Hot QG+M paper by John Barrett

[marcus]

This paper shows an interesting new approach to a theory of geometry + matter. Impressive preliminary results:

http://arxiv.org/abs/1101.6078
Induced standard model and unification


==quote Barrett's introduction==
This article concerns the problem of constructing a quantum theory of gravity coupled to matter. Many approaches to quantum gravity assume that the main difficulty lies in reconciling the dynamics of general relativity with quantum mechanics, and therefore start by describing a purely gravitational theory without matter fields. This article however takes the opposite point of view: that the gravity-matter interaction is in fact the most important feature of the dynamics. The simplest hypothesis is that the dynamics of the gravitational field itself is a side-effect of the gravity-matter interaction.

At energies below the Planck scale it should be possible to describe the theory to a good approximation with continuum fields and an effective action. In the framework due to Alain Connes[C], the fields of the standard model and gravity are packaged very effectively into geometry and matter on a certain non-commutative Kaluza-Klein space consisting of the product of a standard (commutative) four-manifold and a non-commutative ‘internal space’.

In this article a new proposal is given for the action of gravity coupled to standard model matter at high energies near (but not exceeding) the Planck scale. This is done by generalising Sakharov’s idea of induced gravity in which the gravitational terms in the action are induced by matter interactions [SK]. The generalisation is to propose an induced action for all the bosonic fields in Connes’ framework. For this idea to work, it is necessary for the space- time geometry to exhibit discreteness at the Planck scale, so that there is a natural cut-off at the corresponding energy.

Implementing this proposal by defining a functional integral over the matter and gravitational fields with the required discreteness requires some non-trivial mathematical framework. It is noted that the main qualitative features that are required for the bosonic part of the functional integral are found in the construction of various topological gauge theories using the techniques of higher category theory and state sum models. However, as yet a model which realizes all of the requirements remains to be defined, and in particular it is not yet known how to code the standard model geometry into state sum models. Some general perspectives are offered for a programme in which this might be realized.

==endquote==
It should be clear to anyone who reads this that the paper is the starting point of an interesting line of investigation, not an endpoint.
Some of the themes here (like Sakharov induced g.) are ones that have been repeatedly raised here (by e.g. Atyy and others whose names escape me at the moment) at PF Beyond forum. Barrett and Connes separately published a major result in Connes' Noncommutative Geometry, realizing the Standard Model, at about the same time in 2006 ( http://arxiv.org/abs/hep-th/0608221 ).
Barrett does both LQG and NCG.
He will be giving a talk at the March 2011 QG school. (Which I see now has 107 registered participants.)
Have to go, more later.

 

[marcus]

Someone, I think it was Atyy, pointed us to John Barrett's blog/website.
Barrett mentioned this paper's ideas back 6 months ago or more, as I recall. He has given some talks on the subject matter and at least one set of slides is online.

Note that "spectral action" refers to Connes NC geometry, which several people have pointed out would better be described as spectral geometry (it substitutes a Gelfand Naimark spectrum for the manifold).

Induced g. refers to Sakharov's idea and its descendants. Here is an April 2010 blog entry

http://johnwbarrett.wordpress.com/talks/
==sample without the indicated links to slides==
State sum models, induced gravity and the spectral action.

December 2009, IHES Slides of the first, brief, talk

May 2010, Bayrischzell slides of a longer talk with more detail of the proposals

May 2010, Oxford: video of the latest version of the talk, with some detail of the 2-category diagrams explaining the geometry-matter interaction in 3d (currently under development with Catherine Meusburger).
==endquote==

More about this here:
http://johnwbarrett.wordpress.com/

==sample quote==
Quantum gravity with matter
I gave a short talk at IHES in December (and a rather longer one in Marseille, too) on the topic of modifying quantum gravity models so that they contain realistic matter. A lot of work on quantum gravity is done without any matter fields and one gets the impression that matter fields are an optional extra which just make the system more complicated. The icing on the cake, as Chris Isham used to say about topology.

In my talk I suggested that, on the contrary, quantum gravity models with matter can actually be rather simpler than models without matter. This is because the Einstein action is induced by the matter fields, so removing the requirement to put the Einstein action into the theory from the beginning.

Some slides from my talks at Bayrischzell and Oxford are available. I am writing a short paper expanding this.

Update (Nov ’10) I’ve found a good result about this since those talks, hence the delay (and also I’m trying to finish a different paper first).
==endquote==

Here is the conclusions paragraph of the present paper:

==quote Barrett January 2011 paper==
This paper puts forward the proposal that the bosonic action of the standard model coupled to gravity should be induced from the bare fermionic action. A very preliminary calculation of the running of the gauge coupling constant confirms that this scenario is both reasonable and has the potential to fix the non-unification problem of the usual running of the standard model. However a much more detailed analysis is required to test this conclusively.
==endquote==

 

[marcus]

To give a taste of prelim results:
http://arxiv.org/abs/1101.6078
Induced standard model and unification

Figure 1 on page 7 shows how the lines don't intersect (you've seen this picture before)

==quote page 7==
...the running is as shown in figure 1. The couplings fail to meet at the values (3) predicted by grand unification and also by the Connes- Chamseddine spectral action, suggesting that there is some additional new physics.
==endquote==

Figure 2 on page 9 shows how with his induced standard model a preliminary calculation indicates the lines intersect (this may be born out, Barrett has an interesting track record.)

==quote following Figure 2==
Carrying out the correction for (9) for both U(1) and SU(3) couplings, and setting ... for the SU(2) coupling, results in the highly suggestive figure 2. In this calculation, it is necessary to input a value of the neutrino masses. The values mν = 0.1ev have been used for all three.
==endquote==

EDIT: @ Max,
you may be one of the people I've noticed talking about this cluster of ideas here at PF.
I honestly cannot remember who all they are. I don't yet fully understand the proposed approach yet either.

 

[Max™]

What a trip, I was tinkering with some ideas involving emergent matter/induced gravity type concepts a few years ago, got to see what these guys are doing with it, sounds cool!

 

[marcus]

Yes you were someone interested in this embryonic approach and now I remember another PF person, LAHLH. He pointed me to John Barrett's website, with its links to talks and a bit of insight about QG that was very helpful. Also Atyy if I remember right delved into some of the talks. And there were others. It's not clear to me how this approach works...

 

[john baez]

John Barrett will also be talking about this line of work in Zurich this summer. I haven't been following Physics Forums lately, so I don't know if you folks are aware of this conference:

http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start", ETH, Zurich, Switzerland, June 14-24, 2011.

John is one of the organizers!

I'll be going there to talk about what John Huerta has done. I'm looking forward to seeing a bunch of old quantum gravity pals, and talking to my former student Derek Wise.

 

[marcus]

What a blast!

This is going to be the best QG conference ever! The international organizing committee is ideal AFAICS. The topics leave nothing to be desired.

It is a pleasure to learn that you will be one of the speakers.

==quote==
Topics to be covered include:

General quantum theory, relativistic quantum theory, emergence of space(-time)
General quantum field theory, including deformations of QFTs
QFT on curved and NC space-times
Canonical quantum gravity and supergravity
Regge calculus
String theory and M-theory
Loop gravity, spin foam
Quantum cosmology

International Advisory Board:

John Barrett
Harald Grosse
Hermann Nicolai
Carlo Rovelli
Roger Picken
==endquote==
http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:start

 

[marcus]

I'm a fan of Hermann Nicolai. He's my favorite string guy. Excuse the schoolboy enthusiasm but this is more than a conference---it signals the end of snark and the beginning of mutual acceptance and respect. (Something that may have always existed privately even if concealed by public posture). The speaker's list is definitely Big Tent:

http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:speakers

 

[Max™]

Wow, THE John Baez huh?

I dig this weeks finds, and uh... congrats on QG getting more and more attention though you're doing other things. I dig the idea of working out algebraic definitions of foundational physics. :D

 

[marcus]

There really is a lot happening right now to be enthusiastic about. Quantum Geometry/Gravity has become a crossroads of ideas
(higher-gauge-theory, topol. quantum field theory, spinfoams, GFT, noncom. field theory, spectral geometry)
It is hard to keep track of the various intersecting lines of investigation. Several of Baez students, former students, co-authors are actively involved. Derek Wise, John Huerta, Jeffrey Morton.

You can get some sense of the stew or ferment if you look at the abstracts of this Lisbon school/workshop that starts up 7 February, in less than a week:
https://sites.google.com/site/hgtqgr/home

A lot of people that you recognize from the March 2011 Zakopane QG school and or the June Zurich QG conference that John Baez just told us about a few posts back.

John Barrett's QG funding agency within the European Science Foundation (ESF) seems to be playing an important support role in this. It is a kind of outburst of interrelated creative ideas Hard to sort out, or tell where it's going.

The February Lisbon school/workshop is called "Higher Gauge Theory, TQFT, and Quantum Gravity"
I will get a link to the abstracts or thumbnail descriptions of the talks.
You click on the links here and you get the brief summaries:
https://sites.google.com/site/hgtqgr/programme

 

[Careful]

I'm a fan of Hermann Nicolai. He's my favorite string guy. Excuse the schoolboy enthusiasm but this is more than a conference---it signals the end of snark and the beginning of mutual acceptance and respect. (Something that may have always existed privately even if concealed by public posture).

Yeh right. There is only one string theorist present I know which is Nicolai who is not ''very positive'' about LQG to say the very least.

 

[marcus]

I'm a fan of Hermann Nicolai. He's my favorite string guy. Excuse the schoolboy enthusiasm but this is more than a conference---it signals the end of snark and the beginning of mutual acceptance and respect. (Something that may have always existed privately even if concealed by public posture). The speaker's list is definitely Big Tent:

http://www.conferences.itp.phys.ethz.ch/doku.php?id=qg11:speakers

Anyone who looks at the list of some 30 invited speakers I just linked (at the Zurich QG conference that John Baez just told us about) will see a half-dozen or so familiar LQG names.

I judge there are about the same number from the string/M/AdSCFT research crowd. I also see 3 speakers who do CDT (causal dynamical triangulations) another nonstring QG approach.

From the Noncommutative Geometry direction you see both Alain Connes and Ali Chamseddine are speaking.

Plus people who watch Asymptotic Safe QG will notice Martin Reuter is one of the 30.

The conference is interesting for several reasons, and one is the "Big Tent" synthesis aspect. It presents a kind of balanced mix: in the lineup of 30 speakers there is 10 or 20% of this and 10 or 20% of that, with no one dominant contingent.

Also there is strong representation of NEW approaches (ones that we didn't heard much about until a couple of years ago) including talks by John Baez and several of his friends.

I count John Barrett as active in both LQG and these new approaches which I can't pin down. He contributes to both. To me it seems like a good sign that the small organizing committee that I listed a few posts back includes both Hermann Nicolai (string) and Carlo Rovelli (LQG) together with John Barrett.
And Roger Picken (Lisbon) who I think was the main organizer of that February Lisbon workshop I just mentioned: "Higher gauge theory, TQFT, and QG". https://sites.google.com/site/hgtqgr/home

 

[Careful]

I judge there are about the same number from the string/M/AdSCFT research crowd.

First of all I said one string theorist I know, meaning famous. Second, it seems you know string theorists better than I know them, you care to name them ? It would be a pleasure to get to know them.

Usually, when two communities meet, there are many big shots from both sides around to shake hands. I count some important people from the LQG and alternative camp, but string theorists only seem to have send Nicolai to the front. I don't want to offend you or so, just say that your enthusiasm is not very rational.

 

[qsa]

Yeh right. There is only one string theorist present I know which is Nicolai who is not ''very positive'' about LQG to say the very least.

I am not sure why you don't seem to like LQG because it looks trillion times closer to your theory than string is. I know, the next thing you are going to say, I am dead wrong.

 

[Careful]

I am not sure why you don't seem to like LQG because it looks trillion times closer to your theory than string is. I know, the next thing you are going to say, I am dead wrong.

If you know the right answer from the start, then why suggest the wrong one ? :tongue2:
No seriously, if I were to put myself on the convex line between string and LQG (which is wrong because I develop techniques used in neither of them), then I would say the distance to LQG equals 0.9 and to string 0.1. For example, my approach doesn't modify any of the principles of gravitation but it gives quantum mechanics a local relativistic formulation, something which is foreign to both approaches. Personally, I cannot think of any idea I share with LQG apart from the slogan that ''we have to take relativity seriously''.