The neutralino is part of the doubling of the current menagerie of particles necessitated by supersymmetry.
Supersymmetry requires that every fermion should have a boson superpartner, and that every boson should have a fermion superpartner. The neutralino, along with others such as the chargino, gluino, photino, and highly theoretical gravitino, is one of the fermion "sparticles". Virtually invisible, it participates only in weak and gravitational interactions. Its Standard Model counterpart is the Z boson, the electrically neutral carrier of the weak nuclear force.
Of the WIMPs under consideration, the neutralino, as the lightest electrically neutral supersymmetric particle (at 30-500 proton masses), is the leading candidate for cold dark matter.
