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Neutrino mass anarchy and leptogenesis

Qi An, Yan Shao, Zhen-hua Zhao

Abstract

In this paper, we investigate leptogenesis under the neutrino mass anarchy hypothesis in both type-I and type-II seesaw models. We first revisit the corresponding study in the type-I seesaw framework with two improvements: in contrast to Ref.[25], where an approximate $U(1)$ flavor symmetry was imposed to ensure sizable hierarchies among the right-handed neutrino masses and Yukawa couplings, we adopt a fully general anarchy scenario with completely random and structureless neutrino mass and Yukawa matrices; moreover, given the crucial role of lepton flavors in both the generation and washout of the lepton asymmetry, flavor effects are consistently incorporated throughout our analysis. We then extend our investigation to the type-II seesaw framework, in which leptogenesis proceeds via the out-of-equilibrium decays of a scalar triplet.

Neutrino mass anarchy and leptogenesis

Abstract

In this paper, we investigate leptogenesis under the neutrino mass anarchy hypothesis in both type-I and type-II seesaw models. We first revisit the corresponding study in the type-I seesaw framework with two improvements: in contrast to Ref.[25], where an approximate flavor symmetry was imposed to ensure sizable hierarchies among the right-handed neutrino masses and Yukawa couplings, we adopt a fully general anarchy scenario with completely random and structureless neutrino mass and Yukawa matrices; moreover, given the crucial role of lepton flavors in both the generation and washout of the lepton asymmetry, flavor effects are consistently incorporated throughout our analysis. We then extend our investigation to the type-II seesaw framework, in which leptogenesis proceeds via the out-of-equilibrium decays of a scalar triplet.

Paper Structure

This paper contains 6 sections, 23 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Leptogenesis in the type-I seesaw
  3. Random generation of mass matrices without experimental cuts
  4. Random generation of mass matrices with experimental cuts
  5. Leptogenesis in the type-II seesaw
  6. Summary

Figures (4)

  • Figure 1: For randomly generated right-handed neutrino mass matrix $M^{}_{\rm R}$, the probability distribution of the mass ratios $M^{}_{2}/M^{}_{1}$ and $M^{}_{3}/M^{}_{1}$.
  • Figure 2: For the scenario studied in section 2.1, the probability distribution of the baryon asymmetry $Y^{}_{\rm B}$ for $M^{}_0 = 5\times 10^{11}$ GeV.
  • Figure 3: For the scenario studied in section 2.2, the probability distributions of the baryon asymmetry $Y^{}_{\rm B}$ for $M^{}_0 = 7 \times 10^{11}$ GeV and $9 \times 10^{11}$ GeV in the NO (a) and IO (b) cases.
  • Figure 4: For the scenario studied in section 3, the probability distributions of the baryon asymmetry $Y^{}_{\rm B}$ for $M^{}_\Delta = 3\times 10^{11}$ GeV in the cases of $M^{}_{\Delta} = M^{}_{\rm H}/3$ (a) and $M^{}_{\Delta} = M^{}_{\rm H}$ (b).