Electroweak strings produce baryons.

We propose a new mechanism to generate baryons. Electroweak strings produced at the electroweak phase transition will introduce anomalous currents through interactions of the strings with the background electromagnetic field and through changes in the helicity of the string network. These anomalous currents will produce fluctuations in the baryon and lepton number. We show that in the two-Higgs model corrections to the action coming from the effective potential introduce a bias in the baryon asymmetry that leads to a net baryon number production. One implication of the standard hot big bang cosmology is that from the relics of the early universe we should in principle expect the universe to contain the same abundance of baryons and antibaryons. However there is compelling empirical evidence that suggests the universe is made out of matter with a relatively small amount of antimatter. From the present asymmetry we can extrapolate that at the energy scale of the electroweak phase transition there was one part in 108 more matter than antimatter in the universe. The goal of baryogenesis is to explain this asymmetry between the amount of matter and antimatter. Sakharov [1] realized that there are three necessary conditions for any baryogenesis mechanism. First we need the existence of interactions that violate baryon number. The second condition is that the theory in consideration biases processes that violate baryon number towards the production of a net baryon number. This requires interactions that break the symmetries of charge conjugation (C) and the product of charge conjugation and parity (CP ). Finally the interactions have to be in the presence of processes that are out of thermal equilibrium. Recently it has been suggested that baryogenesis takes place at the electroweak phase transition (for a review see Refs.2,3and 4). The three main ingredients of this picture are: First, in the electroweak model we know that in the field configuration space the sphaleron [5] is the saddle point configuration connecting two different minima. These minima correspond to vacuum configurations with different baryon numbers. Transitions among the minima will change the baryon number. Second, in order to produce a net baryon number asymmetry the electroweak interactions must violate C and CP . Extensions of the Minimal Standard Model (MSM) are required because the MSM violates C and CP in amounts too small to explain the baryon to antibaryon asymmetry. Finally if the phase transition is first order, the bubbles produced will nucleate and expand. Near the expanding bubbles we shall have processes that depart from thermal equilibrium.