Warm Inflation and its Microphysical Basis

TL;DR

This work develops the microphysical foundations of warm inflation by embedding it in finite-temperature quantum field theory using the Schwinger-Keldysh real-time formalism to derive an effective, Langevin-type inflaton equation with dissipation Υ and stochastic noise ξ. It shows how a fluctuating, dissipative inflaton dynamics naturally sustains a concurrent radiation bath, enabling a graceful exit without a separate reheating phase and altering the standard cold-inflation predictions for fluctuations. The authors provide explicit microphysical calculations of Υ for various interaction structures (including two-stage SUSY-mediated couplings) and extend the formalism to curved FRW space, furnishing concrete prescriptions for model-building. They further analyze first-principles warm-inflation realizations for monomial, hybrid, and hilltop potentials, demonstrating how strong dissipation relaxes the η-problem, allows sub-Planckian field values, and yields observationally viable spectra with distinct non-Gaussian signatures in certain regimes. Overall, the paper establishes a comprehensive framework connecting quantum thermal field theory to cosmological inflation, with practical implications for constructing and testing warm-inflation models against data.

Abstract

The microscopic quantum field theory origins of warm inflation dynamics are reviewed. The warm inflation scenario is first described along with its results, predictions and comparison with the standard cold inflation scenario. The basics of thermal field theory required in the study of warm inflation are discussed. Quantum field theory real time calculations at finite temperature are then presented and the derivation of dissipation and stochastic fluctuations are shown from a general perspective. Specific results are given of dissipation coefficients for a variety of quantum field theory interaction structures relevant to warm inflation, in a form that can readily be used by model builders. Different particle physics models realising warm inflation are presented along with their observational predictions.

Figures (8)

• Figure 1: Comparison of the cold and warm inflationary pictures tayfra. Top graphs show the scalar field evolution and the bottom graphs show the vacuum and radiation energy density evolution.
• Figure 2: A quadratic inflationary potential with the inflaton initially starting at some large amplitude.
• Figure 3: Contributions to the $\phi$ self-energy of order $g^2$ (left) and $g^4$ (right).
• Figure 4: The different approximations for the friction coefficient are shown in the intermediate and low temperature region. The full expression, plotted on the left, corresponds to Eq. (\ref{['simplegam']}) and the low temperature approximation to Eq. (\ref{['flt']}). These plots include both $\phi\to\chi\to2\sigma$ and $\phi\to\sigma\chi$ decay channels. Coupling constants are $h^2/8\pi=0.025$ and $m_\chi=m$.
• Figure 5: This plot shows the momentum dependence of the particle production rate $S_p$ for the production of low mass fields through an intermediate heavy field. The thermal distribution $n$ is shown for comparison.