The Possible Textures in the Seesaw Realization of the Strong Scaling Ansatz and the Implications for Thermal Leptogenesis

Abstract

We classify the textures of the Dirac and the right-handed Majorana neutrino mass matrices, $M_D$ and $M_R$, which can satisfy the so-called ``Strong Scaling Ansatz'' (SSA) within the framework of the seesaw mechanism $M_{\nu}=-M_D^T M_R^{-1} M_D$. We assume that the Dirac neutrino mass matrix has some texture zeros and examine which elements should be zero in order to satisfy the SSA, by taking into account all possible textures for $M_R$. We find that the resulting Dirac neutrino mass matrices have rank 2 as well as the rank of the effective neutrino mass matrix $M_{\nu}$, or rank 1, depending only on the textures of $M_R^{-1}$. We also consider the three cases of the breaking of the SSA by introducing a complex breaking parameter in $M_{\nu}$ and show that it can generate the CP violation in the lepton sector as well as non-zero $m_3$ and $U_{e3}$. We furthermore discuss the implications of the thermal leptogenesis for the both case which satisfies and breaks the SSA in the basis where $M_R$ is diagonal.