Gravitational EFT for dissipative open systems

We elaborate on the effective field theory (EFT) construction for dissipative open systems coupled to dynamical gravity, in light of recent developments on the EFT of dissipative hydrodynamics (HydroEFT). Our construction is based on the Schwinger-Keldysh formalism and its symmetries as well as microscopic unitarity. A key aspect of dynamical gravity is that gravity couples to all degrees of freedom universally, hence the EFT has to take into account the energy-momentum tensor of the environment to which the energy escapes from the dissipative system of interest. We incorporate this effect by modeling the environment based on HydroEFT, assuming validity of the derivative expansion of the environment sector. For illustration, we apply our EFT recipe to a dissipative scalar field coupled to dynamical gravity that can be used, e.g., for dissipative inflation. In particular we quantify impacts of fluctuations in the environment sector on the scalar dynamics. We also apply the same framework to dissipative gravity, discussing dissipative gravitational waves and the generalized second law of black hole thermodynamics.