Revisiting pseudo-Dirac neutrino scenario after recent solar neutrino data

TL;DR

This paper investigates the pseudo-Dirac neutrino scenario using recent solar neutrino data, constraining the neutrino mass splitting and proposing new experimental approaches to test the model.

Contribution

It provides updated constraints on the pseudo-Dirac neutrino model using recent data and suggests novel methods for experimental verification.

Findings

Both time integrated and seasonal data favor a nonzero mass splitting for ν₂.

The preferred mass splitting is approximately 1.5×10⁻¹¹ eV².

Proposes measurements at intermediate energies and more precise pep flux to test the scenario.

Abstract

It is still unknown whether the mass terms for neutrinos are of Majorana type or of Dirac type. An interesting possibility, known as pseudo-Dirac scheme combines these two with a dominant Dirac mass term and a subdominant Majorana one. As a result, the mass eigenstates come in pairs with a maximal mixing and a small splitting determined by the Majorana mass. This will affect the neutrino oscillation pattern for long baselines. We revisit this scenario employing recent solar neutrino data, including the seasonal variation of the $^7$Be flux recently reported by BOREXINO. We constrain the splitting using these data and find that both the time integrated solar neutrino data and the seasonal variation independently point towards a new pseudo-Dirac solution with nonzero splitting for $\nu_2$ of $\Delta m_2^2\simeq 1.5\times 10^{-11}$ eV$^2$. We propose alternative methods to test this new solution. In particular, we point out the importance of measuring the solar neutrino flux at the intermediate energies $1.5~{\rm MeV}<E_\nu<3.5~{\rm MeV}$ (below the Super-Kamiokande detection threshold) as well as a more precise measurement of the $pep$ flux. The code is available on \href{https://github.com/SaeedAnsarifard/SolarNeutrinos-pseudoDirac.git}{Github}