Tidal Disruption of the First Dark Microhalos

We point out that the usual self-similarity in cold dark matter models isbroken by encounters with individual normal galactic stars on sub-pc scale.Tidal heating and stripping must have redefined the density and velocitystructures of the population of the Earth-mass dark matter halos, which arelikely to have been the first bound structures to form in the Universe. Thedisruption rate depends strongly on {\it galaxy types} and the orbitaldistribution of the microhalos; in the Milky Way, stochastic radial orbits aredestroyed first by stars in the triaxial bulge, microhalos on non-planarretrograde orbits with large pericenters and/or apocenters survive the longest.The final microhalo distribution in the {\it solar neighborhood} is betterdescribed as a superposition of filamentry microstreams rather than as a set ofdiscrete spherical clumps in an otherwise homogeneous medium. We discuss itsimportant consequences to our detections of microhalos by direct recoil signaland indirect annihilation signal.Comment: 13 pages, 3 figures, Astrophysical Journal, accepte