The role of fluctuation-dissipation dynamics in setting initial conditions for inflation

TL;DR

This paper investigates how fluctuation-dissipation dynamics during a radiation epoch can set initial conditions for inflation, potentially leading to a second inflationary phase with low tensor-to-scalar ratio, consistent with observations.

Contribution

It introduces a mechanism where thermal fluctuations and dissipation can naturally localize the inflaton at the origin, enabling slow-roll inflation without spoiling potential flatness.

Findings

Homogeneous inflaton can be localized at the origin via strong interactions.

Thermal inflation can occur after the potential dominates, suppressing nonlinear effects.

A two-stage inflation scenario can prevent early universe overclosure and match observational data.

Abstract

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, in particular, 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. We further conclude that the inflaton can still be held at the origin after its potential begins to dominate the energy balance, leading to a period of thermal inflation. This then suppresses the effects of nonlinear interactions between the homogeneous and inhomogeneous field modes that could prevent the former from entering a slow-roll regime. Finally, we 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.