Reminding everybody of the long discussion of Stephon's paper and the Freidel Starodubtsev paper, which took place here
http://golem.ph.utexas.edu/~distler/blog/archives/000541.html
at Jaques Distler blog
Here for reference is Stephon's paper again
http://arxiv.org/hep-th/0503146
Here is the link for the Freidel Starodubtsev one (we had a thread about it at PF in which
John Baez took part)
https://www.physicsforums.com/showthread.php?t=61041
http://arxiv.org/abs/hep-th/0501191
Quantum gravity in terms of topological observables
Laurent Freidel, Artem Starodubtsev
"We recast the action principle of four dimensional General Relativity so that it becomes amenable for perturbation theory which doesn't break general covariance. The coupling constant becomes dimensionless {(G_{Newton} \Lambda)} and extremely small 10^{-120} . We give an expression for the generating functional of perturbation theory. We show that the partition function of quantum General Relativity can be expressed as an expectation value of a certain topologically invariant observable. This sets up a framework in which quantum gravity can be studied perturbatively using the techniques of topological quantum field theory."
since we are gathering thematic material together I will repeat
the first two paragraphs of Stephon's paper.
They give an overview, which supplements that given by Ohwilleke, of how Stephon sees his paper, where it fits in, and what the main thrust of it is.
---Alexander paper Intro, first two paragraphs---
It has always been a dream to solve the cosmological constant problem by relaxing it to the minimum of a potential [1]. This hope has been especially unsuccessful in conventional canonical quantum gravity. In QCD, the strong CP problem was solved by relaxing the Theta parameter at the minimum of the potential associated with an axion field via the Peccei-Quinn mechanism. It turns out that when quantum gravity is formulated in the Ashtekar-Sen variables (LQG), the theory has a semblance to Yang-Mills theory and the cosmological constant problem becomes analogous to the strong CP problem. It is the purpose of this paper to make this analogy explicit and use a Peccei-Quinn like mechanism to pave a possible route to solving the cosmological constant problem.
Loop Quantum Gravity (LQG) has a one parameter family of ambiguities which is labeled by \gamma, the Barbero Immirizi parameter. This parameter plays a similar role to the QCD Theta parameter which labels the unitarily inequivalent sectors of the quantum theory. These sectors can be accessed by tunneling events due to instanton field configurations. Theta is also a measure of CP violation, which is constrained by the neutron electric dipole moment to be Theta < 10
-9.
In LQG the Barbero-Immirizi parameter is also a measure of CP violation, since it couples to the first Pontrjagin class. Specifically, in the quantum theory \gamma corresponds to unitarily inequivalent representations of the algebra of geometric operators. For example, the simplest eigenvalues of the area operator in the \gamma quantum sector is given by
[familiar LQG formula for area eigenvalues]
What fixes the value of the Barbero-Immirizi parameter? In this letter we will show that this question is connected to another parameter in general relativity, the cosmological constant.
Therefore the question of fixing the Barbero-Immirizi parameter is related to a quantum gravitational determination of the cosmological constant. Through this relationship we will propose a possible dynamical, background independent mechanism to relax the cosmological constant. Specifically, we will demonstrate that a Peccei-Quinn like mechanism associated with a non-vanishing vev of fermion bilinears coupled to gravity will yield an effective potential for a parameter which alters the ratio of Barbero-Immirizi parameter and the cosmological constant.
We then use the value of the Barbero-Immirizi parameter determined from Black Hole quasinormal modes to determine the conditions which relaxes the cosmological constant.
---end quote---
In light of all this it is fascinating to see how Jacques Distler who has devoted much of his career to string theorizing and has what is probably the best string blog, responds to the papers of Stephon and of Laurent Freidel. Lee Smolin also takes part in the thread responding to questions and requests for information from Distler.
this kind of intense string interest in LQG at the detail level and accordingly intense exchanges were rare heretofore---or else were rather noisy occasions
didnt she co-author something with him?
