Heavy Neutral Leptons Beyond Simplified Scenarios

TL;DR

This paper develops a method to reinterpret collider search limits for heavy neutral leptons (HNLs) without relying on common simplifying assumptions, allowing for more general models with multiple HNLs and complex mixing patterns.

Contribution

It introduces a straightforward approach to recast collider bounds for models with multiple HNLs and arbitrary mixing, extending beyond simplified scenarios.

Findings

Provides a recasting recipe for collider limits on HNLs.

Enables analysis of models with multiple HNLs and complex mixing.

Facilitates more accurate experimental constraints on HNL parameter space.

Abstract

Heavy neutral leptons (HNL) constitute the building blocks of several neutrino mass generation mechanisms. Experimental searches depend on their masses and mixings with the active neutrinos, and exclusion regions in the plane of mass and mixing rely most of the time on two assumptions: $(i)$ the existence of $one$ HNL, which $(ii)$ mixes dominantly with only $one$ lepton flavor. In this work we discuss how to reinterpret the limits from collider searches relaxing these assumptions, providing a simple recipe to recast the bounds in models with generic mixing patterns, and in which at least two HNLs are coupled to the active sector.