'Mu-Tau' symmetry, tribimaximal mixing and four zero neutrino Yukawa textures

TL;DR

This paper explores how `mu-tau' symmetry and tribimaximal mixing in the neutrino sector, combined with four-zero Yukawa textures, lead to highly constrained neutrino mass models with specific testable predictions.

Contribution

It demonstrates that imposing exact `mu-tau' symmetry and four-zero textures reduces the allowed neutrino Yukawa matrices to only four forms, significantly constraining the model parameters.

Findings

Reduced 72 textures to 4 under symmetry constraints

Parameters constrained to narrow ranges, nearly fixed by tribimaximal mixing

Implications for leptogenesis and lepton flavor violation

Abstract

Within the type-I seesaw framework with three heavy right chiral neutrinos and in the basis where the latter and the charged leptons are mass diagonal, a near `mu-tau' symmetry in the neutrino sector is strongly suggested by the neutrino oscillation data. There is further evidence for a close to the tribimaximal mixing pattern which subsumes `mu-tau' symmetry. On the other hand, the assumption of a (maximally allowed) four zero texture in the Yukawa coupling matrix Y_nu in the same basis leads to a highly constrained and predictive theoretical scheme. We show that the requirement of an exact `mu-tau' symmetry, coupled with observational constraints, reduces the `seventy two' allowed textures in such a `Y_nu' to 'only four' corresponding to just two different forms of the light neutrino mass matrix `m_nu'. The effect of each of these on measurable quantities can be described, apart from an overall factor of the neutrino mass scale, in terms of two real parameters and a phase angle all of which are within very constrained ranges. The additional input of a tribimaximal mixing reduces these three parameters to `only one' with a very nearly fixed value. Implications for both flavored and unflavored leptogenesis as well as radiative lepton flavor violating decays are discussed. We also investigate the stability of these conclusions under small deviations due to renormalization group running from a high scale where the four zero texture as well as `mu-tau' symmetry or the tribimaximal mixing pattern are imposed.