Baryogenesis from 'electrogenesis' in a scalar field dominated epoch

Scalar fields can play a dominant role in the dynamics of the Universe until shortly before nucleosynthesis. Examples are provided by domination by a kinetic mode of a scalar field, which may be both the inflaton and the late time 'quintessence', and also by more conventional models of reheating. The resultant modification to the pre-nucleosynthesis expansion rate can allow solely an asymmetry in right handed electrons to produce a net baryon asymmetry when reprocessed by the anomalous B+L violating processes of the standard model. The production of such a source asymmetry - what we term 'electrogenesis' - requires no additional B or L violation beyond that in the standard model. We consider a specific model for its generation, by a simple perturbative out-of-equilibrium decay of Higgs like scalar fields with CP-violating Yukawa couplings to the standard model leptons. We show that, because of the much enhanced expansion rate, such a mechanism can easily produce an adequate asymmetry from scalars with masses as low as 1TeV. Kinetic mode domination is strongly favoured because it evades large entropy release which dilutes the asymmetry. We also discuss briefly the effect of the abelian hypercharge anomaly. (author)