Euclid preparation. Review of forecast constraints on dark energy and modified gravity

Abstract

The Euclid mission has been designed to provide, as one of its main deliverables, information on the nature of the gravitational interaction, which determines the expansion of the Universe and the formation of structures. Thus, Euclid has the potential to test deviations from general relativity that will allow us to shed light on long-lasting problems in the standard cosmological model, $Λ$CDM. Euclid will mainly do this by using two complementary probes: weak gravitational lensing and galaxy clustering. In this paper we review pre-launch Euclid analyses for dark energy and modified gravity. These include forecast constraints with future Euclid data on cosmological parameters for different cosmological models, such as a time-varying dark energy component, phenomenological modifications of the perturbation sector and specific modified gravity models, with further extensions that include neutrino physics and the coupling to the electromagnetic sector through the fine-structure constant. We review the study of the impact of nonlinear clustering methods on beyond-$Λ$CDM constraints with Euclid. This is of fundamental importance to efficiently predict the large-scale clustering of matter and dark matter halos, given that we will have access to a wealth of information on scales beyond the linear regime. We inspect the extension of theoretical predictions for observable quantities in alternative cosmologies to $Λ$CDM at fully nonlinear scales by means of $N$-body simulations. We discuss the impact of relativistic corrections in extended cosmological models. Overall, this review highlights the significant potential of the Euclid mission to tightly constrain parameters of dark energy and modified gravity models, or perhaps to detect possible signatures of a $Λ$CDM failure.

Figures (3)

• Figure 1: Marginalized $1\,\sigma$ errors on the model parameters relative to their corresponding fiducial values in the optimistic setting, for PMG-1, and EFT-1 in the US and SS settings. We refer the reader to \ref{['Sec:ForecastsmuSigma', 'Sec:ForecastsEFT']} for the values of the free parameters for each case.
• Figure 2: Marginalized $1\,\sigma$ errors on the model parameters relative to their corresponding fiducial values in the optimistic setting, for JBD (case 1 in blue and case 2 in cyan), nDGP (case 1 in green and case 2 in light green), and KM (case 1 in red and case 2 in light red). We refer the reader to \ref{['Sec:ForecastsJBD', 'Sec:ForecastsKM', 'Sec:ForecastsDGP']} for the values of the free parameters for each case.
• Figure 3: Marginalized $68\%$ and $95\%$ uncertainties on the cosmological parameters $|f_{R0}|$, $h$, and $\sigma_8$ for a flat $f(R)$ model with $|f_{R0}| =5\times 10^{-6}$ in the optimistic scenario. Purple is for GC$_\mathrm{sp}$, pink for all the photometric probes including their cross-correlation XC$_\mathrm{ph}$, and yellow when this is combined with GC$_\mathrm{sp}$, namely GC$_\mathrm{sp}$+WL+GC$_\mathrm{ph}$+XC$_\mathrm{ph}$.