Flavor mixing and proton instability in the grand unification schemes

Flavour mixing in the quark currents connected with baryon number nonconservation, is investigated in framework of the unified models of weak, electromagnetic and strong interactions based on the groups SU(5) and SO(10). Equations are obtained relating the mixing parameters in these currents, as well as those in the left and right charged currents. It is shown that in the SO(10)-symmetric model with six quarks it is impossible to get the stable proton by means of the flavour mixing in the quark sector: the proton decay probability may be suppressed at best by a factor of sin2THETAsub(C), where THETAsub(C) is the Cabibbo-angle