  In the presence of anomaly induced sphaleron process, only a B-L asymmetry
can be partially converted to the baryon asymmetry while any B+L asymmetry
would be completely erased. Thus in any successful baryogenesis theories, B-L
is usually violated above the electroweak scale to explain the observed
matter-antimatter asymmetry of the universe. However, if any lepton asymmetry
is not affected by the sphaleron processes, a B-L conserved theory can still
realize the baryogenesis. We present here an SU(5) GUT realization of this
scenario, which naturally accommodates small masses of Dirac neutrinos.
