X (charge)

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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. For example, a left-handed quark has an X charge of +1, whereas a right-handed quark can have either an X charge of −1 (for up, charm and top quarks), or −3 (for down, strange and bottom quarks).

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: $${\displaystyle X=5(B-L)-2\,Y_{\text{W}}.}$$