3.5.16 Super-symmetry
Super-symmetry assumes that every fundamental fermion has a super-partner that is a boson and vice versa. Its gauge theory, Super-gravity, is an extension of General Relativity. Super-symmetry is a key ingredient for the consistency of String Theory.
Super-symmetry was utilized in order to solve the Hierarchy Problem of the standard model. Since for every particle there is a super-partner with the same mass but different statistics, any loop in a radiative correction is canceled by the loop corresponding to its super-partner, rendering the theory more UV finite. However, no such super partners have been observed, so if super-symmetry existed it should be broken severely. The simplest models of this breaking require that the energy of the super-partners not be too high; in these cases, super-symmetry could be observed by experiments at the Large Hadron Collider. However, to date, after the observation of the Higgs boson there, no such super-particles have been discovered.