Notes on a non-thermal fluctuation-dissipation relation in quantum Brownian motion

We review how unitarity and stationarity in the Schwinger-Keldysh formalism naturally lead to a (quantum) generalized fluctuation-dissipation relation (gFDR) that works beyond thermal equilibrium. Non-Gaussian loop corrections are also presented. Additionally, we illustrate the application of this gFDR in various scenarios related to quantum Brownian motion and the generalized Langevin equation.