M. Ajello et al., Search for Spectral Irregularities due to Photon–Axionlike-Particle Oscillations with the Fermi Large Area Telescope, Phys. Rev. Lett. 116, 161101 (2016), DOI:https://doi.org/10.1103/PhysRevLett.116.161101
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We report on the search for spectral irregularities induced by oscillations between photons and axionlike-particles (ALPs) in the
γ-ray spectrum of NGC 1275, the central galaxy of the Perseus cluster. Using 6 years of Fermi Large Area Telescope data, we find no evidence for ALPs and exclude couplings above 5×10⁻¹² GeV⁻¹ for ALP masses 0.5≲ma≲5 neV at 95% confidence. The limits are competitive with the sensitivity of planned laboratory experiments, and, together with other bounds, strongly constrain the possibility that ALPs can reduce the γ-ray opacity of the Universe.
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