Neutrino Mixing, CP/T Violation and Textures in Four-Neutrino Models

TL;DR

This paper explores the potential to measure CP and T violation in four-neutrino models, which could reveal the existence of sterile neutrinos and help understand neutrino mass textures using current and future experiments.

Contribution

It provides a comprehensive parametrization of four-neutrino models and analyzes the conditions under which CP/T violation can be observed in experiments, highlighting the role of sterile neutrinos.

Findings

Measurable CP/T violation is possible with current constraints.

Additional oscillation effects may be detectable in experiments.

Observable CP/T violation indicates the presence of sterile neutrinos.

Abstract

We examine the prospects for determining the neutrino mixing matrix and for observing CP and T violation in neutrino oscillations in four-neutrino models. We focus on a general class of four-neutrino models with two pairs of nearly degenerate mass eigenstates separated by approximately 1 eV, which can describe the solar, atmospheric and LSND neutrino data. We present a general parametrization of these models and discuss in detail the determination of the mixing parameters and the mass matrix texture from current and future neutrino data in the case where $\nu_e$ and $\nu_\mu$ each mix primarily with one other neutrino. We find that measurable CP/T violation in long-baseline experiments, with amplitude at the level of the LSND signal, is possible given current experimental constraints. Also, additional oscillation effects in short- and long-baseline experiments may be measurable in many cases. We point out that, given separate scales for the mass-squared differences of the solar and atmospheric oscillations, observable CP/T violation effects in neutrino oscillations signals the existence of a sterile neutrino. We examine several textures of the neutrino mass matrix and determine which textures can have measurable CP/T violation in neutrino oscillations in long-baseline experiments. We also briefly discuss some possible origins of the neutrino mass terms in straightforward extensions of the Standard Model.