An open system approach to gravity and cosmology
Effective field theories in particle physics are usually formulated for clean, isolated systems. Many physical settings, however, from condensed matter to gravitating systems, involve noisy and dissipative environments. The Schwinger–Keldysh formalism provides a powerful framework to describe such non-equilibrium dynamics and has enabled important advances in black hole physics, dissipative hydrodynamics, non-equilibrium holography, and primordial cosmology. In the first part of this talk, we will introduce a framework for open gravitational dynamics that combines General Relativity with the Schwinger-Keldysh formalism. We will discuss how symmetries, locality, and unitarity constrain the allowed forms of dissipation and noise. In the second part, we will illustrate the framework by deriving the most general conservative and dissipative dynamics of scalar perturbations during single-clock inflation. We will present how dissipative effects imprint themselves on primordial non-Gaussianities and conclude with observational prospects using CMB and large-scale structure data.