Are there collective modes on Spin Foams or LQG?

[MTd2]

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

 

[tom.stoer]

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.

 

[MTd2]

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

 

[tom.stoer]

Yes,

one can split the analysis according to
- kinematics: SU(2)-allowed "spin flips"
- dynamics: propagation ...

 

[MTd2]

Hmm, really? Any paper on that?

 

[MTd2]

BTW, given that the lattice is random, should we expect quantum chaos?

 

[ensabah6]

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.

Do semiclassical spacetime exist in SF models?

 

[tom.stoer]

Do semiclassical spacetime exist in SF models?

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.

 

[ensabah6]

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.

Can conventional SM QFT be easily coupled to SF models?

 

[tom.stoer]

Can conventional SM QFT be easily coupled to SF models?

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.