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Quarks and Leptons: Fundamental or not?

  1. Nov 30, 2004 #1
    I've been trying to research this area but there doesn't seem to be much out there. Does any one know of any evidence or theory showing that quarks and leptons are or are not fundamental?

    I have heard of String Theory but does string theory actually suggest that quarks and leptons are made up of strings or is there an intermediate particle between strings and quarks and leptons?

    I've also come across a hypothesis called the MATPELUKA hypothesis. But I can't find any info on it. [Part (e) of this Document] Has any one else heard of this?
     
  2. jcsd
  3. Nov 30, 2004 #2

    Haelfix

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    I wouldnt trust every theory you come across on the internet.

    AFAIK, other than String theory the only one I am aware off is the theory of preons, and that suffers from severe theoretical problems.
     
  4. Dec 2, 2004 #3
    Do you have any links about Preons?

    Also, are there any arguments out there to argue that quarks ARE fundamental?
     
  5. Dec 2, 2004 #4
    I don't
    Here's a link about BPS preons and the BPS preon conjecture
    http://xxx.arxiv.cornell.edu/abs/hep-th/0312266 [Broken]
    Well, now that i'm here, I beg if someone can tell me what person proposed the preon model. I've searched for it for a long time without luck
     
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  6. Dec 3, 2004 #5
    Here's a model that postulates that quarks are made of a particles called primons
    http://arxiv.org/PS_cache/hep-ph/pdf/9901/9901234.pdf [Broken]
    The more important theory of particles that we have is the Standard Model, that postulates that quarks are pointlike particles. If is ever found that quark compositeness is true, it will be a revolution in the foundations of the SM
     
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  7. Dec 3, 2004 #6

    Nereid

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    On the experimental/observational side, a quick summary might look like this:
    - the Standard Model (SM) is consistent with all such results, to date
    - in the SM, quarks and leptons are fundamental
    - however, there are several big questions which the SM doesn't address (of course, the questions themselves may turn out to be misconceived)
    - there are a number of solid experimental/observational results which hint at 'new physics', perhaps just beyond the domains within which the SM has been tested to date
    - however, none of these hints are at all strong wrt quarks and/or leptons being not fundamental.
     
  8. Dec 3, 2004 #7
    As an addendum to what Nereid wrote...A friend of mine at college is involved into an experimental study based upon a field theory that is effective. This means that quarks are NOT considered as the degrees of freedom of this theory. In this case, the field theory called Quantum Hadro Dynamics does a better job then QCD at explaining some experimental results.In QHD, the degrees of freedom are hadrons...

    I admit this sound vague but what i am trying to say is the working with fundamental degrees of freedom like quarks in QCD does not always give rise to the best theoretical model.

    regards
    marlon
     
  9. Dec 3, 2004 #8
    QHD is in fact much older than QCD. This is the traditional, effective approach. Historically, people went desperate about QFT exactly because QHD requires to introduce new fields for every single new hadron (or at least hadron multiplet). So yes, QHD might be very efficient, but does not tell you much about Nature at a fundamental level.

    Nereid's post is very clear !
     
  10. Dec 5, 2004 #9

    arivero

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    You can look around scholar for references to Barut & Bracken, Phys Rev D v 23 n 10 p 2454 , where internal structure to the electron was suggested. On the other hand, you could look for technicolor, which in some approaches could let you to think on substructure.
     
  11. Dec 7, 2004 #10
    Alejandro,
    my (scarce) understanding of the technicolor model is that it postulates the compositeness of the Higgs boson (formed by particles called techniquarks) but I have never heard that it suggested compositeness of quarks. If you have a reference I would appreciate it.
     
  12. Dec 15, 2004 #11
    If Abdus Salam was not the originator of a preon model that quarks are composites of smaller particles, he was one of a small group. You might want to read this address in which he predicts the discovery of the preon by 1990: http://nobelprize.org/physics/laureates/1979/salam-lecture.pdf
     
  13. Dec 15, 2004 #12
    Many thanks! Your link has lead me to discover that the preon model was proposed in 1974 by Salam. What I didn't know is that preons could be divided into chromons, flavons and somons
     
  14. Dec 16, 2004 #13

    ohwilleke

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    There are a number of studies which have shown some evidence of fractional electron charge, which would make sense if quarks were fundamental (with their 1/3rd charges), but electrons were not. The trouble is that while some of the fractional electron charge studies seem to show the expected -1/3 charge, others seems to show -1/5th charges or other unexpected values. I don't have the references at hand, but have seen at least three or four such studies.

    See, for example, http://www.bell-labs.com/news/1998/october/13/2.html [Broken] discussing an award granted for discovering the fractional quantum Hall effect. The theoretical reason for this (i.e. is it substructure of an electron or some form of interaction effect with electrons remaining fundamental) is in flux. Dozens of papers in the few years alone address the topic theoretically.
     
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  15. Dec 16, 2004 #14

    Nereid

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    IIRC, all but one of the studies were shown to have flaws and/or gave inconsistent results when repeated by different groups. The only one that seemed to emerge more or less OK was one with Nb spheres, a version of the Millikan oil drop experiment. The problem there was that no other, similar experiments found anything.

    Sorry, I don't have references either.
     
  16. Dec 16, 2004 #15

    ohwilleke

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    Nice charts showing the FQHE are shown here:
    http://www.warwick.ac.uk/~phsbm/fqhe.htm [Broken]

    A survey of the leading FQHE theories is here:
    http://arxiv.org/PS_cache/cond-mat/pdf/0108/0108271.pdf [Broken]

    An interesting theoretical discussion of the possibility of rare electron decay into a neutrino and a photon is discussed in this article: http://xxx.arxiv.cornell.edu/abs/hep-th/0312325 [Broken]

    A clear position is set out in C.S. Kalman, "Why quarks cannot be fundamental particles" here: http://arxiv.org/abs/hep-ph/0411313

    Recent experiments supporting the standard model are found here:
    http://arxiv.org/PS_cache/hep-ex/pdf/0408/0408004.pdf [Broken]
     
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  17. Jan 1, 2005 #16
    The trouble is that while some of the fractional electron charge studies seem to show the expected -1/3 charge, others seems to show -1/5th charges or other unexpected values. I don't have the references at hand, but have seen at least three or four such studies.

    I spent time reading up on the experiment that won the Nobel prize for discovering fractional charged particles. To the best of my recollection no plus or minus sign appeared in the paper, but as reference was made to 'electron field' a minus charge was indicated, However, one writer clearly stated that the one thing Tsui could not explain was "why the fractional charge was positive".
    I lost my files in a computer crash and have not repeated the search. Does anyone know the true situation?

    Before Tsui et al there was a paper published that gave a table of observed and predicted fractional charges. The main column was 1/3 2/5 3/7 4/9 etc with two shorter cols of different fractions on either side. (these were 'fractional charges' not the 'fractionally charged particles' proposed by Tsui et al..
     
  18. Jan 3, 2005 #17
    I'm pretty sure that quarks and leptons aren't fundemental. They probably have some type of substructure. Hey, "atom" in greek means uncuttable, but it was cut. Same with nucleons. Whether or not there constituents are "particles," as we know them, is beyond me.
     
  19. Jan 3, 2005 #18

    Nereid

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    Do you know of any good experimental results which even hint that they may not be? Please give us some links!
     
  20. Jan 4, 2005 #19
    Please revisite what I posted and try notice my logic here. I'm just saying that everything we've labled in the past as "fundemental" has ended up having a type of substructure. Assuming something is fundemental because it's the smallest building block you know of at the time is hasty and unnecessary.

    What evidence hints towards smaller constituents of matter? What evidence is there that says there isn't? I don't know of any evidence that says quarks and leptons cannot be made of smaller components. Perhaps (better yet there propably is) there some papers or experiments that do suggest quarks and leptons are fundemental I'm simply not aware of. If so, let me know.
     
  21. Jan 4, 2005 #20
    Entropy,

    in QCD, quarks are regarded as the fundamental degrees of freedom. Now, whether or not there is some model in which they can be treated as non-fundamental and therefore they exhibit some underlying structure is certainly not well established and therefore very speculative. What i am saying is this...if you wanna describe quarks in any way, QCD will do the best job at this moment. So basically this discussion is speculative and useless. Suppose quarks were not fundamental then their mutual properties wouldn't change because the model you would construct MUST respect the rules and results produced by QCD. Just like QM respects Newtonian physics in the right limit (you know, large enough objects).


    As to your last question : Just goto http://arxiv.org/ and type in QCD or something with quarks...Eitherway, the one will lead to the other...you see my point :wink:


    regards
    marlon
     
  22. Jan 4, 2005 #21

    Nereid

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    Just to add a few words to what marlon said ... no scientist would rule out the possibility of new things being discovered, whether quarks and leptons not being 'fundamental' or G not a 'true' constant, ... :smile:

    However, I was asking if you knew of any good experimental or observational results which even hinted at the possibility of substructure.

    As marlon said, without at least a hint - in good data or theory - that substructure is needed, any discussion on such substructure is (pure?) speculation.
     
  23. Jan 7, 2005 #22

    ohwilleke

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    Most of the speculation that quarks might not be fundamental, I think, flows directly from the fact that there are so many different kinds of quarks and that they show a certain periodicity that shows clear patterns of charge and mass, to which there are various formulas (see elsewhere in PF for the post on this) which could plausible suggest a relationship.

    When we have seen these kinds of patterns before (e.g. in the particle zoo that preceded the discovery of quarks, and in the period before we discovered the proton-neutron theory of the nucleus), this kind of pattern always turned out to be evidence of substructure. The inference is, that the current pattern might also be evidence of substructure, and string theory is one theory that seems to show what that kind of substructure might look like.

    For example, we currently have three "orders" of spin 1/2 particles, the "electron" order, the "mu" order, and the "tau" order (with corrosponding higher order electrons, neurinos and quarks. One could easily propose the entirely plausible theory that there is also a fourth "order" of spin 1/2 particles each with masses a couple of hundred times those of the "tau" order particles, that they decay very rapidly to lower order particles, and that we haven't observed them yet because our particle accellerators don't have enough juice. Indeed, if I wanted a real big particle accellerator, I might spend a good deal of time talking about the theory and I wouldn't even be particularly dishonest in doing so, because the most massive "tau" particle does have an suggestive closeness to the largest particle we have been able to detect.

    The fact that the higher order quarks "decay" while this may simply be a product of deceptive use of language, is also evocative of the idea that quarks are not fundamental.

    The article, suggests theoretical underpinnings for a composite Higgs particle: http://arxiv.org/ftp/hep-ph/papers/0209/0209082.pdf

    "Understanding the Genesis of Mass" by George Triantaphyllou

    We give a pedagogical and concise presentation of dynamical mass generation involving strongly-interacting mirror fermions. As a paradigm which has been explicitly shown to predict correctly the weak scale and the weak angle and thus addressing successfully the essence of the hierarchy problem of energy scales (contrary to "supersymmetric" or "extra-dimension" models) and the unification of fundamental forces, it might have already manifested indirectly its validity experimentally, as first noted by the author in 1998, via the bottom-quark forward-backward asymmetry and the related coupling parameter A_b. After a decade during which the particle-physics community was frequently misled by a particularly obscurantist interpretation of the L.E.P./S.L.C. precision data, this approach emerges as a strong candidate for new physics beyond the standard model of elementary particles to be thoroughly tested in the forthcoming high-energy experiments.
     
    Last edited: Jan 7, 2005
  24. Jan 22, 2005 #23
    There are a number of studies which have shown some evidence of fractional electron charge, which would make sense if quarks were fundamental (with their 1/3rd charges), but electrons were not. The trouble is that while some of the fractional electron charge studies seem to show the expected -1/3 charge, others seems to show -1/5th charges or other unexpected values. I don't have the references at hand, but have seen at least three or four such studies.

    I note that you use a minus sign, there is no plus or minus sign on the papers referred to nor does the words 'positive' or 'negative' appear anywhere in the papers.

    With regard to the fractions the main sequence 1/3, 2/5, 3/7, 4/9 etc also occurs on the cosmological scale, in the distance between, dust bands around a comet, between planets and between the arms of a theoratically perfect spiral galaxy. Although in the planetary case there are errors the results are more accurate than any other inter-planetary distance theory. The key is the peculiar way the fractions appear; imagine four points A B C and D. Then A to B is 1/3 of A to D; B to C is 2/5 of B to D (not A to D) etc.
    This is a simple matter of measurement leaving little room for debate.

    The point that I tried to make is that these fractions (together with four lesser fractional sequences) are somehow part of a grand design. However I have to concede that not a single comment was made in reply to my article. There just is no interest in any non-quantum model even when is does not require any change to QT itself, but merely supplies additional data or underpinning theory.
     
  25. Jan 22, 2005 #24

    Haelfix

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    Well, as far as I know the theory of preons (quark substructure) is weak. The main problem is that the same triangle anomaly that hits quarks has to reappear in the relevant interactions of any substructure. This is hard to do, and constrains any speculation about such an enterprise.
     
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