Broken S3L×S3R flavor symmetry and leptonic CP violation**Supported by NNSFC (11325525), National Recruitment Program for Young Professionals and CAS Center for Excellence in Particle Physics (CCEPP)

Abstract

In the framework of the canonical seesaw model, we present a simple but viable scenario to explicitly break an S3L×S3R flavor symmetry in the leptonic sector. It turns out that the leptonic flavor mixing matrix is completely determined by the mass ratios of the charged leptons (i.e., me/mμ and mμ/mτ) and those of light neutrinos (i.e., m1/m2 and m2/m3). The latest global-fit results of the three neutrino mixing angles {θ12, θ13, θ23} and two neutrino mass-squared differences at the 3σ level are used to constrain the parameter space of {m1/m2,m2/m3}. The predictions for the mass spectrum and flavor mixing are highlighted: (1) the neutrino mass spectrum shows a hierarchical pattern and a normal ordering, e.g., m1≈2.2 meV, m2≈8.8 meV and m3≈52.7 meV; (2) only the first octant of θ23 is allowed, namely, 41.8°≲θ23≲43.3°; (3) the Dirac CP-violating phase δ≈−22° deviates significantly from the maximal value −90°. All these predictions are ready to be tested in ongoing and forthcoming neutrino oscillation experiments. Moreover, we demonstrate that the cosmological matter-antimatter asymmetry can be explained via resonant leptogenesis, including the individual lepton-flavor effects. In our scenario, leptonic CP violation at low- and high-energy scales is closely connected.