Are Preons the Key to Combining Gravity and Matter in Loop Quantum Gravity?

[marcus]

Smolin used these preons to bring matter into Loop Gravity. It looks like we need to learn about Bilson-Thompson type preons.
there is this march 2005 paper
http://arxiv.org/hep-ph/0503213
A topological model of composite preons
Sundance O.Bilson-Thompson
9 pages, 3 figures, submitted to Phys. Lett. B

Arivero started a thread about preons in "Particles" forum and Ohwilleke brought up this paper of B-T and discussed it some, along with earlier work that it derives from.

Here is Ohwilleke's post
https://www.physicsforums.com/showpost.php?p=581108&postcount=7

the basic ideas is since we know that protons and neutrons are composite each being made of 3 quarks (which really exist even tho hard to pull apart)
that perhaps now it is time to discover that QUARKS ARE COMPOSITE AND each quark is made of 3 preons (which are even harder to pull apart) and furthermore NOT ONLY do you get all the different type quarks by combining preons YOU ALSO GET LEPTONS AND BOSONS by combining these same old preons.
so you can get not only quarks (to make your protons with) but you can also get neutrinos and electrons and photons-----the idea is to get all the stuff in the Standard Muddle by tasteful combinations of a small number of preons.
the reason that we need to know about preons in context of QUANTUM GRAVITY is that Smolin found that you could imagine preons as long (sometimes twisted or braided) strands of CONFETTI and that a good way to combine the GRAVITY-states of spin networks with the MATTER-states of the Standard Muddle
would simply be to make the spin networks out of that type of confetti so that the network that described a quantum state of gravity would have its LINKAGE CORDS MADE OUT OF PRION RIBBON
The point is that people have been wanting for a long time to have a quantum theory of spacetime geometry that would also explain the Standard Muddle and hopefully simplify both---and string ideas have not been working out very well----so this could be something to investigate as a way to combine gravity with matter.

 

[marcus]

who is sundance?
maybe Australian
PhD approx 2001-2002 Adelaide
snapshot taken c. 2003 with old buddy (combinatorics/graph theory) also from Adelaide
http://www.chiark.greenend.org.uk/~dricher/friends.html
postdoc in Korea 2003
contributed to some QCD gluon computer graphics that
Frank Wilczek used in his Nobel acceptance talk in 2004
(stunning computer animation of quantum chromodynamics)
http://www.physics.adelaide.edu.au/theory/staff/leinweber/VisualQCD/ImprovedOperators/

I don't really know---think he was back at Adelaide 2004-2005.
right about now---november 2005---he's doing a workshop
with Renate Loll and Xiao-Gang Wen (mit condensed matter) at
Perimeter.
http://perimeterinstitute.ca/activities/scientific/PI-WORK-5/schedule.php

at least that's how it looks because today 16 November he gave a talk on Preons in LQG at perimeter and the workshop (with Loll and Wen) is, I think, this weekend.

 

[marcus]

in March 2005 sundance invented a sort of three-ribbon "cord" (or improved somebody else's similar cord)

which the different variations of this one cord (by varying twists and braiding) gives all the quarks and leptons

and in October 2005 smolin said try making spin networks out of this cord so that quantum gravity states can have matter in
http://loops05.aei.mpg.de/index_files/abstract_smolin.htmltoday 16 November, sundance is giving a talk at Perimeter:
http://www.perimeterinstitute.ca/activities/scientific/seminarseries/alltalks.cfm?CurrentPage=2&SeminarID=604

Topological preon models: a braid new world
Wednesday November 16, 2005, 2:00 PM
"Preon models enjoyed considerable popularity during the early 1980s, but have seen little progress since then. I will describe a correspondence between one of the more successful preon models and a simple game involving the twisting and braiding of ribbons, subject to straightforward topological conditions. This reproduces the fermions and gauge bosons of the standard model, as well as the electromagnetic, weak and colour interactions. The prospect that such structures may occur naturally within Loop Quantum Gravity will be discussed"

 

[marcus]

with Smolin's 10 October talk, the powerpoint slides are slow to print and waste ink on the colored background, so instead of bothering to print out the slides, I will paraphrase them by hand, just typing out the captions or describing the pictures----the following is a rough paraphrase

#57 rule 1: twist number is conserved at nodes
we will be interested in states with triplets of edges

[he shows a Y diagram how if a R-twist comes in then one has to go out, and same with a L-twist.
and he shows triple-ribbon either parallel vanilla or braided.]

#58 some possible topologies for triplets: unbraided, left braid, right braid, each strand also can be twisted

#59 two more rules:
rule 2: conservation of braiding number across nodes.
rule 3: no states with both + and - twists in a single triplet

topological embeddings of ribbon graphs modulo these rules span a Hilbert space H^edg

#60 discrete symmetries
C: reverse the twist on all three ribbons of the triplet
P: braid-swapping----exchange L-braid and R-braid
T: reverse orientation----flip it around head to tail

he says CPT=I (=identity) but I do not see that T means time reversal
I do understand that sundance represents e/3 charge by a twist on a ribbon and having all three ribbons twisted gives you the usual electron charge e.

he says leftbraid---SU(2)_L and
rightbraid---SU(2)_R

#61 next slide says ASSUME this theory has a low energy limit, defined in terms of an emergent 3+1 dim spacetime metric
ASSUME that in the low energy limit the resulting effective dynamics is Poincare invariant.
then WHAT do the twisted braid states look like?

#62 he cites BilsonThompson and he says twist corresp to e/3 charge
and braiding gives the left and right FERMION NUMBER

(now I skip slides building up to #68)

#68 now he has a grand catalog of spin 1/2 states. everything here is either Lbraided or Rbraided with a simple cyclic braid and he gets THREE TYPES OF PARTICLES neutrinos, electrons, quarks

q = 0 and no ribbons are twisted----he gets two different (uncharged) particle neutrino/antineutrino depending is a L braid or a R braid

q = +/- 1 all positive twist or all negative twist and either L braid or R braid-----so he gets four possibilities, he calls them left positron and right positron and left electron and right electron

q = +/- 2/3 and he gets UP QUARKS and variations analogous to that, in the triplet of ribbons there are two ribbons twisted and one that is not twisted----and with a positive twist there are SIX possible particles because say in the L-braid case you have exactly three ways you can CHOOSE WHICH ONE NOT TO TWIST, so you have 3 left upquarks and you have 3 right upquarks
(he doesn't show the negative case but you would get 6 more that way for a total of 12)

q = +/- 1/3 and he gets again SIX possible negative 1/3 charge down quarks and the like, because say in the L-braid case you have exactly three ways you can choose the ribbon that you twist-----so with a negative twist you get six and with a positive twist (which he doesn't show) you get another six---a total of 12 in this case too.

So 24 states with color, and 4 electronpositron states, and 2 neutrinoantineutrino states.

the next slides, #70-73, I don't understand.

 

[Kea]

Marcus

Slide #70 is the famous Kauffman bracket. The parameter $q$ is the same $q$ that gets used to deform the (universal enveloping algebra of) Lie algebras into quantum groups. The condition $q = e^{\frac{i \pi}{9}}$ is an antisymmetry condition for fermions. In other words, this choice is like setting $\hbar = \frac{\pi}{9}$ (modulo factors of 2 or 4).

 

[Kea]

CarlB likes to talk about 9th roots of unity in connection with preons, as in the thread

https://www.physicsforums.com/showthread.php?t=100236

where he also mentions the long running discussion of the Koide mass formula, which (uh hum) says something about actual observed particle masses.

 

[marcus]

well let's say that Kea has kindly taken care of slides #70-73 for us and I will start paraphrasing again at #74.

---74---
suppose this works, so that the observed fermions are all the ends of nonlocal links. so the probability of a link being nonlocal is at least

10⁸⁰/10¹⁸⁰ = 10^-100

there could be many more non-local links and we could still be in a very sparse domain. The effects of non-locality may only become apparent when one looks out to cosmological scales.

could there be macroscopic nonlocal effects that only appear on cosmological scales? These would be effectgs that are characterized by the cosmological constant scale L = Lambda^-1/2
---end of 74---

the way he gets this number 10^-100 is that he imagines the observable universe out to the Hubble radius or somewhere like that, and he imagines its quantum geometry STATE and a big NETWORK with Planckscale links and he calculates that there would be 10¹⁸⁰ little links to make such a big network, and astronmers can estimate how much FERMIONS is in that same big volume and it is about 10⁸⁰ particles. SO ONLY A SMALL FRACTION OF THE LINKS HAVE TO BE LONG-DISTANCE IN ORDER TO ACCOUNT FOR ALL THE PARTICLES in fact only a miniscule fraction 10^-100 have to be long distant links----the rest can be nice local links just as one might imagine a lattice looks.

The relevant research he draws on here was hal finkel computer-simulated an expanding universe with expansion moves and swapping moves and got results where today's links are either local (from expansion) or else if they are non-local then they are WAY non-local. the links are predominantly two kinds----nice-local or else astrononmically non-local.

And then the scale L is the square root of the reciprocal of Lambda...well the cosmological constant is a curvature which is the reciprocal of area. So take reciprocal and it is an area and take square root and it is a LENGTH L-----if the cosmological constant Lambda is in fact a constant, then this length L is a fundamental physical constant.

And Smolin says that IF PARTICLES REALLY ARE THE ENDS OF nonlocal spinnetwork "tri-ribbon" cordage. so that there are these nonlocal links going way out, which is just what matter is----namely the ends.
well then, YOU START LOOKING AT SCALE L FOR THE EFFECTS of these non-local links.

this is very speculative and so we can say that something radical happens in this sequence of slides right here at slide #74 where up till now it was speculative drawing on Preons of Sundance BilsonThompson and computer simulations of Hal Finkel but it was so speak moderate. Now here IMHO it becomes scalp-tingling radical speculative no quarter asked or given no holds barred speculative. Don't misunderstand me there is good, and very necessary, kinds of speculation (as well as bad groundless waste-of-time kind) this is good speculation. but one should be aware what one is dealing with.

Maybe I should stop here at slide #74 and pause for a day or more

 

[garrett]

Cute toy. But it seems unnatural to exclude braids with strand twists of 0+- and the corresponding zoo of unwanted fermions.

 

[marcus]

Cute toy. But it seems unnatural to exclude braids with strand twists of 0+- and the corresponding zoo of unwanted fermions.

within a triplet of ribbons, opposite charges annihilate?

garrett so glad you are here! hoping you might give me some help understanding this B-T preon scheme

the part about having only one kind of charge in any given triplet----well provisionally at least I can picture that

what Sundance B-T says at the end is that what his model does NOT do is deal with inertia and gravitation issues, and what strikes me is that this is exactly the feature that Smolin is providing! by putting these braids into a spin network and having them interact with the rest of the network he seems to offer the possibility of giving them mass somehow.

 

[garrett]

Hi Marcus, I doubt I'll be able to help much, but it is a fun topic.

When evaluating a TOE or GUT, I think it's good to keep an account of several factors:
1. How many mathematical structures are used.
2. The number of arbitrary (unjustified) choices required within the structure.
3. How well it reproduces ALL the fields and dynamics of the standard model and gravity.
4. The number of fields left over and experimentally unacounted for.

This list is off the top of my head, so may take some refining. But when I look at the B-T model to see how it scores:
1. Great! Three ribbons (preons) that can twist and braid.
2. Good. No unlike charges in a braid. (Saying these charges would anihilate probably counts as half a justification.) Three as the number of ribbons.
3. Bad. The model has no dynamics. No spin. No masses. I didn't see a Higgs. No gluons without extreme handwaving. Gravity only through a tenuous connection to spin network constructions.
4. Pretty good.

With those ratings, I think this model makes a good toy. And that's a compliment. It's very easy and instructive to play with, but it seems an extreme long shot that you're ever going to be able to calculate new accelerator results from it or anything based on it.

On the other hand, it probably scores higher overall than string theory. Heh.

 

[marcus]

Hi Marcus, ..., but it is a fun topic.
.

yes!

I am expecting a paper by you on arxiv one of these days, about how you put dynamics into sundance's picture!

3. Bad. The model has no dynamics. No spin. No masses. I didn't see a Higgs. No gluons without extreme handwaving. Gravity only through a tenuous connection to spin network constructions.

OK I hear you
"only through a tenuous"
but even if tenuous what Smolin is proposing is a way to put dynamics, by embedding these things into spin networks and then using some dynamics developed for spin networks (to handle gravity)

so you don't need a Higgs or a separate graviton, the tri-ribbon cord is in the network and the network gives it inertia
and the interaction with geometry (gravity) is automatic because the cord (with its "particle" endpoints) is already part of the network

so dynamics comes down to MOVES like expansion moves and exchange moves, which shift the endpoints around and govern interactions and for which amplitudes can be calculated.

I am trying to paraphrase slides #16,17,18,19 of smolin's 10 October talk
http://loops05.aei.mpg.de/index_files/abstract_smolin.html
Better you should look at the slides yourself---I think it points to a way that the dynamics you see as missing could come in

I realize you expect something less tenuous and maybe i am just restating what you already alluded to, but i am excited by what i see as the place to apply spinnetwork dynamics which could force some innovative improvement in the dynamics

 

[Spin_Network]

in March 2005 sundance invented a sort of three-ribbon "cord" (or improved somebody else's similar cord)

which the different variations of this one cord (by varying twists and braiding) gives all the quarks and leptons

and in October 2005 smolin said try making spin networks out of this cord so that quantum gravity states can have matter in
http://loops05.aei.mpg.de/index_files/abstract_smolin.html


today 16 November, sundance is giving a talk at Perimeter:
http://www.perimeterinstitute.ca/activities/scientific/seminarseries/alltalks.cfm?CurrentPage=2&SeminarID=604

Topological preon models: a braid new world
Wednesday November 16, 2005, 2:00 PM
"Preon models enjoyed considerable popularity during the early 1980s, but have seen little progress since then. I will describe a correspondence between one of the more successful preon models and a simple game involving the twisting and braiding of ribbons, subject to straightforward topological conditions. This reproduces the fermions and gauge bosons of the standard model, as well as the electromagnetic, weak and colour interactions. The prospect that such structures may occur naturally within Loop Quantum Gravity will be discussed"

Marcus the seminar is available here:http://streamer.perimeterinstitute.ca:81/mediasite/viewer/?cid=a9b1d20a-efa7-485f-8d5d-3b62fb7d3e4c

at page 14 and click the link to view.

 

[Kea]

Thank you, SpinNetwork. Fantastic. The media setup is good, but unfortunately it is difficult to hear the audience members (as usual).

Sundance basically goes through the contents of his paper. They are very well presented. Towards the end he begins to discuss work with Fotini Markopoulou and Lee Smolin on initial attempts to fit the helon model into LQG. But actually, Lee gave away more in his Loops 05 talk.

For the String theorists, the idea that these Stringy ribbon diagrams could be LQG and not Strings must be highly amusing. A great quote from Sundance's slides: treat fundamental objects as lines, not points.

 

[Kea]

Are there any CFT experts around?

Fuchs spoke at the Streetfest http://streetfest.maths.mq.edu.au/ about Conformal Field Theory and Frobenius algebras in modular tensor categories, which are structures that use ribbon diagrams. In particular, instead of the usual 2 strand end discs, which represent a morphism
$$a \in \textrm{Hom}(U_{i} \otimes U_{j} , 1)$$
where $U_{x}$ is an object in a category of representations, Fuchs considers discs with three strands emanating from one side, and one from the other, just like the diagrams that Sundance drew up on the blackboard at Perimeter right at the end of the talk. In other words, vertices representing morphisms
$$a \in \textrm{Hom}(U_{i} \otimes A \otimes U_{j} , A)$$
where $A$ is a Frobenius algebra object.

These fancy 3-manifold diagrams represent correlation functions in rational CFT. A collection of Fuchs' papers is available at http://arxiv.org/find/hep-th/1/au:+Fuchs_J/0/1/0/all/0/1

Just wondering.

 

[marcus]

Marcus the seminar is available here:http://streamer.perimeterinstitute.ca:81/mediasite/viewer/?cid=a9b1d20a-efa7-485f-8d5d-3b62fb7d3e4c
at page 14 and click the link to view.

thanks I found it! have only seen a few of the slides so far---company came today, not yet sure the perimeter shows will work on my computer, will try them out some more. thanks for the link.

 

[Spin_Network]

Thank you, SpinNetwork. Fantastic. The media setup is good, but unfortunately it is difficult to hear the audience members (as usual).

Sundance basically goes through the contents of his paper. They are very well presented. Towards the end he begins to discuss work with Fotini Markopoulou and Lee Smolin on initial attempts to fit the helon model into LQG. But actually, Lee gave away more in his Loops 05 talk.

For the String theorists, the idea that these Stringy ribbon diagrams could be LQG and not Strings must be highly amusing. A great quote from Sundance's slides: treat fundamental objects as lines, not points.

Kea, I share your concerns re:audience questions, very hard to even speculate what was talked.

The seminar was very interesting, and it was done in a very easy to understand format. The actual model starts off quite simple, but appears to be far more complex than I expected, but having also downloaded the PDF paper that marcus highlighted earlier in the thread, I am just starting to digest the model and understanding.

Questions that are important: Can mass be related to braiding and Twisting?

There does appear, from 'my' perspective.. to be an issue with the process of "seperations" and/or "reductionism"?

That being said, the format of braiding when coupled to the Fotini and Smolin Geometric (certain) modeling, appears to be quite productive, one can almost see that dimensional overlapping of Quark structure, is foundationally 2-D and 3-D embeddings, and the Quark technique of seperation, is actually a breaking of the dimensional field energy?

Preon substructure has to be Vacuum Dependant?

 

[dubmugga]

Hey Kea...

...can you post a picture of these diagrams with 3 things out one side and one on the other please ?

and why not "treat fundamental objects as spheres" given that we exist in a 3d world (plus time of course) and gravity works to make everything as spherical as possible...

 

[Kea]

Questions that are important: Can mass be related to braiding and twisting?

For the benefit of those readers to whom it is not perfectly obvious, let me state my point of view on this issue: the Bilson-Thompson diagrams can say nothing whatsoever about mass until they are couched in the context of a fully working theory of quantum gravity, which of course is the higher dimensional category theory one.

SpinNetwork, the answer to your question is Yes. Just as knot polynomials can be associated to state sums of 6j symbols there will be an improved knot type invariant that produces mass quantum numbers. Although approximate calculations may yield good numerical values, a real understanding will require a proper category theoretic construction of the invariants. Personally, I believe String theory is closer to obtaining this goal than LQG, despite the fact that LQG has worked more closely with braided monoidal structures in the past.

One essential element in this goal is the so-called breaking of the pentagon which means monoidality is not a feature of the relevant categorical structures. String theoretically, the introduction of triple ribbons replaces the vertex point (single 1-arrow of the braided structure) by a disc. This goes hand in hand with the fact that tri and tetra categories with more structure on the lower levels lose the pentagon condition.

 

[Kea]

One possibility is that the invariant is a vector rather than a scalar (assuming a numerical value for a parameter such as $q$ has been set) and that three associated eigenvalues yield the generation masses. This would mean that the Bilson-Thompson picture would suffice to describe all generations. This also fits with the Koide mass formula investigations. More complex braidings may well say something about allowable mass values, but are not necessarily directly associated to rest masses.

 

[marcus]

directions for finding the recorded talk have changed.
it is still in the menu at
http://streamer.perimeterinstitute....fa7-485f-8d5d-3b62fb7d3e4c&shouldResize=False
but now it is on PAGE ONE, instead of page 14
and something has changed so that my computer plays both the slides and the video simultaneously without trouble.
For me this is an outstanding talk---more than just about any other talk that I have seen so far in the Perimeter Institute library. I am really impressed by Bilson-Thompson's preon scheme. (but note Garrett's justified criticisms of it earlier in this thread)
it looks like the talks are now arranged latest first, so to find Bilson-Thompson talk just scroll down to November 16, 2005. It won't always be on page 1.

 

[Spin_Network]

directions for finding the recorded talk have changed.
it is still in the menu at
http://streamer.perimeterinstitute....fa7-485f-8d5d-3b62fb7d3e4c&shouldResize=False
but now it is on PAGE ONE, instead of page 14
and something has changed so that my computer plays both the slides and the video simultaneously without trouble.
For me this is an outstanding talk---more than just about any other talk that I have seen so far in the Perimeter Institute library. I am really impressed by Bilson-Thompson's preon scheme. (but note Garrett's justified criticisms of it earlier in this thread)
it looks like the talks are now arranged latest first, so to find Bilson-Thompson talk just scroll down to November 16, 2005. It won't always be on page 1.

Thanks Marcus! I have been watching a number of online talks from the site recently, but the David Deutsch one is totally inaudable, I wonder if there is a way of the institute checking sound quality prior to making them available?..there seems to be a vast difference in quality, for instance the Ashfar talk is perfectly clear:http://streamer.perimeterinstitute....fa7-485f-8d5d-3b62fb7d3e4c&shouldResize=False

but I sppose we must be thankful that there is such a wealth of talks ranging across many scientific area's, that we can view and enjoy.