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

[marcus]

According to Alexander, Marciano and Smolin the 2009 paper is an elaboration of the 2007 paper.

"Nesti and Percacci have discussed issues related to the Higgs phenomenon and the electro-weak symmetry breaking in [25], and elaborated those topics for the gravi-GUT unification model they have presented in [19]."

Exactly! That is the passing mention I referred to that occurs at the top of page 5 in AMS paper! But you didn't quote the sentence immediately following it:
"The latter work develops a different perspective than the one addressed in [18], in that the graviweak and color gauge sectors have been accounted separately in [18]."

The paper goes no further with that offshoot approach [19] they tried in 2009. It makes repeated use of the 2007 paper [18].
Same with the two Perimeter talks. Same root different branches. Not to be confused.
We have to get on the road shortly, but I'll try to check in as time permits. I'm glad to see you are reading at least portions of AMS now, but suggest you watch the two brief Perimeter talks. Alexander and Smolin do an excellent job of presenting the ideas to a mixed audience (not all specialized in same area of QG.)

 

[marcus]

We have turned another page so I will bring forward the main links to what we're discussing in this thread. There's an online gravity+weak interaction unification talk coming in a few days from now: Tuesday 26 February.

The links to audio and to slides PDF will be posted here:
http://relativity.phys.lsu.edu/ilqgs/
The title of the talk is Gravity Electroweak Unification
The speaker is Stephon Alexander, a professor of physics at Dartmouth.

I think to understand the ideas here it's important to watch two short talks on this topic (by Alexander and by Smolin). They give a lot of intuition along with the equations, and were 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 talk begins after minute 18, near minute 19.
Smolin's talk comes 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

Alexander's online ILQGS talk next week will be followed later this Spring by a second ILQGS talk, by Marciano, on the emergence of gravi-weak Plebanski models from spinors. http://relativity.phys.lsu.edu/ilqgs/schedulesp13.html

AFAICS the above paper and the talks are so far not directly concerned with quantum gravity. The 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. What mathematicians call a connection seems equivalent (or nearly so) to what physicists call a gauge field. 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, if the program is successful, one might consider some background-independent, nonperturbative way of quantizing this combined gauge theory of geometry and weak interactions. But that is not what this paper is about. If the classical program initiated by Alexander Marciano Smolin is successful, one way to follow up on it would presumably be to quantize it in the context of a lattice gauge theory.

 

[atyy]

Exactly! That is the passing mention I referred to that occurs at the top of page 5 in AMS paper! But you didn't quote the sentence immediately following it:
"The latter work develops a different perspective than the one addressed in [18], in that the graviweak and color gauge sectors have been accounted separately in [18]."

The paper goes no further with that offshoot approach [19] they tried in 2009. It makes repeated use of the 2007 paper [18].
Same with the two Perimeter talks. Same root different branches. Not to be confused.
We have to get on the road shortly, but I'll try to check in as time permits. I'm glad to see you are reading at least portions of AMS now, but suggest you watch the two brief Perimeter talks. Alexander and Smolin do an excellent job of presenting the ideas to a mixed audience (not all specialized in same area of QG.)

The 2007 paper is not [18].

 

[marcus]

Hi, I'm back. Had to rush off earlier
[18] is this 2007 paper by Nesti:
http://arxiv.org/abs/0706.3304
Standard Model and Gravity from Spinors
F. Nesti
(Submitted on 22 Jun 2007)
We propose to unify the Gravity and Standard Model gauge groups by using algebraic spinors of the standard four-dimensional Clifford algebra, in left-right symmetric fashion. This generates exactly a Standard Model family of fermions, and a Pati-Salam unification group emerges, at the Planck scale, where (chiral) self-dual gravity decouples. As a remnant of the unification, isospin-triplets spin-two particles may naturally appear at the weak scale, providing a striking signal at the LHC.
7 pages

The 2007 paper by Nesti and Percacci I referred to earlier is [25]
http://arxiv.org/abs/0706.3307
Graviweak Unification
F. Nesti, R. Percacci
(Submitted on 22 Jun 2007)
The coupling of chiral fermions to gravity makes use only of the selfdual SU(2) subalgebra of the (complexified) SO(3,1) algebra. It is possible to identify the antiselfdual subalgebra with the SU(2)_L isospin group that appears in the Standard Model, or with its right-handed counterpart SU(2)_R that appears in some extensions. Based on this observation, we describe a form of unification of the gravitational and weak interactions. We also discuss models with fermions of both chiralities, the inclusion strong interactions, and the way in which these unified models of gravitational and gauge interactions avoid conflict with the Coleman-Mandula theorem.
18 pages

 

[atyy]

Hi, I'm back. Had to rush off earlier
[18] is this 2007 paper by Nesti:
http://arxiv.org/abs/0706.3304
Standard Model and Gravity from Spinors
F. Nesti
(Submitted on 22 Jun 2007)
We propose to unify the Gravity and Standard Model gauge groups by using algebraic spinors of the standard four-dimensional Clifford algebra, in left-right symmetric fashion. This generates exactly a Standard Model family of fermions, and a Pati-Salam unification group emerges, at the Planck scale, where (chiral) self-dual gravity decouples. As a remnant of the unification, isospin-triplets spin-two particles may naturally appear at the weak scale, providing a striking signal at the LHC.
7 pages

The 2007 paper by Nesti and Percacci I referred to earlier is [25]
http://arxiv.org/abs/0706.3307
Graviweak Unification
F. Nesti, R. Percacci
(Submitted on 22 Jun 2007)
The coupling of chiral fermions to gravity makes use only of the selfdual SU(2) subalgebra of the (complexified) SO(3,1) algebra. It is possible to identify the antiselfdual subalgebra with the SU(2)_L isospin group that appears in the Standard Model, or with its right-handed counterpart SU(2)_R that appears in some extensions. Based on this observation, we describe a form of unification of the gravitational and weak interactions. We also discuss models with fermions of both chiralities, the inclusion strong interactions, and the way in which these unified models of gravitational and gauge interactions avoid conflict with the Coleman-Mandula theorem.
18 pages

So the 2009 paper is relevant, since it elaborates [25], not [18].

 

[marcus]

I see no evidence that it is relevant. It branches off in some other direction.
If that particular "elaboration" were relevant, the AMS authors would certainly have said so. Instead they cited 2007 work of of Nesti&Percacci, and similar 2007 work by Alexander himself.

We'll see. I suppose you think that the 2009 paper will be referenced and cited as substantially important to the forthcoming research.
I think it will NOT relevant and will NOT be cited. Let's see who is right. We will have Alexander's talk and his slides PDF in 3 days, and we will, I think, have a further paper of AMS in the near future.

 

[atyy]

I see no evidence that it is relevant. It branches off in some other direction.
If that particular "elaboration" were relevant, the AMS authors would certainly have said so. Instead they cited 2007 work of of Nesti&Percacci, and similar 2007 work by Alexander himself.

We'll see. I suppose you think that the 2009 paper will be referenced and cited as substantially important to the forthcoming research.
I think it will NOT relevant and will NOT be cited. Let's see who is right. We will have Alexander's talk and his slides PDF in 3 days, and we will, I think, have a further paper of AMS in the near future.

1. The Coleman-Mandula question is discussed in this thread. In the discussion on Distler's blog on the 2009 paper, the Coleman-Mandula theorem is also discussed, Nesti indicating that the 2007 paper applies to the 2009 paper.

2. mitchell porter asked whether it is restricted to SU(2). Nesti and Percacci's 2009 paper suggests no. They say the key is that the order parameter is a soldering form.

 

[marcus]

I found a further video resource, which can be added to the links in post #37

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

This is an hour talk which covers the whole program, as it was in an earlier form, in May 2012. They had worked it out only in a toy model case---3D gravity---and were conjecturing that they could extend the results to 4D.
BTW Coleman-Mandula is mentioned in passing by Marciano. Most people seem to realize it does not apply so not much is made of it, but I think there is one slide.

Marciano does a good job presenting. It's an hour talk. Stephon Alexander is in the audience, Niayesh Afshordi, Joseph Ben Geloun,... and a bunch of others.
==========================
BLACKFOREST, since I can still edit, I'll reply briefly here. I don't think new physics has emerged from LHC as yet. Perhaps someone with more detailed knowledge can speak to this. It could be that the specific prediction you refer to has been ruled out, or it could still be unresolved---I can't say. I do think we would have heard about it if the data had been studied from the perspective of one of these conjectures and hints of confirmation had been found. In general, you are raising an important question. I hope we hear more (in a general way) about this a couple of days from now, when Alexander gives his online seminar talk.

 

[member 11137]

Hi, I'm back. Had to rush off earlier
[18] is this 2007 paper by Nesti:
http://arxiv.org/abs/0706.3304
Standard Model and Gravity from Spinors
F. Nesti
(Submitted on 22 Jun 2007)
We propose to unify the Gravity and Standard Model gauge groups by using algebraic spinors of the standard four-dimensional Clifford algebra, in left-right symmetric fashion. This generates exactly a Standard Model family of fermions, and a Pati-Salam unification group emerges, at the Planck scale, where (chiral) self-dual gravity decouples. As a remnant of the unification, isospin-triplets spin-two particles may naturally appear at the weak scale, providing a striking signal at the LHC.
7 pages...

May I just ask you (intellectual curiosity) if the isospin-triplet spin-two particles appeared (as predicted by that paper)? Even if parts of that 2007 paper are far over my head, I like this paper and especially equation (7) page 4 because of the interplay which is established between the R and L parts. Is it an alternative to the proposition made by L. Smolin and Co? As far I can understand the previous comments on this thread here, the partition between the R and the L parts of the connection in the discussed paper (Smolin and Co) is a central item. And as far as I could read in "googling" and looking for references around the history of the Plebanski approach, I got the feeling that self-duality seems to be a strategic item, especially because Yang-Mills terms can be introduced. Really fascinating... Thanks for the discussion here.

 

[marcus]

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

There are only 16 slides. They are interspersed among a run of some 70 stills of the actual talk, but it is very easy to scroll through. You immediately see what is a clear copy of a slide, as opposed to a photo of the slide projected onto the screen with lecturer pointing stuff out. It's a good way to get an idea of what the talk covers.
As I said earlier, at that point (it was before Lee Smolin joined them) the two had worked
out a toy model case---3D gravity---and were conjecturing that they could extend the results to 4D. Smolin is not in the May 2012 audience. He says he came in on the project when they started seeing how to extend to 4D.

The talk is informative partly because you see that Marciano is a multi-competent particle/cosmologist/quantum-relativist. Bright, organized and articulate.
And because you see his vision of the next step--how he thinks of quantizing once they have the classical 4D picture worked out.

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 also present a way to recover 2-point correlation functions between the connections as a first way to implement scattering amplitudes ... We conclude with speculations about extension of the model to 4D and incorporate a newly developed model of Dark Energy.
14/05/2012

As far as I know, quantizing the 4D model is still ahead, but we may hear something about it on 7 May when Marciano gives his ILQGS talk. The mention of BF theory in the title is significant, since it is by that route that the Ashtekar-Plebanski version of GR is quantized. The overall idea seems to be (1) to include certain matter interactions in the extended BF theory and then (2) triangulate and quantize in the usual way with extended BF theory.

 

[marcus]

It was the title of Marciano's 7 May online ILQGS talk that gave me the impetus to start this thread.
Emergence of BF theories and gravi-weak Plebanski models from spinors
I think what it telegraphs to us is that he plans to talk about how a process of symmetry breaking and parity violation makes "emerge" from the Dirac spinor the various pieces that we see: graviton, neutrino, perhaps Higgs, dark matter candidate...
Of course I don't know what, at that stage, their theory will have in store---at least a graviton and weak bosons I suppose---maybe that and no more. Marciano and friends will have worked out those details by then. And there may be some realistic predictions for the new run at the LHC when it starts back up.

 

[marcus]

http://relativity.phys.lsu.edu/ilqgs/alexander022613.pdf
Alexander's slides are online.

 

[mitchell porter]

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.

 

[marcus]

Thanks for such a lively reaction!
It will be interesting to hear the seminar audience comment and questions today (or whenever the audio goes online). Here is the slide you mentioned.
==quote slide #26==
New Prediction

Left handed spinor transforms like
a weak doublet scalar, what entity carries this quantum number?

Right handed spinor transforms like a weak singlet spin 1/2 particle, what is this?
These two particles transform into each other under parity.
==endquote==

 

[marcus]

Here are the slides for today's talk:
http://relativity.phys.lsu.edu/ilqgs/alexander022613.pdf

The audio is not yet on line. When it's ready, the link will be appearing here:
http://relativity.phys.lsu.edu/ilqgs/

 

[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)!