w0wa or bc: DESI constraints on relative baryon-CDM perturbations
Abstract
We carry out a search for the relative baryon-cold dark matter (CDM) density and velocity modes in the DESI full-shape (FS) data, and investigate whether DESI's preference for evolving dark energy can be affected by these relative perturbations, which are a known contaminant of the baryon acoustic oscillations. For the first time, we use a holistic effective field theory (EFT) treatment of the power spectrum and bispectrum both for the standard terms (without relative perturbations), modeled in EFT to one-loop order, and for the relative perturbations. For the latter we implement an efficient computation of the one-loop power spectrum that allows us to scan over different cosmologies. We obtain robust constraints on the relative density and velocity bias parameters bδbc, and bv2bc for all the DESI DR1 tracers, finding e.g. bδbc=5 ± 6, bv2bc=−0.031± 0.023 (at 68% CL) for the LRG2 sample in a DESI FS-only analysis within ΛCDM, supplemented by CMB priors on the baryon density and spectral tilt. Assuming instead a w0waCDM cosmological model, and combining DESI FS with the CMB primary anisotropies, CMB lensing, and Pantheon+ supernovae, our LRG2 constraints read bδbc=2 ± 5, bv2bc=−0.032± 0.022. Adding the relative velocity divergence biases we find bδbc=−17−17+19, bθbc=−760−680+700, bv2bc=−0.032± 0.024 for the same sample. The constraints on the dark energy equation of state parameters are virtually unchanged when marginalizing over the baryon-CDM modes. We conclude that DESI's preference for evolving dark energy is robust with respect to the baryon-CDM relative perturbations.
Related
- Joint Constraints on the Hubble Constant and Cosmic Baryon Density from Localized Fast Radio Bursts and DESI DR2 Baryon Acoustic Oscillations
- Revisiting self-interacting dark matter with DESI DR2 baryon acoustic oscillation observations
- Model-independent and reconstruction-free evidence for cosmic acceleration from DESI baryon acoustic oscillations
- Field-Level Baryon Acoustic Oscillation Reconstruction of the DESI DR1 Luminous Red Galaxies with Linear Field Transformer (LiFT)
- Baryon Acoustic Oscillations from the C iv Forest with DESI DR2
BibTeX
@misc{smith2026w0wa,
title = {{$w_0w_a$ or $bc$: DESI constraints on relative baryon-CDM perturbations}},
author = {Ananda F. Smith and Mikhail M. Ivanov and Roger de Belsunce and Shi-Fan Chen and Anton Chudaykin and Oliver H. E. Philcox},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.10794},
eprint = {2609.10794},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.10794},
}
RIS
TY - UNPB
TI - w_0w_a or bc: DESI constraints on relative baryon-CDM perturbations
AU - Ananda F. Smith
AU - Mikhail M. Ivanov
AU - Roger de Belsunce
AU - Shi-Fan Chen
AU - Anton Chudaykin
AU - Oliver H. E. Philcox
PY - 2026
DA - 2026/09/09
PB - arXiv
DO - 10.48550/arxiv.2609.10794
UR - https://arxiv.org/abs/2609.10794
AB - We carry out a search for the relative baryon-cold dark matter (CDM) density and velocity modes in the DESI full-shape (FS) data, and investigate whether DESI's preference for evolving dark energy can be affected by these relative perturbations, which are a known contaminant of the baryon acoustic oscillations. For the first time, we use a holistic effective field theory (EFT) treatment of the power spectrum and bispectrum both for the standard terms (without relative perturbations), modeled in EFT to one-loop order, and for the relative perturbations. For the latter we implement an efficient computation of the one-loop power spectrum that allows us to scan over different cosmologies. We obtain robust constraints on the relative density and velocity bias parameters b_δ_bc, and b_v^2_bc for all the DESI DR1 tracers, finding e.g. b_δ_bc=5 ± 6, b_v^2_bc=−0.031± 0.023 (at 68% CL) for the LRG2 sample in a DESI FS-only analysis within ΛCDM, supplemented by CMB priors on the baryon density and spectral tilt. Assuming instead a w_0w_aCDM cosmological model, and combining DESI FS with the CMB primary anisotropies, CMB lensing, and Pantheon+ supernovae, our LRG2 constraints read b_δ_bc=2 ± 5, b_v^2_bc=−0.032± 0.022. Adding the relative velocity divergence biases we find b_δ_bc=−17_−17^+19, b_θ_bc=−760_−680^+700, b_v^2_bc=−0.032± 0.024 for the same sample. The constraints on the dark energy equation of state parameters are virtually unchanged when marginalizing over the baryon-CDM modes. We conclude that DESI's preference for evolving dark energy is robust with respect to the baryon-CDM relative perturbations.
ER -