Alfven modes driven nonlinearly by metric perturbations in Anisotropic Magnetized Cosmologies

Abstract

We consider anisotropic magnetized cosmologies filled with conductive plasma fluid and study the implications of metric perturbations that propagate parallel to the ambient magnetic field. It is known that in the first-order (linear) approximation with respect to the amplitude of the perturbations no electric field and density perturbations arise. However when we consider the nonlinear coupling of the metric perturbations with their temporal derivatives, certain classes of solutions can induce steeply increasing in time, electric field perturbations. This is verified both numerically and analytically. The source of these perturbations can be either high-frequency quantum vacuum fluctuations, driven by the cosmological pump field, in the early stages of the evolution of the Universe, or astrophysical processes, or a nonlinear isotropization process, of an initially anisotropic cosmological space–time.