Rescaled Leptonic Unitarity Triangles and Rephasing Invariants

TL;DR

This paper explores the relationship between leptonic unitarity triangles, rephasing invariants, and matter effects in neutrino oscillations, providing new relations and numerical insights into CP violation measures in matter.

Contribution

It introduces new relations connecting vacuum and matter effective invariants and systematically discusses the impact of matter on leptonic unitarity triangles and CP violation measures.

Findings

Effective invariants in matter are linear combinations of vacuum invariants.

New relations analogous to Naumov relation are established for quartets.

Numerical analysis shows how invariants evolve with matter density.

Abstract

The field of neutrino physics has made significant progress in measuring the strength and frequency of neutrino and antineutrino oscillations in the past two decades. It is clear that the amplitudes involved in the neutrino oscillation probabilities are all rephaping invariants of the quartet forms of the elements of the PMNS mixing matrix. We show in this paper how these quartet observables can be directly linked to the rescaled leptonic unitarity triangles within the framework of three active neutrinos. We provide a systematic discussion of the nine CP-conserving quartets ${\cal R}^{}_{\gamma k} \equiv {\rm Re} \left [ V^{}_{\alpha i} V^{}_{\beta j} V^{*}_{\alpha j} V^{*}_{\beta i}\right ] $ along with the universal Jarlskog invariant of CP violation ${\cal J} \equiv \sum_\gamma \epsilon^{}_{\alpha\beta\gamma} \sum_k \epsilon^{}_{ijk} \; {\rm Im} \left [ V^{}_{\alpha i} V^{}_{\beta j} V^{*}_{\alpha j} V^{*}_{\beta i} \right ]$, and place particular emphasis on the matter effect on these quartets. In addition to the well-known Naumov relation for the Jarlskog invariant ${\cal J}$, similar relations connecting ${\cal R}$ in vacuum and its effective counterparts $\widetilde{\cal R}$ in matter are introduced and examined in detail. We find that the effective CP-conserving invariants $\widetilde{\cal R}^{}_{\alpha i}$ in matter can be regarded as linear combinations of their vacuum counterparts. With the latest global fit data of neutrino masses and mixing elements, numerical analyses are carried out to give an intuitive understanding of how these rephasing invariants evolve as the matter density increases.