Non-linear Pairwise Velocities as a Cosmological Probe
Abstract
Peculiar velocities trace gravitational dynamics directly, complementing density-based clustering as wide-field spectroscopic surveys (DESI, Euclid, PFS) and kinetic Sunyaev-Zel'dovich (kSZ) measurements enter the precision era. Observational analyses of pairwise velocities and the pairwise kSZ signal remain largely restricted to linear and quasi-linear scales (≳20−30 h−1Mpc), despite substantial cosmological information available at smaller separations. We present a simulation-calibrated likelihood for v12(r,a), built on the exact pair conservation equation and PyCAMB HMcode-2020 non-linear clustering, and validate it against the QUIJOTE and TNG300-3 suites across resolution, particle sampling, box size, and redshift. Using QUIJOTE, we show that extending the fit to non-linear scales tightens the 1σ uncertainty on Ωm and σ8 by 74% and 81% at z=0.5 (rmin=4 h−1Mpc), and by 70% and 74% at z=0 (rmin=8 h−1Mpc), relative to the linear-regime baseline (rmin=50 h−1Mpc) (all at fixed rmax=140 h−1Mpc); σ(fσ8) tightens by up to 86%, and the joint Ωm-fσ8 Figure-of-Merit improves by up to 9.1× relative to the same baseline. These constraints are conditional on h fixed at its QUIJOTE fiducial value, due to a near-degenerate response with σ8; jointly sampling h shifts and widens them substantially. This framework provides a validated route to exploiting that information in upcoming direct peculiar-velocity, redshift-space, and kSZ analyses.
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BibTeX
@misc{jaber2026nonlinear,
title = {{Non-linear Pairwise Velocities as a Cosmological Probe}},
author = {Mariana Jaber and Antonela Taverna and Rasmus Strid and Wojciech A. Hellwing},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.07976},
eprint = {2609.07976},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.07976},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Non-linear Pairwise Velocities as a Cosmological Probe
AU - Mariana Jaber
AU - Antonela Taverna
AU - Rasmus Strid
AU - Wojciech A. Hellwing
PY - 2026
DA - 2026/09/07
PB - arXiv
DO - 10.48550/arxiv.2609.07976
UR - https://arxiv.org/abs/2609.07976
AB - Peculiar velocities trace gravitational dynamics directly, complementing density-based clustering as wide-field spectroscopic surveys (DESI, Euclid, PFS) and kinetic Sunyaev-Zel'dovich (kSZ) measurements enter the precision era. Observational analyses of pairwise velocities and the pairwise kSZ signal remain largely restricted to linear and quasi-linear scales (≳20−30 h^−1Mpc), despite substantial cosmological information available at smaller separations. We present a simulation-calibrated likelihood for v_12(r,a), built on the exact pair conservation equation and PyCAMB HMcode-2020 non-linear clustering, and validate it against the QUIJOTE and TNG300-3 suites across resolution, particle sampling, box size, and redshift. Using QUIJOTE, we show that extending the fit to non-linear scales tightens the 1σ uncertainty on Ω_m and σ_8 by 74% and 81% at z=0.5 (r_min=4 h^−1Mpc), and by 70% and 74% at z=0 (r_min=8 h^−1Mpc), relative to the linear-regime baseline (r_min=50 h^−1Mpc) (all at fixed r_max=140 h^−1Mpc); σ(fσ_8) tightens by up to 86%, and the joint Ω_m-fσ_8 Figure-of-Merit improves by up to 9.1× relative to the same baseline. These constraints are conditional on h fixed at its QUIJOTE fiducial value, due to a near-degenerate response with σ_8; jointly sampling h shifts and widens them substantially. This framework provides a validated route to exploiting that information in upcoming direct peculiar-velocity, redshift-space, and kSZ analyses.
ER -