supersymmetry


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supersymmetry,

in physics, theory concerning the relationship of the elementary particleselementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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 called boson to those known as fermions, and vice versa, and linking the four fundamental forcesforce,
commonly, a "push" or "pull," more properly defined in physics as a quantity that changes the motion, size, or shape of a body. Force is a vector quantity, having both magnitude and direction.
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. In supersymmetry every ordinary elementary particle has as its counterpart a supersymmetric particle, or superparticle, with similar properties except for angular momentum, or "spin," which differs by a half unit. According to supersymmetry, each ordinary fermion has a superpartner that is a boson, and each ordinary boson has a superpartner that is a fermion. The superpartners of fermions are named by adding the prefix s- to the fermion's name, e.g., the squark is the quark's counterpart, and those of bosons by adding the suffix -ino to the root of the boson's name, e.g., the photino is the photonphoton
, the particle composing light and other forms of electromagnetic radiation, sometimes called light quantum. The photon has no charge and no mass. About the beginning of the 20th cent.
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's counterpart. Proof of the theory—discovery of the predicted particles through their creation and detection in a particle acceleratorparticle accelerator,
apparatus used in nuclear physics to produce beams of energetic charged particles and to direct them against various targets. Such machines, popularly called atom smashers, are needed to observe objects as small as the atomic nucleus in studies of its
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—requires extremely high energy levels, and it was hoped that the Large Hadron Collider would provide evidence for supersymmetry, but a lack of evidence for the existence of superpartner particles as predicted by the simple version of supersymmetry has called the theory into question. See also string theorystring theory,
description of elementary particles based on one-dimensional curves, or "strings," instead of point particles. Superstring theory, which is string theory that contains a kind of symmetry known as supersymmetry, has been seen by some physicists as a way of unifying
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.
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Supersymmetry

A conjectured enhanced symmetry of the laws of nature that would relate two fundamental observed classes of particles, bosons and fermions.

All particles can be classified as fermions, such as the electron and quarks, or bosons, such as the photon and graviton. A fundamental characteristic distinguishing these two classes is that they carry different quantum-mechanical spin. If the amount of spin of an elementary particle is measured in terms of the fundamental quantum unit of angular momentum—, equal to Planck's constant divided by 2&pgr;—then bosons always have integer amounts of spin (that is, 0, 1, 2 …), while fermions have odd half-integer amounts of spin (that is, 1/2, 3/2, 5/2, …). See Spin (quantum mechanics)

There is seemingly a fundamental distinction between particles with differing amounts of spin. For example, bosons like to act collectively (Bose-Einstein statistics), producing such distinctive behavior as the laser, while, conversely, fermions obey the Pauli exclusion principle (and the Pauli-Dirac statistics), which disallows two identical fermions to be in the same state, and explains the stability of matter. Moreover, all the symmetries that are observed in the world relate different particles of the same spin. See Bose-Einstein statistics, Fermi-Dirac statistics, Quantum statistics, Symmetry laws (physics)

In contrast, supersymmetry would relate bosons and fermions. This would be a remarkable step forward in understanding the physical world. However, if supersymmetry were realized as an exact symmetry, the particles so related should have almost all their characteristics, such as mass and charge, preserved. Explicitly, any fermion of spin 1/2 should have a boson superpartner of spin 0, while any gauge boson of spin 1 should have a fermion superpartner of spin 1/2. This is apparently a disaster for the idea of supersymmetry since it predicts, for instance, that there should exist a spin-0 boson partner of the electron, the selectron, with electric charge and mass equal to that of the electron. Such a particle would be easy to detect and is certainly ruled out by very many experiments.

The crucial caveat to this negative result is the condition that supersymmetry be realized as an exact symmetry. A fundamental concept of modern physics is spontaneously broken symmetry. Physics displays many examples of symmetries that are exact symmetries of the fundamental equations describing a system, but not of their solutions. In particle physics the spontaneous breaking of a symmetry usually results in a difference in the masses of the particles related by the symmetry; the amount of breaking can be quantified by this mass difference. See Symmetry breaking

If supersymmetry is broken by a large amount, then all the superpartners have masses much greater than the particles that are currently observed, and there is little hope of seeing evidence for supersymmetry. However, evidence that supersymmetry is broken by only a moderate amount comes from examination of the properties of the fundamental forces at high energy.

Of the four fundamental forces, the three excluding gravity are very similar in their basic formulation; they are all described by gauge theories, generalizations of the quantum theory of electromagnetism, and quantum electrodynamics (QED). The strength of electrical interaction between two electrons can be quantified in terms of a number, the coupling constant α1. However, the quantity α1 is actually not a constant, but depends on the energies at which the interaction strength is measured. In fact, the interaction strengths, α1, α2, and α3, of the three forces (excluding gravity) all depend on energy, μ. The couplings α1,2,3 satisfy differential equations—renormalization group equations—that depend on the types of elementary particles that exist with mass at or below the energy scale μ and that are charged with respect to each of the three interactions. If the fundamental particles include not only the observed particles but also their superpartners, taken to have masses not greater than 1000 GeV heavier than their (observed) partners, then from the renormalization group equations, the couplings αi are predicted to meet (unify) at a huge energy of 2 × 1016 GeV. In contrast, if either supersymmetry is not an underlying symmetry of the world, or it is very badly broken so that the superpartners are very massive, the couplings fail to unify at a single point. See Fundamental interactions, Quantum electrodynamics, Renormalization

Although the unification of couplings is the most significant indication that supersymmetry is a new law of nature, there are a number of other hints in this same direction. By observing the large-scale motions of the galaxies, the average density of large volumes of the universe can be deduced, resulting in a value that is substantially greater than that directly observed in luminous matter such as stars and hot gas. Therefore, a substantial fraction of the mass of the universe must be composed of some form of nonluminous or dark matter. Remarkably, many attractive models of supersymmetry predict that the lightest of all the superpartners is a weakly interacting massive particle with just the right characteristics to be this dark matter. See Weakly interacting massive particle (WIMP)

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

supersymmetry

(soo-per-sim -ĕ-tree) (SUSY) An extension of the theories (GUTs) seeking to unify the four fundamental forces of nature. It unifies the particles called fermions (with half-integral spin) and the force particles, the bosons (with integral spin). In the simplest SUSY models, this leads to a new family of particles as every fermion has a supersymmetric boson partner and every boson has a supersymmetric fermion partner; for example, photinos and gravitinos are the hypothesized partners of the photon and graviton. Adding supersymmetric particles to the standard model of elementary particles remedies some of its discrepancies, but there is no experimental evidence for them. See also dark matter.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006

supersymmetry

[¦sü·pər′sim·ə·trē]
(particle physics)
A generalization of previously known symmetries of elementary particles to new kinds of supermultiplets that include both bosons and fermions; it is based on graded Lie algebras rather than on Lie algebras.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
He regularly taught an advanced graduate course on supersymmetry and supergravity.
Bakhshi, "Dirac equation and ground state of solvable potentials: supersymmetry method," International Journal of Theoretical Physics, vol.
One must ask whether these CSI solutions preserve any supersymmetry. The condition for preservation of supersymmetry demands that M and K admit Killing spinors which imply the existence of Killing vectors.
(14) Fortunately, Gates' supersymmetry research helps to embolden for us the line between unhealthy, reactive resistance to racism and oppression, and the kind that is electrifying, assertive and enduring.
Supersymmetry says that for every matter particle there exists a corresponding force- carrying particle as well.
We consider the algebra [po.sup.1/N] generated by N + 1 operators [Q.sub.1], [Q.sub.2], ..., [Q.sub.N] (the supersymmetry generators) and H = i[[partial derivative].sub.t](the Hamiltonian), such that {[Q.sub.I], [Q.sub.J]} = 2[[delta].sub.IJ]H and [[Q.sub.1], H] = 0.
He is the author of Dark Cosmos: In Search of Our Universe's Missing Mass and Energy and Nature's Blueprint: Supersymmetry and the Search for a Unified Theory of Matter and Force.
It will probe : * The possibility of powerful extra dimensions "hiding" at an ultra-tiny scale alongside the visible; the theory of Supersymmetry, a world of super-particles that partner the elementary particles we know today; * the nature of dark matter, astonishingly, scientists have found 96% of the universe is not made up of ordinary matter but 76% dark energy and 22% dark matter.
One theory, called "supersymmetry", claims more than five Higgs-like particles may be out there, each with completely different properties.
The Higgs boson also now helps us see how two of the four fundamental forces in the universe, the electromagnetic and weak forces, can be unified, and the discovery has implications of our understanding of what appears to be the symmetry in nature as proposed in theories of supersymmetry.
Handbook of pseudo-Riemannian geometry and supersymmetry.