Recent Progress in Baryogenesis

I give a synopsis, specifically aimed at nonexperts, of some of the recent developments in electroweak baryogenesis. The focus of the talk is on the present status of electroweak baryogenesis in supersymmetric models, since this is a plausible and realistic possibility that is currently being probed by experimental searches for the Higgs boson and the top squark. The question of whether it is viable to have a period of color-breaking during the electroweak phase transition is also discussed. McGill/99-02 BARYON ASYMMETRY OF THE UNIVERSE: REVIEW The baryons within the observed universe appear to consist essentially only of matter and not antimatter. There are no regions of gamma ray emission which would correspond to the collision between a galaxy made of normal matter with one made from antimatter, for instance. Moreover, the theory of Big Bang nucleosythesis gives predictions for the abundances of primordial helium (both He and He), deuterium and lithium, if the ratio of baryons to photons in the universe is in the range 2 < ∼ η10 < ∼ 6; η10 ≡ nB nγ × 10 . If we do live in a universe with equal quantities of matter and antimatter, then the two must somehow be separated on distance scales greater than the present Hubble length, that is, the size of the presently observable universe. The simplest assumption is that indeed the whole universe has the same preponderance of matter over antimatter. It is a deep mystery of cosmology why the abundance of baryons should be this peculiar number, 10, relative to the number of photons. The mystery is intensified by the fact that the most natural initial condition of the universe, at the time of the big bang or shortly thereafter, is to have equal numbers of baryons and antibaryons,