Kea said:
Hi CarlB
I'm thinking of reviving this thread again soon. What do you think?
As Yershov correctly noted in a private email to me,
I personally wrote (or substantially added) this for wikipedia preon
as " 65.26.44.75 " and "216.16.237.110 "
Preon research is motivated by the desire to explain already existing facts (postdiction), which include:
To reduce the large number of particles, many that differ only in charge, to a smaller number of more fundamental particles. For example, the electron and positron are identical except for charge, and preon research is motivated by explaining that electrons and positrons are composed of similar preons with the relevant difference accounting for charge. The hope is to reproduce the reductionist strategy that has worked for the periodic table of elements.
The second and third generation fermions are supposedly fundamental, yet they have have higher masses than those of the first generation, and the quarks are unstable and decay into their first generation counterparts. Historically, the instability and radiactivity of some chemical elements were explained in terms of isotopes. By analogy this suggests a more fundamental structure for at least some fermions. [[1]]
To unify particle physics with gravity, for example, Bilson-Thompson model with loop quantum gravity.
To give prediction for parameters that are otherwise unexplained by the Standard Model, such as particle masses and charges and color, and reduce the number of experimental input parameters required by the standard model.
To provide reasons for the very large differences in energy-masses observed in supposedly fundamental particles, from the electron neutrino to the top quark.
To explain the number of generations of fermions.
To provide alternative explanations for the electro-weak symmetry breaking without invoking a Higgs field, which in turn possibly needs a supersymmetry to correct the theoretical problems involved with the Higgs field. Supersymmetry itself has theoretical problems.
To explain the features of particle physics without the need for higher dimensions, supersymmetry, higgs field, or string theory.
To account for neutrino oscillation and mass.
The desire to make new nontrivial predictions, for example, to provide possible cold dark matter candidates, or to predict that the LHC will not observe a Higgs boson or superpartners.
The desire to reproduce only observed particles, and to prevent prediction within its framework for non-observed particles (which is a theoretical problem with supersymmetry).
The experimental falsification of certain grand unified theories of particle physics as the result of not observing proton decay may suggest that the grand unification scenario, which string theory is predicated on, and supersymmetry, may be false, and different solutions and thinking will be required for the progress of particle physics.
Were string theory successful in its original objectives, preon theory research would not be necessary. String theory was supposed to account for the above issues in terms of string dynamics. The different particles of the standard model were accounted for as different frequencies (tension) of a Planck-scale string, particle dynamics were explained in terms of the worldsheet diagrams, (the string theory equivalent of Feynman diagrams) and the three generations of fermions were explained in terms of strings "wrapping around" specific configuration of higher-dimensional moduli. The continuing failure of string theory to achieve the above objectives as a theory of particle physics Relevant literature include: Peter Woit Not Even Wrong, or Lee Smolin's The Trouble with Physics, or Daniel Friedan's "String theory is a complete scientific failure". Andrew Oh-Willeke states "as string theory develops more doubters, I think [preon theory] will be an obvious direction for non-string theory investigators and theorists."
The vast bulk of recent theoretical research into the particle zoo has been string theory. It was thought string theory has completely supplanted preon research, and that one dimensional supersymmetric strings can reproduce all the particles of the standard model, and their superpartners, the MSSM, their properties, color, charge, parity, chirality, and energy-masses, obviating any need for preon research. To date, string theory has been unable to reproduce the standard model.
A search through Spires and Arxiv, show that approximately over 30, 000 papers in string theory or supersymmetry since 1982, with several hundred new papers being published every month. In comparison, in 2006, since 2003, there have been about a dozen papers in preon theory listed as such in arxiv.
String theories continuing failure to reproduce the particle spectrum of the standard model has given some life for preon theories, and there have been recent papers on preon theory. As of 2006, Yershov, Fredriksson, and Bilson-Thompson have published papers in Preon theory within the past 5 years: a 2003 paper by Fredriksson [4], and a 2005 paper by Bilson-Thompson [5].
When the term "preon" was coined, it was primarily to explain the two families of spin 1/2 fermions: leptons and quarks. More recent preon models also account for spin-1 bosons, and are still called "preons". The term "preon" is the term of choice for Bilson-Thompson, Yershov, and Fredrickson, although they expand the meaning of the term, in addition to accounting for spin 1/2 fermions of leptons and quarks, which the term was used in its early history, the latter theories also accounts for spin-1 bosons.
Yershov's model is patterned after the idea naked singularities in general relativity, and closely resembles geon from John Archibald Wheeler research program into Geometrodynamics. Electron structure in Yershov's theory was further elaborated on in 2006 [6]. 2003 papers by Yershov [7] [8] are notable for being some of the only papers in the field to use the Preon model as a basis for providing specific numerical values from first principles for the masses of the particles described in the Standard Model. Yershov's model does not predict the mass of the Higgs Boson, and does not need the Higgs boson, and predicts it will not be found. Yershov's model deals with the mass paradox by prosposing a huge binding energy for his preons, which acts as a source of mass-energy, as through mass defect. To get around the mass paradox, Yershov's model proposes a new force that is 10^5 stronger than the strong nuclear force, that binds his preons together.
Fredriksson preon theory does not need the Higgs boson, and explains the electro-weak breaking as the rearrangement of preons, rather a Higgs-mediated field. In fact, Fredriksson preon model predicts that the Higgs boson does not exist. In the above cited paper, Fredricksson acknowledges the mass paradox represents a problem in his accounting for neutrino mass, however, he proposes a specific arrangement of preons in his model, which he calls the X-quark, which his theory suggests could be a stable good cold, dark matter candidate.
[edit] Loop quantum gravity and Bilson-Thompson Preon theory
In a 2006 paper [9] Sundance Bilson-Thompson, Fotini Markopolou, and Lee Smolin suggested that in any of a class of quantum gravity theories similar to loop quantum gravity (LQG) in which spacetime comes in discrete chunks, excitations of spacetime itself may play the role of preons, and give rise to the standard model of particle physics as an emergent property of the quantum gravity theory.
Sundance preon model was inspired by the Harari Rishon Model but posits ribbon-like structures that braid in groups of three, rather than point-particles. Proposing extended ribbon-like braided structures helps explains why ordering matters whereas the older point-particle preon model, the Harari Rishon Model, is unable to do so. It has been shown that the properties of Sundance ribbon-like structure can be derived from coherent states of spin foam, which may also give rise to gravity. His ribbon like structures have been described as "pieces of spacetime ribbon-tape", in that the Bilson-Thompson ribbons are made of the same structure that makes up spacetime itself. [10] While Sundance papers do offer braiding and an explanation on how to get fermions and spin-1 bosons, he does not show a braiding that would account for the Higgs boson [11].
Specifically, Bilson-Thompson et al proposed that loop quantum gravity could reproduce the standard model. The first generation of fermions (leptons and quarks) with correct charge and parity properties have been modeled using preons constituted of braids of spacetime as the building blocks[1]. Bilson-Thompson's original paper suggested that the higher-generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given. The electric charge, colour, and parity properties of such fermions would arise in the same way as for the first generation. Utilization of quantum computing concepts made it possible to demonstrate that the particles are able to survive quantum fluctuations.[2]
In a 2006 paper [12], L. Freidel, J. Kowalski--Glikman, A. Starodubtsev suggests that elementary particles are Wilson lines of gravitational field, which implies that the properties of elementary particles, such as mass, energy, and spin, can be described by LQG's Wilson loops, and particle dynamics can be modeled on breaks in these Wilson loops, adding theoretical support to Bilson-Thompson's preon proposals.
Bilson-Thompson's ribbon preon scheme is intended to provide a picture diagram to represent coherent phases of spin foam dynamics whose description is quantum mechanical, not classical. For example, Bilson-Thompson's picture diagram of a preon with a twist, representing a U(1) charge equal to 1/9 of an electron charge, is to map to an eigenstate of spin foam. The spin foam formalism allows for the derivation of certain other particles of the standard model, the spin-1 bosons, such as photons and gluons, [[13]] and gravitons [[14]], [[15]] from loop quantum gravity's fundamental principles, and independent of Bilson-Thompson's braiding scheme for fermions. However, as of 2006, there is not a derivation of Bilson-Thompsons from spin foam formalism, including a derivation of 1/9 e- U(1) charge, and dynamics, as described by braiding. Bilson-Thompsons' braiding scheme does not offer a braiding that would account for a Higgs, but does not rule out the possibility of a Higgs boson. Bilson-Thompson himself observes that since the preons that have mass have charge as part of its internal "structure", it is possible it is this internal structure of charge that interacts with an electric field to give rise to inertial mass, or perhaps interacts with the Higgs field to give rise to inertial mass. et al. (The massless photon is untwisted in Bilson's preon scheme). As of 2006, it remains to be seen whether the derivation of the photon from the spin foam formalism in [[16]] can be matched with Bilson-Thompson's braiding of three untwisted ribbons [17], or perhaps, there are multiple ways to derive photons from the spin foam formalism.
When the term "preon" was first coined, it was used to describe pointlike subparticles that describe spin-1/2 fermions that include leptons and quarks. Such sub-quark pointlike particles would suffer from the mass paradox described below. It is observed that Bilson's ribbon structures are not actually "classical" preons, as defined in the introduction to this article as "pointlike structures or objects" of fermions, but Bilson-Thompson chooses to call his extended ribbon like structures of space-time "preons" in his research papers in the second sense of definition of preon as being more fundamental "subparticles" than elementary particles, and to maintain continuity in terminology with the larger physics community. His braiding also accounts for spin-1 bosons. In many respects, Bilson-Thompson's topological "preon" model resemble the geon more strongly than classical preon, and follows more closely a program inspired by Einstein and John Archibald Wheeler, in which particles are reduced to geometry through Wheeler's program Geometrodynamics (which has its roots in Lord Kelvin's knotting theory of atoms, and possibly to Spinoza's belief that reality is geometrical in structure) and its model of geons and continued through loop quantum gravity. The Wheeler's original Geometrodynamics suffers from the fact that it does not take quantum theory into account, whereas loop quantum gravity does.
[edit] Theoretical objections to preon theories: The mass paradox, chirality, and T'Hooft anomaly matching constraints
Heisenberg's uncertainty principle states that xp >= h bar/2 and thus anything confined to a box smaller than x would have a momentum of uncertainty proportionately greater. Some candidate preon models propose particles smaller than the elementary particles they make up, therefore, the momentum of uncertainty p should be greater than the particles themselves.
One preon model started as an internal paper at the Collider Detector at Fermilab (CDF) around 1994. The paper was written after the occurrence of an unexpected and inexplicable excess of jets with energies above 200 GeV were detected in the 1992—1993 running period.
Scattering experiments have shown that quarks and leptons are "pointlike" down to distance scales of less than 10−18 m (or 1/1000 of a proton diameter). The momentum uncertainty of a preon (of whatever mass) confined to a box of this size is about 200 GeV, 50,000 times larger than the rest mass of an up-quark and 400,000 times larger than the rest mass of an electron.
Thus, the preon model represents a mass paradox: How could quarks or electrons be made of smaller particles that would have many orders of magnitude greater mass-energies arising from their enormous momenta? Yershov's model, referenced above, proposes that when both particles and anti-particles of the proposed Y-particles in the theory are present, such as in the model's proposed neutrino composition, the mass of the constituent parts "cancels out", but can appear again when the structure of the Y-particles is changed. Yershov's model also proposes that particle mass arises as a mass defect binding energy among his preons, which helps account for the mass paradox.
Sundance preon model may avoid this by denying that preons are pointlike particles confined in a box less than 10−18 m, and instead positing that preons are extended 2-dimensional ribbon-like structures, not necessarily smaller than the elementary particles they compose, not necessarily confined in a small box as point particles preon models propose, and not necessarily "particle-like", but more like glitches and topological folds of spacetime that exist in three-fold bound states that interact as though they were point particles when braided in groups of three as a bound state with other particle properties such as mass and pointlike interatcion arising as an emergent property so that their momentum uncertainty would be on the same order as the elementary particles themselves.
String theory posits one-dimensional strings on the order of the Planck scale as giving rise to all the particles of the Standard Model, which would appear to also have the mass paradox problem. String theorist Lubos Motl has offered explanations as to how string theory gets around the mass paradox [18].
Any candidate preon theory must address particle chirality and T'Hooft anomaly matching constraints, and ideally be more parsimonious in theoretical structure than the Standard Model itself. Often, preon models propose additional unobserved forces or dynamics to account for their proposed preons compose the particle zoo, which may make the theory even more complicated than the Standard Model, or have implications in conflict with observation. One specific example: should the LHC observe a Higgs boson, or superpartners, or both, the observation would be in conflict with the predictions of many preon models, which predict the Higgs boson does not exist, or are unable to derive a combination of preons which would give rise to a Higgs Boson.
[edit] String theory and preon theory
String theory proposes that a one dimensional string on the order of a Planck scale has a tension, and differences in tension give rise directly to all the particles of the standard model and their super partners, in interaction with the proper compactified 6 or 7 dimensional Yau-Calabi mainfold and SUSY breaking. To date, string theory has been no more successful than preon theory in achieving this goal.
John Baez and Lubos Motl have discussed the possibility that [19] that should preon theory prove successful, it may be possible to formulate a version of string theory that gives rise to a successful model of preons.
There have been recent research papers that have proposed preon models that are made of superstrings in Arxiv [[20]], [[21]] or supersymmetry [[22]]
