Inflationary background renormalization

Abstract

In cosmic inflation, non-linearities of the curvature perturbation can induce backreaction to the background. To obtain observational predictions at non-linear order on the correct background, one has to redefine the background or introduce background renormalization. We explicitly demonstrate it with a vanishing one-point function of the curvature perturbation as a renormalization condition, so that proper observational predictions can be made even at the nonlinear level. Due to non-linear symmetry of the curvature perturbation, such a procedure induces corrections to the two-point functions, which yield a finite renormalized one-loop correction that depends on the regularization scheme. Cancellation of the divergence is a manifestation of Maldacena's consistency condition. The finite term can be large and highly time-dependent, which indicates evolution outside the horizon.