Annu. Rev. Astron. Astrophys. 1994. 32: 531-590 Copyright © 1994 by Annual Reviews. All rights reserved

3. BARYONIC VS NONBARYONIC DARK MATTER

Candidates for the dark matter may be grouped into nonbaryonic and baryonic types. These will be referred to these as "Inos" and "Population III", respectively, and the candidates are listed explicitly in Table 1 in order of increasing mass. Some of the ino candidates are elementary particles and - depending on their mass - these are usefully classified as "hot" or "cold" since this affects their clustering properties. The term Weakly Interacting Massive Particle or WIMP is often used to describe these particles, though some people restrict this term to particles that are massive enough to be cold. The other inos are more exotic relics from the Big Bang and, for present purposes, primordial black holes are included in this category. [For a comprehensive review of the ino candidates, see Turner (1991).] Table 1 illustrates that there are many forms of nonluminous matter, so it is naive to assume that all the dark matter problems will have a single explanation. Even though some of the candidates in Table 1 can probably be rejected, many viable ones remain.

Table 1. Baryonic and nonbaryonic matter candidates

INOS		POPULATION III
Axions	(10-5 eV)	Snowballs	?
Neutrinos	(10 eV)	Brown dwarfs	(< 0.08 M)
Photinos	(1 GeV)	M-dwarfs	(0.1 M)
Monopoles	(1016 GeV)	White dwarfs	(1 M)
Planck relicts	(1019 GeV)	Neutron stars	(2 M)
Primordial holes	(> 1015 g)	Stellar holes	(~ 10 M)
Quark nuggets	(< 1020 g)	VMO holes	(102-105 M)
Shadow matter	?	SMO holes	(>105 M)