- Key People:
- Edward Witten
supersymmetry
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What is supersymmetry in physics?
In particle physics, supersymmetry refers to a symmetry between fermions and bosons. Fermions are subatomic particles with half-integer values of intrinsic angular momentum (or spin), while bosons have integer values of spin.
Supersymmetry is a mathematical framework that was developed in the early 1970s to understand the increasing number of subatomic particles produced in high-energy particle accelerator experiments. It addresses inconsistencies that arose when scientists tried to unify forces in the Standard Model of particle physics. Supersymmetry is an essential feature of supergravity and string theory, which is an ambitious attempt to provide a quantum theory unifying all particles and forces in nature.
Supersymmetry relates transformations in an internal property of particles (spin) to transformations in space-time. It implies a doubling of the number of known particles. For example, fermions such as electrons and quarks should have bosonic supersymmetric partners, called selectrons and squarks.
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What does supersymmetry try to explain about the universe?
Supersymmetry (SUSY) is a theory in particle physics that attempts to explain the relationship between the two basic classes of subatomic particles: fermions (which have half-integer spin) and bosons (which have integer spin). SUSY suggests that every known particle has a superpartner with different spin, thus reducing the number of basic particle types from two to one.
SUSY also addresses inconsistencies in the Standard Model of particle physics, particularly in unifying fundamental forces. By introducing new particles, SUSY cancels infinite quantities in calculations of particle interactions at high energies. Furthermore, when supersymmetry is treated as a local symmetry, it includes a spin-2 particle, the graviton, linking it to supergravity theories that incorporate gravity with other fundamental forces.
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How are particles grouped in supersymmetry theory?
In supersymmetry, each known particle has a superpartner with different spin. Supersymmetry relates fermions (quarks and leptons with spin 1/2) to bosons of the gauge fields (with spins 1 or 2) and the Higgs boson (spin 0). This theory doubles the number of fundamental particles, as each known particle has a supersymmetric counterpart.
Leptons and quarks with spin 1/2 have superpartners called sleptons and squarks with integer spin. The photon, W, Z, gluon, and graviton have counterparts with half-integer spins called the photino, wino, zino, gluino, and gravitino, respectively.
Researchers believe that superpartner particles have not been detected experimentally due to their weight.
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What are superpartners in supersymmetry?
In particle physics, supersymmetry (SUSY) proposes that every known particle has a superpartner with different spin. Fermions (like electrons and quarks) have bosonic superpartners (selectrons and squarks), while bosons (like photons and gluons) have fermionic superpartners (photinos and gluinos).
These superparticles could resolve inconsistencies in the Standard Model and help unify fundamental forces. However, none have been found yet, suggesting they are very massive, possibly 50 to 1,000 times the mass of the proton. The Large Hadron Collider (LHC) is used to search for them.
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Why do scientists think supersymmetry could help explain dark matter?
Supersymmetry (SUSY) is a theory in particle physics that proposes a symmetry between fermions and bosons. SUSY suggests that every known particle has a superpartner with different spin, potentially helping to unify all fundamental forces.
One significant implication of SUSY is its potential to explain dark matter. SUSY predicts the existence of heavy, weakly interacting particles called WIMPs (Weakly Interacting Massive Particles) like axions or neutralinos. These hypothetical particles are electromagnetically neutral and massive, properties that align with those inferred for dark matter. If WIMPs exist, they could account for a significant portion of the universe's missing mass, offering a compelling explanation for the nature of dark matter.
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How do experiments like those at the Large Hadron Collider search for evidence of supersymmetry?
Experiments at the Large Hadron Collider (LHC) search for evidence of supersymmetry by attempting to produce superparticles through high-energy collisions. Supersymmetry suggests that each known particle has a heavier "superpartner" with different spin.
The LHC, the world’s most powerful particle accelerator, collides beams of heavy ions or protons at extremely high energies. Detectors at collision points collect the particles produced. If superparticles exist, they should appear within the LHC's energy range. Their detection would support supersymmetry, potentially resolving inconsistencies within the Standard Model and unifying fundamental forces.
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supersymmetry, in particle physics, a symmetry between fermions (subatomic particles with half-integer values of intrinsic angular momentum, or spin) and bosons (particles with integer values of spin). Supersymmetry is a complex mathematical framework based on the theory of group transformations that was developed beginning in the early 1970s to understand at a more-fundamental level the burgeoning number of subatomic particles being produced in high-energy particle accelerator experiments. It has evolved to address internal inconsistencies that arose in attempts to unify the forces in the Standard Model of particle physics. Supersymmetry is an essential feature of supergravity, the quantum field theory of the gravitational force, and of string theory, an ambitious attempt to provide a self-consistent quantum theory unifying all particles and forces in nature.
A physical entity is said to exhibit symmetry when it appears unchanged after undergoing a transformation operation. A square, for example, has a fourfold symmetry by which it appears the same when rotated about its centre through 90, 180, 270, and 360 degrees; four 90-degree rotations bring the square back to its original position. Symmetry with respect to time and space transformations is embodied within physical laws such as the conservation of energy and the conservation of momentum. With supersymmetry, fermions can be transformed into bosons without changing the structure of the underlying theory of the particles and their interactions. Thus, supersymmetry provides a relationship between the elementary particles that make up matter—quarks and leptons, which are all fermions—and the “force-carrier” particles that transmit the fundamental interactions of matter (all bosons). By showing that one type of particle is in effect a different facet of the other type, supersymmetry reduces the number of basic types of particle from two to one.
When a fermion is transformed into a boson and then back again into a fermion, it turns out that the particle has moved in space, an effect that is related to special relativity. Supersymmetry therefore relates transformations in an internal property of particles (spin) to transformations in space-time. In particular, when supersymmetry is made a “local” symmetry, so that the transformations vary over space-time, it automatically includes a particle with a spin of 2, which can be identified as the graviton, the “force carrier” associated with gravity. Theories involving supersymmetry in its local form are therefore often known as supergravity theories.
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Supersymmetry also plays an important role in modern theories of particle physics because the new particles that it requires can eliminate various infinite quantities that otherwise appear in calculations of particle interactions at high energies, particularly in attempts at unified theories of the fundamental forces. These new particles are the bosons (or fermions) into which the known fermions (or bosons) are transformed by supersymmetry. Thus, supersymmetry implies a doubling of the number of the known particles. For example, fermions such as electrons and quarks should have bosonic supersymmetric partners, which have been given the names of selectrons and squarks. Similarly, known bosons such as the photon and the gluon should have fermionic supersymmetric partners, called the photino and the gluino. There has been no experimental evidence that such “superparticles” exist. If they do indeed exist, their masses could be in the range of 50 to 1,000 times that of the proton.