Gravitational diffusion of solar system WIMPs

It is shown here that, because of purely gravitational diffusion, the most important solar-bound weakly interacting massive particles (WIMPs) are populated at the same phase-space density as low-velocity unbound orbits. This diffusion occurs on time scales short compared both to the lifetime of the earth and to weak-interaction depletion. The effect is that direct capture from bound and unbound orbits together is very nearly equal to direct capture by the earth considered as a body in free space. The same gravitational diffusion virtually eliminates indirect capture. The net result is that 'free-space' formulas for capture reported in a previous paper may be used without modification despite the fact that the earth is bound in the potential well of the sun.