A symmetry that can be applied to elementary particles so as to include both bosons and fermions. In the simplest supersymmetry theories, every boson has a corresponding fermion partner and every fermion has a corresponding boson partner. The boson partners of existing fermions have names formed by adding ‘s’ to the beginning of the name of the fermion, e.g. selectron, squark, and slepton. The fermion partners of existing bosons have names formed by replacing ‘-on’ at the end of the boson’s name by ‘-ino’ or by adding ‘-ino’, e.g. gluino, photino, wino, and zino. Supersymmetry can be regarded as a generalization of the Lorentz group to include fermionic variables. The analogue of going from special relativity to general relativity is going from supersymmetry to supergravity.

The infinities that cause problems in relativistic quantum field theories (see renormalization) are less severe in supersymmetry theories because infinities of bosons and fermions can cancel one another out.

It is thought that particles associated with supersymmetry may be one of the ingredients of dark matter.

If supersymmetry is relevant to observed elementary particles then it must be a broken symmetry, although there is no convincing theory at present to show at what energy it would be broken. There is, in fact, no experimental evidence for the theory, although it is thought that it may form part of a unified theory of interactions. This would not necessarily be a unified-field theory; the idea of strings with supersymmetry may be the best approach to unifying the four fundamental interactions (see superstring theory). The fact that supersymmetric particles have not been discovered at the Large Hadron Collider has led some physicists to think that the simplest ways of combining supersymmetry with the standard model can be ruled out.