# Introduction To Loop Quantum Gravity

by marlon
Tags: loop quantum gravity
 Astronomy Sci Advisor PF Gold P: 23,114 There is currently a broken link in the Nottingham webpage given in the previous post: Masters program at Nottingham, including Loop and other QG research http://pgstudy.nottingham.ac.uk/post...-msc_1163.aspx The link to "the Quantum Gravity group" near the bottom of the page should be to: http://www.nottingham.ac.uk/mathemat...m-gravity.aspx ======================================= Francesca has created a world map of places where LQG research is being done or where you can do a PhD in Loop. http://maps.google.com/maps/ms?ie=UT...e6c50e&t=h&z=0 It does not have UC Davis but on the whole it is remarkably complete. It's hard to keep such a map up to date. As confirmation that Carlip is advising LQG research as well as other QG, see: http://arxiv.org/pdf/1111.2107v1
 Astronomy Sci Advisor PF Gold P: 23,114 I want to assemble some information and links about the Quantum Geometry/Gravity program at Erlangen. It is getting to be quite a strong program. They have TWO QG groups, one in the Physics department led by Thiemann and now a second group in the Math department led by Meusburger. The intent is to have several postdocs in each, plus PhD students. Here is about Meusburger: http://www.algeo.math.uni-erlangen.d...rch-group.html A postdoc in Meusburger's group is Winston Fairbairn whom we know of as a Rovelli PhD and co-author. There is another postdoc opening. Prof Meusburger recently sent out this email announcement: ==excerpt== A postdoc position will be available in the quantum gravity group within the algebra and geometry group at the Department of Mathematics, University of Erlangen-Nürnberg in Erlangen, Germany... ==endquote== for more information: http://www.algeo.math.uni-erlangen.d...positions.html Here is about the quantum gravity group in the Physics Department led by Thiemann: http://theorie3.physik.uni-erlangen.de/people.html This group has grown by the addition of some strong people who have had experience with various "new models" approaches. Maïté Dupuis comes there from Lyon, for example. She has co-authored a lot with Etera Livine, who was her PhD advisor, and also one paper with Freidel. Enrique Borja, who has co-authored with Etera Livine (several) and Freidel (one) Emanuele Alesci, a Rovelli PhD and coauthor. It's also interesting that John Baez' student Derek Wise is there. αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
 Astronomy Sci Advisor PF Gold P: 23,114 Here are results of an InSpire search is designed to turn up observational test-related Loop gravity/cosmology papers. In conjunction with LQG/LQC, the DESY search categories are gravitational radiation, inflation, power spectrum, cosmic background radiation, primordial. Loop pheno papers (increasingly observational test-related) 2000-2003 2004-2007 2008-2011 6 27 46 Here's for the 4-year stretch (2008-2011)---as of today we get 46 papers. http://inspirehep.net/search?ln=en&l...100&sc=0&of=hb If we look at the earlier 4-year stretch (2004-2007) using the same categories, we get 27 papers. http://inspirehep.net/search?ln=en&l...100&sc=0&of=hb Here's the same search for the previous 4 years (2000-2003 inclusive), 6 papers found. http://inspirehep.net/search?ln=en&l...100&sc=0&of=hb There is a small amount of overlap in the time segments because InSpire counts a paper as having appeared in a certain year, say 2006, if either it was published in professional journal in 2006 or posted as a preprint on arxiv in 2006. αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞(⇐⇑⇒⇓⇔∴∃ℝℤℕℂ⋅)
 Astronomy Sci Advisor PF Gold P: 23,114 Research trends, updated as of 25 November: http://howlonguntil.net/ day 329/365 180*365/329 = 200 855*365/329 = 949 LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam) 2005 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (42 found) 2006 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (77 found) 2007 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (120 found) 2008 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (142 found) 2009 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (145 found) 2010 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (152 found) 2011 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (200 annualized, from 180 found) STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR (search terms "string model", "membrane model" and "AdS/CFT correspondence") 2005 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (988 found) 2006 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1029 found) 2007 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1050 found) 2008 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1128 found) 2009 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1132 found) 2010 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1046 found) 2011 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (949 annualized, from 855 found) αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
 Astronomy Sci Advisor PF Gold P: 23,114 One way to keep track of current developments in LQG is to watch the ILQGS online seminar list. I've shortened some titles for brevity. ILQGS SEMINAR SCHEDULE SPRING 2012 (All seminars will held at 9:00 AM Central Time) DATE Seminar Title Speaker(Institution) 1/31 Physics of Bianchi models in LQC Parampreet Singh(LSU) 2/14 Classical limit of SF on arbitrary triangulation Claudio Perini(PennState) 2/28 Continuous formulation of the LQG phase space Marc Geiller(Paris-Diderot) 3/13 Black hole evaporation in LQG Jacobo Diaz-Polo(LSU) 3/27 BH entropy in LQG new insight from local perspective A.Perez(Marseille) 4/10 Effective Field Theory QG from Shape Dynamics Tim Koslowski(Perimeter) 4/24 Path integral measure and triangulation independence S.Steinhaus(AEI) 5/8 TBA http://relativity.phys.lsu.edu/ilqgs/schedulesp12.html Audio files and slides PDF are made availble online at the ILQGS website. http://relativity.phys.lsu.edu/ilqgs/ The site's blog has commentary by other LQG researchers and background notes. Note that the 2/28 topic is the Freidel Geiller Ziprick paper, currently leading in our MIP poll. The 4/10 talk is on the topic of the current MIP runner-up. Two of the talks are concerned with triangulation independence, an important issue, and one deals with the classical limit of spinfoam LQG. Pretty much all are topics of current interest. ================== For convenience I'll gather some potentially useful links: Here is Rovelli's group at Marseille http://www.cpt.univ-mrs.fr/~quantumgravity/ Here's the QG bunch at Perimeter http://www.perimeterinstitute.ca/Sci...antum_Gravity/ Here is Thiemann's group at Erlangen http://theorie3.physik.uni-erlangen.de/people.html Here is Meusburger's group at Erlangen http://www.algeo.math.uni-erlangen.d...rch-group.html Here is Dittrich's group at AEI http://www.aei.mpg.de/english/resear...ics/index.html http://www.aei.mpg.de/english/resear...bers/index.php Here is Oriti's group at AEI http://www.aei.mpg.de/english/resear...bers/index.php Livine's QG group at Lyon http://www.ens-lyon.fr/PHYSIQUE/inde...uspage=gravite Pullin's QG group at LSU is part of overall gravity physics, no separate page http://relativity.phys.lsu.edu/ Ashtekar's Institute for Gravitation and the Cosmos http://gravity.psu.edu/ see the QG part By now anyone who follows QG will be familiar with the strong research group at Marseille, so I won't list names there. Perimeter has a lot of well-known people, among the younger researchers: Eugenio Bianchi, Valentin Bonzom, Razvan Gurau, Tim Koslowski, Cecelia Flori, Joseph Ben Geloun. Thiemann's group currently includes Maïté Dupuis, Derek Wise, Emanuele Alesci, Enrique Borja among others. Meusburger's group includes Winston Fairbairn. Dittrich's AEI group incudes Dario Benedetti, Song He, James Ryan, Sebastian Steinhaus (giving the ILQGS presentation this semester), Wojciech Kaminski,... Oriti's group includes Fotini Markopoulou (as visitor), Matteo Smerlak, Isabeau Premont-Schwarz, Gianluca Calcagni, Lorenzo Sindoni,... Livine's group at Lyon includes Johannes Tambornino QG at LSU incudes Jorge Pullin, Parampreet Singh, and Jacobo Diaz-Polo I should also ennumerate the QG bunch at Penn State. There is a lot to keep track of. Maybe in a later post. αβγδεζηθικλμνξοπρσςτυφχψωΓΔΘΛΞΠΣΦΨΩ∏∑∫∂√±←↓→↑↔ ~≈≠≡ ≤≥½∞⇐⇑⇒⇓⇔∴∃⋅ℝℤℕℂ
 Astronomy Sci Advisor PF Gold P: 23,114 To continue the above list: In the above I should have noted that Kristina Giesel has joined the faculty of Thiemann's group at Erlangen. Also in the above Perimeter QG bunch I should have included Steffen Gielen. This month he moved from AEI (Dittrich group) to Perimeter. http://www.aei.mpg.de/~gielen/ Barrett's QG group at Nottingham http://www.nottingham.ac.uk/mathemat...m-gravity.aspx (faculty: John Barrett, Kirill Krasnov, Jorma Louko) More detail on QG at Penn State http://cft.igc.psu.edu/ (besides many well-known faculty, younger members include Elena Magliaro, Claudio Perini, William Nelson, Adam Henderson, Ivan Agullo---David Sloan until recently of this group is now at Utrecht, Ed Wilson-Ewing has moved on to Marseille, Jon Engle is now faculty at Florida-Atlantic, Param Singh now faculty at LSU) I shouldn't forget to mention two divisions of the University of Paris: Orsay (Vincent Rivasseau is there) and Paris-Diderot (Marc Geiller). Geiller is giving the February 28 ILQGS talk mentioned in the preceding post, on the Freidel Geiller Ziprick paper. Hanno Sahlmann has started a QG group at the AsiaPacific CPT (Pohang University of Science and Technology) Some resource links: Loops 2011 (many videos and slides pdf of the talks) http://www.iem.csic.es/loops11/ Undergrad LQG textbook http://www.amazon.com/First-Course-L.../dp/0199590753 A First Course in Loop Quantum Gravity Rodolfo Gambini, Jorge Pullin Oxford University Press. Master's program at Nottingham http://pgstudy.nottingham.ac.uk/post...-msc_1163.aspx Latest review papers http://arxiv.org/abs/1201.4598 Introduction to Loop Quantum Gravity (Abhay Ashtekar) and http://arxiv.org/abs/1108.0893 Loop Quantum Cosmology: A Status Report (Abhay Ashtekar, Parampreet Singh) Searches for Loop and String/M papers by year (results for 2011 now appear complete): LOOP RESEARCH BY YEAR (loop quantum gravity, loop quantum cosmology, spin foam) 2006 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (77 found) 2007 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (120 found) 2008 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (142 found) 2009 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (145 found) 2010 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (152 found) 2011 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb (203 found) 2012 http://inspirebeta.net/search?ln=en&...=25&sc=0&of=hb STRING,MEMBRANE,AdS/CFT RESEARCH BY YEAR (search terms "string model", "membrane model" and "AdS/CFT correspondence") 2006 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1029 found) 2007 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1050 found) 2008 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1128 found) 2009 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1133 found) 2010 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (1044 found) 2011 http://inspirebeta.net/search?ln=en&...=10&sc=0&of=hb (928 found) 2012 http://inspirehep.net/search?ln=en&a...=10&sc=0&of=hb A great series of Perimeter video lectures going back to 2003 PIRSA QUANTUM GRAVITY SERIES http://pirsa.org/S005 select "semester"=all and "year"=all. Among the more recent are talks by Eugenio Bianchi, Elena Magliaro, Edward Wilson-Ewing, Aristide Baratin, Philipp Höhn, Maïté Dupuis, Muxin Han, Matteo Smerlak This recent talk by Joseph Ben Geloun was for some reason not catalogued in the QG series http://pirsa.org/12010132/ so it does not show up in the above search. (topic GFT, tensor field theory) ινξςυφΓΘΛΞΠΣΦΨ⋅ℤℕ
 Astronomy Sci Advisor PF Gold P: 23,114 Phenomenology issues affecting various models, which may already be ruled out, are part of the general QG phenomenology picture http://backreaction.blogspot.com/201...time-foam.html that we need to keep track of. Although the observations discussed here seem not relevant to LQG specifically. In LQG space is not in a simple or naive sense "grainy". Its network states are quantum states of geometry (i.e. refer to relations among geometric measurements)---they're not imagined to be "what space is made of". Lorentz violation such as energydependent speed of light or the blurring of images one might get with a grainy substance are not predictions. One way to say it is QG is not about what space IS but rather it is about HOW IT RESPONDS to measurement. Analogous to basic quantum theory in other areas. ==quote Bee, above link== ...the authors have presented an analysis of the images of 157 high-redshift (z > 4) quasi-stellar objects. They found no blurring. With that, also the holographic foam model is ruled out. Or, to be precise, the parameter α is constrained into a range that is implausible for quantum gravitational effects. As it is often the case in the phenomenology of quantum gravity, the plausible models are difficult, if not impossible, to constrain by data. And the implausible ones nobody misses when they are ruled out. This is a case of the latter. ==endquote==
 P: 62 I read alot of Three Roads to Quantum Gravity last night. I found a free, legal, online pdf source if anyone wants to check it out too. Kinda for laymen, but it filled in the blanks for me :)
 Astronomy Sci Advisor PF Gold P: 23,114 Three Roads is certainly one way to get an introduction to QG. Right now I want to focus on the TESTING issue which has surfaced fairly recently. Bee Hossenfelder is a QG phenomenologist and she has just posted a paper written with Leonardo Modesto that discusses a completely new mode of QG testing. It sounds weird to me and dubious but I respect Bee a lot and maybe I have to get used to it. It is based on Modesto's 2008 paper that CLAIMS that in LQG a black hole will not have a singularity but will open up out the bottom to make a new spacetime region. Maybe this could be tested and proved wrong without it showing the whole theory to be wrong. Maybe it is not an airtight case, maybe he made some special assumption or did not derive it correctly from the full LQG theory. Anyway it gives an opportunity to test SOMETHING, and Bee is involved. So here is Modesto s original 2008 paper: ==quote== http://arxiv.org/abs/0811.2196 Space-Time Structure of Loop Quantum Black Hole Leonardo Modesto In this paper we have improved the semiclassical analysis of loop quantum black hole (LQBH) in the conservative approach of constant polymeric parameter. In particular we have focused our attention on the space-time structure. We have introduced a very simple modification of the spherically symmetric Hamiltonian constraint in its holonomic version... =endquote== NOW HERE IS THE NEW PAPER: http://arxiv.org/abs/1202.0412 Emission spectra of self-dual black holes Sabine Hossenfelder, Leonardo Modesto, Isabeau Prémont-Schwarz (Submitted on 2 Feb 2012) We calculate the particle spectra of evaporating self-dual black holes that are potential dark matter candidates. We first estimate the relevant mass and temperature range and find that the masses are below the Planck mass, and the temperature of the black holes is small compared to their mass. In this limit, we then derive the number-density of the primary emission particles, and, by studying the wave-equation of a scalar field in the background metric of the black hole, show that we can use the low energy approximation for the greybody factors. We finally arrive at the expression for the spectrum of secondary particle emission from a dark matter halo constituted of self-dual black holes. 15 pages, 6 figures I LIKE THIS BECAUSE it is a way to DISPROVE the existence of these weird double-mouthed black holes by looking for, and not finding, their distinctive radiation. It's empirical. And if they actually found some matching radiation it might be quite surprising. So good either way.
 Astronomy Sci Advisor PF Gold P: 23,114 A good introduction to the topic of LQBH (loop quantum black holes) Modesto-style is http://arxiv.org/abs/0905.3170 Self-dual Black Holes in LQG: Theory and Phenomenology Leonardo Modesto, Isabeau Prémont-Schwarz (Submitted on 20 May 2009) In this paper we have recalled the semiclassical metric obtained from a classical analysis of the loop quantum black hole (LQBH). We show that the regular Reissner-Nordstrom-like metric is self-dual in the sense of T-duality: the form of the metric obtained in Loop quantum Gravity (LQG) is invariant under the exchange "r ↔ a0/r" where "a0" is proportional to the minimum area in LQG and "r" is the standard Schwarzschild radial coordinate at asymptotic infinity. Of particular interest, the symmetry imposes that if an observer at "r" close to infinity sees a black hole of mass "m" an observer in the other asymptotic infinity beyond the horizon (at "r" close to "0") sees a dual mass "mp/m" ("mp" is the Planck mass). We then show that small LQBH are stable and could be a component of dark matter. Ultra-light LQBHs created shortly after the Big Bang would now have a mass of approximately "10-5 mp" and emit radiation with a typical energy of about 1013 - 1014 eV but they would also emit cosmic rays of much higher energies, albeit few of them. If these small LQBHs form a majority of the dark matter of the Milky Way's Halo, the production rate of ultra-high-energy-cosmic-rays (UHECR) by these ultra light black holes would be compatible with the observed rate of the Auger detector. 18 pages, 32 figures. Extra Plot, Improved Numerical Results I think the more recent paper I'll call HMP http://arxiv.org/abs/1202.0412 Emission spectra of self-dual black holes refines and corrects some of these estimates. Here is an excerpt ==quote Hossenfelder Modesto Prémont-Schwarz (HMP)== Integrating the inverse of dM/dt to obtain the lifetime, one finds that the time it takes for the black hole to completely evaporate exceeds the lifetime of the universe for m >~ 10−5mp. The primordially produced black holes with masses of about 10−3mp thus would still not have entirely decayed today. Moreover, they would have an average temperature of T ≈ 10−9mp ≈ 109 TeV, which is about in the energy range of the ultra high energetic cosmic rays (UHECRs) whose origin is still unclear. We thus see why the self-dual black holes can make for an interesting phenomenology. However, to arrive at observational consequences we have to make this rough estimate more precise. For this, we take ... ==endquote==
 Astronomy Sci Advisor PF Gold P: 23,114 One way to see where a field is going is to check the conferences, what speakers and themes emerge as important. We've done that in the past in this thread. 2011 was a big year for Loop, in terms of research output and conferences, so 2012 is likely to be comparatively quiet. One upcoming event is this June Prague Relativity and Gravitation conference: http://ae100prg.mff.cuni.cz/program Here are excerpts from the invited speaker list. ... Abhay Ashtekar (Institute for Gravitation and the Cosmos, Penn State University, University Park ) T.B.A.[my guess is Loop cosmology: inflation, initial conditions at the bounce, power spectrum] ... Julian Barbour (Department of Physics, University of Oxford, Oxford) Prague and the conception of general relativity: Kepler, Mach and Einstein ... Karel Kuchař (Department of Physics, University of Utah, Salt Lake City ) Canonical quantum gravity: Einstein's posthumous anathema Jerzy Lewandowski (Department of Physics, University of Warsaw, Warsaw) Loop quantum gravity: The status report ... Hermann Nicolai (Albert-Einstein-Institut Golm, Potsdam) Quantum gravity: the view from particle physics ... Misao Sasaki (Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto) Inflation and birth of cosmological perturbations ... Bernard Schutz (Albert-Einstein-Institute Golm, Potsdam) Gravity talks: observing the Universe with gravitational waves Alexei Starobinsky (Landau Institute for Theoretical Physics, Moscow) f(R) gravity--the most straightforward generalization of the Einstein gravity Robert Wald (Enrico Fermi Institute, University of Chicago, Chicago) T.B.A. Clifford Will (Department of Physics, Washington University, St. Louis) Testing general relativity: Centenary highlights and future prospects ================ Ashtekar has new quantum cosmology results with coauthors Agullo and Nelson, that have not been posted yet but were presented in seminar by Nelson http://relativity.phys.lsu.edu/ilqgs/nelson101811.pdf http://relativity.phys.lsu.edu/ilqgs/nelson101811.wav http://relativity.phys.lsu.edu/ilqgs/nelson101811.aif and which will be the subject of an invited presentation by Agullo at the April American Physical Society meeting. They are important results so it seems possible that Ashtekar will feature the new paper in his Prague talk this June. ================ This year's Marcel Grossmann meeting (July, in Stockholm) has these relevant parallel sessions: http://www.icra.it/mg/mg13/parallel_sessions.htm L. Quantum Gravity QG1 Loop Quantum Gravity, Quantum Geometry, Spin Foams (Jerzy Lewandowski) QG2 Quantum Gravity Phenomenology (Giovanni Amelino-Camelia) QG3 Asymptotic Safeness and Symmetry Breaking in Quantum Gravity (Eckehard W. Mielke) QG4 Loop quantum gravity: cosmology and black holes (Jorge Pullin, Parampreet Singh) for more information: http://www.icra.it/mg/mg13/ ================