On the divergences of inflationary superhorizon perturbations

Understand

We discuss the infrared divergences that appear to plague cosmological perturbation theory.

• We show that within the stochastic framework they are regulated by eternal inflation so that the theory predicts finite fluctuations.
• Using the $\Delta N$ formalism to one loop, we demonstrate that the infrared modes can be absorbed into additive constants and the coefficients of the diagrammatic expansion for the connected parts of two and three-point functions of the curvature perturbation.
• As a result, the use of any infrared cutoff below the scale of eternal inflation is permitted, provided that the background fields are appropriately redefined.