Introduction

The study of the interactions of elementary particles at high-energy accelerators over the past 40 years has led us to a paradoxical situation. On one hand, these studies have apparently solved the problem of the nature of the strong and weak nuclear interactions. The precision data from LEP, SLC, the Tevatron and the B-factories has confirmed the leading theory of the strong interactions – QCD – to per cent accuracy and the leading theory of the electroweak interactions SU(2) × U(1) Yang–Mills theory to the accuracy of parts per mil. On the other hand, there are important phenomena in Nature that are completely outside the scope of this ‘Standard Model’. Dark matter, which makes up 80% of the matter in the Universe and cannot be composed of any Standard Model particle, provides the most striking example.

Most of the information that we have now on dark matter relates to the properties we can learn from gravitational measurements. We know the overall cosmic density of dark matter, and the local density of dark matter on the scale of galaxies and clusters. Soon we can hope to have measurements of dark matter at the particle level, of the rates of dark matter annihilation in the Galaxy and of dark matter scattering in underground detectors. To learn what the dark matter particle is and how it fits into a more general theory of Nature, it will be important to interpret these measurements in terms of data obtained from particle physics experiments.