Is Rivasseau switching to agriculture?

[atyy]

No more quantum gravity As we know strings and loops are both about condensed matter (AdS/CMT, tensor networks). So these guys want to apply their skills to real world problems too and grow melons. I think the back-up plan for the people who cloned the potassium channel, if the cloning didn't work out, was to sell melons. Well, the cloning did work, so Rivasseau will have to hope he gets other customers.

http://arxiv.org/abs/1105.3122v1
Critical behavior of colored tensor models in the large N limit
Valentin Bonzom, Razvan Gurau, Aldo Riello, Vincent Rivasseau
(Submitted on 16 May 2011)
Abstract: Colored tensor models have been recently shown to admit a large N expansion, whose leading order encodes a sum over a class of colored triangulations of the D-sphere. The present paper investigates in details this leading order. We show that the relevant triangulations proliferate like a species of colored trees. The leading order is therefore summable and exhibits a critical behavior, independent of the dimension. A continuum limit is reached by tuning the coupling constant to its critical value while inserting an infinite number of pairs of D-simplices glued together in a specific way. We argue that the dominant triangulations are branched polymers.

 

[marcus]

Thanks for spotting this. I was going to ask if anyone could explain it's significance but I see you already have

Correct me if I am wrong. A d-simplex has d+1 faces (e.g. a 2-simplex is a triangle with 3 sides) and a melon is what you get by taking two d-simplices and gluing them together on d of their d+1 faces.
So for example glue two triangles together along two sides each.


Each of the original simplices still has one face free, so a melon has two faces--that can attach to other stuff if desired. So you can for example string melons together in a melon-chain.
I can see how a chain of melons could branch...

Atyy or anybody want to summarize what this paper accomplishes or where it is going?

 

[atyy]

"The i.i.d. model is quite naturally interpreted as a model of dynamical triangulations (DT) [47–51]. In the reminder of this section we switch to notations more familiar in the DT literature."

"The authors are grateful to Jan Ambjørn for his explanations on branched polymers in matrix models and dynamical triangulations."

Looks like they analytically get the large volume limit of DT (by accident). In the conventional interpretation of the formalism, this a branched polymer phase with no smooth geometry (I think, just my quick reading).

This should be very interesting. I've always thought that if Rovellian spin foams are to work, they must link up with CDT, which I believe is the only indication so far that pure gravity could work (By Rovellian spin foam I mean quantum gravity without unification, since others working on spin foams are trying to get unification).

 

[Coin]

Hey you'd actually be surprised, the guys over in the agronomy department are doing some pretty deep stuff!

( <-- First "real" job was writing software for differential sequencing of corn genomes :P )

 

[atyy]

What is differential sequencing?

 

[Coin]

What is differential sequencing?

It refers to any of a number of methods of DNA sequencing where instead of sequencing the whole genome you take a similar organism with a fully sequenced genome and sequence the "differences". So say you want the genome for some strain of rice, instead of paying to sequence the whole thing you instead find a different strain of rice someone else has already sequenced and find some method for discovering just where and what the genetic differences between the two are, which since you already know the genome for #2 allows you to recover the genome for strain #1. I honestly don't know how commonplace this sort of thing is.

Sorry, didn't mean to threadjack :)

 

[atyy]

It refers to any of a number of methods of DNA sequencing where instead of sequencing the whole genome you take a similar organism with a fully sequenced genome and sequence the "differences". So say you want the genome for some strain of rice, instead of paying to sequence the whole thing you instead find a different strain of rice someone else has already sequenced and find some method for discovering just where and what the genetic differences between the two are, which since you already know the genome for #2 allows you to recover the genome for strain #1. I honestly don't know how commonplace this sort of thing is.

Sorry, didn't mean to threadjack :)

Is it done by hybridization to find common sequences, and lots of primers to get handles on the differential bits?

 

[Coin]

Is it done by hybridization to find common sequences, and lots of primers to get handles on the differential bits?

Yes, that sounds right. The method we were using (http://rice.genomics.purdue.edu/docs/ASPB_2003.pdf was the project I was working for) would wash dna fragments with specially prepared sequences named "overgos" which would stick to (hybridize?) DNA they matched. We'd get out these photographs that looked kinda like like microarrays (and I believe were generated with a similar process) but were black and white only, and we'd use that to tell which of the fragments the overgo matched. I am probably not qualified to give a really correct description of how it worked, I was just a code monkey. :)

Conclusion: Melons: The NIH will probably give you a grant to study them.

 

[atyy]

I am probably not qualified to give a really correct description of how it worked, I was just a code monkey. :)

Conclusion: Melons: The NIH will probably give you a grant to study them.

Ah, important stuff. I'm a wetlab sort of dummy, and we appreciate having tools like that made for us.

Let's add this new paper from marcus's bibliography - it too talks about critical behaviour in GFTs.

http://arxiv.org/abs/1105.5687
Gravity as an emergent phenomenon: a GFT perspective
Lorenzo Sindoni
(Submitted on 28 May 2011)
While the idea of gravity as an emergent phenomenon is an intriguing one, little is known about concrete implementations that could lead to viable phenomenology, most of the obstructions being related to the intrinsic difficulties of formulating genuinely pregeometric theories. In this paper we present a preliminary discussion of the impact of critical behavior of certain microscopic models for gravity, based on group field theories, on the dynamics of the macroscopic regime. The continuum limit is examined in light of some scaling assumption, and the relevant consequences for low energy effective theories are discussed, the role of universality, the corrections to scaling, the emergence of gravitational theories and the nature of their thermodynamical behavior.

 

[atyy]

Posted by Mtd2 in marcus's bibliography https://www.physicsforums.com/showpost.php?p=3331466&postcount=1493

ALMOST UNNOTICED, VERY IMPORTANT:

http://arxiv.org/abs/1105.6072v1

A generalization of the Virasoro algebra to arbitrary dimensions

Razvan Gurau
(Submitted on 30 May 2011)
Colored tensor models generalize matrix models in higher dimensions. They admit a 1/N expansion dominated by spherical topologies and exhibit a critical behavior strongly reminiscent of matrix models. In this paper we generalize the colored tensor models to colored models with generic interaction, derive the Schwinger Dyson equations in the large N limit and analyze the associated algebra of constraints satisfied at leading order by the partition function. We show that the constraints form a Lie algebra (indexed by trees) yielding a generalization of the Virasoro algebra in arbitrary dimensions.