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arXiv · 2507.12849

Evolution of coupled scalar perturbations through smooth reheating. II. Thermal fluctuation regime

M. Laine·S. Procacci·A. Rogelj
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Abstract

Curvature perturbations with short wavelengths exit the Hubble horizon when the universe may contain a thermal plasma in addition to an inflaton field that drives its expansion. We solve the corresponding fluctuation-dissipation dynamics at linear order, building upon a previously established set of gauge-invariant evolution equations. The properties of the noise autocorrelator are constrained via a matching of equilibrium correlators to quantum-statistical physics deep inside the Hubble horizon. The curvature power spectrum is determined numerically, without slow-roll approximations or assumptions about the equilibration of the inflaton field. As applications, we scrutinize two issues from recent literature: the model dependence of the thermally modified power spectrum as a function of freeze-out parameters, and the viability of embedding warm inflation within the Standard Model (we offer support for the latter proposal). The role of pre-horizon-exit acoustic oscillations is illustrated.

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M. Laine, S. Procacci, A. Rogelj. 2026-01-02. Evolution of coupled scalar perturbations through smooth reheating. II. Thermal fluctuation regime. https://doi.org/10.1088/1475-7516%2F2025%2F12%2F058

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