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

TL;DR

This paper explores how low-scale leptogenesis can occur through CP-violation from the Dirac phase in neutrino mixing, with testable predictions for future experiments.

Contribution

It demonstrates that viable leptogenesis can be driven solely by the Dirac CP-violating phase, without additional CP-violation sources, within a low-mass neutrino framework.

Findings

Leptogenesis is possible with CP-violation from the Dirac phase alone.

The required heavy neutrino mixing parameters are within future experimental reach.

Distinct parameter space from models with additional CP-violation sources.

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 $\Theta^2=\sum_\alpha\Theta^2_\alpha$ 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 $\Theta_\tau^2:\Theta^2_\mu:\Theta^2_e$ would provide a critical test of the considered scenario.