Supersymmetric

Supersymmetric, in physics, refers to a hypothetical symmetry that relates bosons and fermions. In a supersymmetric theory, every known particle has a superpartner with spin differing by one half. For example, quarks would have scalar partners called squarks, leptons would have sleptons, gluons would have fermionic partners called gluinos, and the photon, W and Z bosons and the Higgs sector have fermionic superpartners such as photinos, winos, zinos and higgsinos. These partners organize into supermultiplets that transform into each other under the symmetry. The symmetry is usually embedded in a larger space-time symmetry generated by supercharges that connect particles of different spin.

Supersymmetry is motivated by several theoretical issues. It helps stabilize the Higgs mass against large quantum corrections (the hierarchy problem), allows for more precise unification of gauge couplings at high energy, and often provides a dark matter candidate when a conserved quantum number called R-parity renders the lightest neutralino stable. The most studied realistic realization is the Minimal Supersymmetric Standard Model (MSSM), which introduces superpartners and a mechanism for breaking SUSY softly so that superpartners can be heavier than their Standard Model counterparts. Many variants exist, such as the NMSSM, split SUSY, and models with compressed spectra.

Experimentally, no direct evidence for supersymmetry has been found. Collider searches, particularly at the Large Hadron Collider, have set lower limits on superpartner masses, especially for coloured particles like squarks and gluinos; in many scenarios these limits lie in the TeV range and depend on decay patterns and model assumptions. SUSY also has implications for cosmology and low-energy observables, but constraints are model dependent.

Beyond particle physics, supersymmetric concepts appear in theoretical contexts such as supersymmetric quantum mechanics, where the algebra of supercharges provides simplified insights into spectral properties. Overall, supersymmetry remains a major area of research in attempts to extend the Standard Model, though its realization in nature is still an open question.