Sphalerons and electroweak baryogenesis

Abstract

It is well known that baryon (lepton) number is not conserved in the standard electroweak theory due to the anomaly. As a consequence, the electroweak phase transition provides plausible ground for producing the baryon number asymmetry of the universe, besides erasing any prexisting asymmetry. This occurs via processes which surmount the instanton potential barrier. The barrier is given by the static saddle point solution of the electroweak theory, called the sphaleron, which we shall briefly expose. This is followed by a pedagogical account of how the asymmetry can be created during the electroweak phase transition including the pitfalls that await the innocent practitioner.