Baryon asymmetry via leptogenesis in a neutrino mass model with complex scaling

TL;DR

This paper explores how a specific neutrino mass model with complex scaling can explain the matter-antimatter asymmetry in the universe through leptogenesis, analyzing different mass regimes and neutrino orderings.

Contribution

It introduces a neutrino mass model with complex scaling that links CP violation and mixing angles to leptogenesis, providing detailed numerical analysis across mass regimes.

Findings

Maximal Dirac CP violation predicted by the model.

Baryon asymmetry consistent with observations in certain mass regimes.

Distinct effects of flavored vs. unflavored leptogenesis analyzed.

Abstract

Baryogenesis via leptogenesis is investigated in a specific model of light neutrino masses and mixing angles. The latter was proposed on the basis of an assumed complex-extended scaling property of the neutrino Majorana mass matrix $M_\nu$, derived with a type-1 seesaw from a Dirac mass matrix $m_D$ and a heavy singlet neutrino Majorana mass matrix $M_R$. One of its important features, highlighted here, is that there is a common source of the origin of a nonzero $\theta_{13}$ and the CP violating lepton asymmetry through the imaginary part of $m_D$. The model predicted CP violation to be maximal for the Dirac type and vanishing for the Majorana type. We assume strongly hierarchical mass eigenvalues for $M_R$. The leptonic CP asymmetry parameter $\varepsilon^\alpha_{1}\hspace{1mm}$ with lepton flavor $\alpha$, originating from the decays of the lightest of the heavy neutrinos $N_1$ (of mass $M_1$) at a temperature $T\sim M_1$, is what matters here with $\varepsilon^\alpha_{2,3}$, originating from the decays of $N_{2,3}$, being washed out. The light leptonic and heavy neutrino number densities (normalized to the entropy density) are evolved via Boltzmann equations down to electroweak temperatures to yield a baryon asymmetry through sphaleronic transitions. The effect of flavored vs. unflavored leptogenesis in the three mass regimes (1) $M_1<10^{9}$ GeV, (2) $10^9$ GeV $<M_1<$ $10^{12}$ GeV and (3) $M_1>10^{12}$ GeV are numerically worked out for both a normal and an inverted mass ordering of the light neutrinos. Corresponding results on the baryon asymmetry of the universe are obtained, displayed and discussed.