Falsifying $\Lambda$CDM: Model-independent tests of the concordance model with eBOSS DR14Q and Pantheon

TL;DR

This paper tests key aspects of the standard cosmological model using model-independent methods with recent observational data, confirming its consistency but also revealing some tensions at high redshifts.

Contribution

It combines model-independent reconstructions from supernovae and BAO data to test the FLRW metric, flatness, and growth of structure in a novel, data-driven way.

Findings

Results are consistent with a flat FLRW universe governed by general relativity.

Strong constraints on matter density, growth index, and amplitude of fluctuations were obtained.

Hints of tension at high redshift observations suggest areas for further investigation.

Abstract

We combine model-independent reconstructions of the expansion history from the latest Pantheon supernovae distance modulus compilation and measurements from baryon acoustic oscillation to test some important aspects of the concordance model of cosmology namely the FLRW metric and flatness of spatial curvature. We then use the reconstructed expansion histories to fit growth measurement from redshift-space distortion and obtain strong constraints on $(\Omega_\mathrm{m},\gamma,\sigma_8)$ in a model independent manner. Our results show consistency with a spatially flat FLRW Universe with general relativity to govern the perturbation in the structure formation and the cosmological constant as dark energy. However, we can also see some hints of tension among different observations within the context of the concordance model related to high redshift observations ($z > 1$) of the expansion history. This supports earlier findings of Sahni et al. (2014) & Zhao et al. (2017) and highlights the importance of precise measurement of expansion history and growth of structure at high redshifts.