cambridge, United Kingdom)
Change has seemed missing in Hamiltonian GR. The lack of a worry for Lagrangian GR motivates reexamining where equivalence to the Lagrangian has been lost. Since the 1980s some authors, such as Mukunda, Castellani, Sugano, Pons, Salisbury, Shepley, and Sundermeyer, have aimed to recover Lagrangian equivalent gauge transformations at least on shell using a 3plus1 version of the Rosenfeld Anderson Bergmann gauge generator, a specially tuned sum of first-class constraints, primary and secondary, as opposed to Dirac's view that any first-class primary alone and perhaps any first-class secondary alone generates a gauge transformation. Are the views equivalent for observables? Pons's proof that Dirac should not have stopped at lowest infinitesimal order and hence with primaries is illuminated by direct calculations in electromagnetism and GR showing that each constraint alone falsifies the Lagrangian constraints, viz., Gauss's law, Gauss Codazzi relations, by affecting the initial data, an effect that Dirac's subtractive calculation cancels out. Likewise a first class constraint fails to leave the canonical action int dt p dq/dt - H quasi-invariant, but the gauge generator G does so. The canonical momenta tend not to notice the spoiling of the Lagrangian constraints because individual constraints also spoil the relations dq/dt-dH/dp equals 0 that gives physical meaning to the momenta, which are mere auxiliary fields in the canonical action and hence dispensable. As argued by Pons, Salisbury and Sundermeyer, observables should be defined in terms of a Poisson bracket with the gauge generator G, not separate constraints.
Given the role of the transport term in Lie differentiation, requiring observables in GR to have 0 Poisson bracket with G is analogous to requiring sameness at 1 am British Summer Time and 1 am GMT an hour later---immediately but implausibly requiring constancy. This argument systematizes Kuchar's critique of observables. A revised definition of observables O is proposed, that the Poisson bracket of O with G is 0 when G generates internal symmetries, but it is the Lie derivative of a geometric object in the classical Nijenhuis sense of components in all coordinates and a transformation law, when G generates 4-dimensional coordinate transformations. Thus Hamiltonian observables, like Lagrangian observables, are internally gauge-invariant geometric objects, including the electromagnetic field strength and the metric.
Parallel Session: Other Related Topics including NCG, CDT, Causal Sets
Tuesday, 16:30 - 18:00, Room: Seminar Room 3
Chair: Karim Noui Causal fermion systems as an approach to quantum gravity
16:30 - 17:00, Felix Finster (Universität Regensburg, Germany)
The theory of causal fermion systems is an approach to describe fundamental physics. It gives quantum mechanics, general relativity and quantum field theory as limiting cases and is therefore a candidate for a unified physical theory including gravity. Instead of introducing physical objects on a preexisting space-time manifold, the general concept is to derive space-time as well as all the objects therein as secondary objects from the structures of an underlying causal fermion system. The dynamics is described by the causal action principle.
The aim of the talk is to give a simple introduction, with an emphasis on conceptual issues. In particular, it will be outlined how quantum gravity is to be described in this framework. Statistical mechanics of reparametrization invariant systems
17:00 - 17:20, Thibaut Josset (Aix Marseille Université, France)
It is notoriously difficult to apply statistical mechanics to generally covariant systems, because the notions of time, energy and equilibrium are seriously modified in this context. However, for a system invariant under reparametrization (without additional gauge), one can generalize the notion of time average. Ergodicity is then used to define statistical states. Finally, if the system splits into subsystems (in some appropriate way), standard results of statistical mechanics and thermodynamics remain valid. This new approach might be a first step in understanding statistical properties of classical or quantum spacetime.
joint work with Goffredo Chirco and Carlo Rovelli, arXiv:1503.08725 Operationalization of basic observables for relativistic dynamics
17:20 - 17:40, Bruno Hartmann (Humboldt University Berlin, Germany)
We start with thought experiments on measurement practice as Einstein did for the foundation of relativistic Kinematics. Seizing on a programmatic proposal by Heinrich Hertz we arrive at quantification of energy-momentum and then, give a relativistic revision. We define these observables from elemental ordering relations for ''capability to execute work'' and ''impact'' in a collision and apply Helmholtz method for quantification, according to which a basic measurement consists in a reconstruction of the measurement object with a material model of concatenated units (reference process of irrelevant internal structure). From simple physical (light principle, principle of inertia, impossibility of Perpetuum Mobile) and measurement methodical principles we derive all fundamental equations of classical and relativistic dynamics. In this foundation, which explains the mathematical formalism from the operationalization of basic observables, one can address and understand scope and limitations of the formalism, with significance also for other formalisms in physics. Intrinsic Time Quantum Geometrodynamics
17:40 - 18:00, Eyo Ita (US Naval Academy, USA)
Quantum Geometrodynamics with intrinsic time development and momentric variables is presented. An underlying SU(3) group structure at each spatial point regulates the theory. The intrinsic time behavior of the theory is analyzed, together with its ground state and primordial quantum fluctuations. Cotton-York potential dominates at early times when the universe was small; the ground state naturally resolves Penrose's Weyl Curvature Hypothesis, and thermodynamic and gravitational 'arrows of time' point in the same direction. Ricci scalar potential corresponding to Einstein's General Relativity emerges as a zero-point energy contribution. A new set of fundamental commutation relations without Planck's constant emerges from the unification of Gravitaion and Quantum Mechanics.
Parallel Session: Homogeneous and Hybrid Loop Quantum Cosmology (LQC)
Tuesday, 16:30 - 18:00, Room: Seminar Room 4
Chair: Edward Wilson-Ewing LQC, Non-Gaussianity and CMB anomalies
16:30 - 17:00, Ivan Agullo (LSU, USA)
This talk will summarize the prediction of LQC for the spectrum of Non-Gaussianity and its role as a potential source for the power asymmetry observed at large angular scales in the CMB Suppresion of power at large scales in loop quantum cosmology
17:00 - 17:30, Brajesh Gupt (IGC Penn State, USA)
An important feature of singularity resolution in loop quantum cosmology (LQC) is the occurrence of the quantum bounce when the spacetime curvature becomes Planckian leading the pre-inflationary evolution of the universe to be greatly modified. Due to the modified dynamics in the pre-inflationary era the initial conditions for both the background and cosmological perturbations are different from those in the standard inflationary scenario. We find that such modifications can lead to observational signatures on the cosmic microwave background (CMB) anisotropy spectrum. In particular we find that there exist initial states in LQC that could lead to suppression of power at low multipoles in the temperature anisotropy spectrum--a 3$\sigma$ anomaly observed in the recent CMB experiments. In this talk we describe these initial conditions, discuss their consequences on the inflationary power spectrum, and compare our results with data from recent CMB experiments. Phenomenology of Starobinsky inflation in LQC
17:30 - 18:00, Beatrice Bonga (Penn State, USA)
Recent observations by the Planck collaboration favor Starobinsky inflation over other inflationary models. However, predictions in the setting of LQC have only been made in the context of a quadratic potential. In this work, we close this gap by studying the singularity resolution, probability of inflation and powerspectrum of cosmological perturbations for the Starobinsky model using the framework of QFT on quantum space-time in the effective description of LQC. We investigate the parameter space of initial data at the bounce that lead to slow-roll inflation consistent with observations. We find that, similar to the quadratic potential, there is a limited range in which the LQC predictions differ from the standard inflationary scenario. Phenomenological consequences are also discussed.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Thursday, 14:30 - 16:00, Room: Seminar Room 5
Chair: Benjamin Bahr The area-law sector of loop quantum gravity
14:30 - 15:00, Eugenio Bianchi (Penn State, USA)
In this talk I present a concrete realization of the conjecture that semiclassical states in quantum gravity satisfy an area law. In loop quantum gravity the entanglement entropy of a random spin-network state scales linearly with the volume of a region of space. I describe a class of spin-network states that are fully characterized by the expectation value and the 2-point correlation function of geometric observables. Such states are semiclassical, have non-vanishing graviton-graviton correlations, and satisfy the area law. The framework extends previous results about the black hole horizon entropy to all regions of space. Area-law and its consequences for LQG
15:00 - 15:30, Antonino Marciano (Fudan University, China)
We will first comment on the importance of quantum entanglement entropy in characterizing semiclassical properties of quantum theories. We will then introduce techniques mutuated from quantum many-body theory in order to calculate entanglement in LQG, taking into account gauge invariance. In preparation for Mingyi Zhang seminar, we will present a one-link state that satisfies the area-law, and is a viable building block for constructing new semi-classical states in LQG. We will finally comment on the eigenvalues distribution for these newly found states. Derivation of the area law in LQG
15:30 - 16:00, Mingyi ZHANG (Fudan University, China)
I will present a preliminary result on computing the entanglement entropy in the context of loop quantum gravity. The gauge invariance is concerned, and the area law can be obtained in the semi-classical limit and low energy limit of spin foam model. This talk follows Prof. Antonino Marciano's talk.
Parallel Session: Foundations of Canonical LQG
Thursday, 14:30 - 16:00, Room: Lecture Hall
Chair: Norbert Bodendorfer Coherent States and Intertwiners
14:30 - 15:00, John Schliemann (University of Regensburg, Germany)
Coherent states provide a natural connection of quantum systems to their classical limit and are employed in various fields of physics. Here we derive general systematic expansions, with respect to quantum parameters, of expectation values of products of arbitrary operators within both oscillator coherent states and SU(2) coherent states. In particular, we generally prove that the energy fluctuations of an arbitrary Hamiltonian are in leading order entirely due to the time dependence of the classical variables. We apply our general results to the calculation of expectation values within coherent intertwiners in spin networks. For expectation values of rotationally invariant operators (and these are the only ones contributing) one finds here a subleading correction to the classical limit given in terms of universal (i.e. operator-independent) expansion coefficients which contain only geometric information about the network node and show an interesting formal analogy to classical inertia tensors of rigid bodies. A stability criterion for coherent states
15:00 - 15:30, Antonia Zipfel (University of Warsaw, Poland)
Coherent states play an important role in the semiclassical analysis of a given quantum theory. In order to also study the semiclassical features of the dynamics it is necessary to construct a system of states that does not loose its semiclassical properties during the evolution. I will introduce and discuss a stability criterion for complexifier coherent states, which are used in LQG. It turns out that already for quantum mechanical system the introduced criterion is quite restrictive. However, there is a way to circumvent these restrictions by introducing action-angle coordinates. These mechanisms are potentially also applicable in symmetry reduced models such as LQC. Typicality and local thermalisation in spin networks
15:30 - 16:00, Goffredo Chirco (CPT - AMU, France)
We investigate the notion of quantum typicality in spin networks, by applying the general approach proposed by Popescu, Short and Winter in 2006, in the context of LQG. In particular, we focus on a basic spin network building block consisting in a N-valent SU(2) intertwiner with fixed total spin, the equivalent of a space of convex polyhedra with N face and fixed total boundary area at the classical level. On the fixed-area subspace of the intertwiner, we study the reduced state associated to a small region of the boundary surface.
By exploiting the "concentration of measure phenomenon", we show how the distribution for such a state is highly peaked around the "thermal state" for almost all pure states of the global intertwiner. We obtain a Gibbs state written in terms of the area preserving generator of the U(N) group, the area having the role played by the energy in the standard canonical picture. Local thermalisation arises as the result of the degree of correlations between local state and environment.
We study the temperature of the local surface patch state and we confront the specific structure of correlations of our result with the previous derivations of a single link thermal state present in the literature.
Parallel Session: Isolated Horizons and Quantum Black Holes
Thursday, 14:30 - 16:00, Room: Seminar Room 4
Chair: Jonathan Engle BF Theory Explanation of Isolated Horizon Entropy in Loop Quantum Gravity
14:30 - 15:00, Yongge Ma (Beijing Normal University, China)
We consider an isolated horizon as the inner boundary of a four-dimensional asymptotically flat spacetime region. Due to the isolated horizon condition, it turns out that in certain gauge the boundary degrees of freedom can be described by a SO(1,1) BF theory with sources. This
provides a new alternative approach to the usual one using Chern-Simons theory to study the black hole entropy. To count the microscopical degrees of freedom with the boundary BF theory, the entropy of the isolated horizon can also be calculated in the framework of loop quantum gravity. This approach is applicable in arbitrary dimensions of spacetime. Neutron Star Masses : A Black Hole Entropic Perspective
15:00 - 15:30, Parthasarathi Majumdar (Ramakrishna Mission Vivekananda Univ, India)
This talk is motivated by the need to understand the observed absence of neutron stars heavier than 2 solar masses. Extant approaches to this involve an adaptation of Chandrasekhar’s ideas of a limiting mass for white dwarf stars, based on hydrostatic equilibrium, to situations where general relativity can no longer be ignored. We survey the complications that this might introduce to the already difficult problem of determining the equation of state of this superdense system as an essential part of hydrostatic equilibrium. We then describe an alternative perspective, still under construction, to this problem, based on certain results from the analysis of (quantum) black hole entropy and thermal stability. These results, derived from a non perturbative, background-independent formulation of canonical quantum gravity (Loop Quantum Gravity), will be discussed in some detail. Some attempts to incorporate entanglement entropy ideas into the construction are also to be discussed. The aim here is a formulation of the issue of neutron star instability in terms of the stability and growth of a nascent quantum horizon deep inside a collapsing neutron star. If this perspective works, this might be a first indirect evidence of quantum gravity playing an important role in the gravitational collapse of neutron stars. Dilatonic black holes in LQG
15:30 - 16:00, Saeed Rastgoo (Universidad Autonoma Metropolitana, Mexico)
We review some of the more recent results about the dilatonic black holes in LQG. These include the singularity resolution in the CGHS model, derivation of a true local Hamiltonian in this generic class, to be used in reduced phase space methods, and the problem of access to the saddle point approximation in these systems, and how and if, one can overcome this issue using polymerization.
We will also briefly comment on some of the works in progress.
Parallel Session: Group Field Theory and Tensor Models
Thursday, 14:30 - 16:00, Room: Seminar Room 3
Chair: John Barrett FRG approach for tensorial group field theory
14:30 - 15:00, Joseph Bengeloun (Max-Planck Institute, AEI, Germany)
The functional renormalization group approach for tensorial group field theory models will be introduced. Focusing on concrete examples, the peculiarities of the FRG method when applied to tensorial models will be then emphasized. FRG methods for a tensorial group field theory on R
15:00 - 15:30, Riccardo Martini (Alma Mater Studiorum, University of Bologna, Italy)
I will present an application of Functional Renormalization Group methods to a rank 3 Tensorial Group Field Theory model endowed with phi^4 interaction and defined over three copies of R. This is the first renormalization analysis for TGFT's on non-compact groups. The model has non-Gaussian fixed points which suggest the existence of phase transitions in the IR regime. Conservation laws in Group Field Theory
15:30 - 16:00, Alexander Kegeles (Albert Einstein Institute, Germany)
Group Field Theories are quantum field theories which perturbative description is strongly connected to spin foam models in Loop Quantum Gravity. On the other hand it was recently shown that already classical equations of motion of Group Field Theory can encode cosmological data. From this perspective a natural question arise: what are the fundamental implications to spin foams and/or cosmology of the general frame work of Group Field Theory. In this talk I am addressing the consequences of symmetries in Group Field Theory and show that for such theories the usual conservation equations have to be modified, which can lead to interesting results in applications to spin foams and cosmology.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Thursday, 16:30 - 18:00, Room: Seminar Room 5
Chair: Benjamin Bahr On the observable algebra of local covariant effective field theories
16:30 - 17:00, Jose A. Zapata (Centro de Ciencias Matematicas UNAM, Mexico)
In previous work we developed a geometrical formalism for local covariant effective field theories: we developed a discrete version of the first jet bundle and a multisymplectic geometry in it. Here we describe aspects of the algebraic counterpart of the formalism. The approach follows the spirit of general boundary field theory. Regge Quantum Gravity
17:00 - 17:30, Aleksandar Mikovic (Lusofona University, Portugal)
If we assume that the short-distance structure of the spacetime is a picewise linear manifold corresponding to a triangulation of a smooth manifold, then we can obtain a finite state-sum model which is a generalization of the Regge path integral for GR. By using the effective action approach we show how to compute the quantum corrections and how the diffeomorphism invariance appears. We also show how the model can solve the problem of the cosmological constant. Spincube model of QG and connection to CDT
17:30 - 18:00, Marko Vojinovic (GFM Lisbon, Portugal)
Spincube model is a categorical generalization of spinfoam models, based on the Poincare 2-group. Its main advantage is the automatic and explicit presence of the tetrads as basic degrees of freedom, which simplifies the model and allows for seamless coupling of all matter fields. An additional unexpected property is that, if the simplicity constraint is enforced strongly, the model contains the Causal Dynamical Triangulations state-sum as its special case. This relationship between SC model and CDT is a novel result, and will be explained in detail, along with other interesting properties of the SC approach to QG.
Parallel Session: Foundations of Canonical LQG
Thursday, 16:30 - 18:00, Room: Lecture Hall
Chair: Norbert Bodendorfer Correlations and entanglement in loop quantum gravity
16:30 - 16:55, Alexandre Feller (ENS LYON, France)
In a background independent context, correlations are essential to understand the emergence of geometry, locality and a metric to describe gravity. Typical kinematical states have trivial correlations but physical states are expected to have non trival ones, reproducing for instance the graviton propagator.
Another landmark of quantum gravity is black hole entropy and one of its interpretation as entanglement entropy.
What I wish to present here is a first investigation of those topics in loop quantum gravity with a quantum information and condensed matter perspective by constructing Ising and toric code types states and analysing their properties and structure, in particular which constraints they solve for the first and the area law for entanglement entropy for the second. Such a point of view has the potential to shed some lights on the coarse graining of spin networks and the dynamic of loop gravity. Entangled spin network states
16:55 - 17:20, Lucas Hackl (IGC, Pennsylvania State University, USA)
We present a class of entangled spin network states that are labeled by symplectic matrices and are generated via unitary transformations of the Ashtekar-Lewandowski vacuum. We show that the entanglement entropy between a subgraph and its complement can be calculated analytically as a function of the symplectic matrix labeling the state. In particular, we identify states whose entanglement entropy satisfies an area law. Projecting these states onto the kinematical Hilbert space provides a new candidate for highly entangled semi-classical states.
[based on work with Eugenio Bianchi & Nelson Yokomizo] Tagged and Loopy Spin Networks
17:20 - 17:40, Christoph Charles (ENS Lyon, France)
In the context of the coarse-graining of loop quantum gravity, we introduce tagged and loopy spin networks, which generalize the standard spin network states to account explicitly for non-trivial curvature and torsion. We illustrate their use in some simple dynamical toy-models. Statistical geometry: classical and quantum picture
17:40 - 18:00, Seramika Ariwahjoedi (CPT Marseille, France)
We study the statistical aspect of a system of quanta of space in both classical discrete and canonical loop quantum gravity picture, by proposing a coarse-graining and averaging procedure. This procedure could provide a link between theory described by finite degrees of freedom with a theory described by infinite degrees of freedom (its 'continuum limit'), both in the classical discrete and quantum picture.
Parallel Session: Quantum Gravity Phenomenology
Thursday, 16:30 - 18:00, Room: Seminar Room 3
Chair: Aurelien Barrau Time, vacuum energy, and the cosmological constant
16:30 - 17:00, Viqar Husain (University of New Brunswick, Canada)
I review the assumptions (and their limitations) underlying the standard formulation of the cosmological constant problem. I then describe a link between the cosmological constant problem and the problem of time in quantum gravity. This arises by examining the relationship between the cosmological constant and vacuum energy in non-perturbative formulations of quantum gravity. Dimensional reduction and scale-invariant primordial fluctuations
17:00 - 17:30, Giulia Gubitosi (Imperial College, UK)
I discuss the properties of vacuum fluctuations in general theories with modified dispersion relations which represent dimensional running at high energies, showing that in all theories which run to 2 dimensions in the ultraviolet the vacuum fluctuations, in this regime, are scale-invariant. This is true in flat space but also for “inside the horizon” modes in an expanding universe. I discuss the conditions upon the gravity theory for this scale-invariance to be preserved as the modes are frozen-in outside the horizon. Planck scale modified dispersion relations in FRW spacetime
17:30 - 18:00, Giacomo Rosati (University of Wroclaw, Poland)
In recent years Planck scale modifications of the dispersion relation have been attracting increasing interest also from the viewpoint of possible applications in astrophysics and cosmology, where spacetime curvature cannot be neglected. Nonetheless the interplay between Planck scale effects and spacetime curvature is still poorly understood, particularly in cases where curvature is not constant. These challanges have been so far postponed by relying on an ansatz, first introduced by Jacob and Piran. We here propose a general strategy of analysis of the effects of modifications of dispersion relation in FRW spacetimes, applicable both to classical cases where the relativistic equivalence of frames is spoiled (preferred frame scenarios) and to the alternative possibility of theories that are fully relativistic but with relativistic laws deformed so that the modified dispersion relation is observer independent.
Parallel Session: Homogeneous and Hybrid Loop Quantum Cosmology (LQC)
Thursday, 16:30 - 18:00, Room: Seminar Room 4
Chair: Mercedes Martin-Benito Loop quantization of the linearly polarized Gowdy T3 model with local rotational symmetry
16:30 - 17:00, Daniel Martín de Blas (Universidad Nacional Andrés Bello, Chile)
In this talk we will present a full quantization of the vacuum linearly polarized Gowdy three torus model with local rotational symmetry using the techniques of loop quantum gravity. First, we consider a redefinition of the constraints such that the new scalar constraint Poisson-commutes with itself. Then we apply of the canonical quantization program of loop quantum gravity. We identify the exact solutions of the constraints and the physical observables, and we construct the physical Hilbert space. It is remarkable that quantum spacetimes are free of singularities. Besides, new quantum observables (not present at the classical level) appear codifying partially the discretization of the geometry. Approximate solutions of the hybrid quantum Gowdy model with FRW dynamics
17:00 - 17:30, Beatriz Elizaga de Navascués (Instituto de Estructura de la Materia - CSIC, Spain)
We construct approximate solutions of the hybrid quantum Gowdy cosmology with three-torus topology, linear polarization, and local rotational symmetry, in the presence of a massless scalar field. More specifically, we determine some families of states for which the complicated inhomogeneous and anisotropic Hamiltonian constraint operator of the Gowdy model is approximated by a much simpler one. Our quantum states follow the dynamics governed by this simpler constraint, while being at the same time also approximate solutions of the full Gowdy model. This is so thanks to the quantum correlations that the considered states present between the isotropic and anisotropic sectors of the model. Remarkably, this simpler constraint can be regarded as that of a flat Friedmann-Robertson-Walker universe filled with different kinds of perfect fluids and geometrically corrected by homogeneous and isotropic curvature-like terms. Therefore, our quantum states, which are intrinsically inhomogeneous, admit approximate homogeneous and isotropic effective descriptions similar to those considered in modified theories of gravity. Extension of LQC to arbitrary spacetime dimensions
17:30 - 18:00, Xiangdong Zhang (FAU Erlangen, Germany)
Loop quantum cosmology(LQC) is the symmetric model of loop quantum gravity. In this talk, we generalize the structure of loop quantum cosmology to the theories with arbitrary spacetime dimensions. The isotropic and homogenous cosmological model in n+1 dimensions is quantized by the loop quantization method. Interestingly, we find that the underlying quantum theories are divided into two qualitatively different sectors according to spacetime dimensions. The effective Hamiltonian and modified dynamical equations of n+1 dimensional LQC are obtained. Moreover, our results indicate that the classical big bang singularity is resolved in arbitrary spacetime dimensions by a quantum bounce. We also briefly discuss the similarities and differences between the n+1 dimensional model and the 3+1 dimensional one.
Friday parallel sessions (10 July) Loops 2015 Parallel Session: Foundations of Covariant LQG (Spin Foams)
Friday, 14:30 - 16:00, Room: Lecture Hall
Chair: Wolfgang Wieland Spin foam sums for polyhedral atoms
14:30 - 15:00, Johannes Thürigen (AEI Potsdam, Germany)
While spin foam models are mostly restricted to (locally) simplicial complexes, compatibility with canonical LQG demands a generalization to polyhedral building blocks.
I will present proposals for polyhedral spin foam sums and discuss the implementation of simplicity constraints on polyhedral atoms in these models. Symmetric spin-foam model with the Lorentzian EPRL vertex
15:00 - 15:30, Marcin Kisielowski (FAU Erlangen, Germany)
In the Euclidean signature we introduced a version of the EPRL model that is symmetric with respect to certain moves including an edge splitting move and a face splitting move. In this talk we present a symmetric version of the Lorentzian EPRL model. The face splitting move is particularly problematic. In this move there appear vertex graphs that are not 3-edge connected and in the Lorentzian theory the standard regularization is not sufficient to make them finite. We propose a regularization of the vertex amplitudes that solves this problem. TBA
15:30 - 16:00, Marco Finocchiaro (Albert Einstein Institute, Potsdam-Golm, Germany)
Spin foam models are constructed by imposing, directly at the quantum level, the required geometricity constraints turning topological quantum simplicial BF theory into quantum simplicial gravity. Therefore they depend on the specific prescription adopted for implementing the constraints, on additional choices in the construction, e.g. the prescription for gluing simplicial cells and on the choice of the quantization map, that is the choice of the operator ordering ambiguities. In my talk I will discuss these aspects and their implications by comparing the resulting spin foam amplitudes (more in detail the corresponding fusion coeffcients) for different models proposed in the literature (and new ones obtained as variations of the known constructions). The analysis will be performed by rewriting the spin foam amplitudes in terms of different sets of variables (spins, group elements, flux variables). Moreover I will introduce a general definition of embedding map applicable to all these models and discuss its properties. Other relevant issues as the choice of the boundary Hilbert space and the requirement of proper behaviour of the amplitudes under composition will be also considered.
Parallel Session: Foundations of Canonical LQG
Friday, 14:30 - 16:00, Room: Seminar Room 5
Chair: Christian Fleischhack TBA
14:30 - 15:00, Jędrzej Świeżewski (Faculty of Physics, University of Warsaw, Poland)
During the talk I will present some of the results concerning the radial gauge and employing it to define spherically symmetric loop quantum gravity. Spinor approach to 3D Lorentzian loop quantum gravity
15:00 - 15:30, Giuseppe Sellaroli (University of Waterloo, Canada)
We consider the generalization of the “spinor approach” to the Lorentzian case, in the context of 3d loop quantum gravity with cosmological constant Λ = 0. The key technical tool that allows this generalization is the recoupling theory between unitary infinite-dimensional representations and non-unitary finite-dimensional ones, obtained in the process of generalizing the Wigner–Eckart theorem to SU(1,1). We use SU(1,1) tensor operators to build observables and a solvable quantum Hamiltonian constraint, analogue of the one introduced by V. Bonzom and his collaborators in the Euclidean case (with both Λ = 0 and Λ = 0). We show that the Lorentzian Ponzano–Regge amplitude is solution of the quantum Hamiltonian constraint by recovering the Biedenharn–Elliott relation (generalized to the case where unitary and non-unitary SU(1, 1) representations are coupled to each other). 3D gravity with cosmological constant from Yang-Mills theory with dynamical dual
15:30 - 16:00, Mariano Celada (Cinvestav, Mexico)
Since 3D general relativity with cosmological constant can be identified with a topological sector of Yang-Mills theory where the Yang-Mills field is the spin connection and the spacetime metric is constructed from the Yang-Mills strength, we start from Yang-Mills equations where the Hodge dual operator is replaced by a dynamical entity, and show that 3D gravity with cosmological constant arises.
Parallel Session: Isolated Horizons and Quantum Black Holes
Friday, 14:30 - 16:00, Room: Seminar Room 3
Chair: Eugenio Bianchi Anyonic statistics and large horizon diffeomorphisms for LQG black holes
14:30 - 15:00, Andreas Pithis (King's College London, UK)
We investigate the role played by large diffeomorphisms of quantum isolated horizons for the statistics of LQG black holes by means of their relation to the braid group. To this aim the symmetries of Chern-Simons theory are recapitulated with particular regard to the aforementioned type of diffeomorphisms. For the punctured spherical horizon, these are elements of the mapping class group of S^2, which is almost isomorphic to a corresponding braid group on this particular manifold. The mutual exchange of quantum entities in two dimensions is achieved by the braid group, rendering the statistics anyonic. With this we argue that the quantum isolated horizon model of LQG based on SU(2)_k-Chern-
Simons theory exhibits non-Abelian anyonic statistics. In this way a connection to the theory behind the fractional quantum Hall effect and that of topological quantum computation is established, where non-Abelian anyons play a significant role. (The talk is based on Phys. Rev. D 91, 064053.) How big is a black hole?
15:00 - 15:30, Marios Christodoulou (CPT, Aix-Marseille University, France)
It is possible to give a coordinate independent definition of the 3D volume of the interior of a black hole. The definition extends that of the volume inside a 2-sphere in flat-spacetime by making use of the existence of well defined geometrical features of such spacetimes; maximal surfaces. Using this result, we can answer the physical question of the amount of spatial volume inside the horizon of a collapsed star. The result is surprising: the volume is very large and increases monotonically with the time since the collapse. The internal volume is still large even if the black hole horizon is shrank to Planckian size by the back reaction of the Hawking radiation. These results have implications for the non-singular black holes and remnant scenarios, for the information paradox, the notion of gravitational entropy and the plausibility of holography. A heuristic energy quantization of equilibrium black hole horizons
15:30 - 16:00, Abhishek Majhi (Institute of Mathematical Sciences, India)
We propose a heuristic model Hamiltonian operator for equilibrium black hole horizons, modeled as quantum isolated horizons in loop quantum gravity framework, followed by a heuristic top-down analysis. We explain how the motivations behind adopting the heuristic top-down approach to the concerned problem germinate from the bulk-boundary interplay manifested by the underlying quantum theory. The reasons behind the {\it necessity} of the requirement of the commutation of the Hamiltonian operator and the area operator of a quantum isolated horizon are explained. The analysis is carried out for generic quantum isolated horizons admitting {\it arbitrary} number of topological defects (a.k.a. punctures), explaining the observations of both local and asymptotic observers. In addition to these, we highlight a crucial quantum mechanical aspect of our findings -- even though we require that the Hamiltonian operator$(\hat H_S)$ commutes with the area operator$(\hat A_S)$ and the classical energy of the horizon is a function of its classical area, we {\it do not} require $\hat H_S\equiv \hat H_S(\hat A_S)$; indeed we can have a very generic form of the Hamiltonian operator such that $\hat H_S\not\equiv \hat H_S(\hat A_S)$, which still respects the commutativity and yields the classical energy as a function of its classical area. We find it logical enough to speculate that this particular aspect of our work might prove to be of inherent merit by finding its applicability for larger class of quantum mechanical systems having Hilbert space structures similar to that of a quantum isolated horizon and admitting smeared operators.
Parallel Session: Homogeneous and Hybrid Loop Quantum Cosmology (LQC)
Friday, 14:30 - 16:00, Room: Seminar Room 4
Chair: Parampreet Singh Quantum Reduced Loop Gravity: theory and perspectives
14:30 - 15:00, Francesco Cianfrani (University of Wroclaw, Poland)
I will give an overview of Quantum Reduced Loop Gravity and of its implications in Quantum Cosmology. Quantum scalar field coupled to reduced loop gravity
15:00 - 15:30, Jakub Bilski (Fudan University, China)
Working within the framework of Quantum Reduced Loop Gravity (QRLG), I will show the quantization of the Hamiltonian constraint for the Einsteinian theory of gravity minimally coupled to a scalar field. This procedure relies on the method proposed by T. Thiemann (QSD V) and developed in the collaboration with E. Alesci and C. Cianfrani. The scalar field is described in terms of point-holonomies, located at the nodes of the graph. I will show how to regularize the action of the scalar field Hamiltonian in the diffeomorphism invariant Hilbert space of QRLG, and present the resulting action of the Hamiltonian constraints operator, which contains only analytic coefficients. I will then explain how in the large j limit, the Hamiltonian eigenvalues approach the classical Hamiltonian at the leading order. The next-to-the-leading order corrections are purely quantum, and can be discussed in conjunction with their possible phenomenological implications. A Dynamical Cosmological Sector in Loop Quantum Gravity
15:30 - 16:00, Phillip Mendonca (Florida Atlantic University, USA)
We introduce diffeomorphism and gauge-covariant functions on phase space, show they are first-class, and then quantize them, whereupon they become a set of symmetry constraints for LQG. We then investigate using them as the foundation for an embedding scheme. We show how the embedding works in cosmological models, and how we can then gain information about one model from the other.
Parallel Session: Foundations of Covariant LQG (Spin Foams)
Friday, 16:30 - 18:00, Room: Lecture Hall
Chair: Wolfgang Wieland Graviton propagator of the "proper" vertex
16:30 - 17:00, Atousa Chaharsough Shirazi (Florida Atlantic University, USA)
The “proper” spin-foam vertex amplitude was obtained from the EPRL vertex by projecting out all but a single gravitational sector, in order to enable correct semi-classical behavior. We calculated the gravitational two-point function predicted by the proper spin-foam vertex to lowest order in the vertex expansion. We find the same answer as in the EPRL case, so that the theory is consistent with the predictions of linearized gravity in the regime of small curvature. Proper Vertex asymptotics and Graviton Propagator
17:00 - 17:30, Ilya Vilensky (Florida Atlantic University, US)
The EPRL vertex amplitude provides a consistent formulation of dynamics of loop quantum gravity states. However, its semi-classical limit does not exactly match classical Regge calculus. We present a modification of the EPRL amplitude - the proper vertex amplitude - that has the correct semi-classical limit. We use the proper vertex amplitude to calculate graviton propagator and find that in semi-classical limit it agrees with the result from Lorentzian Regge calculus. A new way to impose simplicity constraints
17:30 - 18:00, Andrzej Banburski (Perimeter Institute, Canada)
I will present a new way to impose simplicity constraints in a Riemannian holomorphic spin foam model. Rather than imposing the constraints on the boundary spin network, one can impose the constraints on the spin foam propagator. Surprisingly, to first order in the asymptotic expansion (the one giving Regge calculus) the two ways of imposing constraints are equivalent, with differences appearing at higher order. This means that one can get the same asymptotic behavior with wildly different full quantum theory.
Parallel Session: Foundations of Canonical LQG
Friday, 16:30 - 18:00, Room: Seminar Room 5
Chair: Christian Fleischhack Quantum Cauchy Surfaces in Canonical Quantum Gravity
16:30 - 16:55, Chun-Yen Lin (Physics Dep., National Central University, Taiwan)
For certain Dirac theories of canonical quantum gravity, I propose an exact and quantum notion of Cauchy surfaces. Similar to its classical counterpart, a quantum Cauchy surface is defined in conjunction with the Dirac observables representing the complete quantum fluctuations localized at the surface. Each of the Dirac theories (most importantly canonical loop quantum gravity) has a timeless physical Hilbert space $\mathbb H$, which is the image of a rigging map $\hat P$ acting on a kinematic Hilbert space $\mathbb K$ to extract the kernel of the quantum scalar constraints. The proposed quantum Cauchy surfaces would be given by the inverse maps of $\hat P$, each of which describes $\mathbb H$ with a specific subspace of $\mathbb K$ that has only partial quantum fluctuations in $\mathbb K$, and with the rest of the fluctuations being frozen. Each quantum Cauchy surface leads to the Dirac observables representing the specified fluctuations, measured at the moment labeled by the frozen fields' values. Among these observables, certain exact and complete conjugate pairs may define a Schr\"odinger theory. The goal of the proposal is thus to re-introduce the Schr\"odinger pictures in a timeless Dirac theory, as viewed from the different observer frames. The explicit application to a simple model will be demonstrated. A gauge connection formulation for general relativity
16:55 - 17:20, Diego Gonzalez (Cinvestav, Mexico)
We propose an action principle for GR with either a vanishing or a nonvanishing cosmological constant, which depends functionally on a gauge connection and a complex-valued 4-form. In particular, with a vanishing cosmological constant, it leads to a new action principle that turns out to be a modification of the CDJ action principle. While, in the case of a nonvanishing cosmological constant, it leads to the Krasnov's action principle. Discrete WKBJ method for the volume operator
17:20 - 17:40, Dimitri Marinelli (University of Waterloo, Canada)
In this talk, I will present Braun's WKBJ method for discrete three terms recurrence relations. This method can be applied to LQG geometric operators with discrete spectrum to disclose their classical dynamics. In particular, I will focus on the volume operator. Also, I will present a set of orthogonal polynomials associated with it. Entropic Motion and Quantum Gravity
17:40 - 18:00, Manuel Garcia-Islas (National Autonomous University of Mexico, Mexico)
Entropic forces result from an increase of the entropy of a thermodynamical physical system. It has been proposed that gravity is such a phenomenon and many articles have appeared on the literature concerning this problem. We propose an idea which may reproduce an entropic force in loop quantum gravity.
Parallel Session: Group Field Theory and Tensor Models
Friday, 16:30 - 18:00, Room: Seminar Room 4
Chair: Aristide Baratin A new representation for loop quantum gravity
16:30 - 17:00, Marc Geiller (ICG Penn State, USA)
One of the key results of loop quantum gravity is the existence of a diffeomorphism-invariant representation of the holonomy-flux algebra of observables, and the construction of a continuum inductive limit Hilbert space. After briefly recalling the properties and the role played by the so-called Ashtekar-Lewandowski vacuum state in this construction, I will describe how a dual formulation can be obtained by trading the roles of the holonomies and the fluxes. This dual representation is built upon a vacuum based on states of topological BF theory, and therefore cast canonical loop quantum gravity in a formulation closer to the spirit of spin foam models. Furthermore, this new vacuum allows for the construction of a continuum limit Hilbert space carrying a (unitarily inequivalent) representation of the holonomy-flux algebra, and gives a new perspective on the derivation of quantum geometry and on the extraction of physics from the theory. Continuum limit of canonical tensor model and general relativity
17:00 - 17:30, Naoki Sasakura (Yukawa Institute for Theoretical Physics, Kyoto University, Japan)
Canonical tensor model is a rank-three tensor model formulated as a totally constrained system in Hamilton formalism. The constraints satisfy a non-linear first-class constraint algebra, which has a similar structure as the Dirac algebra in the ADM formalism of GR. We discuss a formal limit, in which the constraint algebra of the canonical tensor model exactly reproduces the Dirac algebra of ADM. The limit is described by an almost diagonal form of a rank-three tensor, and the lowest of a moment expansion of off-diagonal components can be identified with the metric tensor field of GR. We also give a preliminary discussion on a possible dynamical origin of the formal limit. Random Tensor Networks and Canonical Tensor Model
17:30 - 18:00, Yuki Sato (University of the Witwatersrand, South Africa)
Canonical tensor model (CTM) is a model of dynamical fuzzy space based on the canonical formalism aiming for a model of quantum gravity; a canonically conjugate pair of rank-three tensors with cardinality N are dynamical variables characterising a fuzzy space.
We have proposed a different and relatively simpler model which is supposed to be related to CTM, i.e.,
a statistical system on random networks or random tensor networks (RTN), in which rank-three tensors appear as vertices of random networks.
In this talk I will show that the boundary of the Hamiltonian vector flow of CTM coincides with the phase transition line of RTN at least for N=2. This coincidence happens because the renormalisation-group flow of RTN is given by the Hamiltonian vector flow of CTM, which is true for arbitrary N. My talk is based on the works with Naoki Sasakura (YITP, Japan).
Parallel Session: Quantum Gravity Phenomenology
Friday, 16:30 - 18:00, Room: Seminar Room 3
Chair: Hal Haggard Spinning Particles in the Worldline Formalism
16:30 - 17:00, Trevor Rempel (Perimeter Institute, Canada)
In this talk I present a wordline formulation of the classical spinning particle. After establishing a suitable parameterization of the phase space action I consider the three point interaction vertex and derive a necessary and sufficient condition for consistency. A novel reinterpretation of the model as a classical system of two coupled particles is then presented. I conclude with some preliminary results arising when the phase space is reparameterized in terms of spinors. Comparison of primordial tensor power spectra from the deformed algebra and dressed metric approaches in loop quantum cosmology
17:00 - 17:30, Boris Bolliet (LPSC Grenoble, France)
Loop quantum cosmology tries to capture the main ideas of loop quantum gravity and to apply them to the Universe as a whole. Two main approaches within this framework have been considered to date for the study of cosmological perturbations: the dressed metric approach and the deformed algebra approach. They both have advantages and drawbacks. In this talk, we will compare their predictions. In particular, we present the computation of the associated primordial tensor power spectra. We will see – numerically and analytically – that the large scale behavior is similar for both approaches and compatible with the usual prediction of general relativity. The small scale behavior is, the other way round, drastically different. Most importantly, in a range of wavenumbers explicitly calculated, both approaches do agree on predictions that, in addition, differ from standard general relativity and do not depend on unknown parameters. These features of the power spectrum at intermediate scales might constitute a universal loop quantum cosmology prediction that can hopefully lead to observational tests and constraints. The Volume Operator in Loop Quantum Gravity: The Spectrum in the High Valence Limit
17:30 - 18:00, Felix Winterhalter (FAU Erlangen, Germany)
The International Society for General Relativity and Gravitation (ISGRG) holds triennial conferences. GR20 was in 2013, in Warsaw. There were over 800 participants.
The next one, GR21, will be in New York. July 10-15 2016, at Columbia University (upper West side of Manhattan, nice location)
http:www.gr21.org
I suspect we won't know very much until after January, when the organizers start taking proposals/abstracts for talks.
A small conference on the black hole puzzles is taking place this week at Stockholm KTH --24-29 August. Participants include a number of prominent physicists. I've highlighted those giving talks (16) and the conclusions wrap-up at the end.
Stephen Hawking, University of Cambridge
Jim Bardeen, University of Washington, Seattle
Philip Candelas, University of Oxford
Steve Christensen, UNIX Packages LLC
Ulf Danielsson, Uppsala University
Paul Davies, Arizona State University
Fay Dowker, Imperial College London
Michael Duff, Imperial College London
Larry Ford, Tufts University
Katie Freese, Nordita
Steve Fulling, Texas A&M University
Jim Hartle, University of California, Santa Barbara
Gerard t’Hooft, Utrecht University
Gary Horowitz, University of California, Santa Barbara
Werner Israel, University of Victoria
Claus Kiefer, University of Cologne
Jorma Louko, University of Nottingham
Laura Mersini-Houghton, University of North Carolina
Charles Misner, University of Maryland
Emil Mottola, Florida Atlantic University
Jack Ng, University of North Carolina at Chapel Hill
Jerome Novak, French National Centre for Science
Don Page, University of Alberta
Leonard Parker, University of Wisconsin, Milwaukee
Malcolm Perry, Cambridge University
Joe Polchinski, University of California, Santa Barbara
Carlo Rovelli, Aix-Marseille University
Philippe Spindel, University of Mons
Kelly Stelle, Imperial College London
Andy Strominger, Harvard University
Bo Sundborg, Stockholm University
Gerard 't Hooft, University of Utrecht
Paulo Vargas Moniz, Universidade da Beira Interior
Francesca Vidotto, Radboud University Nijmegen
Bob Wald, University of Chicago
- See more at: http://global.unc.edu/events/hawkingradiation/#sthash.ZTJ0XAXx.dpuf
The program:
MONDAY, 24 August
10.45 – 11.00 Welcome Remarks P. Gudmundsson, KTH Chancellor;
A. Söderbergh Widding, Stockholm University Chancellor;
C. L. Folt, UNC Chancellor;
K. Freese, Nordita Director;
L. Mersini-Houghton, UNC, Organizer of the Conference
11.00 – 11.45 "Backreaction and Conformal Symmetry" G. 't Hooft
14.15 – 15.00 "Backreaction of Hawking Radiation and Singularities" L. Mersini-Houghton
16.00 – 16.45 "Physical interpretation of the semi-classical energy-momentum tensor in a Schwarzschild background" J. Bardeen
19.00 http://www.nordita.org/hawkingradiation/program/lecture/index.php , at Stockholm Waterfront Congress Centre
TUESDAY, 25 August
11.00 – 11.45 "The Information Paradox" S. Hawking
14.15 - 15.00 "Black Hole Memory" M. J. Perry
16.00 – 16.40 "Black to White Hole Tunnelling: Before or After Hawking Radiation?" C. Rovelli
16.40 – 17.10 "A new Quantum Black Hole Phenomenology" F. Vidotto
WEDNESDAY, 26 August
11.00 – 11.45 "Black Holes as Open Quantum Systems" C. Kiefer
14.15 - 15.00 "Particle Creation from vacuum in gravitational expansion and collapse" L. Parker
16.00 - 16.45 "Gravitational Condensate Stars or What's the (Quantum) Matter with Black Holes?" E. Mottola
19.30 Conference Banquet and Concert at the Gold Foyer of the Royal Opera
THURSDAY, 27 August
11.00 – 11.45 "Did the chicken survive the firewall" J. Louko
14.15 – 15.00 "Gravity = (Yang-Mills)^2" M. Duff
16.00 – 16.45 "Black holes and other solutions in higher derivative gravity" K. Stelle
FRIDAY, 28 August
11.00 - 11.45 "Quantum Damping or Decoherence: Lessons from Molecules, Neutrinos, and Quantum Logic Devices" L. Stodolsky
14.15 – 15.00 "Puzzle Pieces: Do any fit?" Ch. Misner
16.00 – 16.45 "The Generalised Second Law and the unity of physics" F. Dowker
SATURDAY, 29 August
11.00 – 12.00 Group Discussion: Summary of Results and Open Questions
12.00 – 12.30 Status Report S. Hawking [TBC]
12.30 – 13.00 Conclusions P. Davies
