Constraints on axion-like particles with H.E.S.S. from observations of PKS 2155-304

TL;DR

This paper uses H.E.S.S. gamma-ray observations of PKS 2155-304 to set the first astrophysical constraints on axion-like particles, limiting their coupling strength to photons based on spectral irregularities.

Contribution

It provides the first astrophysical constraints on axion-like particles using gamma-ray data, extending the search for these particles beyond laboratory experiments.

Findings

Established upper limits on axion-like particle-photon coupling strength.

First astrophysical exclusion regions for axion-like particles from gamma-ray observations.

Constraints apply to both pseudo-scalar and scalar bosons.

Abstract

Axion-like particles are hypothetical new light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of axion-like particles can modify the energy spectrum of the gamma rays. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac PKS 2155-304 are used to derive conservative upper limits on the strength of the axion-like particle coupling to photons. This study gives rise to the first exclusions on axion-like particles from gamma-ray astronomy. The derived constraints apply to both light pseudo-scalar and scalar bosons that couple to the electromagnetic field.