X-ray line signal from decaying axino warm dark matter
  We consider axino warm dark matter in a supersymmetric axion model with R-parity violation. In this scenario, axino with the mass $m_\axino\simeq 7$ keV can decay into photon and neutrino resulting in the X-ray line signal at $3.5$ keV, which might be the origin of unidentified X-ray emissions from galaxy clusters and Andromeda galaxy detected by the XMM-Newton X-ray observatory. 
Ki-Young Choi and Osamu Seto
hep-ph astro-ph.HE