Axino dark matter in light of an anomalous X-ray line

Abstract

Axino as the superpartner of axion that solves the strong CP problem can be a good candidate of dark matter. Inspired by the 3.5 keV X-ray line signal found to be originated from galaxy clusters and Andromeda galaxy, we study axino models with R-parity violations, and point out that axino dark matter with trilinear R-parity violations is an attractive scenario that reproduces the X-ray line. The Peccei-Quinn scale is required to be $f_a\sim \mathcal{O}(10^9-10^{11})$ GeV for trilinear R-parity violating couplings $\lambda \sim \mathcal{O}(10^{-3}-10^{-1})$ in order to explain the line signal. Moreover, the right-handed stau is predicted to be light, i.e. $\sim \mathcal{O}(100)$ GeV, and thus can be looked for at the LHC. Cosmological aspects of the model are also discussed in this study.

Comments: 13 pages, 1 figure. Added discussions, including the BICEP2 result. Published version