Sterile neutrino dark matter with dipole interaction
  We consider the possibility of the lightest sterile neutrino dark matter
which has dipole interaction with heavier sterile neutrinos. The lifetime can
be long enough to be a dark matter candidate without violating other
constraints and the correct amount of relic abundance can be produced in the
early Universe. We find that a sterile neutrino with the mass of around MeV and
the dimension-five non-renormalisable dipole interaction suppressed by
$\Lambda_5 \gtrsim 10^{15}$ GeV can be a good candidate of dark matter, while
heavier sterile neutrinos with masses of the order of GeV can explain the
active neutrino oscillations.
