The Photophobic ALP

TL;DR

This paper investigates photophobic axion-like particles (ALPs) with suppressed photon couplings, highlighting their natural UV origin, unique collider signatures, and the current experimental constraints affecting related relaxion models.

Contribution

It introduces the concept of naturally occurring photophobic ALPs, analyzes their phenomenology, and discusses their experimental signatures and constraints, especially in collider experiments.

Findings

Photophobic ALPs have suppressed photon couplings due to their UV properties.

Collider signatures of photophobic ALPs differ significantly from typical ALPs.

Existing bounds on photophobic ALPs are generally weaker than those on standard ALPs.

Abstract

We explore models and phenomenology of a photophobic axion-like particle (ALP), an axion whose coupling to photons is maximally suppressed without fine-tuning of the underlying parameters. We demonstrate that photophobia can be a natural UV property of ALP models and determine the irreducible coupling of photophobic ALPs to photons induced by violations of the axion shift symmetry. The signatures of photophobic axions are radically different from those of typical ALPs and are of particular interest for collider-based experiments, for which Standard Model triboson measurements provide a significant probe at higher masses. A variety of terrestrial and astrophysical measurements constrain the parameter space of photophobic ALPs, though bounds are typically much weaker compared to typical ALPs. We discuss implications for particle production relaxion models based on photophobic ALPs, finding that they are in mild tension with existing experimental constraints.