In particle physics, the X charge (or simply X) is a conserved quantum number associated with the SO(10) grand unification theory.
It is thought to be conserved in strong, weak, electromagnetic, gravitational, and Higgs interactions.
Because the X charge is related to the weak hypercharge, it varies depending on the helicity of a particle.
Similarly, all experimentally confirmed forms of decay also conserve the X charge value.
The following table lists the X charge values for the standard model fermions and their antiparticles.
Note that the CP conjugate of a fermion has the opposite X charge (e.g. eL vs. eR, X = −3 vs. +3).