  We explore the possibility of light and superlight sterile neutrinos in the
recently proposed Minimal Radiative Inverse Seesaw extension of the Standard
Model for neutrino masses, in which all existing neutrino data can be
explained. In particular, we discuss two benchmark scenarios with one of the
three sterile neutrino states in the keV-range, having very small mixing with
the active neutrinos to account for the Dark Matter in the Universe, while (i)
the other two light sterile neutrino states could be in the eV-range,
possessing a nonzero mixing with the active states as required to explain the
LSND+MiniBooNE+reactor neutrino data, or (ii) one of the light sterile states
is in the eV-range, whereas the second one could be superlight and almost
mass-degenerate with the solar neutrinos. Such superlight sterile neutrinos
could give rise to potentially observable effects in future neutrino
oscillation experiments and may also offer a possible explanation for the extra
radiation observed in the Universe.
