# Statistical sensitivity on right-handed currents in presence of eV scale sterile neutrinos with KATRIN

## TL;DR

This paper evaluates KATRIN's potential to detect or constrain right-handed currents mediated by W bosons in the presence of eV-scale sterile neutrinos, using Bayesian analysis of beta decay spectra.

## Contribution

It introduces a Bayesian MCMC method to estimate KATRIN's sensitivity to right-handed currents with sterile neutrinos, considering interference effects near the beta decay endpoint.

## Key findings

- KATRIN can set sterile neutrino mass-dependent limits on interference strength.
- Sensitivity improves with better constraints on the beta decay Q-value.
- Current limits from LHC W boson searches are more restrictive than KATRIN's sensitivity.

## Abstract

The KATRIN experiment aims to determine the absolute neutrino mass by measuring the endpoint region of the tritium $\beta$ spectrum. As a large-scale experiment with a sharp energy resolution, high source luminosity and low background it may also be capable of testing certain theories of neutrino interactions beyond the standard model (SM). An example of a non-SM interaction are right-handed currents mediated by right-handed W bosons in the left-right symmetric model (LRSM). In this extension of the SM, an additional SU(2)$_\mathrm R$ symmetry in the high-energy limit is introduced, which naturally includes sterile neutrinos and predicts the seesaw mechanism. In tritium $\beta$ decay, this leads to an additional term from interference between left- and right-handed interactions, which enhances or suppresses certain regions near the endpoint of the beta spectrum. In this work, the sensitivity of KATRIN to right-handed currents is estimated for the scenario of a light sterile neutrino with a mass of some eV. This has been performed with a Bayesian analysis using Markov Chain Monte Carlo (MCMC). The simulations show that in principle KATRIN is able to set sterile neutrino mass-dependent limits on the interference strength. Thereby, the sensitivity is significantly increased if the $Q$ value of the $\beta$ decay can be sufficiently constrained. However, the sensitivity is not high enough to improve current upper limits from right-handed W boson searches at the LHC.