There is broad class of particle physics candidates for the dark matter that are referred to as Weakly Interacting Massive Particles or WIMPs. This class includes several proposed particles (massive Dirac neutrinos, cosmions, SUSY relics) that have masses of order a few GeV to a few hundred GeV and interact through the exchange of W's, Z's, higgs bosons and other intermediaries. In this talk, I will give a brief introduction to WIMPs. I refer interested readers to recent, more detailed reviews [61,50,37].
The early universe is a wonderful particle accelerator.
WIMPs could be produced through reactions such as
, where X denotes
the WIMP particle. WIMPs, of course, can be
annihilated through the backreaction,
.
As long
as 
, the WIMP number density would
be comparable to the number density of
electrons, positrons, and photons. However,
once the temperature drops below 
, the WIMP
abundance begins to drop. It will fall until
the WIMP number density is so low that
the WIMP mean free time for annihilation exceeds
the age of the universe. This ``freeze-out'' occurs
at a density determined by the WIMP annihilation cross-section
and implies that
The first proposed WIMP candidates were heavy fourth
generation neutrinos [36,41].
If the neutrino mass was of order 2 GeV, then
its relic abundance would be sufficient for 
.
Experimental dark matter searches [1] ruled
out these particles as dark matter candidates.
Supersymmetry is an elegant extension of the standard model of particle physics. It is the only so-far ``unused'' symmetry of the Poincare group and has the virtue of protecting the weak scale against radiative corrections from GUT and Planck scale. Local supersymmetry appears to be an attractive route towards unifying all four forces and is a basic ingredient in superstring theory. Supersymmetry transforms bosons into fermions (and vice-versa). As supersymmetry has a new symmetry, R parity, it can imply the existence of a new stable particle. In much of the parameter space of the minimal supersymmetric model, this new stable particle (which we will refer to as the``neutralino'') has predicted properties such that it would comprise much of the density of the universe [25].