Towards Testing Sterile Neutrino Dark Matter with
  Spectrum-Roentgen-Gamma Mission
  We investigate the prospects of the SRG mission in searches for the keV-scale
mass sterile neutrino dark matter radiatively decaying into active neutrino and
photon. The ongoing all-sky X-ray survey of the SRG space observatory with data
acquired by the ART-XC and eROSITA telescopes can provide a possibility to
fully explore the resonant production mechanism of the dark matter sterile
neutrino, which exploits the lepton asymmetry in the primordial plasma
consistent with cosmological limits from the Big Bang Nucleosynthesis. In
particular, it is shown that at the end of the four year all-sky survey, the
sensitivity of the eROSITA telescope near the 3.5 keV line signal reported
earlier can be comparable to that of the XMM-Newton with all collected data,
which will allow one to carry out another independent study of the possible
sterile neutrino decay signal in this area. In the energy range below
$\approx2.4$ keV, the expected constraints on the model parameters can be
significantly stronger than those obtained with XMM-Newton. From the ART-XC
data, in the energy range approximately from 5 to 20 keV, it can be possible to
get more stringent constraints than those obtained with NuSTAR so far. We
conclude that the SRG mission has a very high potential in testing the sterile
neutrino dark matter hypothesis.
