Self-Interacting Dark Matter from Gravitational Scattering
  I show that gravitational scattering of dark-matter objects of 10^4 solar
masses and speeds of 10 km/s, provides the cross-section per unit mass required
in self-interacting dark matter models that alleviate the small-scale structure
challenges to the collisionless cold dark matter model. For primordial objects
of mass 10^4*(M_4) solar masses, moving at the velocity dispersion
characteristic of dwarf galaxies, 10*(v_1) km/s, the cross-section per unit
mass for gravitational scattering is 10*[M_4/(v_1)^4] cm^2/g. The steep decline
in interaction with increasing velocity explains why self-interaction is not
evident in data on massive galaxies and clusters of galaxies.
