Type-III Seesaw in Non-Holomorphic Modular Symmetry and Leptogenesis

TL;DR

This paper develops a non-holomorphic modular invariant Type-III seesaw model that explains neutrino masses, mixing, and baryogenesis via leptogenesis, linking low-energy neutrino data with the Universe's matter-antimatter asymmetry.

Contribution

It introduces a novel non-holomorphic modular symmetry framework for Type-III seesaw and leptogenesis, fitting neutrino data and demonstrating successful baryogenesis at high energy scales.

Findings

Neutrino mass hierarchy is normal with constrained CP phases.

The model reproduces the observed baryon-to-photon ratio.

Leptogenesis scale is around 10^{12} GeV, consistent with bounds.

Abstract

Recently, Qu and Ding, have proposed a formalism where modular invariance is extended to non-supersymmetric scenario considering Yukawa couplings as non-holomorphic functions of modules field $\tau$. Adopting this formalism in this work, we propose a Type-III seesaw model as a unified framework to explain lepton masses and mixing and baryogenesis via leptogenesis. $\chi^2$ analysis is performed to fit the neutrino oscillation data from NuFIT~6.0 leading to a normal hierarchical pattern of neutrino masses and constrained $CP$ phases. Furthermore, we analyze the generation of the observed baryon asymmetry of the Universe via thermal leptogenesis where the decays of the lightest fermion triplet $\Sigma_1$ into lepton-Higgs final states produce a $CP$ asymmetry $\varepsilon_{CP}$. The complex modules $\tau$ is responsible for the $CP$ asymmetry produced during leptogenesis. The washout processes dominated by gauge scatterings and inverse decays are studied through the full set of Boltzmann equations. The resulting $B-L$ asymmetry, $Y_{B-L}\sim 10^{-9}$ successfully reproduces the baryon-to-photon ratio demonstrating the model's capability to link low-energy neutrino data with the baryogenesis. The strong gauge-mediated washout of fermion triplets necessitates a leptogenesis scale of $\mathcal{O}(10^{12}\,\mathrm{GeV})$ ensuring compatibility with both the Davidson-Ibarra bound and the thermal history of the Universe. Future pursuits remain open to the exploration of novel avenues aimed at lowering the energy scale associated with leptogenesis.