Abstract
Axion-like particles (ALPs), predicted in theories beyond the Standard Model, can have observational effects on the transparency of the Universe to γ rays in the presence of magnetic fields. In this work, we search for effects compatible with the existence of ALPs with 80 months of data from the Fermi Large Area Telescope, by comparing the distributions of observed highest energy photons from sources beyond redshifts of z ⩾ 0.1 with theoretical predictions in the presence of ALPs. We find no evidence for an increased γ-ray transparency due to ALPs and therefore we set limits on the ALPs parameters assuming a value of the intergalactic magnetic field strength of 1 nG. Photon-ALP couplings above 10−11 GeV−1 are excluded for ALP masses ma ≲ 3.0 neV . As the allowed magnetic field parameter space is large, we also test lower magnetic field strengths and no constraints can be set for B⩽0.1 nG below the CAST limit. These constraints exclude a region of the parameter space not covered by other γ-ray telescopes and are compatible with limits imposed by other experiments.
Highlights
Axion-like particles (ALPs), predicted in theories beyond the Standard Model, can have observational effects on the transparency of the Universe to γ rays in the presence of magnetic fields
We search for effects compatible with the existence of ALPs with 80 months of data from the Fermi Large Area Telescope, by comparing the distributions of observed highest energy photons from sources beyond redshifts of z ≥ 0.1 with theoretical predictions in the presence of ALPs
We find no evidence for an increased γ-ray transparency due to ALPs and we set limits on the ALPs parameters assuming a value of the intergalactic magnetic field strength of 1 nG
Summary
The EBL is the accumulated radiation in the Universe from the infrared to the ultraviolet wavelengths This background radiation has its roots in stars formation processes, AGN and the starlight re-processed by dust in galaxies [15, 16, 33]. The survival probability, or attenuation factor, is described by a decreasing exponential law, Pγγ = exp [−τ (E, z)] It depends on the optical depth parameter τ (E, z), which is an increasing function of the photon energy and the distance to the source. If there were modifications of the canonical γ-ray propagation, the observed HEP event for each source should change correspondingly. This is what we use in order to search for ALPs effects
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