Searching for supersymmetric dark matter: The directional rate and the modulation effect due to caustic rings

Abstract

The detection of the theoretically expected dark matter is central to particle physics and cosmology. Current fashionable supersymmetric models provide a natural dark matter candidate, which is the lightest supersymmetric particle (LSP). The allowed parameter space of such models combined with fairly well understood physics (quark substructure of the nucleon and nuclear structure) permit the evaluation of the event rate for LSP-nucleus elastic scattering. The thus obtained event rates, which sensitively depend on the allowed parameter space parameters, are usually very low or even undetectable. So, for background reduction, one would like to exploit two nice features of the reaction: the directional rate, which depends on the Sun's direction of motion, and the modulation effect, i.e., the dependence of the event rate on the Earth's annual motion. In the present paper we study these phenomena in a specific class of nonisothermal models, which take into account the late in-fall of dark matter into our galaxy, producing flows of caustic rings. We find that the modulation effect arising from such models is smaller than that found previously with isothermal symmetric velocity distributions and much smaller compared to that obtained using a realistic asymmetric distribution with enhanced dispersion in the galactocentric direction. The directional rate shows a strong correlation with the Sun's direction of motion.