Generalized perturbations in neutrino mixing

TL;DR

This paper derives general expressions for how complex perturbations to neutrino mass and charged lepton matrices affect neutrino mixing parameters, highlighting the significant impact of phases and initial symmetries on observable mixing angles and phases.

Contribution

It provides a unified framework to analyze the effects of complex perturbations on neutrino mixing, applicable to various initial conditions and perturbation sources.

Findings

Perturbation phases and initial phases significantly influence mixing corrections.

Small perturbations can lead to large changes in the Dirac phase under certain symmetries.

The method is applied to scenarios with nonstandard interactions affecting neutrino oscillations.

Abstract

We derive expressions for the neutrino mixing parameters that result from complex perturbations on (1) the Majorana neutrino mass matrix (in the basis of charged lepton mass eigenstates) and on (2) the charged lepton mass matrix, for arbitrary initial (unperturbed) mixing matrices. In the first case, we find that the phases of the elements of the perturbation matrix, and the initial values of the Dirac and Majorana phases, strongly impact the leading order corrections to the neutrino mixing parameters and phases. For experimentally compatible scenarios wherein the initial neutrino mass matrix has $\mu-\tau$ symmetry, we find that the Dirac phase can take any value under small perturbations. Similarly, in the second case, perturbations to the charged lepton mass matrix can generate large corrections to the mixing angles and phases of the PMNS matrix. As an illustration of our generalized procedure, we apply it to a situation in which nonstandard scalar and nonstandard vector interactions simultaneously affect neutrino oscillations.