A potential WIMP signature for the caustic ring halo model

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 not yet being 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 sign of the annual modulation in the event rate changes as a function of recoil energy, providing a potentially distinctive experimental signal. We then compare the theoretical predictions of this models with the experimental signal found by the DAMA experiment. We find that the DAMA data allow less than $\sim 30%$ of the local halo density to be in the form of velocity flows.