© CAMBRIDGE UNIVERSITY PRESS 1999

1.5.2 Cold Dark Matter Candidates

The two sorts of particle candidates for cold dark matter that are best motivated remain supersymmetric Weakly Interacting Massive Particles (WIMPs) and the axion. They are both well motivated because both supersymmetry and Peccei-Quinn symmetry (associated with the axion) are key ideas in modern particle physics that were proposed independently of their implications for dark matter (for a review emphasizing direct and indirect methods of detecting both of these, see Primack, Seckel, & Sadoulet 1988). There are many other dark matter candidates whose motivations are more ad hoc (see Table 1.3) from the viewpoint of particle physics. But there is observational evidence that Massive Compact Halo Objects (MACHOs) may comprise a substantial part of the mass of the Milky Way's dark matter halo.