Abstract
The extragalactic background light is comprised of the cumulative radiation from all galaxies across the history of the universe. The angular power spectrum of the anisotropies of such a background at near-infrared (IR) frequencies lacks of a complete understanding and shows a robust excess which cannot be easily explained with known sources. Dark matter in the form of axion-like particles (ALPs) with a mass around the electronvolt will decay into two photons with wavelengths in the near-IR band, possibly contributing to the background intensity. We compute the near-IR background angular power spectrum including emissions from galaxies, as well as the contributions from the intra-halo light and ALP decay, and compare it to measurements from the Hubble Space Telescope and Spitzer. We find that the preferred values for the ALP mass and ALP-photon coupling to explain the excess are in tension with star cooling data and observations of dwarf spheroidal galaxies.
Highlights
The cosmological and astrophysical evidence for the presence of non-baryonic matter, the dark matter, is overwhelming
As already anticipated, we fit them in each band before running the Markov Chain Monte Carlo (MCMC) for two reasons: first, this should not interfere with the actual fitting procedure, given that the contributions from axionlike particles (ALPs) and the IntraHalo Light (IHL) are relevant at much larger angular scales; second, given the complexity of each term, we found numerically much more convenient to first fit the shot noise in order to determine a conservative limiting magnitude that specifies the emission from low-z galaxies
From the analysis of the previous section, we find that the combination of IHL and ALP decay partially explains the excess in the Hubble Space Telescope (HST) and Spitzer data, but the combined fit is not good, as one can see from the χ2
Summary
The cosmological and astrophysical evidence for the presence of non-baryonic matter, the dark matter, is overwhelming. Appealing dark matter candidates are those which can help to solve other puzzles of the Standard Model (SM) of particle physics. A aγγ where ma is the axion mass and gaγγ its effective coupling to photons. Many extensions of the Standard Model, e.g string theory, predict light particles which share the same coupling to photons of the QCD axion, but that might not be related to the strong CP problem, and for which ma and gaγγ are independent parameters. These are referred to as axionlike particles (ALPs). Depending on the ALP mass various searches of this decay have been proposed, ranging from radio to optical and X-ray frequencies [10–24]
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