Searching for heavy sterile neutrinos in kaon decays

TL;DR

This paper investigates how heavy sterile neutrinos could affect kaon decays, providing new constraints on their properties and highlighting potential signals of physics beyond the Standard Model.

Contribution

It introduces a simplified model with heavy sterile neutrinos affecting kaon decays and derives new constraints from experimental data, emphasizing the decay $K_L ightarrow u u$ as a potential signature.

Findings

Heavy sterile neutrinos can cause large deviations in leptonic kaon decays.

Experimental measurements constrain the leptonic mixing of heavy sterile neutrinos.

Semileptonic decays show no significant tension with the Standard Model.

Abstract

We present here a study of the impact of a heavy neutrino (or heavy neutral lepton) on leptonic and semileptonic kaon decays. We used a simplified model consisting of 3 light neutrinos responsible for neutrino oscillations and a heavy sterile neutrino. We found that it can lead to large deviations from the Standard Model predictions for leptonic decays, in conflict with experimental measurements of $K_{e2}$ and the lepton universality test $R_K$. This allows to derive new constraints on the leptonic mixing for heavy sterile neutrinos. No tension was found when considering the semileptonic decays. Finally, we point out the potential of the decay $K_L \rightarrow \nu \nu$ as a clear signature of physics beyond the Standard Model.