Tri-bimaximal Neutrino Mixing and Flavor-dependent Resonant Leptogenesis

Abstract

We propose a particularly economical neutrino mass model, in which there are only two right-handed Majorana neutrinos of $\mathcal{O}(1)$ 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 ${\eta }_{\mathrm{B}}^{}\approx 6.1\times 10^{-10}$ 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 ${\eta }_{\mathrm{B}}^{}$ in the $m_1^{}=0$ case or magnify the magnitude of the flavor-independent prediction for ${\eta }_{\mathrm{B}}^{}$ about 50 times in the $m_3^{}=0$ case.

Comments: REVTeX4 18 pages (including 1 PS figure). Title and Abstract changed; flavor effects in leptogenesis recalculated, new results obtained and discussions extended; A comparison between different formulas of CP asymmetries in resonant leptogenesis performed; references updated. Accepted for publication in PLB