#1
Jun2106, 04:00 AM

P: n/a

With any luck, sometime soon you can read this paper on the arXiv:
Aristide Baratin and Laurent Freidel Hidden quantum gravity in 4d Feynman diagrams: emergence of spin foams The idea is that any ordinary quantum field theory in 4d Minkowski spacetime can be reformulated as a spin foam model. This spin foam model is thus a candidate for the G > 0 limit of any spin foam model of quantum gravity and matter! In other words, we now have a precise target to shoot at. We don't know which if any spin foam model gives gravity in 4 dimensions, but now we know one that gives the G > 0 limit of gravity: i.e., ordinary quantum field theory. So, we should make up a spin foam model that reduces to Baratin and Freidel's when G > 0. The fascinating thing I noticed is that their spin foam model seems to be based on the Poincare 2group. I invented this 2group in my first paper on higher gauge theory: http://www.arxiv.org/abs/hepth/0206130 and Marnie Sheppeard and Louis Crane wrote a paper proposing a spin foam model based on this 2group: http://www.arxiv.org/abs/math.QA/0306440 The physical meaning of their spin foam model was unclear, and some details were not worked out, but it was very tantalizing. What did it mean?? I now conjecture  and so do Baratin and Freidel  that when everything is properly worked out, Crane and Sheppeard's spin foam model is the same as Baratin and Freidel's. So, it gives ordinary particle physics in Minkowski spacetime, at least after matter is included (which Baratin and Freidel explain how to do). If this is true, one can't help but dream... ... that deforming the Poincare 2group into some sort of "quantum 2group" could give a more interesting spin foam model: ideally, something that describes 4d quantum gravity coupled to matter! This more interesting spin foam model should reduce to Baratin and Freidel's in the limit G > 0. Of course this dream sounds "too good to be true", but there are some hints that it might work, to be found in the paper by Freidel and Starodubtsev: http://arxiv.org/abs/hepth/0501191 In particular, they describe gravity in way (equation 26) which reduces to BF theory as G > 0. BF theory is a theory of flat spacetime and that's what Baratin and Freidel's spin foam model describes. So, it may all fit together. Optimistic hopes in quantum gravity are usually dashed, but stay tuned. 


Register to reply 
Related Discussions  
Baratin and Freidel: a spin foam model of ordinary particle physics  Beyond the Standard Model  133  
Spin foam model from canonical quantization  Beyond the Standard Model  3  
How similar is Wen's "spin lattice" model to LQG's 4D spin foam theories?  Beyond the Standard Model  0  
Baratin and Freidel: a spin foam model of ordinary particle physics  General Physics  0  
Baratin Freidel Beef Baez and the Higher YumYums  Beyond the Standard Model  18 