Revisiting Flavor Model and Leptogenesis

TL;DR

This work revisits a SUSY flavor model based on $SU(2)_L \times A_4 \times Z_3 \times U(1)_R$ to account for lepton masses and the nonzero reactor angle via flavon-driven symmetry breaking. While the leading-order Dirac neutrino texture yields vanishing CP asymmetry and thus cannot generate the baryon asymmetry, next-to-leading-order corrections to the Dirac Yukawa couplings produce nonzero CP violation, enabling successful thermal leptogenesis in the model. A detailed numerical analysis using NuFit-6.0 data shows regions of parameter space where neutrino oscillation data and the observed BAU can be simultaneously fit, yielding a lightest neutrino mass bound of $m_{\text{light}} \ge 5$ meV for normal ordering and $\ge 15$ meV for inverted ordering, with Majorana phases and $|m_{ee}|$ potentially testable in upcoming experiments. The results highlight a concrete link between flavor symmetry breaking, CP violation, and cosmological baryogenesis with falsifiable predictions for future neutrino and neutrinoless double-beta decay experiments.

Abstract

We revisit a supersymmetric flavor model based on the symmetries $SU(2)_L \times A_4 \times Z_3 \times U(1)_R$, which extends the original Altarelli and Feruglio construction by introducing flavon and driving superfields responsible for the spontaneous breaking of the flavor symmetry in order to obtain non-zero reactor angle. The vacuum alignments of flavon fields are achieved through the minimization of the scalar potential derived from the superpotential. This setup leads to specific mass matrices for the charged leptons and neutrinos that are consistent with current experimental data, including the measured values of the lepton mixing angles and neutrino mass squared differences. We investigate whether the model can simultaneously accommodate successful thermal leptogenesis. In particular, we analyze the CP asymmetry generated in the decay of heavy Majorana neutrinos, the resulting lepton asymmetry, and its conversion to the baryon asymmetry through the electroweak sphalerons. However the CP asymmetry is zero, since the Dirac neutrino mass matrix is simple texture in the leading order for our model. Then we consider the next-to-leading order in Yukawa interactions of the Dirac neutrinos. Therefore, we can realize the baryon asymmetry of the universe at the present universe. By numerically scanning the parameter space, we identify the regions consistent with both neutrino oscillation data and the observed baryon asymmetry. In the specific case such that one of the couplings for the right-handed Majorana neutrinos is real parameter, the predicted lightest neutrino mass is at least $5$ meV and $15$ meV for the normal and inverted neutrino mass hierarchies, respectively. In addition, the range of the Majorana phases may be tested in future experiments.

Figures (7)

• Figure 1: The allowed regions of the lepton mixing anlges and Dirac CP phase. Horizontal axis:$\sin \theta_{12}$, Vertical axis:$\sin \theta_{13}$.
• Figure 2: The $\sin \theta _{23}$-$\delta _{CP}$ in the NH case.
• Figure 3: The $\sin \theta _{23}$-$\delta _{CP}$ in the IH case.
• Figure 5: The $\eta _1$-$\eta _2$ plane in the NH.
• Figure 6: The $\eta _1$-$\eta _2$ plane in the IH.