Adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm inflation

TL;DR

This paper demonstrates that in warm inflation, particle densities evolve adiabatically out of equilibrium, enabling baryogenesis with minimal isocurvature perturbations, and explores broader applications of such states.

Contribution

It introduces a framework for adiabatic out-of-equilibrium solutions to the Boltzmann equation in warm inflation, with an explicit baryogenesis mechanism and potential for other applications.

Findings

Particle number density is suppressed but retains an approximate equilibrium form.

Baryogenesis during warm inflation produces small, correlated isocurvature perturbations.

The approach offers new insights into out-of-equilibrium dynamics in cosmology.

Abstract

We show that, in warm inflation, the nearly constant Hubble rate and temperature lead to an adiabatic evolution of the number density of particles interacting with the thermal bath, even if thermal equilibrium cannot be maintained. In this case, the number density is suppressed compared to the equilibrium value but the associated phase-space distribution retains approximately an equilibrium form, with a smaller amplitude and a slightly smaller effective temperature. As an application, we explicitly construct a baryogenesis mechanism during warm inflation based on the out-of-equilibrium decay of particles in such an adiabatically evolving state. We show that this generically leads to small baryon isocurvature perturbations, within the bounds set by the Planck satellite. These are correlated with the main adiabatic curvature perturbations but exhibit a distinct spectral index, which may constitute a smoking gun for baryogenesis during warm inflation. Finally, we discuss the prospects for other applications of adiabatically evolving out-of-equilibrium states.