Second-Order Graviton Propagator in Rovelli-Smolin's Loop Quantum Gravity

[Sauron]

I have finished a quick first reading of the rovelli at all paper ingraviton propagator http://arxiv.org/gr-qc/0604044

I couldn´t dive too much into the details because spin foams was a prerequisite and i only could do an equally fast reading of the alejandro perez review of the subjecto (i am tourning into the math exams now and i have less time for LQG).

But still with these porr knowledge i guess an aspecto is not trated as deep as it deserves in these articles.

I men,they get second order in a [tex]\lamdba[\tex] constant which appears in the Barret-Crane model, that is, it multiplies te "interaction" term. I didn´t see it firmly stablished but i guess that is somewhat equivalent to a second order in a series in the usual gravity G constant.That is, second order of perturbation theory in linear perturbative quantum gravity.

If these is true these would mean that they second order graviton propagator would correspond to the renormalized (loosely speaking) second order graviton propagator of the "naive" linear quantum gravity, isn´t it?

That would be a mayor succes because, as it is well known, linear quantum gravity isn´t renormalizable. So LQG would be, among other things, a way of ding renormalization in linear quantum gravity (i can´t brief it because it also would be LQG ).

Of course one of the mayor claims of loop QG is that you don´t need renormalization because it provides a natural cut´.off and et, etc.

As i said these doubt come from an inadequate fast rading. Hope not too disturb people if i made a too stupid question.

 

[marcus]

(i am tourning into the math exams now and i have less time for LQG)...

good luck with the math exams, Sauron!

since you have little time for reading right now, I will suggest a paper by Smolin that gives a brief non-technical description of Rovelli's graviton work.

http://arxiv.org/hep-th/0605052

I am finding this Smolin paper gives a helpful survey of current developments that is easy to read, and picks out the most important developments, and is intuitive without many equations.

Look on page 12, for a paragraph about Rovelli's graviton work
and also a paragraph about Loll triangulations.
It can be interesting to see these things through Smolin's eyes, as he looks at research of other people in the field of Loop-and-allied gravity and tries to understand the significance.

when will your exams be finished?

 

[hossi]

I apologize in advance, but you might want to check Lubos' blog

http://motls.blogspot.com/2006/04/carlo-rovelli-and-graviton-propagator.html"

 

[f-h]

Motl demonstrates one thing clearly: If you think in terms of perturbative QFT on around classical backgrounds LQG doesn't make sense.

As for lambda, this parameter arises in the group field method to generate spinfoam state sums. The order in lambda should correspond to the amount of detail you are resolving in your expansion. Last I heard (but I'm definitely not up to speed on this) the meaning of this parameter was not clear.