Searching for cold dark matter. A case of symbiosis of supersymmetry and nuclear physics

There is evidence that the most of the matter of the Universe is non-luminous. In fact it appears that most of this non-luminous matter is exotic in the sense that it is beyond that which is predicted by the standard model. To understand the large scale structure of the Universe, one needs the so called hot dark matter or HDM and the cold dark matter or CDM. If one goes beyond the standard model one has an obvious candidate for CDM, namely the neutrino, provided that is it massive, (in the few eV region). In the context of supersymmetric extensions of the standard model the most natural candidate for CDM is the lightest supersymmetric particle or LSP. The LSP is cosmologically stable due to R-parity conservation (+1 for ordinary matter and -1 for supersymmetric particles). It thus appears that the detection of the LSP is one of the crucial tests of both supersymmetry and cosmological models. Clearly, the direct detection of the LSP is the most desirable. Since, however, the LSP is extremely heavy with a mass heavier than 30 GeV and non-relativistic, with an average energy of less than 100 keV, it can only be directly detected by cryostatically measuring the recoiling nucleus following elastic scattering. A variety of nuclear targets are available for this purpose. Current fashionable supersymmetric models, in conjunction with understanding of the quark substructure of the nucleon and knowledge of the nuclear form factor and the spin response function of the nucleus, permit the evaluation of the event rate. By considering representative phenomenologically acceptable input in the restricted SUSY parameter space, detectable rates are predicted for some choices of the parameters. In most cases the obtained rates are very low. So it is imperative to try to exploit the modulation effect, i.e. the dependence of the event on the earth's annual motion. We find that even though the modulation amplitude is small, ≤ 4 %, there exist regions of the phase space where it can become sizable, reaching 20 %. (author)