Magnetogenesis from an anisotropic universe

The existence of large-scale anisotropy cannot be ruled out by the cosmic microwave background (CMB) radiation. Over the years, several models have been proposed in the context of anisotropic inflation to account for the CMB's cold spot and hemispheric asymmetry. However, any small-scale anisotropy, if it exists during inflation, is not constrained, due to its nonlinear evolution in the subsequent phase. This small-scale anisotropy during inflation can play a nontrivial role in giving rise to the cosmic magnetic field, which is the subject of our present study. Assuming a particular phenomenological form of an anisotropic inflationary universe, we have shown that it can generate a large-scale magnetic field at the 1 Mpc scale with a magnitude 410^-20 G, within the observed bound. Because of the anisotropy, the conformal flatness property is lost, and the Maxwell field is generated even without explicit coupling. This immediately resolves the strong coupling problem in the standard magnetogenesis scenario. In addition, assuming very low conductivity during the reheating era, we can further observe the evolution of the electromagnetic field with the equation of state ₄₅₅ and its effects on the present-day magnetic field.