On Particle Production from Bubble Collisions in the Non-runaway Regime
Abstract
Particle production from bubble collisions during First-Order Phase Transitions (FOPTs) has been studied as an efficient mechanism for baryogenesis and dark matter production, but existing semi-analytical treatments assume runaway bubbles with wall velocity vw→ 1. We generalize this treatment to arbitrary vw< 1, relevant for scenarios such as electroweak baryogenesis and transitions with significant wall friction. We first extend the analytical trapping-equation approach to finite-thickness boosted kink profiles for both elastic and inelastic collisions, then go beyond this by numerically solving the full Klein-Gordon equation without assuming SO(1,1) symmetry or thin walls, across a broad grid of vw and potential shapes. We find the analytical generalization underestimates the true efficiency factor by orders of magnitude away from vw→ 1, and provide new semi-analytic fit functions consisting of a power-law continuum plus a resonance peak, which reproduce the main spectral features of the numerical results across the parameter range studied. Applying these to a toy dark sector model, we show particle production is strongly suppressed as vw decreases from unity, enhanced for lighter produced particles, and that the relative contribution from the oscillatory peak differs from prior runaway-regime estimates. We also discuss limitations of the trapping equation and the off-shell effective-action truncation underlying this formalism.
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BibTeX
@misc{abuajamieh2026particle,
title = {{On Particle Production from Bubble Collisions in the Non-runaway Regime}},
author = {Fayez Abu-Ajamieh and Amine Ahriche and Sagar Modak and Nobuchika Okada},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.30106},
eprint = {2610.30106},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.30106},
}
RIS
TY - UNPB
TI - On Particle Production from Bubble Collisions in the Non-runaway Regime
AU - Fayez Abu-Ajamieh
AU - Amine Ahriche
AU - Sagar Modak
AU - Nobuchika Okada
PY - 2026
DA - 2026/10/21
PB - arXiv
DO - 10.48550/arxiv.2610.30106
UR - https://arxiv.org/abs/2610.30106
AB - Particle production from bubble collisions during First-Order Phase Transitions (FOPTs) has been studied as an efficient mechanism for baryogenesis and dark matter production, but existing semi-analytical treatments assume runaway bubbles with wall velocity v_w→ 1. We generalize this treatment to arbitrary v_w< 1, relevant for scenarios such as electroweak baryogenesis and transitions with significant wall friction. We first extend the analytical trapping-equation approach to finite-thickness boosted kink profiles for both elastic and inelastic collisions, then go beyond this by numerically solving the full Klein-Gordon equation without assuming SO(1,1) symmetry or thin walls, across a broad grid of v_w and potential shapes. We find the analytical generalization underestimates the true efficiency factor by orders of magnitude away from v_w→ 1, and provide new semi-analytic fit functions consisting of a power-law continuum plus a resonance peak, which reproduce the main spectral features of the numerical results across the parameter range studied. Applying these to a toy dark sector model, we show particle production is strongly suppressed as v_w decreases from unity, enhanced for lighter produced particles, and that the relative contribution from the oscillatory peak differs from prior runaway-regime estimates. We also discuss limitations of the trapping equation and the off-shell effective-action truncation underlying this formalism.
ER -