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arXiv · 2508.05047

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

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 $τ$. 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. $χ^2$ 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 $Σ_1$ into lepton-Higgs final states produce a $CP$ asymmetry $\varepsilon_{CP}$. The complex modules $τ$ 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.

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Priya, Labh Singh, B. C. Chauhan, Surender Verma. 2025-08-07. Type-III Seesaw in Non-Holomorphic Modular Symmetry and Leptogenesis. https://arxiv.org/abs/2508.05047

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