Majorana CP phases in bi-pair neutrino mixing and leptogenesis

Abstract

We estimate Majorana CP phases for a given flavor neutrino mass matrix (M_\nu) consistent with the bi-pair neutrino mixing, which is recently proposed to describe neutrino mixings given by \sin\theta_{13}=0 for the reactor neutrino mixing, \sin^2\theta_{12} = 1-1/\sqrt{2} for the solar neutrino mixing and either \sin^2\theta_{23} = \tan^2\theta_{12} or \sin^2\theta_{23}=1-\tan^2\theta_{12} for the atmospheric neutrino mixing. Sizes of Majorana CP phases are evaluated so as to generate the observed baryon asymmetry in the universe via a leptogenesis scenario within the framework of the minimal seesaw model, where M_\nu satisfies det(M_\nu)=0 and one active Majorana CP phase (\phi) is present. Assuming the normal mass hierarchy for light neutrinos and one zero texture for a 3X2 Dirac neutrino mass matrix, we find that \phi lies in the region of 0.69<|\phi|<0.92 [rad], which is converted into allowed regions of \alpha=arg(M_{e\mu}) and \beta=arg(M_{e\tau}), where M_{ij} (i,j=e,\mu,\tau) denote the i-j matrix element of M_\nu. The phases \alpha and \beta turn out to satisfy 0.31<|\alpha|<0.40 [rad] and -1.25<\beta<-0.32 [rad]. The approximate numerical equality of |\phi|\approx 2|\alpha| is consistent with our theoretical estimation of \phi=\phi_2-\phi_3 for \phi_2=-(\alpha+\beta) and \phi_3\approx \alpha-\beta valid for the normal mass hierarchy. We also find the following scaling property: (M'^{\mu\mu}-M'^{ee}/t^2_{12})/M'^{\mu\tau}=M'^{\mu\tau}/(M'^{\tau\tau}-M'^{ee}/t^2_{12})=-M'^{e\tau}/M'^{e\mu} (t^2_{12}=\tan^2\theta_{12}=\sqrt{2}-1), where M'^{ij} stands for M_{ij} evaluated on the basis of the Particle Data Group's phase convention.