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Leptogenesis in the littlest inverse seesaw model

Yan Shao, Zhen-hua Zhao, Yi-Fei Duan

Abstract

The littlest inverse seesaw (LIS) model represents the first low-scale seesaw framework to successfully account for all six physical observables of the neutrino sector with merely two effective free parameters, making it highly worthy of in-depth investigation. In this work, we investigate realizations of leptogenesis in this framework. We consider two distinct scenarios. In the first, the two pseudo-Dirac sterile neutrino pairs are initially exactly degenerate and subsequently acquire small mass splittings via the RGE effects, enabling resonant leptogenesis to occur across different PD pairs and consequently enhancing leptogenesis. In the second, the two PD pairs feature a hierarchical mass spectrum, and leptogenesis proceeds via sterile neutrino oscillations through the ARS mechanism. We show that the observed baryon asymmetry can be successfully reproduced in sizable regions of the parameter space without introducing additional free parameters, demonstrating that the LIS framework provides a viable and predictive setting for low-scale leptogenesis.

Leptogenesis in the littlest inverse seesaw model

Abstract

The littlest inverse seesaw (LIS) model represents the first low-scale seesaw framework to successfully account for all six physical observables of the neutrino sector with merely two effective free parameters, making it highly worthy of in-depth investigation. In this work, we investigate realizations of leptogenesis in this framework. We consider two distinct scenarios. In the first, the two pseudo-Dirac sterile neutrino pairs are initially exactly degenerate and subsequently acquire small mass splittings via the RGE effects, enabling resonant leptogenesis to occur across different PD pairs and consequently enhancing leptogenesis. In the second, the two PD pairs feature a hierarchical mass spectrum, and leptogenesis proceeds via sterile neutrino oscillations through the ARS mechanism. We show that the observed baryon asymmetry can be successfully reproduced in sizable regions of the parameter space without introducing additional free parameters, demonstrating that the LIS framework provides a viable and predictive setting for low-scale leptogenesis.
Paper Structure (7 sections, 34 equations, 4 figures)

This paper contains 7 sections, 34 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Some basic formulas of ISS model and leptogenesis
  3. Leptogenesis assisted by renormalization group evolution
  4. Viability of leptogenesis
  5. Consequence for charged lepton flavor violation
  6. Leptogenesis via ARS mechanism
  7. Summary

Figures (4)

  • Figure 1: For the scenario studied in section 3, the parameter space of $M^{}_0$ versus $\mu^{}_0$ for successful leptogenesis.
  • Figure 2: For the scenario studied in section 3.1, in the parameter space that allows for a reproduction of the observed value of $Y^{}_{\rm B}$, the allowed values of ${\rm BR}(\mu \to e \gamma)$ as functions of $M_0$. The horizontal line stands for the current upper bound on ${\rm BR}(\mu \to e \gamma)$.
  • Figure 3: For the scenario studied in section 4, the parameter space of $M^{}_0$ versus $\mu^{}_0$ for successful leptogenesis.
  • Figure 4: For the scenario studied in section 4, in the parameter space that allows for a reproduction of the observed value of $Y^{}_{\rm B}$, the allowed values of ${\rm BR}(\mu \to e \gamma)$ as functions of $M_0$. The horizontal line stands for the current upper bound on ${\rm BR}(\mu \to e \gamma)$.