Supersymmetry

Supersymmetry is a proposed extension of spacetime symmetries that relates bosons and fermions. In a supersymmetric theory every fermion has a bosonic superpartner and every boson has a fermionic superpartner, differing by half a unit of spin. The symmetry is generated by fermionic operators that convert a particle into its partner.

In four dimensions, supersymmetry doubles the particle spectrum. The Minimal Supersymmetric Standard Model (MSSM) contains squarks and sleptons for quarks and leptons, and gauginos and higgsinos for gauge and Higgs fields. The MSSM requires two Higgs doublets. If R-parity is conserved, the lightest supersymmetric particle is stable and can be a dark matter candidate, often the lightest neutralino.

Supersymmetry addresses several theoretical issues: it stabilizes the Higgs mass against large quantum corrections, facilitates gauge coupling unification at high energies, and provides a natural dark matter candidate. It also offers mechanisms for supersymmetry breaking that can explain the absence of observed superpartners at current energies.

No conclusive experimental evidence for superpartners has been found. Searches at the Large Hadron Collider have set lower bounds on superpartner masses that depend on the model and spectrum, pushing natural scenarios toward higher scales. Alternative breaking patterns and extended models have been proposed to accommodate current limits.

Supersymmetry was developed in the 1970s as a symmetry relating bosons and fermions, with foundational contributions by several groups. It remains an active area in theoretical and experimental physics.