Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

AsymSafe, LQG, Verlinde at the Paris ICHEP

  1. Jul 24, 2010 #1

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    What can we learn, if anything, from how the organizers of the ICHEP chose to represent the growing research activity in nonstring approaches to QG?
    ICHEP is currently going on in Paris and has somewhat more than 1000 participants. International Conf on High Energy Physics. Largely experimental HEP, with most theory sticking close to the Standard Model.

    To get perspective, there were 12 parallel sessions labeled "Beyond the Standard Model" and string talks were segregated into FOUR of these, all of which took place the first day, Thursday 22 July.
    These Thursday BSM sessions were labeled "BSM (including string theory)".
    It is these four Thursday BSM sessions which had some Loop, AsymSafe, and Verlinde gravity in their makeup.

    The other eight BSM parallel sessions took place Friday and Saturday and were straight particle physics with no string or QG. The plenary talks will take place next week Monday-Wednesday.

    So the QG presence at ICHEP is quite light, as one would expect. The interest, if any, is in what the organizers picked to have on display, in Thursday's four BSM sessions. The following is a sample:
    ==quote==
    Planck Scale Cosmology and Asymptotic Safety in Resummed Quantum Gravity

    Content: In Weinberg’s asymptotic safety approach to quantum gravity, one has a finite dimensional critical surface for a UV stable fixed point to generate a theory of quantum gravity with a finite number of physical parameters. The task is to demonstrate how this fixed point behavior actually arises. We argue that, in a recently formulated extension of Feynman’s original formulation of the theory, which we have called resummed quantum gravity, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. We argue that the results we obtain are consistent both with the exact field space Wilsonian renormalization group results of Reuter and Bonanno and with recent Hopf-algebraic Dyson-Schwinger renormalization theory results of Kreimer. We calculate the first "first principles" predictions of the respective dimensionless gravitational and cosmological constants and argue that they support the Planck scale cosmology advocated by Bonanno and Reuter as well. Comments on the prospects for actually predicting the currently observed value of the cosmological constant are also given.
    Id: 159
    Place:
    Room: Salle 252A
    Starting date:
    22-Jul-2010 17:43 (Europe/Paris)
    Duration: 14'
    Contribution type: Parallel Session Talk
    Primary Authors: WARD, Bennie (Baylor University, Waco, TX, USA)
    ==============
    Link to Ward's slides is here:
    http://indico.cern.ch/contributionDisplay.py?sessionId=47&contribId=159&confId=73513
     
    Last edited: Jul 24, 2010
  2. jcsd
  3. Jul 24, 2010 #2

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I should stress that there were 80 parallel sessions at the ICHEP, 24 on Thursday and 28 on each of the following two days. We are only talking about the 4 out of those 80 which had stringy/QG content. But even though a small portion, I think the makeup is worth noting. Here are further samples:
    ==quote==
    Loop quantum gravity and the early universe

    Content: Loop quantum gravity is, together with string theory, one on the major candidate approach to quantize gravity. It provides a framework which allows for a non-perturbative and background-independant canonical quantization of general relativity. In this talk, I will briefly go through the basic conceptual groundings of the theory and switch to the latests developments associated with its implementation in the cosmological context. I will show that the Big Bang is replaced by a Big Bounce (therefore solving the initial singularity problem) and that inflation unavoidably occurs. Furthermore, the primordial tensor power spectrum should exhibit some characteristic features that could lead to experimental tests of this "Planck-scale" physics.
    Id: 126
    Place:
    Room: Salle 252A
    Starting date:
    22-Jul-2010 12:06 (Europe/Paris)
    Duration: 18'
    Contribution type: Parallel Session Talk
    Primary Authors: Dr. BARRAU, Aurelien (LPSC Laboratoire de Physique Subatomique et de Cosmologie (LPSC))
    ==endquote==

    Link to Barrau's slides is here:
    http://indico.cern.ch/contributionDisplay.py?sessionId=47&contribId=126&confId=73513

    ==quote==
    Gravity as an Emergent Force

    Content: Starting from first principles and general assumptions Newton's law of gravitation is shown to arise naturally and unavoidably in a theory in which space is emergent through a holographic scenario. Gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations. When space is emergent even Newton's law of inertia needs to be explained. The equivalence principle leads us to conclude that it is actually this law of inertia whose origin is entropic.
    Id: 1201
    Place:
    Room: Salle 252A
    Starting date:
    22-Jul-2010 14:00 (Europe/Paris)
    Duration: 37'
    Contribution type: Parallel Session Talk
    Primary Authors: Prof. VERLINDE, Erik (ITP, University of Amsterdam)
    ==endquote==

    Link to Verlinde's slides is here:
    http://indico.cern.ch/contributionDisplay.py?sessionId=47&contribId=1201&confId=73513
    Links to overall schedule is here:
    http://indico.cern.ch/conferenceTimeTable.py?confId=73513&ttLyt=room#all [Broken]
     
    Last edited by a moderator: May 4, 2017
  4. Jul 24, 2010 #3
    Last edited: Jul 24, 2010
  5. Jul 24, 2010 #4

    MTd2

    User Avatar
    Gold Member

    Now I get it. Closed strings carries gravitons explicitly, so they do not really exit. LOL.

    Or not to LOL?!?

    So, the true superstring is the Type I, and just the open type. And the holographic screen is a brane...

    But... the holographic screen should be intangible.
     
    Last edited: Jul 24, 2010
  6. Jul 24, 2010 #5

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

  7. Jul 24, 2010 #6

    MathematicalPhysicist

    User Avatar
    Gold Member

    Is any of this real?!
    A question everyone ponders anyways.. (-:
     
  8. Jul 24, 2010 #7
    I am curios if anyone on physicsforums has read any of wards papers on Resummed Gravity...?
    Doesn't he basically claim that the resummation makes Quantum gravity UV finite and ?

    He also spoke at the asymptotic safety conference at perimeter? I vaguely remember the talk... everyone seemed suprised, polite, and a bit disbelieving...

    Why is there so little interst in Wards method, if it is sound it would be quite big news wouldn't ist... but it seems he did all the work on it allone, and he rarely gets cited? Why is this?

    Ok sorry, if i just wrote a lot of incoherent mumbeling, ... it's pretty late her in austria,
    good night everybody...
     
  9. Jul 24, 2010 #8

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Past 3:00 hours in Austria, high time ins Bett gehen.

    You mention Bennie Ward gave a talk at the November AsymSafe conference. I will get the link to the video.
    http://pirsa.org/09110043/
    As I recall many prominent AS people were in the audience: Steven Weinberg, Martin Reuter, Roberto Percacci, Frank Saueressig, Lee Smolin, Mario Benedetti, etc etc. The video shows some mild audience reaction.
    But now that you mention it there could have been that "politeness".

    I think they HAVE to be paying some attention, just from the soft evidence that he gets invited to talk ICHEP, a big-deal conference. But I have no hard evidence that he has engaged others in the community.
    ====================

    My personal take is that the only one that grabs me is the talk by Aurelien Barrau about ways to observe the effects of LQG in the CMB. He and a few others (mostly French and Polish) have been writing about that in the past 18 months or so. It is good that the people at ICHEP hear about that.
     
    Last edited: Jul 24, 2010
  10. Jul 25, 2010 #9

    marcus

    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    The interesting thing for me is that some 18 months ago Barrau out of the blue, with no previous association with the LQG community, started to write about how Loop Quantum Cosmology might be tested by detailed observation of the CMB, the microwave background.

    He is a cosmologist, with fairly broad interests in fundamental physics. I think he earlier did some string-related papers. Last time I checked he was at Grenoble, and his co-author Julien Grain was in Paris.

    This is just the kind of dispassionate outside phenomenological scrutiny that one could wish for. Also they seem to be young: Barrau is young faculty and Grain was a postdoc.
    There were also some Polish scientists. Jakub Mielczarek comes to mind. So a string of papers resulted. I will get the links.

    http://arxiv.org/abs/1003.4660
    Inflation in loop quantum cosmology: Dynamics and spectrum of gravitational waves
    Jakub Mielczarek, Thomas Cailleteau, Julien Grain, Aurelien Barrau
    (Submitted on 24 Mar 2010)
    Loop quantum cosmology provides an efficient framework to study the evolution of the Universe beyond the classical Big Bang paradigm. Because of holonomy corrections, the singularity is replaced by a "bounce". The dynamics of the background is investigated into the details, as a function of the parameters of the model. In particular, the conditions required for inflation to occur are carefully considered and are shown to be generically met. The propagation of gravitational waves is then investigated in this framework. By both numerical and analytical approaches, the primordial tensor power spectrum is computed for a wide range of parameters. Several interesting features could be observationally probed.
    Comments: 11 pages, 14 figures. Matches version published in Phys. Rev. D

    http://arxiv.org/abs/0911.3745
    Loop quantum gravity and the CMB: toward pre-Big Bounce cosmology
    Aurelien Barrau
    (Submitted on 19 Nov 2009)
    This brief article sums up the possible imprints of loop quantum gravity effects on the cosmological microwave background. We focus on semi-classical terms and show that "Big Bounce" corrections, together with the "pre Big Bounce" state, could modify the observed spectrum.
    Comments: Proceedings of the 12th Marcel Grossman Meeting on General Relativity. 3 pages.

    http://arxiv.org/abs/0910.2892
    Fully Loop-Quantum-Cosmology-corrected propagation of gravitational waves during slow-roll inflation
    J. Grain, T. Cailleteau, A. Barrau, A. Gorecki
    (Submitted on 15 Oct 2009)
    The cosmological primordial power spectrum is known to be one of the most promising observable to probe quantum gravity effects. In this article, we investigate how the tensor power spectrum is modified by Loop Quantum Gravity corrections. The two most important quantum terms, holonomy and inverse volume, are explicitly taken into account in a unified framework. The equation of propagation of gravitational waves is derived and solved for one set of parameters.
    Comments: Physical Review D, 9 pages.

    http://arxiv.org/abs/0902.3605
    Inverse volume corrections from loop quantum gravity and the primordial tensor power spectrum in slow-roll inflation
    J. Grain, A. Barrau, A. Gorecki
    (Submitted on 20 Feb 2009)
    Together with holonomy corrections, inverse volume terms should be taken into account when studying the primordial universe in loop quantum cosmology. We investigate how the tensor power spectrum is modified with respect to the standard general relativistic prediction by those semiclassical corrections. Depending on the values of the free parameters of the model, it is shown that the spectrum can exhibit a very large deviation from its usual shape, in particular with a very red slope and a strong running in the infrared limit.
    Comments: Physical Review D 15 pages, 5 figures.

    http://arxiv.org/abs/0902.0145
    Cosmological footprints of loop quantum gravity
    J. Grain, A. Barrau
    (Submitted on 2 Feb 2009)
    The primordial spectrum of cosmological tensor perturbations is considered as a possible probe of quantum gravity effects. Together with string theory, loop quantum gravity is one of the most promising frameworks to study quantum effects in the early universe. We show that the associated holonomy correction should modify the potential seen by gravitational waves during the inflationary amplification. The resulting power spectrum should exhibit a characteristic tilt. This opens a new window for cosmological tests of quantum gravity.
    Comments: Physical Review Letters, 7 pages, 2 figures.
     
    Last edited: Jul 25, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook