In particle physics, G-parity is a multiplicative quantum number that results from the generalization of C-parity to multiplets of particles.
C-parity applies only to neutral systems; in the pion triplet, only ÃÂ<sup>0</sup> has C-parity. On the other hand, strong interaction does not see electrical charge, so it cannot distinguish amongst ÃÂ<sup>+</sup>, ÃÂ<sup>0</sup> and ÃÂ<sup>−</sup>. We can generalize the C-parity so it applies to all charge states of a given multiplet:
where ÷<sub>G</sub> = ñ1 are the eigenvalues of G-parity. The G-parity operator is defined as
where is the C-parity operator, and is the operator associated with the 2nd component of the isospin "vector", which in case of isospin takes the form , where is the second Pauli matrix. G-parity is a combination of charge conjugation and a àrad (180ð) rotation around the 2nd axis of isospin space. Given that charge and isospin are preserved by strong interactions, so is G. Weak and electromagnetic interactions, though, does not conserve G-parity.
Since G-parity is applied on a whole multiplet, charge conjugation has to see the multiplet as a neutral entity. Thus, only multiplets with an average charge of 0 will be eigenstates of G, that is
In general
where ÷<sub>C</sub> is a C-parity eigenvalue, and I is the isospin.
Since no matter whether the system is fermionâÂÂantifermion or bosonâÂÂantiboson, always equals to , we have