Constraints on Decaying Sterile Neutrinos from Solar Antineutrinos

TL;DR

This paper investigates how solar neutrino experiments constrain models with decaying sterile neutrinos, setting limits on their mixing and exploring implications for anomalies like LSND and MiniBooNE.

Contribution

It adapts solar neutrino searches to non-minimal sterile neutrino models involving decay chains, providing new upper limits on neutrino mixing parameters and analyzing their compatibility with existing anomalies.

Findings

Upper limits on $|U_{e4}|^2$ at the per mille level.

Tension between sterile neutrino explanations and solar antineutrino flux constraints.

Potential for future constraints from Borexino and Super-Kamiokande with Gd.

Abstract

Solar neutrino experiments are highly sensitive to sources of $\nu\to\overline{\nu}$ conversions in the $^8$B neutrino flux. In this work we adapt these searches to non-minimal sterile neutrino models recently proposed to explain the LSND, MiniBooNE, and reactor anomalies. The production of such sterile neutrinos in the Sun, followed the decay chain $\nu_4 \to \nu \phi \to \nu \nu \overline{\nu}$ with a new scalar $\phi$ results in upper limits for the neutrino mixing $|U_{e4}|^2$ at the per mille level. We conclude that a simultaneous explanations of all anomalies is in tension with KamLAND, Super-Kamiokande, and Borexino constraints on the flux of solar antineutrinos. We then present other minimal models that violate parity or lepton number, and discuss the applicability of our constraints in each case. Future improvements can be expected from existing Borexino data as well as from future searches at Super-Kamiokande with added Gd.