ShapeFit: extracting the power spectrum shape information in galaxy surveys beyond BAO and RSD

TL;DR

ShapeFit enhances traditional galaxy survey analysis by capturing additional cosmological information in a model-independent way, matching full modelling results while improving robustness and understanding of systematics.

Contribution

The paper introduces ShapeFit, an extension to classic analysis that captures full modelling information with an extra parameter, improving model independence and systematic control.

Findings

ShapeFit matches full modelling constraints on cosmological parameters.

It provides a more model-independent analysis approach.

ShapeFit offers better understanding of the origin of extra information.

Abstract

In the standard (classic) approach, galaxy clustering measurements from spectroscopic surveys are compressed into baryon acoustic oscillations and redshift space distortions measurements, which in turn can be compared to cosmological models. Recent works have shown that avoiding this intermediate step and fitting directly the full power spectrum signal (full modelling) leads to much tighter constraints on cosmological parameters. Here we show where this extra information is coming from and extend the classic approach with one additional effective parameter, such that it captures, effectively, the same amount of information as the full modelling approach, but in a model-independent way. We validate this new method (ShapeFit) on mock catalogs, and compare its performance to the full modelling approach finding both to deliver equivalent results. The ShapeFit extension of the classic approach promotes the standard analyses at the level of full modelling ones in terms of information content, with the advantages of i) being more model independent; ii) offering an understanding of the origin of the extra cosmological information; iii) allowing a robust control on the impact of observational systematics.