An expansion for Neutrino Phenomenology

TL;DR

This paper introduces a new formalism for analyzing neutrino masses and mixing matrices based on a seesaw mechanism, linking structure and symmetry implications without specific basis choices.

Contribution

It develops an expansion formalism for the PMNS matrix and neutrino masses that systematically relates structure to symmetry, independent of charged lepton basis choices.

Findings

Relates PMNS structure to neutrino mass differences

Provides a systematic way to study deviations from tri-bimaximal mixing

Comments on implications of Daya-Bay results for neutrino symmetries

Abstract

We develop a formalism for constructing the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix and neutrino masses using an expansion that originates when a sequence of heavy right handed neutrinos are integrated out, assuming a seesaw mechanism for the origin of neutrino masses. The expansion establishes relationships between the structure of the PMNS matrix and the mass differences of neutrinos, and allows symmetry implications for measured deviations from tri-bimaximal form to be studied systematically. Our approach does not depend on choosing the rotation between the weak and mass eigenstates of the charged lepton fields to be diagonal. We comment on using this expansion to examine the symmetry implications of the recent results from the Daya-Bay collaboration reporting the discovery of a non zero value for theta_{13}, indicating a deviation from tri-bimaximal form, with a significance of 5.2 sigma.