Evolving only the observed spacetime region: perfectly parallel lightcone simulations with sCOLA
Abstract
Cosmological analyses of Stage-IV galaxy surveys require large ensembles of lightcone mock catalogues, but a full survey-scale N-body run costs of order 107 CPU hours, putting such ensembles out of reach. We present a framework that produces survey-scale dark matter lightcones for a typical cost of order 103 CPU hours each, based on the spatial COmoving Lagrangian Acceleration (sCOLA) method. sCOLA decomposes an arbitrarily large volume into small tiles that are evolved independently, with buffer regions and non-periodic boundary conditions on the gravitational potential. We combine it with on-the-fly lightcone building, so that the evolved spacetime region reduces to the observed one: each tile is stopped as soon as the observer's past lightcone has left it, and only the tiles intersecting the region of interest are simulated at all. We further introduce two accuracy improvements to the sCOLA formalism: an LPT buffer that approximates the inflow of particles from outside the sCOLA box, and a second-order perturbative approximation to the gravitational potential at its boundaries; together they remove the large-scale inaccuracies of previous work and allow smaller tiles and buffers. Against a \texttt{Gadget4} reference in a 3.84 h−1 Gpc box with 3 8403 particles, up to k ≃ 0.4 h Mpc−1 the sCOLA lightcone reproduces the matter power spectrum to 1%, the velocity divergence power spectrum to 1.5% and the equilateral bispectrum to 2%, with no visible discontinuity at tile boundaries. The run cost 1 300 CPU hours, a factor of 2 600 below our Gadget4 run. Perfect parallelism at this cost brings ensembles of thousands of survey-scale lightcones within reach of a single allocation: ∼ 25 000 realisations of the Euclid Galactic north cap with a mass resolution of 1011 M⊙ for 107 CPU hours.
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BibTeX
@misc{aubin2026evolving,
title = {{Evolving only the observed spacetime region: perfectly parallel lightcone simulations with sCOLA}},
author = {Mayeul Aubin and Florent Leclercq and Guilhem Lavaux},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.26639},
eprint = {2610.26639},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.26639},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Evolving only the observed spacetime region: perfectly parallel lightcone simulations with sCOLA
AU - Mayeul Aubin
AU - Florent Leclercq
AU - Guilhem Lavaux
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.26639
UR - https://arxiv.org/abs/2610.26639
AB - Cosmological analyses of Stage-IV galaxy surveys require large ensembles of lightcone mock catalogues, but a full survey-scale N-body run costs of order 10^7 CPU hours, putting such ensembles out of reach. We present a framework that produces survey-scale dark matter lightcones for a typical cost of order 10^3 CPU hours each, based on the spatial COmoving Lagrangian Acceleration (sCOLA) method. sCOLA decomposes an arbitrarily large volume into small tiles that are evolved independently, with buffer regions and non-periodic boundary conditions on the gravitational potential. We combine it with on-the-fly lightcone building, so that the evolved spacetime region reduces to the observed one: each tile is stopped as soon as the observer's past lightcone has left it, and only the tiles intersecting the region of interest are simulated at all. We further introduce two accuracy improvements to the sCOLA formalism: an LPT buffer that approximates the inflow of particles from outside the sCOLA box, and a second-order perturbative approximation to the gravitational potential at its boundaries; together they remove the large-scale inaccuracies of previous work and allow smaller tiles and buffers. Against a \texttt{Gadget4} reference in a 3.84 h^−1 Gpc box with 3 840^3 particles, up to k ≃ 0.4 h Mpc^−1 the sCOLA lightcone reproduces the matter power spectrum to 1%, the velocity divergence power spectrum to 1.5% and the equilateral bispectrum to 2%, with no visible discontinuity at tile boundaries. The run cost 1 300 CPU hours, a factor of 2 600 below our Gadget4 run. Perfect parallelism at this cost brings ensembles of thousands of survey-scale lightcones within reach of a single allocation: ∼ 25 000 realisations of the Euclid Galactic north cap with a mass resolution of 10^11 M_⊙ for 10^7 CPU hours.
ER -