Anisotropic cosmic optical background bound for decaying dark matter in light of the LORRI anomaly

Abstract

Recently anomalous flux in the cosmic optical background (COB) is reported by the New Horizon observations. The COB flux is 16.37 ± 1.47 nWm −2 sr −1 , at the LORRI pivot wavelength of 0.608 µm, which is ∼ 4σ level above the expected flux from the Hubble Space Telescope (HST) galaxy count. It would be great if this were a hint for the eV scale dark matter decaying into photons. In this paper, we point out that such a decaying dark matter model predicts a substantial amount of anisotropy in the COB flux, which is accurately measured by the HST. The data of the HST excludes the decay rate of the dominant cold dark matter larger than 10 −24 -10 −23 s −1 in the mass range of 5-20 eV. As a result, the decaying cold dark matter explaining the COB excess is excluded by the anisotropy bound. We discuss some loopholes: e.g. warm/hot dark matter or two-step decay of the dark matter to explain the COB excess.

Advancing globular cluster constraints on the axion-photon coupling

“…We have adapted the limits from [9]. This includes constraints from the CERN Axion Solar Telescope (CAST) [10], dark matter haloscopes , cosmology [36] and a variety of astrophysical analyses, the most restrictive of which come from magnetic white dwarf polarisations [37] and X-rays [38], neutron stars [39][40][41], the R-parameter of globular clusters [42], the MUSE [43] and VIMOS [44] spectroscopes and the Hubble Space Telescope [45]. The region of the ALP plane inhabited by the (QCD) axion is indicated by the yellow/orange line, the width of which originates from different ultra-violet completions.…”