Search for bosonic superweakly interacting massive dark matter particles
  with the XMASS-I detector
  Bosonic superweakly interacting massive particles (super-WIMPs) are a
candidate for warm dark matter. With the absorption of such a boson by a xenon
atom these dark matter candidates would deposit an energy equivalent to their
rest mass in the detector. This is the first direct detection experiment
exploring the vector super-WIMPs in the mass range between 40 and 120 keV.
Using 165.9 days of data no significant excess above background was observed in
the fiducial mass of 41 kg. The present limit for the vector super-WIMPs
excludes the possibility that such particles constitute all of dark matter. The
absence of a signal also provides the most stringent direct constraint on the
coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented
sensitivity was achieved exploiting the low background at a level $10^{-4}$
kg$^{-1}$keV$_{ee}^{-1}$day$^{-1}$ in the detector.
