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Quantum Gravity and the Standard Model (Sundance + PI)

  1. Mar 5, 2006 #1

    marcus

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    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. jcsd
  3. Mar 5, 2006 #2

    Kea

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    Cool! :cool: :smile:
     
  4. Mar 5, 2006 #3

    marcus

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    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: Mar 5, 2006
  5. Mar 5, 2006 #4

    Kea

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    Marcus

    Despite a long line of muscular beaus, I have never gone out with an Australian. :smile:
     
    Last edited: Mar 5, 2006
  6. Mar 5, 2006 #5

    arivero

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    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.
     
  7. Mar 5, 2006 #6

    Kea

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    Categories make it geometric.
     
  8. Mar 5, 2006 #7

    marcus

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    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."

    we also had a PF thread called "Preons of Bilson-Thompson"
    https://www.physicsforums.com/showthread.php?t=100183
    that has some more links
     
  9. Mar 6, 2006 #8
  10. Mar 6, 2006 #9

    arivero

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    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.
     
  11. Mar 6, 2006 #10

    marcus

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    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
  12. Mar 6, 2006 #11

    arivero

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    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.
     
  13. Mar 6, 2006 #12

    arivero

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    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.
     
  14. Mar 6, 2006 #13

    Kea

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    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.
     
  15. Mar 6, 2006 #14

    Kea

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    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 [itex]J[/itex] at 5th roots of unity for universal quantum computation, one finds that

    [tex]J_{\textrm{Hopf}} = d = 1.618 \cdots[/tex]

    the golden ratio. Now let a deformation parameter be

    [tex]q = e^{\frac{2 \pi}{2 + d}}[/tex]

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

    [tex]\alpha = 4 (q + q^{-1})^{2} = 137.08[/tex]

    This is of course an extremely coarse estimate, and hence not particularly accurate. :smile:
     
    Last edited: Mar 6, 2006
  16. Mar 6, 2006 #15

    marcus

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    Of course.
    Had you performed the calculation more delicately it would doubtless have come out spot on 137.0359... :smile:
     
  17. Mar 7, 2006 #16

    marcus

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    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
  18. Mar 7, 2006 #17

    arivero

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    Quicksilver to Gold is actually childs-play, as a look to the table of isotopic weights reveals :biggrin: 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
  19. Mar 7, 2006 #18
    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 :wink:
    (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
     
  20. Mar 7, 2006 #19

    Kea

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    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.
     
  21. Mar 8, 2006 #20

    f-h

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    Smolin talked about this a bit at Loops05, John Baez says about this talk in week 208:

    "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.
     
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