Natural mass hierarchy among three heavy Majorana neutrinos for resonant leptogenesis under modular $A_4$ symmetry

TL;DR

This paper proposes a radiative seesaw model with modular $A_4$ symmetry that naturally explains the mass hierarchy among heavy Majorana neutrinos, enabling resonant leptogenesis at TeV scales to account for the Universe's baryon asymmetry.

Contribution

It introduces a novel modular $A_4$ symmetry framework that naturally produces degenerate heavy Majorana neutrino masses suitable for resonant leptogenesis.

Findings

Degenerate heavy Majorana neutrino masses are achievable with large imaginary part of $ au$.

Resonant leptogenesis can generate the observed baryon asymmetry at TeV scale.

CP asymmetry is mainly influenced by the real part of $ au$.

Abstract

It is clear that matter is dominant in the Universe compared to antimatter. We call this problem baryon asymmetry. The baryon asymmetry is experimentally determined by both cosmic microwave background and big bang nucleosynthesis measurements. To resolve the baryon number asymmetry of the Universe as well as neutrino oscillations, we study a radiative seesaw model in a modular $A_4$ symmetry. Degenerate heavy Majorana neutrino masses can be naturally realized in an appropriate assignments under modular $A_4$ with large imaginary part of modulus $\tau$, and it can induce measured baryon number via resonant leptogenesis that is valid in around TeV scale energy theory. We also find that the dominant contribution to the CP asymmetry arises from Re[$\tau$] through our numerical analysis satisfying the neutrino oscillation data.