  We study the impact of the interaction between DM and the cosmic neutrino
background on the evolution of galactic dark matter halos. The energy transfer
from the neutrinos to the dark matter can heat the center of the galaxy and
make it cored. This effect is efficient for the small galaxies such as the
satellite galaxies of the Milky Way and we can put conservative constraint on
the non-relativistic elastic scattering cross section as
$\sigma_{\chi\nu}\lesssim 10^{-31} {\rm cm}^2$ for 0.1 keV dark matter and 0.1
eV neutrino.
