Potential weakly interacting massive particle signature for the caustic ring halo model

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Abstract
Weakly interacting massive particle (WIMP) direct detection event rate calculations usually rely on fairly simple, essentially static, analytic halo models. This is largely since the resolution of numerical simulations is not yet large enough to allow the full numerical calculation of the WIMP density and velocity distribution. In this paper we study the direct detection rate, in particular its energy dependence and annual modulation, for the caustic ring halo model. In this model, which uses simple assumptions to model the infall of dark matter onto the halo, the distribution of the cold dark matter particles at the Earth’s location has a series of peaks in velocity space. We find that the recoil energy spectrum contains distinctive steps and the sign of the annual modulation in the event rate changes as a function of recoil energy. These effects provide a potentially distinctive experimental signal.