Majorana particle

The term Majorana particle (aka Majorana fermion) refers to any (theoretical) fermion that happens to be its own antiparticle. The Majorana equation, which was devised by Etta Majorana in the 1930s in the style of the Dirac equation for fermions (a quantum-mechanical wave equation much like the Schrödinger equation, but also including the effects of special relativity), states what must be true of such a particle. Thus far, no subatomic particles have been established to be Majorana particles, but neutrinos, of which current understanding is limited, are candidates, and determining that some or all neutrino flavors are Majorana particles would reveal much about neutrino characteristics. A number of current experiments are attempting to detect neutrinoless double beta decay, a nuclear phenomenon that could occur through annihilation of two identical neutrinos as two beta particles are emitted, and would constitute evidence that neutrinos are Majorana particles.

Any Majorana particle must be electrically neutral: a charged particle's wave equation would include an imaginary part, which would make its wave equation's values different than that of its antiparticle; a particle and its antiparticle have wave equations that are complex conjugates of each other, which cannot be the same if each has an imaginary part.