Constraining Scale Dependent Growth with Redshift Surveys

TL;DR

This paper demonstrates a model-independent method to constrain scale-dependent growth of cosmic structures using redshift surveys, achieving high accuracy and revealing potential modifications to gravity.

Contribution

It introduces a binning approach for $G_{eff}(k,z)$ that matches scalar-tensor predictions with high precision and explores the benefits of combining velocity and redshift data for improved constraints.

Findings

Binning $G_{eff}(k,z)$ matches scalar-tensor results to 0.02%-0.27% accuracy.

Constraints on bin values can reach 1.4%-28% with DESI-quality data.

Combining velocity and redshift data improves constraints by a factor of 6-7.

Abstract

Ongoing and future redshift surveys have the capability to measure the growth rate of large scale structure at the percent level over a broad range of redshifts, tightly constraining cosmological parameters. Beyond general relativity, however, the growth rate in the linear density perturbation regime can be not only redshift dependent but scale dependent, revealing important clues to modified gravity. We demonstrate that a fully model independent approach of binning the gravitational strength $G_{\rm eff}(k,z)$ matches scalar-tensor results for the growth rate $f\sigma_8(k,z)$ to $0.02\%$-$0.27\%$ rms accuracy. For data of the quality of the Dark Energy Spectroscopic Instrument (DESI) we find the bin values can be constrained to 1.4\%-28\%. We also explore the general scalar-tensor form, constraining the amplitude and past and future scalaron mass/shape parameters. Perhaps most interesting is the strong complementarity of low redshift peculiar velocity data with DESI-like redshift space distortion measurements, enabling improvements up to a factor 6-7 on 2D joint confidence contour areas. Finally, we quantify some issues with gravity parametrizations that do not include all the key physics.