# Quantum Gravity and the Standard Model (Sundance + PI)

1. Mar 5, 2006

### marcus

http://arxiv.org/abs/hep-th/0603022
Quantum Gravity and the Standard Model
Sundance O. Bilson-Thompson, Fotini Markopoulou, Lee Smolin
12 pages, 21 figures

"We show that a class of background independent models of quantum spacetime have local excitations that can be mapped to the first generation fermions of the standard model of particle physics. These states propagate coherently as they can be shown to be noiseless subsystems of the microscopic quantum dynamics. These are identified in terms of certain patterns of braiding of graphs, thus giving a quantum gravitational foundation for the topological preon model proposed by one of us.
These results apply to a large class of theories in which the Hilbert space has a basis of states given by ribbon graphs embedded in a three-dimensional manifold up to diffeomorphisms, and the dynamics is given by local moves on the graphs, such as arise in the representation theory of quantum groups. For such models, matter appears to be already included in the microscopic kinematics and dynamics."

Probably important.

=============================

also posted today:

http://arxiv.org/abs/gr-qc/0603008
Reconstructing Quantum Geometry from Quantum Information: Area Renormalisation, Coarse-Graining and Entanglement on Spin Networks
Etera R. Livine, Daniel R. Terno
27 pages, 12 figures

"After a brief review of spin networks and their interpretation as wave functions for the (space) geometry, we discuss the renormalisation of the area operator in loop quantum gravity. In such a background independent framework, we propose to probe the structure of a surface through the analysis of the coarse-graining and renormalisation flow(s) of its area. We further introduce a procedure to coarse-grain spin network states and we quantitatively study the decrease in the number of degrees of freedom during this process. Finally, we use these coarse-graining tools to define the correlation and entanglement between parts of a spin network and discuss their potential interpretation as a natural measure of distance in such a state of quantum geometry."

Last edited: Mar 5, 2006
2. Mar 5, 2006

Cool!

3. Mar 5, 2006

### marcus

besides which Sundance is from Oz and amazingly attactive to women (even I can tell, it's not so difficult)

anyone who hasnt seen Sundance in action go here
http://streamer.perimeterinstitute....fa7-485f-8d5d-3b62fb7d3e4c&shouldResize=False
and flip to page 5
where he has a lecture called "Braid New World"
which you can view the streamer

the reason it is on page 5 is that it is dated 16 November 2005 and they list the most recent seminar talks first, so it is a pushdown stack and this talk keeps getting a larger page number as it recedes into the past

this is a great talk. I just watched some of it as a refresher. I recommend it without reservation.

Last edited by a moderator: Apr 22, 2017
4. Mar 5, 2006

### Kea

Marcus

Despite a long line of muscular beaus, I have never gone out with an Australian.

Last edited: Mar 5, 2006
5. Mar 5, 2006

### arivero

Note that one needs to get the previous papers (from Sundance, and the ones on preons quoted by Sundance) in order to get the feeling of the thread. Perhaps some chapters of Zee's book, on GUT theories and bits, could be of interest.

To me is a bit of surprise, I'd expect the standard model femions to be more a geometric object than a topological object.

6. Mar 5, 2006

### Kea

Categories make it geometric.

7. Mar 5, 2006

### marcus

excellent suggestion
http://arxiv.org/abs/hep-ph/0503213
A topological model of composite preons
Sundance O.Bilson-Thompson
9 pages, 3 figures, submitted to Phys. Lett. B

"We present a modification of the preon model proposed independently by Shupe and Harari. A basic dynamics is developed by treating the binding of preons as topological in nature and identifying the substructure of quarks, leptons and gauge bosons with elements of the braid group B_3. Topological considerations and a straightforward set of assumptions lead directly to behaviour consistent with much of the known phenomenology of the Standard Model. The preons of this model may be viewed as composite in nature, and composed of sub-preons, representing exactly two levels of substructure within quarks and leptons."

8. Mar 6, 2006

### yanniru

Lubos Motl makes fun of this paper on his blog today (i.e., QG & SM)
http://schwinger.harvard.edu/~motl/sf/frames.html [Broken]

Last edited by a moderator: May 2, 2017
9. Mar 6, 2006

### arivero

In this case I welcome Lubos' vents. The team of Smolin is doing here a risky bet and some moderation voice must be heard, even if it is Lubos. Knotting is an old art, legend tolds (I can not remember/quote the paper) that it was used even as an explanation of nuclear structure before the age of neutron and protons. And weaving the fermions into "Space-Time Code" is also a old dream nobody risks to touch (five dimensional and Connes-Lott theory have got a good step about weaving the bosons into).

Lubos asks how "the manifestly different octopi should transform as a representation of a group". Well, he asks "why", but I think that "how" it is already a good point to understand.

The other problem I see is how to put CKM matrix to play.

Last edited by a moderator: May 2, 2017
10. Mar 6, 2006

### marcus

I enjoyed Lubos satire too---he is good at making fun. but I don't think his mockery is the kind of critical response that is needed

some "moderation voice must be heard" and I think there will inevitably be some thoughtful questioning responses (that go beyond Lubos mockery)

the critical evaluation was ALREADY INSUFFICIENT for Bilson-Thompson's paper of a year ago
http://arxiv.org/abs/hep-ph/0503213
A topological model of composite preons

this is possibly a very good idea and a way to generate the standard model particles with a small elegant set of components----it needs to be examined and either tried out in development or discarded---but it did not get enough examination

Smolin has given Bilson-Thompson preon model a lot of new visibility by making QG contact with it and connecting it to spin-network.

this involves risk, and that is part of the researcher's job I think
Since you, arivero, are skilled with humorous spanish proverbs I will challenge you with the obvious english proverb:
"Nothing ventured, nothing gained."

Last edited: Mar 6, 2006
11. Mar 6, 2006

### arivero

Hmm now I get the title of the thread. "Pi" got the "best director" award in Sundance festival in 1998. Darren Aronofsky was, the director.

12. Mar 6, 2006

### arivero

Hmm I am not sure. We know that each fermion has a metrical quantity assigned, its mass. And we know that mass eigenstates do not coincide with charge eigenstates (thus cabibbo mixing). A preon model needs always to show how this kind of things, mass and CKM, are managed.

The electroweak group is very peculiar because it is doubly broken: the bosons are massive, and the particles in the same SU(2) multiplet have different mass.

13. Mar 6, 2006

### Kea

The authors make it very clear in the paper that they are not answering these questions. When I mentioned categories, I didn't mean a simple re-interpretation of this paper, I meant a whole lot more stuff.

14. Mar 6, 2006

### Kea

In this spirit:

Note that the reduced link of the electron (figure 17) is just the Hopf link, when the ends are connected up. Now taking Jones polynomials $J$ at 5th roots of unity for universal quantum computation, one finds that

$$J_{\textrm{Hopf}} = d = 1.618 \cdots$$

the golden ratio. Now let a deformation parameter be

$$q = e^{\frac{2 \pi}{2 + d}}$$

namely the $SU(2)_{q}$ conformal field theory expression. It is well known that the spin half rep quantum dimension is given by $[ 2 ]_{q} = q + q^{-1}$. Putting two of these electron graph invariants together one estimates

$$\alpha = 4 (q + q^{-1})^{2} = 137.08$$

This is of course an extremely coarse estimate, and hence not particularly accurate.

Last edited: Mar 6, 2006
15. Mar 6, 2006

### marcus

Of course.
Had you performed the calculation more delicately it would doubtless have come out spot on 137.0359...

16. Mar 7, 2006

### marcus

In the starter, a second paper was mentioned
did anyone look at this paper? any reactions?
coarse-graining (which underlies the notion of entropy) has always been something of a mystery to me. so it sounds hopeful if one can define a regular "procedure" for coarsegraining----to me it would be like the philosopher's stone of the ancient alchemists, if you could actually say in generality what coarse-graining is then changing lead to gold would be mere childs-play.

Last edited: Mar 7, 2006
17. Mar 7, 2006

### arivero

Quicksilver to Gold is actually childs-play, as a look to the table of isotopic weights reveals On the contrary, lead to gold requires energy.

As for the paper, it also requires energy to get something out of it, it seems mostly a technical one, interested on how to recover classical distance from quantum gravity. I guess that via some decimation procedure, but I have not read it, only glanced over very very fast.

Last edited: Mar 7, 2006
18. Mar 7, 2006

### Careful

The Smolin octopussy leaves different impressions:
(a) it is an old an cute idea, especially the fact that you can get out the first generation of SM - particles from simple knotted configurations carrying only one type of U(1) charge is what I would like it to be. Actually, this resembles *very* much an old idea of Lorentz who postulated all matter to be electromagnetic in origin.
(b) I would at least expect the paper to contain the inclusion of the second and third generations of particles as well as a verification that all known *scattering* processes can be recovered diagramatically. It gave me the creeps when I noticed their toy model was about a noiseless dynamics...
(c) So, this is as LQG itself (not LQC) - all just kinematics, where is the (classical) dynamics which is supposed to:
(i) be invariant under some representation of the strong and electroweak groups
(ii) allows for the different effective dynamical (distributional) moves, including the ones which should account for interactions.
(iii) why do the fermions satisfy the pauli exclusion priciple (under conditions where the spin statistics theorem is valid anyway) - I am not insisting that they should be spinors
(d) In principle, the theory could remain entirely topological : one could try to define the measure stick by counting the number of particles in chains containing particles of the same species. However, causal set practice learns that this is an almost impossible task to do and I would not bet my money on it.

Now is the time for hard work.

Cheers,

Careful

19. Mar 7, 2006

### Kea

Marcus

I glanced at it. It doesn't really belong in the same thread as the Sundance+PI paper. In the latter they emphasise a quite different view on classical limits when they talk about micro vs macro locality.

20. Mar 8, 2006

### f-h

"Now that I've thrown around enough buzzwords to scare off the kids, I can tell you about Lee Smolin's talk, which was definitely X-rated: for adults only, people who can listen to speculations with just the right mixture of disbelief and open-mindedness."

It's an old idea indeed, Riemann, Einstein, Wheeler. Relativists have always thought about reducing matter to ripples in geometry. But matter is Quantum Mechanical so it's worth a shot now that we have at least a framework for a decent theory of Quantum Gravity/Geometry.

In this sense these ideas are extremely significant. If they pan out LQG predicts matter.

Just ponder that for a moment. Take a Lorentzian Manifold with geometry, quantize it, and you find matter degrees of freedom.

The next question then is if it predicts the right kind of matter.

21. Mar 8, 2006

### Kea

22. Mar 8, 2006

### Mike2

Wouldn't this mean that the geometry of emtpy space is determined by the virtual particles of the vacuum energy? And wouldn't this mean that the more curved space is, the more the ZPE is in that region? Thanks.

23. Mar 9, 2006

### Careful

**
It's an old idea indeed, Riemann, Einstein, Wheeler. Relativists have always thought about reducing matter to ripples in geometry. But matter is Quantum Mechanical so it's worth a shot now that we have at least a framework for a decent theory of Quantum Gravity/Geometry.
**

I disagree in three ways:

(a) first at all: QM does not say *anything* about matter itself, only about its dynamics´´, remember the parameters in the standard model (particle masses, electron charge, the disputed mass of the Higgs and so on)! QM does not explain the appearantly discrete´´ (at least within some bounds of measurement) nature of elementary particles, it uses it. So, these are complementary ideas; therefore there is no a priori reason to wait for development in QG (whatever that may be) before one gives a unified matter model a shot. On the contrary, I think that the construction of a suitable matter model is indispensible for a good theory of microscopic phenomena.

(b) LQG is still being far form a THEORY of quantum gravity (they would better solve the Hamiltonian constraint first).

(c) I repeat that this paper does not really add much to already existing ideas and that the real problems in this framework are as wide open as they were before. One would expect more in depth results to be presented in such paper...

Cheers,

Careful

Last edited: Mar 9, 2006
24. Mar 10, 2006

### marcus

Discussion of the Sundance + PI paper at Christine's

http://christinedantas.blogspot.com/2006/03/quantum-gravity-and-standard-model.html [Broken]

Jacques Distler and Lee Smolin converse about it.

Last edited by a moderator: May 2, 2017
25. Mar 10, 2006

### marcus

I will copy exerpts of the discussion at Christine's to look at a bit more closely
=====quote from Christine's blog "QG and SM" thread=====

AARON
Gravatar Worse, and I'm trying to be as kind as possible here, Smolin and his collaborators seem to be confused about what anomaly matching means. It is a condition on the global anomalies of the theory. If it had something to do with gauge anomalies (which render a theory inconsistent), they wouldn't be of much use.

It's also a good thing. At least in the old preon models based on QFT, it was matching the anomalies that ensured that you got the 'massless' bound states to match up with the standard model spectrum.
Aaron Bergman | 03.09.06 - 5:34 pm | #
---------------------

LEE

3/09/2006 09:37:19 PM
Lee Smolin said...
Dear Johan,

In Sundance's original model there are vector bosons and rules that govern interactions. A consequence of the rules that govern the vector bosons is that electrons cannot turn into quarks. Whether or how those rules are realized in the quantum gravity embedding is still under study.

Dear Aaron, Thanks, but even if we expressed it in a way that confused you, the point is that the condition cannot be applied to this kind of theory. Do you have an argument that this is wrong? Beyond expressing your dislike, do you have an actual objection to any of the actual results of the paper? (the comment on amomalies being just a side comment and not a result.) By the way were it not for Christine's rule against personal comments I would protest your tone which as usual is a bit unpleasant. Rather than nitpicking on a side comment, do you actually have an objection against the main results of the paper?

Dear Christine, thanks very much for all the support. Its nice to be commented on in a blog where someone actually spends more than 38 minutes reading the paper and making fun of it.

Thanks,

Lee

-----------------
AARON

3/10/2006 12:57:38 AM
Aaron Bergman said...
Lee,

What am I supposed to make of the statement "we already know there is none, as it is the standard model."? The standard model has anomalies. Anomaly matching is a constraint on matching any effective field theory with some UV theory. If your UV theory doesn't have anomalies and if you claim that it really is a QFT, you have a problem. This is hardly nitpicking.

I chose to comment on this particular aspect of the paper because this is a well-known physical constraint on preon models and because it's fairly concrete. I don't have anything helpful to say about the rest.

-------------
JACQUES

3/10/2006 02:06:03 AM
Jacques Distler said...
Lee,

Since the Bilson-Thompson model does not have a Higgs, and you wish to take the compositeness scale to be the Planck scales, what is it that unitarizes W-W scattering at energy scales above a few 10s of TeV?

Of course, my vain attempt to pierce the fog of Bilson-Thompson's earlier paper did not reveal the vertices (which we know must be there) which lead to W-W scattering in the first place
------------
LEE

3/10/2006 11:30:46 AM
Lee Smolin said...
Dear Jacques,

These of course are very fair comments. We don't claim to have now more than we claim in the paper and, as I hope is clear, we are well aware of how much else has to go right before this is physics. At the same time, it is important to know that local excitations naturally arise in a large classs of quantum gravity models that might be elementary particles. Whether there are any such models that get elementary particle physics exactly right is of course an open question which we are only at the beginning of investigating. But it is a question that could not be asked before we had Fotini and Sundance's work.

Thanks,

Lee

-------------------
JACQUES

3/10/2006 11:44:20 AM
Jacques Distler said...
One more question, which is the issue that Aaron raised.

Normally, in a preon model, one expects all of the bound states to have masses on the order of the compositeness scale. (Think QCD, where the proton and neutron have masses of order the QCD scale, even in the limit of massless quarks.)

The 't Hooft anomaly-matching conditions are what guarantee, in preon models, that there are fermions with masses much much lower than the compositeness scale.

(If you want the gauge bosons to also be composites, then you have a much tougher row to hoe, as you need to find a mechanism by which the gauge-invariance, that ensures their masslessness, arises in the IR. But let's stick to the fermions.)

I found your response to Aaron a little unsatisfactory. There certainly are some conditions which would follow by attempting to impose the 't Hooft anomaly matching conditions on your UV theory. Do the quarks and leptons of the Standard Model saturate the 't Hooft anomaly matching conditions of your theory, or don't they?

======endquote=======