Mu-tau symmetry and the Littlest Seesaw

TL;DR

This paper reviews mu-tau symmetry in neutrino physics, introduces a new general form of neutrino mass matrix with this symmetry, and applies it to the Littlest Seesaw model to explain maximal atmospheric mixing and CP violation.

Contribution

It presents a new general form of neutrino mass matrix with mu-tau symmetry and applies it to the Littlest Seesaw model, clarifying its role in neutrino mixing predictions.

Findings

The new mass matrix form exhibits mu-tau symmetry.

The Littlest Seesaw model approximately satisfies the new form.

This symmetry explains maximal atmospheric mixing and CP violation.

Abstract

Motivated by the latest neutrino oscillation data which is consistent with maximal atmospheric mixing and maximal leptonic CP violation, we review various results in $\mu\tau$ symmetry, then include several new observations and clarifications, including identifying a new general form of neutrino mass matrix with $\mu\tau$ symmetry. We then apply the new results to the neutrino mass matrix associated with the Littlest Seesaw model, and show that it approximately satisfies the new general form with $\mu\tau$ symmetry, and that this is responsible for its approximate predictions of maximal atmospheric mixing and maximal CP violation in the lepton sector.