Large U_{e3} and Tri-bimaximal Mixing

TL;DR

This paper explores how to perturb tri-bimaximal neutrino mixing to achieve a large |U_{e3}| value (~0.1) while maintaining solar neutrino mixing near its measured value, analyzing three breaking mechanisms and their implications.

Contribution

It provides a model-independent analysis of perturbations to tri-bimaximal mixing, identifying conditions for sizable |U_{e3}| and their effects on neutrino mass and mixing parameters.

Findings

Charged lepton corrections can produce large |U_{e3}| with near-maximal CP violation.

Renormalization group effects require quasi-degenerate neutrinos for sizable |U_{e3}|.

Large cancellations in Majorana phases constrain neutrinoless double beta decay mass.

Abstract

We investigate in a model-independent way to what extent one can perturb tri-bimaximal mixing in order to generate a sizable value of |U_{e3}|, while at the same time keeping solar neutrino mixing near its measured value, which is close to sin^2 theta_{12} = 1/3. Three straightforward breaking mechanisms to generate |U_{e3}| of about 0.1 are considered. For charged lepton corrections, the suppression of a sizable contribution to sin^2 theta_{12} can be achieved if CP violation in neutrino oscillations is almost maximal. Generation of the indicated value of |U_{e3}| of about 0.1 through renormalization group corrections requires the neutrinos to be quasi-degenerate in mass. The consistency with the allowed range of sin^2 theta_{12} together with large running of |U_{e3}| forces one of the Majorana phases to be close to pi. This implies large cancellations in the effective Majorana mass governing neutrino-less double beta, constraining it to lie near its minimum allowed value of m_0 cos 2 theta_{12}, where m_0 is greater than about 0.1 eV. Finally, explicit breaking of the neutrino mass matrix in the inverted hierarchical and quasi-degenerate neutrino mass spectrum cases is similarly correlated with the effective Majorana mass, although to a lesser extent. The implied values for the atmospheric neutrino mixing angle theta_{23} are given in all cases.