Majorana spinor

A Majorana spinor equals its charge conjugate. In the Weyl representation it can be written ${\psi }_M=(u_L,i{\sigma }^2{u}_L^{\ast }{)}^T$ from one left-handed Weyl spinor.

A Majorana mass term pairs a Weyl field with itself and violates its continuous phase symmetry. Gauge invariance therefore permits it only when the field is neutral under every unbroken gauge charge.