Weakly Interacting Massive Particles - Theoretical Arguments

Theoretical Arguments

Although the existence of WIMPs in nature is hypothetical at this point, it would resolve a number of astrophysical and cosmological problems related to dark matter. The main theoretical characteristics of a WIMP are:

• Interaction only through the weak nuclear force and gravity, or at least with interaction cross-sections no higher than the weak scale;
• Large mass compared to standard particles (WIMPs with sub-GeV masses may be considered to be light dark matter).

Because of their lack of interaction with normal matter, they would be dark and invisible through normal electromagnetic observations. Because of their large mass, they would be relatively slow moving and therefore cold. As a result they would tend to remain clumpy. Simulations of a universe full of cold dark matter produce galaxy distributions that are roughly similar to that which is observed. WIMPs are considered one of the main candidates for cold dark matter, the others being massive compact halo objects (MACHOs) and axions. (These names were deliberately chosen for contrast, with MACHOs named later than WIMPs.) Also, in contrast to MACHOs, there are no known stable particles within the standard model of particle physics that have all the properties of WIMPs. The particles that have little interaction with normal matter, such as neutrinos, are all very light, and hence would be fast moving or hot. Hot dark matter would smear out the large-scale structure of galaxies and thus is not considered a viable cosmological model. WIMP-like particles are predicted by R-parity-conserving supersymmetry, a popular type of extension to the standard model, although none of the large number of new particles in supersymmetry have been observed.