Right-Handed Leptonic Mixing and Enhancement Band in Left-Right Symmetry

TL;DR

This paper explores how parity symmetry in left-right models leads to a unique enhancement band in right-handed leptonic mixing, revealing new patterns and structural features in the Dirac leptonic sector.

Contribution

It analytically derives solutions showing how parity violation and near-degeneracies create a distinct, predictive right-handed leptonic mixing pattern in minimal left-right models.

Findings

Identification of a localized enhancement band in right-handed leptonic mixing.

Analytic solutions to the LR consistency equation.

Discovery of a new pattern of right-handed mixing due to spectral near-degeneracies.

Abstract

Left-right (LR) symmetric theories predict right-handed charged currents whose flavor structure encodes the realization of parity. While the right-handed quark mixing matrix closely tracks its left-handed counterpart, the leptonic sector with purely Dirac neutrinos has remained structurally unclear. We show that, in contrast to the quark case, parity in the Dirac leptonic sector generically induces a localized, branch-dependent enhancement band in which RH--LH misalignment becomes parametrically large despite small parity breaking. We derive analytic solutions of the LR consistency equation and demonstrate that the interplay between spontaneous parity violation and spectral near-degeneracies leads to a qualitatively new pattern of right-handed mixing. This establishes the Dirac leptonic sector of the minimal LR model as a predictive and structurally distinct regime.