Model-independent parameters from DESI DR1 LRG2 with an explicitly varying power-spectrum shape
Abstract
Distinguishing between dark energy and modified gravity as the origin of the accelerated expansion requires the cosmic distances and the growth of structure to be measured in a model-independent way. Such measurements are difficult to perform while the primordial shape parameters are varied at the same time, and those parameters are therefore usually held fixed at the values determined by cosmic microwave background experiments. In this work, we present a methodology that constrains the shape parameters simultaneously with the model-independent distance and growth parameters, using an emulator built upon a hybrid model in which perturbative predictions are supplemented by templates measured from N-body simulations. {Because these templates are measured rather than expanded, the model carries non-linear corrections beyond the order at which its perturbative part is truncated, so that its accuracy on small scales is set by the simulations rather than by the reach of the expansion.} A Gaussian process emulator supplies these templates rapidly across the space of scale-dependent parameters, which makes the joint analysis computationally feasible, and the emulator is trained and validated over a range spanning 5σ of the Planck constraints. Applying the method to the LRG2 sample of DESI DR1, we obtain measurements of the Alcock--Paczynski parameters α⊥ and α|| and of the growth rate fσ8. {With the tight Planck prior adopted here the constraints differ from those obtained with the shape parameters held fixed by less than a twentieth of their own uncertainties, so that the choice of template contributes at that level to the error budget of the measurement. Projected onto flat ΛCDM after the fit, the three measurements are mutually consistent, with χ2=0.7 for two degrees of freedom, and require h=0.724±0.017.
Related
- Forecasting Coupled Dark Energy Parameters with the One-Loop Galaxy Power Spectrum
- CosmoForge. I. A unified framework for quadratic maximum likelihood power spectrum estimation and pixel-based likelihood analysis
- Measurement of the Dispersion-Galaxy Cross-Power Spectrum with the Second CHIME/FRB Catalog
- From quantum fluctuations to galaxy power spectrum multipoles
- Angular power spectrum of induced gravitational waves: breaking model and parameter degeneracies in PTA observations
BibTeX
@misc{song2026modelindependent,
title = {{Model-independent parameters from DESI DR1 LRG2 with an explicitly varying power-spectrum shape}},
author = {Yong-Seon Song and M. Icaza-Lizaola and Minji Oh and Yi Zheng},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.21235},
eprint = {2610.21235},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.21235},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Model-independent parameters from DESI DR1 LRG2 with an explicitly varying power-spectrum shape
AU - Yong-Seon Song
AU - M. Icaza-Lizaola
AU - Minji Oh
AU - Yi Zheng
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.21235
UR - https://arxiv.org/abs/2610.21235
AB - Distinguishing between dark energy and modified gravity as the origin of the accelerated expansion requires the cosmic distances and the growth of structure to be measured in a model-independent way. Such measurements are difficult to perform while the primordial shape parameters are varied at the same time, and those parameters are therefore usually held fixed at the values determined by cosmic microwave background experiments. In this work, we present a methodology that constrains the shape parameters simultaneously with the model-independent distance and growth parameters, using an emulator built upon a hybrid model in which perturbative predictions are supplemented by templates measured from N-body simulations. {Because these templates are measured rather than expanded, the model carries non-linear corrections beyond the order at which its perturbative part is truncated, so that its accuracy on small scales is set by the simulations rather than by the reach of the expansion.} A Gaussian process emulator supplies these templates rapidly across the space of scale-dependent parameters, which makes the joint analysis computationally feasible, and the emulator is trained and validated over a range spanning 5σ of the Planck constraints. Applying the method to the LRG2 sample of DESI DR1, we obtain measurements of the Alcock--Paczynski parameters α_⊥ and α_|| and of the growth rate fσ_8. {With the tight Planck prior adopted here the constraints differ from those obtained with the shape parameters held fixed by less than a twentieth of their own uncertainties, so that the choice of template contributes at that level to the error budget of the measurement. Projected onto flat ΛCDM after the fit, the three measurements are mutually consistent, with χ^2=0.7 for two degrees of freedom, and require h=0.724±0.017.
ER -