Global Constraints on a Heavy Neutrino

TL;DR

This paper provides comprehensive constraints on the existence of a heavy sterile neutrino with masses from 10 eV to 1 TeV by combining various experimental and observational data.

Contribution

It performs a global analysis incorporating diverse experimental inputs to refine bounds on heavy neutrino mixing parameters, expanding previous studies.

Findings

Stringent limits on $|U_{e4}|^2$, $|U_{64}|^2$, and $|U_{ au4}|^2$ across the mass range.

Inclusion of cosmological and neutrino oscillation data tightens constraints.

Constraints are consistent with no heavy neutrino detection within current sensitivities.

Abstract

We estimate constraints on the existence of a heavy, mostly sterile neutrino with mass between 10 eV and 1 TeV. We improve upon previous analyses by performing a global combination and expanding the experimental inputs to simultaneously include tests for lepton universality, lepton-flavor-violating processes, electroweak precision data, dipole moments, and neutrinoless double beta decay. Assuming the heavy neutrino and its decay products are invisible to detection, we further include, in a self-consistent manner, constraints from direct kinematic searches, the kinematics of muon decay, cosmology, and neutrino oscillations, in order to estimate constraints on the values of $|U_{e4}|^2$, $|U_{\mu4}|^2$, and $|U_{\tau4}|^2$.