Stochastic effective theory for scalar fields in de Sitter

by Arttu Rajantie (Imperial College London)

Wednesday Nov 19, 2025, 11:30 AM → 12:30 PM Europe/Zurich

4/2-011 - TH common room (CERN)

The dynamics of the Higgs and other light scalar fields during inflation can have important cosmological consequences, but because of the infrared problem, they cannot be computed using perturbation theory. A powerful alternative is the stochastic Starobinsky-Yokoyama approach, which is based on the observation that on superhorizon distances the field behaves classically, with a noise term produced by subhorizon quantum modes. It has been mostly used to calculate the one-point probability distribution of the field, but its real power lies in describing the asymptotic long-distance dynamics through a spectral expansion. I demonstrate this by calculating correlation functions and decay rates of metastable vacua. I use them to determine the parameters of the theory at one-loop order in perturbation theory, showing that they do not suffer from the same infrared problems as a direct perturbative computation of observables, and providing evidence that they are given by the constraint effective potential.