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Are there collective modes on Spin Foams or LQG?

  1. May 4, 2010 #1

    MTd2

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    Like phonons?
    Even if SF is a random lattice, there might be modes emerging from some space of phase space.

    Look at this example from BEC quantum Chaos:

    http://www.theo-phys.uni-essen.de/tp/forsch/bec.html
     
  2. jcsd
  3. May 4, 2010 #2

    tom.stoer

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    What exactly do you mean by "collective"?

    I would say that coherent states are - from the perspective of elementary excitations - something like collective modes.

    I am not sure if the concept of collective excitations carries over to SF, because the foam does not "vibrate", it exists. And the existence of a huge macroscopic SF is already in some sense a collective excitation on the vacuum, just as a macrosocopic coherent state of photons.

    So I would say that a semiclassical spacetime is a collective mode. Therefore your question is closely related to the question if semiclassical spacetime exists in SF models.
     
  4. May 4, 2010 #3

    MTd2

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    I was thinking about the spins on nodes. Maybe quai- particles could emerge from strongly spin systems, like spin waves.
     
  5. May 5, 2010 #4

    tom.stoer

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    Yes,

    one can split the analysis according to
    - kinematics: SU(2)-allowed "spin flips"
    - dynamics: propagation ...
     
  6. May 5, 2010 #5

    MTd2

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    Hmm, really? Any paper on that?
     
  7. May 5, 2010 #6

    MTd2

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    BTW, given that the lattice is random, should we expect quantum chaos?
     
  8. May 5, 2010 #7
    Do semiclassical spacetime exist in SF models?
     
  9. May 5, 2010 #8

    tom.stoer

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    I have to check. There are papers regarding coherent states; I think these are rather close to semiclassical spacetime. In addition there are papers regarding the long-wavelength limit for the graviton propagator, again related to semiclassical spacetime.
     
  10. May 5, 2010 #9
    Can conventional SM QFT be easily coupled to SF models?
     
  11. May 5, 2010 #10

    tom.stoer

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    For "old fashioned" LQG there are derivations at least for scalars and vector particles. For fermions I have seen classical approaches studying the Holst or Nieh-Yan action, but never a full LQG / SF model. Nevertheless people are talking about LQG methods applied to SUGRA.

    Honestly: nobody expects serious obstacles - not even for fermions - but there is no detailed derivation for SM+SF yet.
     
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