BeGroMaS: gravity was renormalizable after all, so why all the fuss?

[tom.stoer]

KKL are the LQG camp that proposes the same (though Rovelli has tried to undo it).

The problem with LQG is that the Barbero-Immirzi parameter and the cosmological constant are treated differently than all other couplings

 

[atyy]

The problem with LQG is that the Barbero-Immirzi parameter and the cosmological constant are treated differently than all other couplings

What do you make of stuff like http://arxiv.org/abs/0903.4407 ?

This seems to me a step even further from the AS heuristic, but I find it intriguing.

 

[tom.stoer]

I totally forgot about these BI-field ideas. Yeah, the BI-parameter may become an "ordinary" field and the AS program needs to be adjusted accordingly (applied to the Holst action / Nieh-Yan invariant based on Ashtekar variables). Nevertheless the cc as a quantum deformation SU_q(2) or something like that does not fit to the AS program.

 

[atyy]

I'm not terribly keen on the cc as q-deformation. It seems a lot to take care of an IR divergence, which is probably not a problem in the first place. I would like to see the "UV-like" divergence taken care of, perhaps through Rivasseau's GFT renormalization programme.

 

[erkokite]

Kinda new paper here (2 mos. old). BFL Ward uses his resummation approach, which is similar to and consistent with asymptotic safety to derive a value for the cosmological constant which is close to the observational value (2.4e-3 eV vs 2.368e-3 eV).

Planck Scale Cosmology and Asymptotic Safety in
Resummed Quantum Gravity

In Weinberg’s asymptotic safety approach, a finite dimensional critical surface for a UV stable
fixed point generates a theory of quantum gravity with a finite number of physical parameters. We argue that, in an extension of Feynman’s original formulation of the theory, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. Our results are consistent with the exact field space Wilsonian renormalization group results of Reuter et al. and with recent Hopf- algebraic Dyson-Schwinger renormalization theory results of Kreimer. We obtain the first "first principles" predictions of the dimensionless gravitational and cosmological constants and our results support the Planck scale cosmology of Bonanno and Reuter. We conclude with an estimate for the currently observed value of the cosmological constant

http://arxiv.org/PS_cache/arxiv/pdf/1012/1012.2680v1.pdf"

I'm not 100% sure of the exact link between Ward's work and the AS approach, but it seems to be this- Ward has found that a generalized YFS resummation of the perturbative expansion in Feynman's formulation of quantum gravity which is claimed to produce a perturbatively renormalizable and UV complete formulation of QG which also results in a fixed point. It seems to me that Ward's approach is probably equivalent to the RG picture, but he has found a resummation that produces consistent results as opposed to using the RG directly.

 

[marcus]

BFL Ward's paper was on our poll (about the relative interest/importance of QG papers that appeared in the last 3 months, Oct-Dec 2010.)

https://www.physicsforums.com/showthread.php?t=458853

Check it out. It is a multichoice poll so you can vote for several, and the poll is public, so if you click "results" and then on the number of votes a paper got, you can see who selected it.
It's still open, so anyone who hasn't registered their picks can do so.

 

[arivero]

Ward has found that a generalized YFS resummation of the perturbative expansion in Feynman's formulation of quantum gravity which is claimed to produce a perturbatively renormalizable and UV complete formulation of QG which

Do they sum order by order, or all the series? I mean, there are two structures of divergences in perturbative QCD: the divergences at a given order of the coupling, and the divergence of the renormalised series itself.

 

[murray92]

Do they sum order by order, or all the series? I mean, there are two structures of divergences in perturbative QCD: the divergences at a given order of the coupling, and the divergence of the renormalised series itself.

Maybe you want to watch the talk he gave at the asym conferenze last year.
http://www.perimeterinstitute.ca/Events/Asymptotic_Safety/Abstracts/#ward

I think he also gave one at ICHEP in Paris this year about his resummed Quantum Gravity

 

[A. Neumaier]

Maybe you want to watch the talk he gave at the asym conferenze last year.
http://www.perimeterinstitute.ca/Events/Asymptotic_Safety/Abstracts/#ward

I think he also gave one at ICHEP in Paris this year about his resummed Quantum Gravity

See also
http://arxiv.org/pdf/hep-ph/0610232 (published as: Int.J.Mod.Phys.D17:627-633,2008),
and more recently arXiv:1008.1046, arXiv:0908.1764.