A Unified Numerical Study of Axion Stars: From the Nonrelativistic Regime to General Relativity
Abstract
Axion-star mass-radius relations are commonly computed using different orders of relativistic approximation, making it important to determine where these descriptions remain reliable. We perform a unified numerical comparison of axion-star ground-state configurations in the Newtonian Schrödinger-Poisson description, first- and second-order relativistic effective field theories, and the full Einstein-Klein-Gordon system for a real scalar field. Using the same attractive quartic self-interaction in all four descriptions, we scan |λ̃|=(MPl/fa)2 and determine the maximum masses and corresponding enclosed-mass radii. All descriptions recover the common large-|λ̃| dilute-star scaling, while substantial differences appear at weak and moderate coupling. The relativistic EFTs interpolate systematically between the Newtonian and full-GR results. For part of the maximum-mass sequence where max|ϕ|/fa=O(1), we test the temporal-harmonic and potential truncations explicitly in full GR. The higher-harmonic expansion shows rapid convergence, while restoring the complete single-cosine potential changes the maximum mass only at the percent level and R95 at the several-percent level. Together with the systematic convergence of the relativistic EFT descriptions toward full GR, these results show that the large weak-coupling departure from the Schrödinger-Poisson prediction reflects the breakdown of the nonrelativistic structural description. Our results provide a systematic benchmark for determining when Newtonian, relativistically corrected, or fully general-relativistic descriptions are required for axion-star structure. The numerical implementation used in this work is available in the Axion Star Solvers repository at https://github.com/Parisa-Arabameri/AxionStar.
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BibTeX
@misc{arabameri2026unified,
title = {{A Unified Numerical Study of Axion Stars: From the Nonrelativistic Regime to General Relativity}},
author = {Parisa Arabameri and Paola Arias and Francisco Colipí-Marchant and Enrico D. Schiappacasse},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.13638},
eprint = {2609.13638},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.13638},
}
RIS
TY - UNPB
TI - A Unified Numerical Study of Axion Stars: From the Nonrelativistic Regime to General Relativity
AU - Parisa Arabameri
AU - Paola Arias
AU - Francisco Colipí-Marchant
AU - Enrico D. Schiappacasse
PY - 2026
DA - 2026/09/12
PB - arXiv
DO - 10.48550/arxiv.2609.13638
UR - https://arxiv.org/abs/2609.13638
AB - Axion-star mass-radius relations are commonly computed using different orders of relativistic approximation, making it important to determine where these descriptions remain reliable. We perform a unified numerical comparison of axion-star ground-state configurations in the Newtonian Schrödinger-Poisson description, first- and second-order relativistic effective field theories, and the full Einstein-Klein-Gordon system for a real scalar field. Using the same attractive quartic self-interaction in all four descriptions, we scan |λ̃|=(M_Pl/f_a)^2 and determine the maximum masses and corresponding enclosed-mass radii. All descriptions recover the common large-|λ̃| dilute-star scaling, while substantial differences appear at weak and moderate coupling. The relativistic EFTs interpolate systematically between the Newtonian and full-GR results. For part of the maximum-mass sequence where max|ϕ|/f_a=O(1), we test the temporal-harmonic and potential truncations explicitly in full GR. The higher-harmonic expansion shows rapid convergence, while restoring the complete single-cosine potential changes the maximum mass only at the percent level and R_95 at the several-percent level. Together with the systematic convergence of the relativistic EFT descriptions toward full GR, these results show that the large weak-coupling departure from the Schrödinger-Poisson prediction reflects the breakdown of the nonrelativistic structural description. Our results provide a systematic benchmark for determining when Newtonian, relativistically corrected, or fully general-relativistic descriptions are required for axion-star structure. The numerical implementation used in this work is available in the Axion Star Solvers repository at https://github.com/Parisa-Arabameri/AxionStar.
ER -