A neutralino is a proposed type of particle in theoretical models termed supersymmetry, in which there exists another set of particles analogous to known particles but differ by one quantum number, spin, the difference being 1/2. The four neutralinos are the result of quantum mixing of some of the superparticles (in a similar manner to the mixing of quarks or neutrinos). Three of the four types of neutralinos would decay quickly, but the lightest would be stable. It is a candidate particle to serve as a WIMP, because in some models of the universe's formation (Big Bang nucleosynthesis in light of supersymmetry), the mass of the expected remaining neutralinos would equal the universe's current mass credited to dark matter. This coincidence is termed the WIMP miracle.