Tri-bimaximal Neutrino Mixing and Flavor-dependent Resonant Leptogenesis

We propose a particularly economical neutrino mass model, in which there are only two right-handed Majorana neutrinos of ${\cal O}(1)$ TeV and their masses are highly degenerate. Its novel Yukawa-coupling texture together with the seesaw mechanism allows us to achieve the normal neutrino mass hierarchy with $m^{}_1 = 0$ and a nearly tri-bimaximal neutrino mixing pattern with the maximal CP-violating phase: $\theta^{}_{23} = \pi/4$, $|\delta| = \pi/2$ and $\sin^2 \theta^{}_{12} = (1 - 2 \tan^2 \theta^{}_{13})/3$. One may also obtain the inverted neutrino mass hierarchy with $m^{}_3 = 0$ and the corresponding neutrino mixing pattern with $\theta^{}_{23} =\pi/4$ and $\theta^{}_{13} = \delta = 0$. In both cases, it is possible to interpret the cosmological baryon number asymmetry $\eta^{}_{\rm B} \approx 6.1 \times 10^{-10}$ through the resonant leptogenesis mechanism. We demonstrate the significance of flavor-dependent effects in this leptogenesis scenario: they can either flip the sign of the flavor-independent prediction for $\eta^{}_{\rm B}$ in the $m^{}_1 = 0$ case or magnify the magnitude of the flavor-independent prediction for $\eta^{}_{\rm B}$ about 50 times in the $m^{}_3 = 0$ case.