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Freidel Utrecht 1 May Latent qg Endgame Scenario

  1. Apr 9, 2006 #1

    marcus

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    On 1 May, around three weeks from now, Laurent Freidel will speak at the Utrecht ITP, probably discussing latent QG in 4D among other things.

    If you follow QG and are convenient to Utrecht, you may wish to attend this talk, which I expect will suggest an endgame scenario for quantum spacetime and matter synthesis.

    If anyone wants to report to us here on the 1 May talk, it would be very interesting to hear about it.
     
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  3. Apr 9, 2006 #2

    marcus

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    I am using the key word Latent, meaning "hidden", in reference to the titles of some recent and current work.

    Freidel et al are digging out a version of non-string QG which is latent in usual flat QFT. Specifically it is latent in the Feynman diagrams of QFT.

    The point is that there could be a lot of different spinfoam QG models, depending on what vertex/edge amplitudes one uses to define the partition function. With luck, the particular model that Freidel is unearthing is the RIGHT one because it is already in some sense implicit in the established QFT that describes matter fields in flat Minkowski space.

    About the recent and current Freidel et al work, F-H mentioned this talk by Baratin, on-line at the Loops '05 website

    Baratin: "Emergence of Spin Foam in Feynman Graphs"

    and there is also this Freidel/Baratin paper

    Hidden Quantum Gravity in 3d Feynman diagrams
    http://arxiv.org/abs/gr-qc/0604016

    and this one to appear
    Hidden Quantum Gravity in 4d Feynman diagrams: Emergence of spin foams

    One reason the 1 May talk at Utrecht is interesting is that it will give an idea how the 4D case is going.
     
  4. Apr 9, 2006 #3

    marcus

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    Here is a quote from Baratin's October 2005 talk that I want to think about. It is from slide #2:

    Can one formulate 4D Feynman graphs in a background independent manner?

    the usual feynman graph is defined using a flat background and one can integrate over all possible locations of the N vertices of the graph.

    but Freidel et al have found a way of getting feynman graphs as the no-gravity limit of spinfoams. and spinfoams are defined WITHOUT assuming any background geometry, flat or otherwise. so it looks like Freidel et al have found a new way of defining feynman graphs----one that does not require fixing on some background geometry ahead of time.

    Related quotes from Baratin:

    "Usual...Feynman graphs recovered as the no-gravity limit of spinfoams coupled to particles." (this was shown for 3D in the earlier preprint and the authors say it can be extended to 4D, as per the preprint to appear.)

    "...perturbative formulation of 4D quantum gravity..."

    the perturbative formulation refers to the 2005 paper of Freidel and Starodubtsev. We had some discussion of that here at PF a year or so ago.

    the quote in blue relates to a passage in the recent preprint for example here is a quote from the conclusions paragraph on page 27:

    "The main point was to show that the language of spin foam models - which was developed in order to address the problem of a background independent approach to quantum gravity - naturally arises in the context of quantum field theory, and that a careful study of Feynman amplitudes can even lead to a purely algebraic understanding of the quantum weights. It was also shown that usual field theory can be given a background independent perspective in the sense that the flat space geometry is purely encoded in terms of a choice of weights controlling the dynamics of the geometry."
     
    Last edited: Apr 9, 2006
  5. Apr 9, 2006 #4

    marcus

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    Here is a evocative quote from the recent Freidel Baratin preprint page 26 section right before the conclusions section:

    "Before concluding, we would like to give some continuum explanation for the results we have obtained here. The fact that our state-sum model is built from 6j-symbols of the Poincaré group shows, from standard arguments [11], that the topological theory which we have described in terms of a spin foam model is the quantization of a Poincaré BF theory. This theory can be written in terms of a one-form E and a connection A, both valued in the Poincaré algebra, ..."
     
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