Preheating - cosmic magnetic dynamo? art. no. 103515

We study the amplification of large-scale magnetic fields during preheating and inflation in several different models. Preheating can resonantly ampli fy seed fields on cosmological scales. In the presence of conductivity, how ever, the effect of resonance is typically weakened and the amplitude of pr oduced magnetic fields depends sensitively on the evolution of conductivity during the preheating and thermalization phases. In addition we discuss ge ometric magnetization, where amplification of magnetic fields occurs throug h coupling to curvature invariants. This can be efficient during inflation due to a negative coupling instability. Finally we discuss the breaking of the conformal flatness of the background metric whereby magnetic fields can be stimulated through the growth of scalar metric perturbations during met ric preheating.