Spin foam phase space, classical action (Wieland's talk is online)

[marcus]

Wieland gave his ILQGS talk yesterday, 16 September. Audio and slides are on line.

Title: Covariant loop quantum gravity: Its classical action, phase space and gauge symmetries
http://relativity.phys.lsu.edu/ilqgs/wieland091614.pdf
http://relativity.phys.lsu.edu/ilqgs/wieland091614.wav

The short title was "The spin foam action"
Abstract: I present an action for simplicial gravity in first-order area-connection variables. The theory has a Hamiltonian and local gauge symmetries. Generic solutions represent twisted geometries, and have curvature – there is a deficit angle around triangles.

Some references:
*ww, New action for simplicial gravity in four dimensions (2014), arXiv:1407.0025.
*ww, One-dimensional action for simplicial gravity in three dimensions, Phys. Rev. D 90 (2014), arXiv:1402.6708.
*ww, Hamiltonian spinfoam gravity, Class. Quant. Grav. 31 (2014), arXiv:1301.5859.
*M Cortês and L Smolin, Spin foam models as energetic causal sets (2014), arXiv:1407.0032.
*L Freidel and S Speziale, From twistors to twisted geometries, Phys. Rev. D 82 (2010), arXiv:1006.0199.

 

[marcus]

The audio is 1 hour 16 minutes and concludes with one of the longest, most active and interesting discussions which I have heard at ILQGS (Wolfgang, Abhay, Carlo, Lee, Simone, Eugenio, and possibly others).
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In slide 5 Weiland mentions some unresolved issues in spinfoam QG, and puts forward his view on how they should be addressed.

... ongoing debates:
How can we find continuum GR? Which limit? Summing, refining?
Do we miss additional secondary (torsional) constraints?
Is there a flatness problem?
Is there a notion of causality in spin foams?

I think, these issues have little to do with the quantum theory itself. We should address these question already at the classical level. What we need is a framework of simplicial gravity in area–connection variables.

 

[marcus]

In case this talk interests readers in hearing more of the ILQGS talks (while following the slides) here is the main page, with links to audio and slides PDF.
http://relativity.phys.lsu.edu/ilqgs/
This can serve as a menu covering Fall and Spring semesters of past years, as well as the current semester.

Here is the current semester schedule:
http://relativity.phys.lsu.edu/ilqgs/schedulefa14.html

Sep 2	 [B]Casimir effect on a quantum geometry[/B]	 Javier Olmedo	 LSU
Sep 16   [B]Cov LQG: classical action, phase space & gauge symmetries[/B]  Wolfgang Wieland PSU
Sep 30   [B]Phenomenological consequences of quantum geometries in LQC[/B] Brajesh Gupt  PSU
Oct 14	 [B]White holes[/B]	 Carlo Rovelli	 CNRS Marseille
Oct 28	 [B]New applications for LQG[/B]	 Jerzy Lewandowski	 University of Warszaw
Nov 11	 [B]Lorentz transformations from abstract quantum theory[/B]	 Philip Hoehn  PI
Nov 25	 TBA	 Derek Wise	 FAU Erlangen
Dec 9	 [B]Invariance of Connections and Measures in LQC[/B]  Maximilian Hanusch Uni Paderborn