Preon
Encyclopedia
In particle physics
, preons are postulated "point-like" particles
, conceived to be subcomponents of quark
s and lepton
s. The word was coined by Jogesh Pati
and Abdus Salam
in 1974. Interest in preon models peaked in the 1980s but has slowed as the Standard Model
of particle physics continues to describe the physics mostly successfully, and no experimental evidence for lepton and quark compositeness has been found.
(SM) was developed in the 1970s (the key elements of the Standard Model known as quark
s were proposed by Murray Gell-Mann
and George Zweig
in 1964), physicists observed hundreds of different kinds of particles in particle accelerator
s. These were organized into relationships on their physical properties in a largely ad-hoc system of hierarchies, not entirely unlike the way taxonomy
grouped animals based on their physical features. Not surprisingly, the huge number of particles was referred to as the "particle zoo
".
The Standard Model, which is now the prevailing model of particle physics, dramatically simplified this picture by showing that most of the observed particles were meson
s, which are combinations of two quark
s, or baryon
s which are combinations of three quarks, plus a handful of other particles. The particles being seen in the ever-more-powerful accelerators were, according to the theory, typically nothing more than combinations of these quarks.
Within the Standard Model, there are several different types of particles. One of these, the quark
s, has six different types, of which there are three varieties in each (dubbed "colors
", red, green, and blue, giving rise to quantum chromodynamics
). Additionally, there are six different types of what are known as lepton
s. Of these six leptons, there are three charged particle
s: the electron
, muon
, and tau. The neutrino
s comprise the other three leptons, and for each neutrino there is a corresponding member from the other set of three leptons. In the Standard Model, there are also boson
s, including the photon
s; W+, W−, and Z bosons
; gluon
s; and a few open spaces left for the graviton
and Higgs boson
, which have not yet been discovered. Almost all of these particles come in "left-handed" and "right-handed" versions (see chirality
). The quarks, leptons and W boson all have antiparticle
s with opposite electric charge.
The Standard Model also has a number of problems which have not been entirely solved. In particular, no successful theory of gravitation
based on a particle theory has yet been proposed. Although the Model assumes the existence of a graviton, all attempts to produce a consistent theory based on them have failed. Additionally, mass
remains a mystery in the Standard Model. Although the mass of each successive particle follows certain patterns, predictions of the rest mass of most particles cannot be made precisely. The Higgs boson
explains why particles show inertial mass (but does not explain rest mass), but to date the Higgs mechanism
remains unproven.
The Model also has problems predicting the large scale structure of the universe. For instance, the Model generally predicts equal amounts of matter and antimatter
in the universe, something that is observably not the case. A number of attempts have been made to "fix" this through a variety of mechanisms, but to date none have won widespread support. Likewise, basic adaptations of the Model suggest the presence of proton decay
, which has not yet been observed.
Preon theory is motivated by a desire to replicate the achievements of the periodic table, and the later Standard Model which tamed the "particle zoo", by finding more fundamental answers to the huge number of arbitrary constants present in the Standard Model. It is one of several models to have been put forward in an attempt to provide a more fundamental explanation of the results in experimental and theoretical particle physics. The preon model has attracted comparatively little interest to date among the particle physics community.
), which include
Other names which have been used for these proposed fundamental particles (or particles intermediate between the most fundamental particles and those observed in the Standard Model) include prequarks, subquarks, maons, alphons, quinks, rishons
, tweedles, helons, haplons, and Y-particles. Preon is the leading name in the physics community.
Efforts to develop a substructure date at least as far back as 1974 with a paper by Pati and Salam in Physical Review
. Other attempts include a 1977 paper by Terazawa, Chikashige and Akama, similar, but independent, 1979 papers by Ne'eman, Harari, and Shupe, a 1981 paper by Fritzsch and Mandelbaum, and a 1992 book by D'Souza and Kalman. None has gained wide acceptance in the physics world.
In his 1989 Nobel Prize
acceptance lecture, Hans Dehmelt
described a most fundamental elementary particle, with definable properties, which he called the cosmon, as the likely end result of a long but finite chain of increasing more elementary particles.
Each of the preon models postulates a set of far fewer fundamental particles than those of the Standard Model, together with the rules governing how those fundamental particles operate. Based on these rules, the preon models try to explain the Standard Model
, often predicting small discrepancies with this model and generating new particles and certain phenomena, which do not belong to the Standard Model. The Harari Rishon Model
illustrates some of the typical efforts in the field.
Many of the Preon models theorize that the apparent imbalance of matter and antimatter in the universe is in fact illusory, with large quantities of preon level antimatter confined within more complex structures.
Many preon models either do not account for the Higgs boson
or rule it out, and propose that electro-weak symmetry is broken not by a scalar Higgs field but by composite preons. For example, Fredriksson preon theory does not need the Higgs boson, and explains the electro-weak breaking as the rearrangement of preons, rather than a Higgs-mediated field. In fact, Fredriksson preon model predicts that the Higgs boson does not exist.
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".
(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. However, 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/c, 50,000 times larger than the rest mass of an up-quark and 400,000 times larger than the rest mass of an electron.
Heisenberg's uncertainty principle
states that ΔxΔp ≥ ħ/2 and thus anything confined to a box smaller than Δx would have a momentum of uncertainty proportionally greater. Thus, the preon model proposed particles smaller than the elementary particles they make up, since the momentum of uncertainty Δp should be greater than the particles themselves. And so 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? This paradox is resolved by postulating a large binding force between preons cancelling their mass-energies.
constraints, and would ideally have simpler theoretical structure than the Standard Model itself.
For 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 with respect to the existence of the Higgs boson.
By contrast, should a Higgs boson not appear in the increasingly constrained circumstances where the Standard Model predicts that it will be found, the preon theory would receive a significant theoretical boost, while many competing theories would be falsified.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, preons are postulated "point-like" particles
Point particle
A point particle is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space...
, conceived to be subcomponents of quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s and lepton
Lepton
A lepton is an elementary particle and a fundamental constituent of matter. The best known of all leptons is the electron which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons , and neutral...
s. The word was coined by Jogesh Pati
Jogesh Pati
Jogesh C. Pati is an Indian American theoretical physicist at the University of Maryland, College Park.-Biography:...
and Abdus Salam
Abdus Salam
Mohammad Abdus Salam, NI, SPk Mohammad Abdus Salam, NI, SPk Mohammad Abdus Salam, NI, SPk (Urdu: محمد عبد السلام, pronounced , (January 29, 1926– November 21, 1996) was a Pakistani theoretical physicist and Nobel laureate in Physics for his work on the electroweak unification of the...
in 1974. Interest in preon models peaked in the 1980s but has slowed as the Standard Model
Standard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
of particle physics continues to describe the physics mostly successfully, and no experimental evidence for lepton and quark compositeness has been found.
Background
Before the Standard ModelStandard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
(SM) was developed in the 1970s (the key elements of the Standard Model known as quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s were proposed by Murray Gell-Mann
Murray Gell-Mann
Murray Gell-Mann is an American physicist and linguist who received the 1969 Nobel Prize in physics for his work on the theory of elementary particles...
and George Zweig
George Zweig
George Zweig was originally trained as a particle physicist under Richard Feynman and later turned his attention to neurobiology...
in 1964), physicists observed hundreds of different kinds of particles in particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s. These were organized into relationships on their physical properties in a largely ad-hoc system of hierarchies, not entirely unlike the way taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
grouped animals based on their physical features. Not surprisingly, the huge number of particles was referred to as the "particle zoo
Particle zoo
In particle physics, the term particle zoo is used colloquially to describe a relatively extensive list of the known elementary particles that almost look like hundreds of species in the zoo....
".
The Standard Model, which is now the prevailing model of particle physics, dramatically simplified this picture by showing that most of the observed particles were meson
Meson
In particle physics, mesons are subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometer: 10−15 m, which is about the size of a proton...
s, which are combinations of two quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s, or baryon
Baryon
A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...
s which are combinations of three quarks, plus a handful of other particles. The particles being seen in the ever-more-powerful accelerators were, according to the theory, typically nothing more than combinations of these quarks.
Within the Standard Model, there are several different types of particles. One of these, the quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s, has six different types, of which there are three varieties in each (dubbed "colors
Color charge
In particle physics, color charge is a property of quarks and gluons that is related to the particles' strong interactions in the theory of quantum chromodynamics . Color charge has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD,...
", red, green, and blue, giving rise to quantum chromodynamics
Quantum chromodynamics
In theoretical physics, quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons . It is the study of the SU Yang–Mills theory of color-charged fermions...
). Additionally, there are six different types of what are known as lepton
Lepton
A lepton is an elementary particle and a fundamental constituent of matter. The best known of all leptons is the electron which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons , and neutral...
s. Of these six leptons, there are three charged particle
Charged particle
In physics, a charged particle is a particle with an electric charge. It may be either a subatomic particle or an ion. A collection of charged particles, or even a gas containing a proportion of charged particles, is called a plasma, which is called the fourth state of matter because its...
s: the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
, muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...
, and tau. The neutrino
Neutrino
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
s comprise the other three leptons, and for each neutrino there is a corresponding member from the other set of three leptons. In the Standard Model, there are also boson
Boson
In particle physics, bosons are subatomic particles that obey Bose–Einstein statistics. Several bosons can occupy the same quantum state. The word boson derives from the name of Satyendra Nath Bose....
s, including the photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s; W+, W−, and Z bosons
W and Z bosons
The W and Z bosons are the elementary particles that mediate the weak interaction; their symbols are , and . The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle. The Z boson is electrically neutral and its own...
; gluon
Gluon
Gluons are elementary particles which act as the exchange particles for the color force between quarks, analogous to the exchange of photons in the electromagnetic force between two charged particles....
s; and a few open spaces left for the graviton
Graviton
In physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton must be massless and must have a spin of 2...
and Higgs boson
Higgs boson
The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. Its existence is postulated as a means of resolving inconsistencies in the Standard Model...
, which have not yet been discovered. Almost all of these particles come in "left-handed" and "right-handed" versions (see chirality
Chirality (physics)
A chiral phenomenon is one that is not identical to its mirror image . The spin of a particle may be used to define a handedness for that particle. A symmetry transformation between the two is called parity...
). The quarks, leptons and W boson all have antiparticle
Antiparticle
Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite electric charge. For example, the antiparticle of the electron is the positively charged antielectron, or positron, which is produced naturally in certain types of radioactive decay.The...
s with opposite electric charge.
The Standard Model also has a number of problems which have not been entirely solved. In particular, no successful theory of gravitation
Gravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
based on a particle theory has yet been proposed. Although the Model assumes the existence of a graviton, all attempts to produce a consistent theory based on them have failed. Additionally, mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
remains a mystery in the Standard Model. Although the mass of each successive particle follows certain patterns, predictions of the rest mass of most particles cannot be made precisely. The Higgs boson
Higgs boson
The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. Its existence is postulated as a means of resolving inconsistencies in the Standard Model...
explains why particles show inertial mass (but does not explain rest mass), but to date the Higgs mechanism
Higgs mechanism
In particle physics, the Higgs mechanism is the process in which gauge bosons in a gauge theory can acquire non-vanishing masses through absorption of Nambu-Goldstone bosons arising in spontaneous symmetry breaking....
remains unproven.
The Model also has problems predicting the large scale structure of the universe. For instance, the Model generally predicts equal amounts of matter and antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...
in the universe, something that is observably not the case. A number of attempts have been made to "fix" this through a variety of mechanisms, but to date none have won widespread support. Likewise, basic adaptations of the Model suggest the presence of proton decay
Proton decay
In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron...
, which has not yet been observed.
Preon theory is motivated by a desire to replicate the achievements of the periodic table, and the later Standard Model which tamed the "particle zoo", by finding more fundamental answers to the huge number of arbitrary constants present in the Standard Model. It is one of several models to have been put forward in an attempt to provide a more fundamental explanation of the results in experimental and theoretical particle physics. The preon model has attracted comparatively little interest to date among the particle physics community.
Motivations
Preon research is motivated by the desire to explain already known facts (retrodictionRetrodiction
Retrodiction is the act of making a "prediction" about the past. This is especially useful when one wishes to test a theory whose actual predictions are too long-term to be of immediate use...
), 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 electronElectronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
and positronPositronThe positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
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. - To explain the three generationGeneration (particle physics)In particle physics, a generation is a division of the elementary particles. Between generations, particles differ by their quantum number and mass, but their interactions are identical....
s of fermions. - To calculate parameters that are currently unexplained by the Standard Model, such as particle massMassMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
es, electric chargeElectric chargeElectric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
s, and color chargeColor chargeIn particle physics, color charge is a property of quarks and gluons that is related to the particles' strong interactions in the theory of quantum chromodynamics . Color charge has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD,...
s, 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 neutrinoElectron neutrinoThe electron neutrino is a subatomic lepton elementary particle which has no net electric charge. Together with the electron it forms the first generation of leptons, hence its name electron neutrino...
to the top quarkTop quarkThe top quark, also known as the t quark or truth quark, is an elementary particle and a fundamental constituent of matter. Like all quarks, the top quark is an elementary fermion with spin-, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and...
. - To provide alternative explanations for the electro-weak symmetry breakingSymmetry breakingSymmetry breaking in physics describes a phenomenon where small fluctuations acting on a system which is crossing a critical point decide the system's fate, by determining which branch of a bifurcation is taken. To an outside observer unaware of the fluctuations , the choice will appear arbitrary...
without invoking a Higgs field, which in turn possibly needs a supersymmetrySupersymmetryIn particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners...
to correct the theoretical problems involved with the Higgs field. Supersymmetry itself has theoretical problems. - To account for neutrino oscillationNeutrino oscillationNeutrino oscillation is a quantum mechanical phenomenon predicted by Bruno Pontecorvowhereby a neutrino created with a specific lepton flavor can later be measured to have a different flavor. The probability of measuring a particular flavor for a neutrino varies periodically as it propagates...
and mass. - The desire to make new nontrivial predictions, for example, to provide possible cold dark matterCold dark matterCold dark matter is the improvement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material that cannot be observed by its electromagnetic radiation and whose constituent particles move slowly...
candidates. - To explain why there exists only the observed variety of particle species and not something else and to reproduce only these observed particles (since the prediction of non-observed particles is one of the major theoretical problems, as, for example, with supersymmetry).
History
A number of physicists have attempted to develop a theory of "pre-quarks" (from which the name preon derives) in an effort to justify theoretically the many parts of the Standard Model that are known only through experimental data.Other names which have been used for these proposed fundamental particles (or particles intermediate between the most fundamental particles and those observed in the Standard Model) include prequarks, subquarks, maons, alphons, quinks, rishons
Harari Rishon Model
The rishon model is the earliest efforts to develop a preon model to explain the phenomena appearing in the Standard Model of particle physics. It was first developed by Haim Harari and Michael A...
, tweedles, helons, haplons, and Y-particles. Preon is the leading name in the physics community.
Efforts to develop a substructure date at least as far back as 1974 with a paper by Pati and Salam in Physical Review
Physical Review
Physical Review is an American scientific journal founded in 1893 by Edward Nichols. It publishes original research and scientific and literature reviews on all aspects of physics. It is published by the American Physical Society. The journal is in its third series, and is split in several...
. Other attempts include a 1977 paper by Terazawa, Chikashige and Akama, similar, but independent, 1979 papers by Ne'eman, Harari, and Shupe, a 1981 paper by Fritzsch and Mandelbaum, and a 1992 book by D'Souza and Kalman. None has gained wide acceptance in the physics world.
In his 1989 Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
acceptance lecture, Hans Dehmelt
Hans Georg Dehmelt
Hans Georg Dehmelt is a German-born American physicist, who co-developed the ion trap technique with Wolfgang Paul, for which they shared one-half of the Nobel Prize in Physics in 1989...
described a most fundamental elementary particle, with definable properties, which he called the cosmon, as the likely end result of a long but finite chain of increasing more elementary particles.
Each of the preon models postulates a set of far fewer fundamental particles than those of the Standard Model, together with the rules governing how those fundamental particles operate. Based on these rules, the preon models try to explain the Standard Model
Standard Model
The Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...
, often predicting small discrepancies with this model and generating new particles and certain phenomena, which do not belong to the Standard Model. The Harari Rishon Model
Harari Rishon Model
The rishon model is the earliest efforts to develop a preon model to explain the phenomena appearing in the Standard Model of particle physics. It was first developed by Haim Harari and Michael A...
illustrates some of the typical efforts in the field.
Many of the Preon models theorize that the apparent imbalance of matter and antimatter in the universe is in fact illusory, with large quantities of preon level antimatter confined within more complex structures.
Many preon models either do not account for the Higgs boson
Higgs boson
The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. Its existence is postulated as a means of resolving inconsistencies in the Standard Model...
or rule it out, and propose that electro-weak symmetry is broken not by a scalar Higgs field but by composite preons. For example, Fredriksson preon theory does not need the Higgs boson, and explains the electro-weak breaking as the rearrangement of preons, rather than a Higgs-mediated field. In fact, Fredriksson preon model predicts that the Higgs boson does not exist.
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 mass paradox
One preon model started as an internal paper at the Collider Detector at FermilabFermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
(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. However, scattering
Scattering
Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of...
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
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
uncertainty
Uncertainty
Uncertainty is a term used in subtly different ways in a number of fields, including physics, philosophy, statistics, economics, finance, insurance, psychology, sociology, engineering, and information science...
of a preon (of whatever mass) confined to a box of this size is about 200 GeV/c, 50,000 times larger than the rest mass of an up-quark and 400,000 times larger than the rest mass of an electron.
Heisenberg's uncertainty principle
Uncertainty principle
In quantum mechanics, the Heisenberg uncertainty principle states a fundamental limit on the accuracy with which certain pairs of physical properties of a particle, such as position and momentum, can be simultaneously known...
states that ΔxΔp ≥ ħ/2 and thus anything confined to a box smaller than Δx would have a momentum of uncertainty proportionally greater. Thus, the preon model proposed particles smaller than the elementary particles they make up, since the momentum of uncertainty Δp should be greater than the particles themselves. And so 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? This paradox is resolved by postulating a large binding force between preons cancelling their mass-energies.
Chirality and the 't Hooft anomaly-matching constraints
Any candidate preon theory must address particle chirality and the 't Hooft Chiral anomalyChiral anomaly
A chiral anomaly is the anomalous nonconservation of a chiral current. In some theories of fermions with chiral symmetry, the quantization may lead to the breaking of this chiral symmetry. In that case, the charge associated with the chiral symmetry is not conserved.The non-conservation happens...
constraints, and would ideally have simpler theoretical structure than the Standard Model itself.
Possible manner of experimental falsification
Often, preon models propose additional unobserved forces or dynamics to account for the observed properties of elementary particles, which may have implications in conflict with observation.For example, should the LHC
Large Hadron Collider
The Large Hadron Collider is the world's largest and highest-energy particle accelerator. It is expected to address some of the most fundamental questions of physics, advancing the understanding of the deepest laws of nature....
observe a Higgs boson, or superpartners, or both, the observation would be in conflict with the predictions of many preon models with respect to the existence of the Higgs boson.
By contrast, should a Higgs boson not appear in the increasingly constrained circumstances where the Standard Model predicts that it will be found, the preon theory would receive a significant theoretical boost, while many competing theories would be falsified.
Preons in popular culture
- In the 1931 Olaf StapledonOlaf StapledonWilliam Olaf Stapledon was a British philosopher and author of several influential works of science fiction.-Life:...
science fictionScience fictionScience fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
novel Last and First MenLast and First MenLast and First Men: A Story of the Near and Far Future is a "future history" science fiction novel written in 1930 by the British author Olaf Stapledon. A work of unprecedented scale in the genre, it describes the history of humanity from the present onwards across two billion years and eighteen...
, a history of the future development of the human raceHuman RaceHuman Race refers to the Human species.Human race may also refer to:*The Human Race, 79th episode of YuYu Hakusho* Human Race Theatre Company of Dayton Ohio* Human Race Machine, a computer graphics device...
for the next two billion years, the highly advanced future civilizations of the Fifth Men and the Eighteenth Men are powered by what Stapledon calls sub-etheric energy, i.e., the systematic interaction and mutual annihilation of subatomic particles. - In the 1948 reprint/redit of his 1930 novel Skylark Three, E. E. SmithE. E. SmithEdward Elmer Smith, Ph.D., also, E. E. Smith, E. E. "Doc" Smith, Doc Smith, "Skylark" Smith, and Ted was a food engineer and early science fiction author who wrote the Lensman series and the Skylark series, among others...
postulated a series of 'subelectrons of the first and second type' with the latter being fundamental particles that were associated with the gravitation force. While this may not have been an element of the original novel (the scientific basis of some of the other novels in the series was revised extensively due to the additional eighteen years of scientific development), even the edited publication may be the first, or one of the first, mentions of the possibility that electrons are not elementary particles. - In the novelized version of the 1982 motion picture Star Trek II: The Wrath of KhanStar Trek II: The Wrath of KhanStar Trek II: The Wrath of Khan is a 1982 American science fiction film released by Paramount Pictures. The film is the second feature based on the Star Trek science fiction franchise. The plot features James T...
, written by Vonda McIntyreVonda McIntyreVonda Neel McIntyre is an American science fiction author.-Biography:Vonda N. McIntyre, daughter of H. Neel and Vonda B. Keith McIntyre, earned a degree in biology from the University of Washington in 1970. That same year, she attended the Clarion Writers Workshop, founded at the Clarion...
, two of Dr. Carol Marcus' Genesis project team, Vance Madison and Delwyn March, have studied sub-elementary particles they've named "boojums" and "snarks", in a field they jokingly call "kindergarten physics" because it is lower than "elementary" (analogy to school levels). - James P. Hogan's novel "Voyage from YesteryearVoyage from YesteryearVoyage from Yesteryear is a 1982 science fiction novel by the author James P. Hogan. It explores themes of anarchism and the appropriateness of certain social values in the context of high-technology....
" discussed preons (called tweedles) the physics of which became central to the plot. Hogan's "tweedle" physics was patently derived from the Rishon model.
See also
- Technicolor (physics)Technicolor (physics)Technicolor theories are models of physics beyond the standard model that address electroweak symmetry breaking, the mechanism through which elementary particles acquire masses...
- Preon star
- Preon-degenerate matter
- Harari Rishon ModelHarari Rishon ModelThe rishon model is the earliest efforts to develop a preon model to explain the phenomena appearing in the Standard Model of particle physics. It was first developed by Haim Harari and Michael A...