electric charge does in electromagnetism, and color charge in the strong interaction; a different number with a similar name, weak charge, discussed below, is used for interactions with the . All left-handed fermions have a weak isospin value of either or ; all right-handed fermions have 0 isospin. For example, the up quark has and the down quark has A quark never decays through the weak interaction into a quark of the same : Quarks with a of only decay into quarks with a of and conversely. In any given strong, electromagnetic, or weak interaction, weak isospin is conserved: The sum of the weak isospin numbers of the particles entering the interaction equals the sum of the weak isospin numbers of the particles exiting that interaction. For example, a (left-handed) with a weak isospin of +1 normally decays into a (with ) and a (as a right-handed antiparticle, ). For the development of the electroweak theory, another property, weak hypercharge, was invented, defined as where is the weak hypercharge of a particle with electrical charge (in elementary charge units) and weak isospin . Weak hypercharge is the generator of the U(1) component of the electroweak gauge group; whereas some particles have a weak isospin of zero, all known spin- particles have a non-zero weak hypercharge. Interaction types There are two types of weak interaction (called vertices). The first type is called the "charged-current interaction" because the weakly interacting fermions form a current with total electric charge that is nonzero. The second type is called the "neutral-current interaction" because the weakly interacting fermions form a current with total electric charge of zero. It is responsible for the (rare) deflection of neutrinos. The two types of interaction follow different selection rules. This naming convention is often misunderstood to label the electric charge of the and bosons, however the naming convention predates the concept of the mediator bosons, and clearly (at least in name) labels the charge of the current (formed from the fermions), not necessarilly the bosons. Charged-current interaction In one type of charged current interaction, a charged lepton (such as an electron or a muon, having a charge of −1) can absorb a boson (a particle with a charge of +1) and be thereby converted into a corresponding neutrino (with a charge of 0), where the type ("flavour") of neutrino (electron, muon or tau) is the same as the type of