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BtSM Event Announcements

  1. Jun 8, 2014 #61

    marcus

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    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 (Text):

    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 [Broken]
    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.
    =================
     
    Last edited by a moderator: May 6, 2017
  2. Jun 14, 2014 #62

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    Talk titles for the Strings 2014 conference speaker list were posted today, about 9 days in advance of the conference. Here's the link:
    http://physics.princeton.edu/strings2014/Talk_titles.shtml
    Name Title
    Code (Text):
    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
     
    Last edited: Jun 14, 2014
  3. Jun 24, 2014 #63

    marcus

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    In case anyone is interested, the slides and videos of the Strings 2014 talks are being posted here:
    http://physics.princeton.edu/strings2014/Talk_titles.shtml

    So far no videos (it is just the second day of the conference), but slides for several of the talks are now up. Here's a sample:

    Polchinski: "Black Hole Information: Spacetime versus Quantum Mechanics"
    http://physics.princeton.edu/strings2014/slides/Polchinski.pdf (this works)

    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.
     
    Last edited: Jun 24, 2014
  4. Jun 28, 2014 #64

    marcus

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    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.
     
    Last edited: Jun 28, 2014
  5. Jul 27, 2014 #65

    marcus

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    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 [Broken]
     
    Last edited by a moderator: May 6, 2017
  6. Aug 16, 2014 #66
    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.

    http://ctcqg2014.relativerest.org/
     
  7. Aug 20, 2014 #67

    marcus

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    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,...
     
  8. Aug 20, 2014 #68

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    The ILQGS Fall schedule is posted!
    Code (Text):

    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
     
  9. Aug 20, 2014 #69

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    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.
     
  10. Sep 3, 2014 #70

    marcus

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    Slides for some of the ESQG talks have been put online
    http://www.sissa.it/app/esqg2014/
    Here is the speaker list with asterisks marking those who have already given their talks and whose slides have already been posted:
    http://www.sissa.it/app/esqg2014/speakers.php


    Code (Text):
    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
     
    Last edited: Sep 3, 2014
  11. Sep 3, 2014 #71

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    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.
     
  12. Sep 4, 2014 #72

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    More slide sets from the ESQG have been posted. Of particular interest, I think, is the talk by Vidotto on the Planck Star model of BH. I'll give the link here for easy access.
    http://www.sissa.it/app/esqg2014/schedule.php
    http://www.sissa.it/app/esqg2014/slides/Vidotto_Trieste_2014.pdf

    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
     
    Last edited: Sep 4, 2014
  13. Sep 15, 2014 #73

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    http://relativity.phys.lsu.edu/ilqgs/schedulefa14.html
    Wieland's talk is a couple of days from now, on Tuesday 16th.
    The ILQGS schedule has been updated:
    http://relativity.phys.lsu.edu/ilqgs/
    Code (Text):

    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
    (
     
    Last edited: Nov 13, 2014
  14. Dec 28, 2014 #74

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    http://www.gravity.physik.fau.de/events/tux3/tux3.shtml

    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.

    tux_glacier.jpg
    Hintertux Glacier
    Topics covered by the conference include
    • canonical and covariant LQG
    • QFT in curved spacetime
    • quantum physics of⁄near black holes
    • physical observables of general relativity
    Organizers of the conference are
    • Norbert Bodendorfer <Norbert.Bodendorfer_at_googlemail.com>
    • 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
    • Tomasz Pawlowski, Andres Bello University
    • Jorge Pulin, Louisiana State University
    • Saeed Rastgoo, Autonomous University Mexico City
    • Carlo Rovelli*, University Aix-Marseille
    • Hanno Sahlmann, University Erlangen-Nürnberg
    • John Schliemann, University Regensburg
    • Atousa Shirazi* Florida Atlantic University
    • Jan Sikorski, Warsaw University
    • Simone Speziale, University Aix-Marseille
    • Jedrzej Swiezewski, Warsaw University
    • Francesca Vidotto, Radboud University Nijmegen
    • Wolfgang Wieland, Pennsylvania State University
    • Edward Wilson-Ewing Albert-Einstein-Institute
    • Antonia Zipfel, Warsaw University


    *: To be confirmed.
     
  15. Dec 28, 2014 #75

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    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==
     
    Last edited: Dec 28, 2014
  16. Jan 18, 2015 #76

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    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.
     
    Last edited: Jan 18, 2015
  17. Jan 18, 2015 #77

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    Spring 2015 ILQGS schedule http://relativity.phys.lsu.edu/ilqgs/
    Code (Text):

    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
     
     
    Last edited: Feb 23, 2015
  18. Jun 13, 2015 #78

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    Strings 2015 will be held in Bangalore 22-26 June, so in a week or so.
    https://strings2015.icts.res.in/index.php
    These talk titles have been posted:
    https://strings2015.icts.res.in/talkTitles.php

    Timothy Adamo
    Field theory as a string theory

    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
     
    Last edited: Jun 13, 2015
  19. Jul 1, 2015 #79

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    loops 15 (6-10 July) Parallel Session abstracts
    http://www.gravity.physik.fau.de/events/loops15/program_abstracts.shtml

    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.
     
    Last edited: Jul 1, 2015
  20. Jul 1, 2015 #80

    marcus

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    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.
     
    Last edited: Jul 1, 2015
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