What type of fermion is predicted to be its own antiparticle?

A Majorana fermion is a fermion predicted to be its own antiparticle. In other words, a Majorana particle would be indistinguishable from the corresponding antimatter particle, unlike an electron, whose antiparticle is the positron.

The concept was proposed by Italian physicist Ettore Majorana in 1937. His formulation used a real-valued wave equation for electrically neutral spin-one-half particles. Because complex conjugation relates particle and antiparticle wavefunctions, a suitable neutral particle could coincide with its antiparticle.

A Majorana fermion must be electrically neutral, since a charged particle cannot be identical to an antiparticle with the opposite charge. The longstanding candidate is the neutrino, but experiments have not established whether neutrinos are Majorana or Dirac particles.

The term also appears in condensed-matter physics, where a superconducting system can host a Majorana bound state. This is a quasiparticle excitation rather than necessarily a fundamental particle. The main mix-up is with a Dirac fermion: Dirac fermions and their antiparticles are distinct, while Majorana fermions are self-conjugate.