  Dirac neutrinos with lepton-number-violating interactions can give rise to a
new leptogenesis mechanism. In its simplest renormalizable realization, based
on a gauged B-L symmetry spontaneously broken by four units, the decay of a new
scalar creates an asymmetry in the right-handed neutrinos. A neutrinophilic
two-Higgs-doublet model converts this asymmetry to the baryons, provides a
natural explanation of the small neutrino masses, and can lead to an effective
number of relativistic degrees of freedom of N(eff) = 3.29 due to the
entropy-suppressed contribution of the right-handed neutrinos.
