Magnetic field production during preheating at the electroweak scale.

We study the generation of magnetic fields during preheating within a scenario of hybrid inflation at the electroweak scale. We find that the nonperturbative and strongly out-of-equilibrium process of generation of magnetic fields with a nontrivial helicity occurs along the lines predicted by Vachaspati many years ago. The magnitude (rho_{B}/rho_{EW} approximately 10{-2}) and correlation length of these helical magnetic fields grow linearly with time during preheating and are consistent with the possibility that these seeds gave rise to the microgauss fields observed today in galaxies and clusters of galaxies.