Improving Electro-Weak Fits with TeV-scale Sterile Neutrinos

TL;DR

This paper investigates how TeV-scale sterile neutrinos influence electroweak precision measurements, showing that their inclusion can improve the fit to experimental data by affecting key observables.

Contribution

It provides explicit formulas for oblique parameters in a type-I see-saw model and demonstrates improved fits to electroweak data with active-sterile mixing.

Findings

Active-sterile mixing improves fit to Z-decay width

Enhanced fit for neutrino scattering ratios

Better agreement for W boson mass deviation

Abstract

We study the impact of TeV-scale sterile neutrinos on electro-weak precision observables and lepton number and flavour violating decays in the framework of a type-I see-saw extension of the Standard Model. At tree level sterile neutrinos manifest themselves via non-unitarity of the PMNS matrix and at one-loop level they modify the oblique radiative corrections. We derive explicit formulae for the S,T,U parameters in terms of the neutrino masses and mixings and perform a numerical fit to the electro-weak observables. We find regions of parameter space with a sizable active-sterile mixing which provide a better over-all fit compared to the case where the mixing is negligible. Specifically we find improvements of the invisible Z-decay width, the charged-to-neutral-current ratio for neutrino scattering experiments and of the deviation of the W boson mass from the theoretical expectation.