# Heavy neutral leptons and high-intensity observables

## TL;DR

This paper reviews how adding sterile fermions to the Standard Model can impact high-intensity observables like lepton flavor violation and electric dipole moments, highlighting the importance of combined experimental efforts.

## Contribution

It provides a comprehensive overview of the potential signals of sterile neutrinos in high-intensity experiments and discusses the synergy between different observables for new physics discovery.

## Key findings

- Sterile neutrinos can significantly affect charged lepton flavor violation.
- Correlations between observables enhance the discovery potential.
- Current and future experiments can probe relevant parameter spaces.

## Abstract

New Physics models in which the Standard Model particle content is enlarged via the addition of sterile fermions remain among the most minimal and yet most appealing constructions, particularly since these states are present as building blocks of numerous mechanisms of neutrino mass generation. Should the new sterile states have non-negligible mixings to the active (light) neutrinos, and if they are not excessively heavy, one expects important contributions to numerous high-intensity observables, among them charged lepton flavour violating muon decays and transitions, and lepton electric dipole moments. We briefly review the prospects of these minimal SM extensions to several of the latter observables, considering both simple extensions and complete models of neutrino mass generation. We emphasise the existing synergy between different observables at the Intensity Frontier, which will be crucial in unveiling the new model at work.