New Spin Foams are broken.

MTd2

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According to this recent paper:

http://arxiv.org/abs/1010.4886

The graviton of the new spin foam models fall like 1/r^4 and not like 1/r^2 as it should be. Is it that bad?
 

atyy

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They think it's the complex conjugate terms in Eq 9 and 10 which is bad. I think Bianch et al tried to fix this. http://arxiv.org/abs/1004.4550

But the new spin foams have a divergent physical inner product, so that's another problem. Group field theory renormalization?

But if the theory is renormalized, how can it have a fundamental scale of discreteness?
 

marcus

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They already posted a result of this type in May 2010. So far it has not been published or cited.
In the acknowledgements of the May paper they thank John Barrett for discussion. He heads the QG group at Nottingham and has published key results on spinfoam asymptotics. He also directs the branch of ESF that funds QG.
If you think that the Mikovic paper could possibly be valid, you might get some clarification from Barrett or from someone in that group.

Something that strikes me as curious is that the October Mikovic paper does not have any regular acknowledgements at all. No indication that there were further discussions with Barrett or with anyone else.

Here is the May preprint:
http://arxiv.org/abs/1005.1866

Here are Mikovic's papers after 2006:
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+A+MIKOVIC+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE= [Broken]

There are eight papers (date > 2006) of which two were published. The two that were published garnered a total of 6 citations--two by Mikovic himself and the other four in papers (co)authored by Cecilia Flori.
The other six papers appear not to have been cited at all.

In 2004 Mikovic published a paper which contain errors, in the journal Classical and Quantum Gravity (CQG, where a lot of quantum gravity research is published).
In 2006 he published a correction in CQG. No sign that he has submitted anything to CQG since then.
http://arXiv.org/abs/gr-qc/0606081
 
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atyy

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Citations apart, their content of their criticism is discussed in Rovelli's two latest summary papers, and addressed in Bianchi et al, so it is criticism of substance.
 

marcus

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Citations apart, their content of their criticism is discussed in Rovelli's two latest summary papers, and addressed in Bianchi et al, so it is criticism of substance.
You mention the April paper by Bianchi et al. Can you point me to the line or lines in that paper that you are talking about? I am not so much interested in the May and October papers of Mikovic, which would be "after the fact". I'd like to see what problems Bianchi et al discovered and addressed.

If you could also point to an equation or paragraph in Rovelli's April paper that would be great.
 

atyy

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http://arxiv.org/abs/0907.2440 , Eq 53 and 54

Discussions are in

http://arxiv.org/abs/1004.1780
"In fact, what is shown in [45] is that Wv ~ eiSRegge +eiSRegge. Concern has been raised by the fact that two terms appear in this sum."

http://arxiv.org/abs/1004.4550
"We argue that the presence of the second undesired classical solution in the semiclassical expansion is an artifact of the representation used"

http://arxiv.org/abs/1010.4886
"In conclusion, let us note that if the vertex amplitude had the asymptotic behavior Ws ~ eiSR(v) ... one would obtain the correct graviton propagator asymptotics. ...However, the presence of the complex conjugate terms ... is responsible for the result S = O(1), which gives the wrong asymptotics for the propagator."
 

MTd2

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Nice finding. It settles the assumptions of the paper as wrong.
 

atyy

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Nice finding. It settles the assumptions of the paper as wrong.
I haven't read the paper carefully - do you know whether their boundary assumptions are the same as Bianchi et al's?
 

MTd2

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No, I didn't. Lol.

Anyway. I am waiting Marcus to open a thread about Rovelli's new paper. It seems to be the best paper of this year, in my opinion. But I want him to give an explanation, to be sure of that.
 

marcus

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No, I didn't. Lol.

Anyway. I am waiting Marcus to open a thread about Rovelli's new paper. It seems to be the best paper of this year, in my opinion. But I want him to give an explanation, to be sure of that.
I responded to you here:
https://www.physicsforums.com/showthread.php?p=2957318#post2957318
since it is all part of a coherent plan of development.

I am beginning to agree with your intributing importance to the "Summing=refining" paper. Although at first I was considering it just as filling in details for a more concise statement in 1010.1939 ("Simple model" paper)
 

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