Universality classes of sharp gravitational production of light particles
Abstract
We establish a classification of the gravitational production of light particles across sharp transitions connecting different asymptotic forms of the scale factor. A family of smooth scale factors with a transition duration Δη is characterized by its regularity in the sharp-transition limit Δη→ 0, leading to three qualitatively different universality classes: C0, C1, and C2-or-smoother. We find that the C0 class exhibits a quadratic enhancement in the energy density of produced particles, ρ∝Δη−2, while the C1 class shows a logarithmic enhancement, ρ∝ln(1/Δη). No sharp-transition enhancement occurs for the C2-or-smoother class. Using a specific C∞ model of the scale factor, we derive the energy density analytically and confirm both the predicted quadratic scaling and its coefficient by numerically solving the mode equation. These results identify the regularity of the scale factor in the sharp limit as the key property controlling the sharp-transition enhancement.
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BibTeX
@misc{ito2026universality,
title = {{Universality classes of sharp gravitational production of light particles}},
author = {Kanta Ito and Yusuke Mikura and Shuichiro Yokoyama},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.32202},
eprint = {2609.32202},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.32202},
}
RIS
TY - UNPB
TI - Universality classes of sharp gravitational production of light particles
AU - Kanta Ito
AU - Yusuke Mikura
AU - Shuichiro Yokoyama
PY - 2026
DA - 2026/09/26
PB - arXiv
DO - 10.48550/arxiv.2609.32202
UR - https://arxiv.org/abs/2609.32202
AB - We establish a classification of the gravitational production of light particles across sharp transitions connecting different asymptotic forms of the scale factor. A family of smooth scale factors with a transition duration Δη is characterized by its regularity in the sharp-transition limit Δη→ 0, leading to three qualitatively different universality classes: C^0, C^1, and C^2-or-smoother. We find that the C^0 class exhibits a quadratic enhancement in the energy density of produced particles, ρ∝Δη^−2, while the C^1 class shows a logarithmic enhancement, ρ∝ln(1/Δη). No sharp-transition enhancement occurs for the C^2-or-smoother class. Using a specific C^∞ model of the scale factor, we derive the energy density analytically and confirm both the predicted quadratic scaling and its coefficient by numerically solving the mode equation. These results identify the regularity of the scale factor in the sharp limit as the key property controlling the sharp-transition enhancement.
ER -