Initial conditions for inflation: the role of fluctuation-dissipation dynamics

We study the problem of initial conditions for slow-roll inflation along a plateau-like scalar potential within the framework of fluctuation-dissipation dynamics. We consider that inflation was preceded by a radiation-dominated epoch where the inflaton is coupled to light degrees of freedom and may reach a near-equilibrium state. We show that the homogeneous field component can be sufficiently localized at the origin to trigger a period of slow-roll if the interactions between the inflaton and the thermal degrees of freedom are sufficiently strong and argue that this does not necessarily spoil the flatness of the potential at the quantum level. Previous to slow-roll inflation, there will be a period of thermal inflation which then suppresses the effects of nonlinear interactions between the homogeneous and inhomogeneous field modes. We also discuss the possibility of an early period of chaotic inflation, at large field values, followed by a first stage of reheating and subsequently by a second inflationary epoch along the plateau about the origin. This scenario could prevent an early overclosure of the Universe, at the same time yielding a low tensor-to-scalar ratio in agreement with observations.