Low-Scale Leptogenesis with Low-Energy Dirac CP-Violation

Abstract

We study the freeze-in scenario of leptogenesis via oscillations within the type-I seesaw model with two quasi-degenerate heavy Majorana neutrinos $N_{1,2}$ having masses $M_2>M_1\sim (0.1-100)\text{GeV}$, $(M_2-M_1)/M_1\ll 1$, focusing on the role of the CP-violation provided by the Dirac phase $\delta$ of the Pontecorvo-Maki-Nakagawa-Sakata lepton mixing matrix. We find that viable leptogenesis can be due solely to CP-violating values of $\delta$ and that the $N_{1,2}$ total mixing squared ${\Theta }^2={\sum }_{\alpha }{\Theta }_{\alpha }^2$ needed is within the reach of future experiments, ${\Theta }_{\alpha }$ parameterising the coupling to the charged lepton $\alpha =e,\mu ,\tau$. Furthermore, the required parameter space differs from that associated with additional Casas-Ibarra sources of CP-violation. Future determination of $\delta$, ${\Theta }^2$ and/or the ratios ${\Theta }_{\tau }^2:{\Theta }_{\mu }^2:{\Theta }_e^2$ would provide a critical test of the considered scenario.

Comments: 7 pages, 2 figures; matches version published in PRD