The box within the Universe: anisotropies in periodic cosmological simulations I. Dark-matter-only simulations
Abstract
The vast majority of cosmological simulations employ periodic boundary conditions to achieve statistical homogeneity and to mimic the infinite spatial extent of our Universe. In a cubic periodic domain the Green function breaks full rotational invariance and introduces a geometry-induced anisotropy in the gravitational interaction. We quantify how this intrinsic anisotropy affects cosmic structure growth and investigate the extent to which it biases the commonly used large-scale structure and halo-based observables in dark-matter-only simulations. We analyse an ensemble of 498 cosmological dark-matter-only N-body simulations in cubic T3 topological manifolds, evolved to z=0, spanning box sizes from L=6.25 Mpc to L=100 Mpc at fixed mass and force resolution. We compare anisotropy-sensitive statistics across the suite, including the matter power spectrum, halo abundance, merger histories, shapes and alignments, and filament orientations. Finite periodic boundaries imprint orientation-dependent signatures aligned with the box geometry. These signatures propagate beyond the largest modes and can induce systematic shifts in both field-level and halo-level statistics. The detectable effects propagate to scales much smaller than the box size. Our results demonstrate that periodic-box anisotropy is a non-negligible source of systematics for small simulation volumes, including those commonly employed in modern hydrodynamical simulations.
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BibTeX
@misc{racz2026within,
title = {{The box within the Universe: anisotropies in periodic cosmological simulations I. Dark-matter-only simulations}},
author = {Gábor Rácz and Till Sawala},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.08223},
eprint = {2611.08223},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.08223},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The box within the Universe: anisotropies in periodic cosmological simulations I. Dark-matter-only simulations
AU - Gábor Rácz
AU - Till Sawala
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.08223
UR - https://arxiv.org/abs/2611.08223
AB - The vast majority of cosmological simulations employ periodic boundary conditions to achieve statistical homogeneity and to mimic the infinite spatial extent of our Universe. In a cubic periodic domain the Green function breaks full rotational invariance and introduces a geometry-induced anisotropy in the gravitational interaction. We quantify how this intrinsic anisotropy affects cosmic structure growth and investigate the extent to which it biases the commonly used large-scale structure and halo-based observables in dark-matter-only simulations. We analyse an ensemble of 498 cosmological dark-matter-only N-body simulations in cubic T^3 topological manifolds, evolved to z=0, spanning box sizes from L=6.25 Mpc to L=100 Mpc at fixed mass and force resolution. We compare anisotropy-sensitive statistics across the suite, including the matter power spectrum, halo abundance, merger histories, shapes and alignments, and filament orientations. Finite periodic boundaries imprint orientation-dependent signatures aligned with the box geometry. These signatures propagate beyond the largest modes and can induce systematic shifts in both field-level and halo-level statistics. The detectable effects propagate to scales much smaller than the box size. Our results demonstrate that periodic-box anisotropy is a non-negligible source of systematics for small simulation volumes, including those commonly employed in modern hydrodynamical simulations.
ER -