HYPERCHARGE AND THE COSMOLOGICAL BARYON ASYMMETRY

Stringent bounds on baryon- and lepton-number-violating interactions h ave been derived from the requirement that such interactions, together with electroweak instantons, do not destroy a cosmological baryon asy mmetry produced at an extremely high temperature in the big bang. Whil e these bounds apply in specific models, we find that they are generic ally avoided. In particular, the only requirement for a theory to avoi d these bounds is that it contain charge particles which, during a cer tain cosmological epoch, carry a nonzero hypercharge asymmetry. Hyperc harge neutrality of the Universe then dictates that the remaining part icles must carry a compensating hypercharge density, which is necessar ily shared among them so as to give a baryon asymmetry. Hence the gene ration of a hypercharge density in a sector of the theory forces the U niverse to have a baryon asymmetry.