BARYOGENESIS AT THE ELECTROWEAK SCALE

We explore some issues involved in generating the baryon asymmetry at the electroweak scale. A simple two-dimensional model is analyzed which illustrates the role of the effective action in computing the asymmetry. We stress the fact that baryon production ceases at a very small value of the Higgs field; as a result, certain two-Higgs models which have been studied recently cannot produce sufficient asymmetry, while quite generally models with only doublets can barely produce the observed baryon density; models with gauge singlets are more promising. We also review limits on Higgs masses coming from the requirement that the baryon asymmetry not be wiped out after the phase transition. We note that there are a variety of uncertainties in these calculations, and that even in models with a single Higgs doublet one cannot rule out a Higgs mass below 55 GeV.