Annual Modulation of Dark Matter in the Presence of Streams

In addition to a smooth component of Weakly Interaction Massive Particle (WIMP) dark matter in galaxies, there may be streams of material; the effects of WIMP streams on direct detection experiments is examined in this paper. The contribution to the count rate due to the stream cuts off at some characteristic energy. Near this cutoff energy, the stream contribution to the annual modulation of recoils in the detector is comparable to that of the thermalized halo, even if the stream represents only a small portion (∼5% or less) of the local halo density. Consequently the total modulation may be quite different than would be expected for the standard halo model alone: it may not be cosine-like and can peak at a different date than expected. The annual modulation of this cutoff energy together with the annual modulation of the overall signal provide a “smoking gun” for WIMP detection.