Inflation's quantum randomness gets a rigorous field theory framework

Early-universe inflation produces quantum fluctuations that seed all cosmic structure, but describing their randomness rigorously has been ad hoc. This paper constructs a proper effective field theory for the long-wavelength modes of inflation treated as an open quantum system, revealing that alongside the usual Wilsonian flow there is a distinct 'stochastic' renormalization flow with no ordinary counterpart. The result is a systematic matching procedure that derives Fokker-Planck and Klein-Kramers equations — the workhorses of stochastic inflation — from first principles, including non-Gaussian and non-Markovian corrections.