Weak isospin

In particle physics, weak isospin is a quantum number relating to the electrically charged part of the weak interaction. Particles with nonzero weak isospin can interact with the W±
bosons, while particles with zero weak isospin do not. Weak isospin is a concept parallel to the idea of isospin under the strong interaction. Weak isospin is usually given the symbol T or I, with the third component written as T3 or I3 . T3 is more important than T; typically "weak isospin" is used as short form of the proper term "3rd component of weak isospin". It can be understood as the eigenvalue of a charge operator.