The bestiary of dark matter species

Abstract

Large amounts of invisible matter have been discovered back in 1933 when the Swiss astronomer Fritz Zwicky measured for the first time the velocity dispersion of individual galaxies inside the Coma cluster. Since then, this pioneering observation has been confirmed on scales ranging from galactic radii to cosmological distances. The existence of the so–called astronomical dark matter is now well established. The puzzle lies in the fact that this essential component of the universe is not made of ordinary atoms and electrons. The astronomical dark matter is indeed non–baryonic. Its nature is still an unresolved issue. Many theoretical ideas and proposals have flourished in the past thirty years and yet none of them provides a definite answer. I have the challenging task to introduce the cohort of these dark matter candidates to you. They make up a bestiary of exotic species which have been recently proliferating. Instead of a liste à la Prévert, I will present a tentative classification of the various models.