Retrieving Inverse Seesaw parameter space for Dirac Phase Leptogenesis

TL;DR

This paper explores how the inverse seesaw mechanism can enable Dirac phase leptogenesis, identifying specific parameter space regions and their implications for baryon asymmetry and lepton flavor violation.

Contribution

It introduces a novel $R$ matrix structure in the inverse seesaw framework that allows successful Dirac phase leptogenesis, which was previously unexplored.

Findings

Successful leptogenesis driven by Dirac CP phase in ISS with specific $R$ matrix structure.

Calculated LFV decay branching ratio exceeding current experimental bounds.

Leptogenesis constrains Dirac CP phase to oscillate around $rac{}$ for certain $R$ matrix choices.

Abstract

This work addresses the viability of \textit {Dirac phase leptogenesis}, in a scenario where the light Majorana neutrinos acquire masses by the inverse seesaw (ISS) mechanism. We show that, a successful leptogenesis in the ISS, driven (only) by the Dirac CP phase can be achieved with the involvement of an unorthodox form of the rotational matrix $R = e^{i{\bf A}} \,\,\,(e^{{\bf A}})$ in the Casas-Ibarra parametrisation. This particular structure of $R$ turns out to be an artefact in explaining the observed baryon asymmetry of the Universe in a pure ISS scenario. We detail here the confined regions of the $R$ matrix parameter space, essential for a successful leptogenesis. The $R$-matrix parameter space assists in rescuing the ISS parameter space needed for successful leptogenesis. This finding is otherwise unprecedented in the ISS set up. Making use of the resulted $R$ matrix parameter space we have calculated the branching ratio for the LFV decay $\mu \rightarrow e\gamma$. This accounts for an indirect probe of the $R$-matrix parameter space. The branching ratio obtained from the leptogenesis parameter space surpasses the existing bound on the branching ratio that resulted in a scenario of combined effect of linear and inverse seesaw. We also report here that, for $R = e^{i{\bf A}}$ choice leptogenesis demands the Dirac CP phase ($\delta$) to oscillate around $\pi/2$, although for the later choice the constraint on $\delta$ is much relaxed.