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

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 mu m, which is similar to 4 sigma 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 HSTexcludes 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 strongly disfavored 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.

Automated summary

The recent observation of anomalous flux in the cosmic optical background suggests the possibility of dark matter decaying into photons, although the measurements from the Hubble Space Telescope have contradicted this theory.