Weakly model-independent determination of total expansion during inflation
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.
Keywords
Cite
@article{arxiv.2509.21850,
title = {Weakly model-independent determination of total expansion during inflation},
author = {Dayeong Choi and Subin Jeon and Jinn-Ouk Gong},
journal= {arXiv preprint arXiv:2509.21850},
year = {2026}
}
Comments
(v1) 14 pages, 2 figures, 2 tables; (v2) 18 pages, 3 figures, 2 tables, discussions expanded including the degeneracies between different profiles of w{rh} in a new section, to appear in Journal of Cosmology and Astroparticle Physics