ALPs and HNLs at LHC and Muon Colliders: Uncovering New Couplings and Signals

TL;DR

This paper explores new detection strategies for axion-like particles and heavy neutral leptons at the LHC and muon colliders, considering multiple HNLs and diverse processes to uncover their couplings and signals.

Contribution

It extends previous simplified models to include multiple HNLs and broader processes, enhancing the understanding of ALP and HNL phenomenology at future colliders.

Findings

Broader range of production processes analyzed at LHC and muon colliders.

Complex signals emerge with multiple HNLs, requiring detailed phenomenological study.

Potential for collider experiments to uncover ALP and HNL dynamics.

Abstract

Axion-like particles (ALPs) and heavy neutral leptons (HNLs) are two well-motivated classes of particles beyond the Standard Model. It is intriguing to explore the new detection opportunities that may arise if both particle types coexist. Part of the authors already investigated this scenario in a previous publication, within a simplified model containing an ALP and a single HNL, identifying particularly promising processes that could be searched for at the LHC. In this paper, we first consider the same setup with a broader range of both production processes and final states, both at the High-Luminosity LHC and at a future muon collider. Subsequently, we expand it to the more realistic scenario with at least two HNLs, necessary to describe the active neutrino masses. Different phenomenological signals are expected and we examine the complexities that emerge in this setup. This study paves the way for dedicated analysis at (forthcoming) colliders, potentially pinpointing the dynamics of ALPs and HNLs.