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A New Type of Complex Neutrino Mass Texture and μ-τ Symmetry

  • TOKAI-HEP/TH-0505  with Ichiro Aizawa, published in Phys. Rev. D 73 No.1 (2006) 015002 1-10 (Received date: October, 2005).
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Relying upon the usefulness of the \mu-\tau symmetry, we find a new type of neutrino mass texture with a single phase parameter \delta that describes maximal atmospheric neutrino mixing and Dirac CP violation due to the presence of \delta.  The Majorana phase associated with the third massive neutrino turns out to be identical to the Dirac phase while other Majorana phases vanish.  The nonvanishing reactor neutrino mixing angle \theta_{13} is induced by a \mu-\tau symmetry breaking effect.  Flavor neutrino masses that supply the \mu-\tau symmetry breaking terms become pure imaginary for \delta=\pm \pi/2, leading to maximal CP violation.  There is a parameter denoted by \eta, which is either O(\sqrt{\Delta m^2_\odot/\Delta m^2_{atm}}) in the normal mass hierarchy, or O(\Delta m^2_\odot/\Delta m^2_{atm}) in the inversed mass hierarchy.  In the inversed mass hierarchy, the contribution of O(\sin^2\theta_{13}) is found to be significant and cannot be neglected. Our texture also leads to quasi degenerate neutrinos with masses of O(\sqrt{\Delta m^2_{atm}}), which serves as the scale for the effective neutrino mass in (\beta\beta)_{0\nu}-decay.  This texture does not include \eta, and \Delta m^2_\odot naturally arises from contributions of O(\sin^2\theta_{13}) to give \Delta m^2_\odot/\Delta m^2_{atm}\sim(\sin^2\theta_{13}), yielding the prediction of \sin^2(\theta_{13})=O(10^{-2}).

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