  We discuss the issue on dark matter capture by neutron stars, in particular
the process of dark matter thermalization, by which the scattering cross
section and the mass of dark matter can be constrained. At first, we evaluate
the thermalization time of self-interacting dark matter and find the effect of
the self-interaction is small compared with that of the interaction with
nucleons. Then we generalize the thermalization time by introducing a set of
new parameters. We show how the cross section is affected by those new
parameters. It turns out that the cross section gets very sensitive to and
strongly constrained by one of the new parameters.
