Dark-energy dependent test of general relativity at cosmological scales

TL;DR

This paper tests general relativity at cosmological scales using observational data within the DM framework, confirming its predictions under standard assumptions but highlighting degeneracies when dark energy properties are varied.

Contribution

It introduces an extended Newtonian approach to test the relation between energy content and curvature, and explores degeneracies when dark energy's equation of state is not fixed.

Findings

General relativity's predictions are verified under DM assumptions.

Relaxing dark energy's equation of state reveals degeneracies between curvature and total energy.

Observational data supports standard DM model predictions.

Abstract

The $\Lambda$CDM framework offers a remarkably good description of our universe with a very small number of free parameters, which can be determined with high accuracy from currently available data. However, this does not mean that the associated physical quantities, such as the curvature of the universe, have been directly measured. Similarly, general relativity is assumed, but not tested. Testing the relevance of general relativity for cosmology at the background level includes a verification of the relation between its energy contents and the curvature of space. Using an extended Newtonian formulation, we propose an approach where this relation can be tested. Using the recent measurements on cosmic microwave background, baryonic acoustic oscillations and the supernova Hubble diagram, we show that the prediction of general relativity is well verified in the framework of standard $\Lambda$CDM assumptions, i.e. an energy content only composed of matter and dark energy, in the form of a cosmological constant or equivalently a vacuum contribution. However, the actual equation of state of dark fluids cannot be directly obtained from cosmological observations. We found that relaxing the equation of state of dark energy opens a large region of possibilities, revealing a new type of degeneracy between the curvature and the total energy content of the universe.