CP-conserving SO(3) parameterization of the neutrino mixing matrix

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Main Authors: Duda, Jarosław, Gluza, Janusz, Karmakar, Biswajit
Format: Preprint
Published: 2025
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author Duda, Jarosław
Gluza, Janusz
Karmakar, Biswajit
author_facet Duda, Jarosław
Gluza, Janusz
Karmakar, Biswajit
contents The pattern of neutrino mixing, usually parameterized by the Pontecorvo-Maki-Nakagawa-Sakata $U_{\rm PMNS}$ matrix, still remains a striking puzzle in particle physics. $U_{\rm PMNS}$ is one of six possible products of multiplying three Euler matrices. Here we discuss the neutrino mixing matrix parameterization for three known flavours of neutrinos based on the SO(3) group represented by one three-dimensional rotation matrix $U_{\rm SO3}$ and the CP-conserving phases $δ_{\rm CP}=0^{\circ}$ and $180^\circ$. The mixing matrix $U_{\rm SO3}$ with cyclic order of the Lie group generators implies $δ_{\rm{CP}}=180^\circ$ for clockwise rotation in three dimensions, a viable scenario for normal mass ordering. We determine a range of rotation angles for $U_{\rm SO3}$ which deviate substantially from the almost maximal mixings in the standard $U_{\rm PMNS}$ scenario, yielding `democratic' values for the mixing angles. On the other hand, $δ_{\rm CP}=0^{\circ}$ CP-conserving case supports near-maximal mixing scenario. With the fixed $δ_{\rm CP}$ value, the $U_{\rm SO3}$ parameterization can be validated or falsified by the next generation of neutrinoless double beta decay experiments and puts a stringent constraint on the absolute neutrino mass. The proposed $U_{\rm SO3}$ neutrino mixing parameterization is suited for independent CP-conserving neutrino oscillation experimental analysis.
format Preprint
id arxiv_https___arxiv_org_abs_2509_25328
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle CP-conserving SO(3) parameterization of the neutrino mixing matrix
Duda, Jarosław
Gluza, Janusz
Karmakar, Biswajit
High Energy Physics - Phenomenology
The pattern of neutrino mixing, usually parameterized by the Pontecorvo-Maki-Nakagawa-Sakata $U_{\rm PMNS}$ matrix, still remains a striking puzzle in particle physics. $U_{\rm PMNS}$ is one of six possible products of multiplying three Euler matrices. Here we discuss the neutrino mixing matrix parameterization for three known flavours of neutrinos based on the SO(3) group represented by one three-dimensional rotation matrix $U_{\rm SO3}$ and the CP-conserving phases $δ_{\rm CP}=0^{\circ}$ and $180^\circ$. The mixing matrix $U_{\rm SO3}$ with cyclic order of the Lie group generators implies $δ_{\rm{CP}}=180^\circ$ for clockwise rotation in three dimensions, a viable scenario for normal mass ordering. We determine a range of rotation angles for $U_{\rm SO3}$ which deviate substantially from the almost maximal mixings in the standard $U_{\rm PMNS}$ scenario, yielding `democratic' values for the mixing angles. On the other hand, $δ_{\rm CP}=0^{\circ}$ CP-conserving case supports near-maximal mixing scenario. With the fixed $δ_{\rm CP}$ value, the $U_{\rm SO3}$ parameterization can be validated or falsified by the next generation of neutrinoless double beta decay experiments and puts a stringent constraint on the absolute neutrino mass. The proposed $U_{\rm SO3}$ neutrino mixing parameterization is suited for independent CP-conserving neutrino oscillation experimental analysis.
title CP-conserving SO(3) parameterization of the neutrino mixing matrix
topic High Energy Physics - Phenomenology
url https://arxiv.org/abs/2509.25328