In the framework of canonical seesaw model, we present a simple but viable scenario to explicitly break an $S^{ }_{ 3{ \rm L}} \times S^{ }_{ 3{ \rm R}}$ flavor symmetry in the leptonic sector. It turns out that the leptonic flavor mixing matrix is completely determined by the mass ratios of charged leptons (i.e., $m^{ }_e/m^{ }_\mu$ and $m^{ }_\mu/m^{ }_\tau$) and those of light neutrinos (i.e., $m^{ }_1/m^{ }_2$ and $m^{ }_2/m^{ }_3$). The latest global-fit results of three neutrino mixing angles $\{ \theta^{ }_{ 12}, \theta^{ }_{ 13}, \theta^{ }_{ 23}\}$ and two neutrino mass-squared differences $\{ \Delta m^2_{ 21}, \Delta m^2_{ 31}\}$ at the $3\sigma$ level are used to constrain the parameter space of $\{ m^{ }_1/m^{ }_2, m^{ }_2/m^{ }_3\}$. 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., $m^{ }_1 \approx 2.2~{ \rm meV}$, $m^{ }_2 \approx 8.8~{ \rm meV}$ and $m^{ }_3 \approx 52.7~{ \rm meV}$; (2) Only the first octant of $\theta^{ }_{ 23}$ is allowed, namely, $41.8^\circ \lesssim \theta^{ }_{ 23} \lesssim 43.3^\circ$; (3) The Dirac CP-violating phase $\delta \approx -22^\circ$ deviates significantly from the maximal value $-90^\circ$. All these predictions are ready to be tested in the 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, the leptonic CP violation at low- and high-energy scales are closely connected.
Categories: hep-ph