On sterile neutrino mixing with \nu_{\tau}

TL;DR

This paper investigates the mixing of sterile neutrinos with tau neutrinos, analyzing their impact on various tau and meson decays to establish new, more stringent limits on the mixing parameter $U_{ au N}$ using experimental data.

Contribution

It provides the first model-independent constraints on $U_{ au N}$ from leptonic and semileptonic tau and meson decays, improving existing bounds.

Findings

New limits on $U_{ au N}$ are more stringent than previous constraints.

Analysis includes both SM-allowed and forbidden lepton decays.

Constraints are derived without assumptions on the relative sizes of sterile neutrino mixings.

Abstract

Matrix element $U_{\tau N}$ of sterile neutrino N mixing with $\nu_{\tau}$ is the least constrained in the literature among the three $U_{\alpha N}$ ($\alpha=e,\mu,\tau$) mixing parameters characterizing the sterile neutrino phenomenology. We study the contribution of massive dominantly sterile neutrinos to purely leptonic $\tau$-decays and semileptonic decays of $\tau$ and K, D mesons. We consider some decays allowed in the Standard Model (SM) as well as Lepton Flavor and Lepton Number Violating (LFV, LNV) decays forbidden in the SM. From the existing experimental data on the branching ratios of these processes we derived new limits on $U_{\tau N}$ more stringent than the ones existing in the literature. These limits are extracted in a model independent way without any ad hoc assumptions on the relative size of the three different sterile neutrino mixing parameters.