Mitigating prior-volume effects in galaxy clustering by adopting Mpc over Mpc/h units
Abstract
We investigate prior-volume effects in Bayesian analyses of galaxy clustering based on state-of-the-art models, such as the EFT and the VDG∞ model. We show that these effects are largely driven by imposing priors on the model parameters defined in Mpc/h units, thereby introducing a spurious correlation with the Hubble parameter h, and that they can be strongly mitigated by adopting a more physically motivated formulation in Mpc units. We test this approach using a set of synthetic data vectors designed to reproduce the clustering signal expected in a Stage-IV survey across a range of cosmological models, including ΛCDM, KCDM, wCDM, and w0waCDM. We find that the resulting constraints are largely free from shifts induced during the marginalisation process, even in the challenging w0waCDM runs, reducing discrepancies with the fiducial values from several standard deviations to well within 1σ. The performance of this approach is comparable to that of alternative mitigation strategies, such as the adoption of invariant priors or the reparametrisation of nuisance parameters in terms of growth and geometrical amplitudes. For the latter, we find that using σ12 in place of the commonly adopted σ8 to describe the amplitude of density fluctuations improves the performance of the reparametrisation technique, even at high redshifts, where constraints on the dark-energy equation of state are weaker. We further show that these conclusions hold with the inclusion of additional BAO constraints, and for data sets with reduced statistical power. These results add to the benefits of working with Mpc units, avoiding an explicit dependence on h, with direct relevance for the analyses of Stage-IV galaxy surveys.
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BibTeX
@misc{pezzotta2026mitigating,
title = {{Mitigating prior-volume effects in galaxy clustering by adopting Mpc over Mpc/h units}},
author = {Andrea Pezzotta and Alejandro Pérez-Fernández and Giosuè Gambardella and Ariel G. Sánchez and Alexander Eggemeier and Martin Crocce and Benjamin Camacho-Quevedo},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.08751},
eprint = {2610.08751},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.08751},
}
RIS
TY - UNPB
TI - Mitigating prior-volume effects in galaxy clustering by adopting Mpc over Mpc/h units
AU - Andrea Pezzotta
AU - Alejandro Pérez-Fernández
AU - Giosuè Gambardella
AU - Ariel G. Sánchez
AU - Alexander Eggemeier
AU - Martin Crocce
AU - Benjamin Camacho-Quevedo
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.08751
UR - https://arxiv.org/abs/2610.08751
AB - We investigate prior-volume effects in Bayesian analyses of galaxy clustering based on state-of-the-art models, such as the EFT and the VDG_∞ model. We show that these effects are largely driven by imposing priors on the model parameters defined in Mpc/h units, thereby introducing a spurious correlation with the Hubble parameter h, and that they can be strongly mitigated by adopting a more physically motivated formulation in Mpc units. We test this approach using a set of synthetic data vectors designed to reproduce the clustering signal expected in a Stage-IV survey across a range of cosmological models, including ΛCDM, KCDM, wCDM, and w_0w_aCDM. We find that the resulting constraints are largely free from shifts induced during the marginalisation process, even in the challenging w_0w_aCDM runs, reducing discrepancies with the fiducial values from several standard deviations to well within 1σ. The performance of this approach is comparable to that of alternative mitigation strategies, such as the adoption of invariant priors or the reparametrisation of nuisance parameters in terms of growth and geometrical amplitudes. For the latter, we find that using σ_12 in place of the commonly adopted σ_8 to describe the amplitude of density fluctuations improves the performance of the reparametrisation technique, even at high redshifts, where constraints on the dark-energy equation of state are weaker. We further show that these conclusions hold with the inclusion of additional BAO constraints, and for data sets with reduced statistical power. These results add to the benefits of working with Mpc units, avoiding an explicit dependence on h, with direct relevance for the analyses of Stage-IV galaxy surveys.
ER -