X (charge)

X is related to the difference between the baryon number B and the lepton number L (that is, B – L), and the weak hypercharge Y_W via the relation: $${\displaystyle X=5(B-L)-2Y_{\text{W}}.}$$

X charge in proton decay

Proton decay is a hypothetical form of radioactive decay, predicted by many grand unification theories. During proton decay, the common baryonic proton decays into lighter subatomic particles. However, proton decay has never been experimentally observed and is predicted to be mediated by hypothetical X and Y bosons. Many protonic decay modes have been predicted, one of which is shown below: $${\displaystyle {\mathrm{p}}^{+}⟶{\mathrm{e}}^{+}+{\pi }^0}$$

This form of decay violates the conservation of both baryon number and lepton number, however the X charge is conserved. Similarly, all experimentally confirmed forms of decay also conserve the X charge value.