Revisiting Magnetogenesis during Inflation
  We revisit the mechanism of primordial magnetogenesis during inflation by
taking into account the dynamics of the stochastic noises of the
electromagnetic perturbations. We obtain the associated Langevin and
Fokker-Planck equations for the electromagnetic fields and solve them
analytically. It is shown that while the backreactions of the electric field
energy density may spoil inflation too early, but there are regions of
parameter space where the usual decaying behavior of the magnetic fields are
replaced by a mean-reverting process of stochastic dynamics. As a result, the
magnetic fields settle down into an equilibrium state with the amplitude
significantly larger than what is obtained in the absence of the stochastic
noises. We show that magnetic fields with present time amplitude $\sim
10^{-13}$ Gauss and coherent length ${\rm Mpc}$ can be generated while the
backreactions of the electric field perturbations are under control.
