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arXiv · 2602.03961

On the importance of radiation-era initial conditions for tensor perturbations

Dražen Glavan·Juraj Klarić·Philipp Klose·Ignacy Sawicki
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Abstract

Conservation of super-horizon tensor fluctuations is crucial for connecting inflation to observations. Starting from first principles, recent works have found violations of this conservation if free-streaming radiation is produced during reheating. We show that the non-conservation is sensitive to the radiation initial state, and argue that the physical state should be affected by tensor perturbations that are already present during reheating. The deviation from super-horizon conservation is then negligible, recovering the standard result from kinetic theory. In contrast, a globally homogeneous and isotropic plasma state leads to a large suppression of tensor amplitudes. This difference between the local (physical) and global thermal equilibrium settles the discrepancy between the older and recent literature.

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Dražen Glavan, Juraj Klarić, Philipp Klose, Ignacy Sawicki. 2026-02-03. On the importance of radiation-era initial conditions for tensor perturbations. https://arxiv.org/abs/2602.03961

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