Speaker
Description
Understanding stochastic inflation beyond the Gaussian approximation
remains an open problem. In this talk I present a framework in which it
emerges as the infrared limit of a controlled coarse-graining procedure.
First, I construct an open effective field theory for long-wavelength
modes from the reduced density matrix. Time locality follows from the
thin-shell expansion, while spatial locality emerges in the
super-Hubble regime. The resulting Schwinger--Keldysh EFT contains
dissipation and diffusion operators, with diffusion dominating in the
infrared, yielding the Fokker--Planck equation and systematic
corrections.
Second, I reinterpret coarse-graining as an RG flow for the density
matrix. Stochastic dynamics arises after taking the super-Hubble and
gradient-expansion limits. The flow obeys a Polchinski-type equation,
which generates the EFT structure and leads to a generalised
Fokker--Planck equation capturing subleading corrections.