Influence of ~7 keV sterile neutrino dark matter on the process of
  reionization
  Recent reports of a weak unidentified emission line at ~3.5 keV found in
spectra of several matter-dominated objects may give a clue to resolve the
long-standing problem of dark matter. One of the best physically motivated
particle candidate able to produce such an extra line is sterile neutrino with
the mass of ~7 keV. Previous works show that sterile neutrino dark matter with
parameters consistent with the new line measurement modestly affects structure
formation compared to conventional cold dark matter scenario. In this work, we
concentrate for the first time on contribution of the sterile neutrino dark
matter able to produce the observed line at ~3.5 keV, to the process of
reionization. By incorporating dark matter power spectra for ~7 keV sterile
neutrinos into extended semi-analytical 'bubble' model of reionization we
obtain that such sterile neutrino dark matter would produce significantly
sharper reionization compared to widely used cold dark matter models,
impossible to 'imitate' within the cold dark matter scenario under any
reasonable choice of our model parameters, and would have a clear tendency of
lowering both the redshift of reionization and the electron scattering optical
depth (although the difference is still below the existing model
uncertainties). Further dedicated studies of reionization (such as 21 cm
measurements or studies of kinetic Sunyaev-Zeldovich effect) will thus be
essential for reconstruction of particle candidate responsible the ~3.5 keV
line.
