Leptogenesis with lepton-number-violating Dirac neutrinos

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 $N_{\mathrm{eff}}\simeq 3.29$ due to the entropy-suppressed contribution of the right-handed neutrinos.

Figure 1

$CP$-violating vertex and self-energy loop corrections to the LNV decay ${\Xi }_i\to {\nu }_{R,\alpha }{\nu }_{R,\beta }$ relevant for leptogenesis.