Gravi-weak unification at ILQGS (online talk by Marciano)

[marcus]

Since we're on a new page I'll bring forward the links to what we're discussing in this thread. There's an online gravity+weak interaction unification talk today by Stephon Alexander, a field theorist at Dartmouth

http://relativity.phys.lsu.edu/ilqgs/
The title of the talk is Gravity Electroweak Unification

Before taking the professorship at Dartmouth, Alexander was at various places (Stanford-SLAC, London Imperial, Princeton, Haverford...). This particular unification program is one he has been working on with Marciano. Here's a talk by Marciano given at Perimeter in May of last year. It provides a good introduction to the main ideas. At that time Alexander and Marciano were working out the 3D case, as a preparation for attacking the problem in 4D.

http://pirsa.org/12050079/
Gravity and Yang-Mills Sectors from a Unified Theory and Their Relation with Dark Energy
Antonino Marciano
We propose a new method of unifying gravity and the Yang-Mills fields by introducing a spin-foam model. We realize a unification between an SU(2) Yang-Mills interaction and 3D general relativity by considering a constrained Spin(4) ~SO(4) Plebanski action. The theory is quantized a la spin-foam by implementing the analogue of the simplicial constraints for the Spin(4) symmetry, providing a way to couple Yang-Mills fields to spin-foams. We also present a way to recover 2-point correlation functions between the connections as a first way to implement scattering amplitudes between particle states. We conclude with speculations about extension of the model to 4D and incorporate a newly developed model of Dark Energy.
14/05/2012

Marciano will give an online ILQGS talk later this Spring (7 May) titled:
Emergence of BF theories and gravi-weak Plebanski models from spinors
This will be, in effect, a continuation of today's talk by Alexander which we now have slides for and hopefully will be hearing soon.

Another good introduction to this approach to unification is a couple of 15 minute talks presented at the October 2012 Perimeter conference on Experimental Search for QG.
http://pirsa.org/12100116
Quantum Gravity and the Weak Interactions
(Recorded in October 2012)
Alexander's segment begins after minute 18, around minute 19.
Smolin's talk follows immediately after that and begins around minute 35.

There is also a recent paper:
http://arxiv.org/abs/1212.5246
Gravitational origin of the weak interaction's chirality
Stephon Alexander, Antonino Marciano, Lee Smolin
(Submitted on 20 Dec 2012)
We present a new unification of the electro-weak and gravitational interactions based on the joining the weak SU(2) gauge fields with the left handed part of the space-time connection, into a single gauge field valued in the complexification of the local Lorentz group. Hence, the weak interactions emerge as the right handed chiral half of the space-time connection, which explains the chirality of the weak interaction. This is possible, because, as shown by Plebanski, Ashtekar, and others, the other chiral half of the space-time connection is enough to code the dynamics of the gravitational degrees of freedom.
This unification is achieved within an extension of the Plebanski action previously proposed by one of us. The theory has two phases. A parity symmetric phase yields, as shown by Speziale, a bi-metric theory with eight degrees of freedom: the massless graviton, a massive spin two field and a scalar ghost. Because of the latter this phase is unstable. Parity is broken in a stable phase where the eight degrees of freedom arrange themselves as the massless graviton coupled to an SU(2) triplet of chirally coupled Yang-Mills fields. It is also shown that under this breaking a Dirac fermion expresses itself as a chiral neutrino paired with a scalar field with the quantum numbers of the Higgs.
21 pages

My comment: The 4D work here has been carried out on a classical level. The Plebanski action is a formulation of classical GR (where the variable is a connection rather than a metric) and the idea here is to extend the Plebanski action to include some types of matter interaction. So this line of research seems to be aimed at opening a way to treat both geometry and matter as gauge fields in a single Plebanski-type action. Later on, as was done already in the 3D case, one might consider some background-independent, nonperturbative way of quantizing this combined gauge theory of geometry and weak interactions.

I should also bring forward Mitchell's most recent comment, which highlights the novelty of what Alexander and Marciano have initiated:

On slide 26, the idea of a boson and fermion being related by parity is repeated.

I know the people reading this thread are not field theorists and so I shouldn't expect an answer, but really, I defy anyone to produce a lagrangian or otherwise define a meaningful theory in which that is the case.

If you look closely I think you will see they have delineated a symmetry that exchanges spin and isospin. Interesting.

 

[marcus]

The main topic at present is Alexander's 26 Feb talk on Gravity and Electroweak Unification. When the audio is posted, the link will be appearing at:
http://relativity.phys.lsu.edu/ilqgs/ Here are the slides:
http://relativity.phys.lsu.edu/ilqgs/alexander022613.pdf

Whether or not this particular Gravity and EW unification ultimately proves correct, I expect this work to play an important part in the emergence of a new research field. For the time being, I'll call it LQGM (loop quantum geometry-and-matter).

I think of LQG as being a practice run or rehearsal for this field---which developed the appropriate concepts, mathematical tools, and an understanding of how to use them.

It's worth noting that every scientific field is based on a body of observed behavior which it attempts to explain. Pure LQG without adjoining matter has little in the way of observed behavior to explain. It concerns the microscopic structure of empty space, which is not revealed in a large body of observed phenomena.

Rather I think LQG is a special sector of what I am calling LQGM---what you get when you add matter to the picture, and carry over to it the concepts and mathematical tools prepared so far in this specialized area, for use in the general theory.

This is why I regard the Alexander and Marciano talks as laying out an essential step in the development of this general area of research.

We are talking about background independent quantization of the Ashetekar-Plebanski formulation of classical geometry (GR) which we now see is capable of naturally including matter.

 

[member 11137]

Blackforest, I replied in post #43--nothing very helpful I regret to say. Although I find Nesti's work admirable, what seems most exciting/promising at present is the similar but distinct line begun by Marciano and Alexander. I can't recommend too much scanning down Marciano's May 2012 slides pdf:
http://pirsa.org/12050079/12050079.pdf

Any way: thank you very much for your answer and for the try to help me. I have seen the Alexander's work post 52. It is complicated () but interesting for the pedagogy. Perhaps I shall try to develop my own basic BF theory (as a toy model); it is just a question of time and of energy ...

 

[marcus]

Here's the list of invited speakers at Loops 2013
http://www.perimeterinstitute.ca/conferences/loops-13
If their results are confirmed and this unification proposal is well received then I guess we'd expect either Alexander or Marciano's name to appear on the Loops conference speakers list. So that's something to keep an eye on.

I expect the audio of Alexander's 26 February talk to be posted tomorrow--I'm curious to see how it is received.

 

[marcus]

Stephon Alexander's talk (Gravity Electroweak Unification) went well.
http://relativity.phys.lsu.edu/ilqgs/
Both the slides PDF and the audio are online.
I couldn't identify one of the people who asked a question. He came in at around minute 39:00. He said his name but so rapidly I didn't catch it. Does anyone know who that is?

 

[atyy]

Wow, never knew Alexander was a Rubio fan (7:47)!