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arXiv · 2509.21850

Weakly model-independent determination of total expansion during inflation

Dayeong Choi·Subin Jeon·Jinn-Ouk Gong
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Abstract

We study systematically the total expansion experienced by a certain perturbation mode during single-field inflation, not resorting to explicit models of inflation or reheating. By assuming that during the reheating stage the equation of state w{rh} can be written as a function of e-folds, the unknown dynamics during reheating parametrized by w{rh} is confined within a time integral so that any dependence on the models of inflation and reheating is isolated from model-independent contributions. Especially, the dependence on the reheating dynamics via w{rh} and the reheating temperature T{rh} is dominating. We give two illustrative examples of w{rh} to discuss its impacts on the total expansion, which can be different as much as 10 even for the same reheating temperature, depending on the shape of w{rh}. We also discuss the profile degeneracy of w{rh}, and argue when the degeneracy is lifted.

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Dayeong Choi, Subin Jeon, Jinn-Ouk Gong. 2025-09-26. Weakly model-independent determination of total expansion during inflation. https://arxiv.org/abs/2509.21850

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