GALACTIC HALO MODELS AND PARTICLE DARK-MATTER DETECTION

Rates for detection of weakly interacting massive-particle (WIMP) dark matter are usually carried out assuming the Milky Way halo is an isot hermal sphere. However, it is possible that our halo is not precisely spherical; it may have some bulk rotation; and the radial profile may differ from that of an isothermal sphere. In this paper, we calculate detection rates in observationally consistent alternative halo models that produce the same halo contributions to the local and asymptotic r otation speeds to investigate the effects of the theoretical uncertain ty of the WIMP spatial and velocity distribution. We use self-consiste nt models to take into account the effects of various mass distributio ns on the local velocity distribution. The local halo density may be i ncreased up to a factor of 2 by flattening or by an alternative radial profile (which may also decrease the density slightly). However, chan ges in the WIMP velocity distribution in these models produce only neg ligible changes in the WIMP detection rate. Reasonable bulk rotations lead to only an O(10%) effect on event rates. We also show how the nuc lear recoil spectrum in a direct-detection experiment could provide in formation on the shape and rotation of the halo.