Investigating scalar-tensor-gravity with statistics of the cosmic large-scale structure

Abstract

Future observations of the large-scale structure have the potential to investigate cosmological models with a high degree of complexity, including the properties of gravity on large scales, the presence of a complicated dark energy component, and the addition of neutrinos changing structures on small scales. Here we study Horndeski theories of gravity, the most general minimally coupled scalar-tensor theories of second order. While the cosmological background evolution can be described by an effective equation of state, the perturbations are characterised by four free functions of time. We consider a specific parametrisation of these functions tracing the dark energy component. The likelihood of the full parameter set resulting from combining cosmic microwave background primary anisotropies including their gravitational lensing signal, tomographic angular galaxy clustering and weak cosmic shear, together with all possible non-vanishing cross-correlations is evaluated; both with the Fisher-formalism as well as without the assumption of a specific functional form of the posterior through Monte-Carlo Markov-chains (MCMCs). Our results show that even complex cosmological models can be constrained and could exclude variations of the effective Newtonian gravitational coupling larger than 10% over the age of the Universe. In particular, we confirm strong correlations between parameter groups. Furthermore, we find that the expected contours from MCMC are significantly larger than those from the Fisher analysis even with the vast amount of signal provided by stage IV experiments, illustrating the importance of a proper treatment of non-Gaussian likelihoods and the high level of precision needed for unlocking the sensitivity on gravitational parameters.

Effective field theory of dark energy: A review

“…Since the EFT framework does not rely on a specific model but allows to make general prediction on large classes of models, it provides a powerful benchmark for forecasting the cosmological signals to which the future missions will give access to. In the following, we review the cosmological forecasts analyses performed using the pure EFT approach [217,199,218,65,216,219,130]. Also in this case, the class of models that has been largely explored belongs to the pure Horndeski models.…”

“…Bottom panel : Figure 4 in Ref. [216]. 68% constraints region on the free parameters of pure Horndeski models with c t = 1 modeled with the linear-de form (eq.…”

“…In particular, in Figure 20 (top panel) one can observe the effects of BAO and RSD data by an independent DESI-like experiment on top of CMB-S4, LSST and SKA measurements on the parameter constraints. Tighter constraints are obtained by setting c t = 1 [216] as shown in Figure 20 (bottom panel). Such constraints exclude variations of the effective Newtonian constant larger than 10% at all times [216].…”

“…Tighter constraints are obtained by setting c t = 1 [216] as shown in Figure 20 (bottom panel). Such constraints exclude variations of the effective Newtonian constant larger than 10% at all times [216]. However, the contours obtained from the MCMC analysis are larger than those obtained from a Fisher analysis.…”

Cosmological constraints on dark energy in light of gravitational wave bounds

“…parameters Ω cdm , Ω b , θ s , A s , n s and τ reio -for technical details regarding the MCMC implementation (as well as for additional details on the implementation and use of the data sets involved) see [34]. For related cosmological parameter constraints on deviations from GR using general parameterised approaches and a variety of (current and forecasted) experimental data, see [17,18,34,[48][49][50][51][52][53][54][55][56][57][58][59][60] All the constraints computed here assume α T = 0 as a prior to ensure compatibility with the speed of gravity constraints from GW170817 (as discussed in detail above), but we consider constraints with and without the further prior (7) from requiring the absence of GW-induced gradient instabilities. For reference throughout the remainder of this section, we adopt the following shorthands in referring to the datasets we use (as well as the additional GW prior):…”