Particle Physicists' Candidates for Dark Matter

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 320; no. 1556; p. 475
• Main Author: J. R. Ellis
• Format: Journal Article
• Language: English
• Published: The Royal Society 17.12.1986
• ISSN: 1364-503X; 1471-2962
• DOI: 10.1098/rsta.1986.0130

A review is presented of the candidates for dark matter that arise in different particle theories. These include massive neutrinos and monopoles in grand unified theories, axions arising from attempts to explain CP conservation in the strong interactions, stable supersymmetric particles such as photinos, gravitinos or sneutrinos, and other possible stable relics from the Big Bang. Wherever possible, relations to laboratory information and possible experiments directly sensitive to the different dark-matter candidates are discussed. There is clearly no shortage of particle candidates for dark matter, but no consensus as to which is the most plausible. Most of them would provide cold dark matter. There is no good reason why most of the candidates should have a density close to the closure density, but supersymmetric relics are an exception. The general feature that their individual masses are not greatly different from those of baryons, unlike, say, plancktons or polonyions, gives one reason to hope that perhaps $\rho _{\tilde{\gamma}}\approx \rho _{\text{baryons}}$, and hence that the supersymmetric relic density may not be much less than the closure density. Indeed, we have seen that $\rho _{\tilde{\gamma}}\gtrsim $ O(10$^{-2}$)$\rho _{\text{c}}$ in a class of minimal supergravity models. Moreover, supersymmetric relics are theoretically well motivated, and relatively easy to detect. Supersymmetric particles should also be accessible to accelerator searches in general. Thus they offer the best prospects for rapid experimental progress on dark matter. The time is approaching when the study of dark matter should evolve from a province of theory and astrophysics to become an experimental subject.