Majorana Fermions
The Majorana fermion is a charge-neutral, zero-energy quasiparticle. The Majorana is unique in being its own antiparticle, hence existing on the shadowy border between matter and antimatter; hence its designation as quasiparticle. That may not make the Majorana novel.
The nature of neutrinos is unsettled. As neutrinos have no charge, they too may be Majorana fermions, rather than Dirac fermions, where a particle has a mirror image antimatter partner.
Mathematically, neutral spin 1/2 particles, such as neutrinos and the Majorana fermion, can be characterized by a real wave equation (the Majorana equation), instead of the more typical wave function that predicts a particle and antiparticle via complex conjugation.
A complex conjugate is a complex-number pair, where the real components are identical, but the imaginary parts, though of equal magnitude, have opposite signs. 1 + 2i and 1–2i are exemplary complex conjugates.
The Majorana is not included in the Standard Model particle clique even though its existence is certain. Majoranas do not comfortably fit within SM owing to their uniqueness, especially the mathematics that characterize them.
Whereas Majoranas have no charge, and do not interact very strongly with light or other electromagnetic radiation, they can be detected by electrical measurements, and are affected by the electrical environment. Majorana fermions facilitate superconductivity.
When 2 Majoranas are repositioned relative to each other in a superconducting region, they essentially remember their previous position. This property has been suggested as valuable in constructing a quantum computer, with Majoranas as a memory mechanism.
The oddity of Majoranas as chargeless, and yet subtlety interacting electromagnetically, may be explained by Majoranas having a magnetic anapole moment. An anapole is a toroidal dipole: a solenoid field bent into a torus.
Particles with electrical and magnetic dipole moments interact with electromagnetic fields regardless of their momentum. In contrast, electromagnetic interaction with an anapole particle strengthens with speed. The Majorana having an anapole moment fits well with its mass, speed, and electromagnetic properties.
Neutrinos travel near light speed because they are theoretically nearly massless. An accurate measurement of neutrino mass has eluded experimental physicists. Majoranas are assumed to be like neutrinos, albeit slower moving.
