1. E. Bulbul et al., Detection of an unidentified emission line in the stacked X-ray spectrum of galaxy clusters, Astrophys. J. 789 (2014) 13 [arXiv:1402.2301] [INSPIRE].
2. A. Boyarsky, O. Ruchayskiy, D. Iakubovskyi and J. Franse, An unidentified line in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster, arXiv:1402.4119 [INSPIRE].
3. S. Chakraborty, D.K. Ghosh and S. Roy, 7 keV sterile neutrino dark matter in U(1) R − lepton number model, arXiv:1405.6967 [INSPIRE].
4. K. Nakayama, F. Takahashi and T.T. Yanagida, Extra light fermions in E 6 -inspired models and the 3.5 keV X-ray line signal, Phys. Lett. B 737 (2014) 311 [arXiv:1405.4670] [INSPIRE].
5. S. Baek, P. Ko and W.-I. Park, The 3.5 keV X-ray line signature from annihilating and decaying dark matter in Weinberg model, arXiv:1405.3730 [INSPIRE].