Sterile Neutrino Production Through a Matter Effect Enhancement at Long Baselines

TL;DR

This paper explores how sterile neutrinos with neutral vector couplings could be produced more efficiently at long baselines due to matter effects, potentially leading to observable excesses in neutral-current events, and evading previous experimental bounds.

Contribution

It demonstrates that sterile neutrinos with a neutral vector coupling can bypass existing bounds and produce detectable signals in long baseline experiments, expanding the parameter space for sterile neutrino models.

Findings

Sterile neutrinos with vector couplings can evade MINOS bounds.

Certain parameter fits predict excess neutral-current events.

Enhanced production due to matter effects at long baselines.

Abstract

If sterile neutrinos have a neutral coupling to standard model fermions, matter effect resonant transitions to sterile neutrinos and excess neutral-current events could manifest at long baseline experiments. Assuming a single sterile neutrino with a neutral coupling to fermionic matter, we re-examine bounds on sterile neutrino production at long baselines from the MINOS result $P_{\nu_{\mu} \rightarrow \nu_s} < 0.22$ (90% CL). We demonstrate that sterile neutrinos with a neutral vector coupling to fermionic matter could evade the MINOS limit, allowing a higher fraction of active to sterile neutrino conversion at long baselines. Scanning the parameter space of sterile neutrino matter effect fits of the LSND and MiniBooNe data, we show that in the case of a vector singlet coupling of sterile neutrinos to matter, some favored parametrizations of these fits would create neutral-current event excesses above standard model predictions at long baseline experiments (e.g. MINOS and OPERA).