Title: Primordial magnetic fields from second-order cosmological perturbations:Tight coupling approximation

Abstract: We explore the possibility of generating large-scale magnetic fields from second-order cosmological perturbations during the pre-recombination era. The key process for this is Thomson scattering between the photons and the charged particles within the cosmic plasma. To tame the multi-component interacting fluid system, we employ the tight coupling approximation. It is shown that the source term for the magnetic field is given by the product of the first order perturbations and so the intrinsically second-order quantities do not contribute to magnetogenesis. The magnetic fields generated by this process are estimated to be \sim 10^{-26},Gauss on the horizon scale.