Viablef(T)models are practically indistinguishable fromΛCDM

Abstract

We investigate the cosmological predictions of several fðTÞ models, with up to two parameters, at both the background and the perturbation levels. Using current cosmological observations (geometric supernovae type Ia, cosmic microwave background and baryonic acoustic oscillation and dynamical growth data) we impose constraints on the distortion parameter, which quantifies the deviation of these models from the concordance à cosmology at the background level. In addition we constrain the growth index predicted in the context of these models using the latest perturbation growth data in the context of three parametrizations for. The evolution of the best fit effective Newton constant, which incorporates the fðTÞ-gravity effects, is also obtained along with the corresponding 1 error regions. We show that all the viable parameter sectors of the fðTÞ gravity models considered practically reduce these models to ÃCDM. Thus, the degrees of freedom that open up to ÃCDM in the context of fðTÞ gravity models are not utilized by the cosmological data leading to an overall disfavor of these models.

Precision growth index using the clustering of cosmic structures and growth data

“…Alternatively, considering the Planck prior [7] of Ω m0 = 0.30 and minimizing with respect to γ and p 2 = (M h , n eff ) we find γ = 0.56 ± 0.05 and p 2 = (2.0 ± 0.10) × 10 13 h −1 M ⊙ , 0.30 ± 0.20 with χ 2 t,min /df ∼ 16.52/24. With respect to other recent studies, our best fit values of γ are in agreement, within 1σ errors, to that of [57] (see also [58]) who found γ = 0.597 ± 0.046, using a combined statistical analysis of expansion and growth data (SNIa/BAOs/CMB shift /f σ 8 ). However, our joint Ω m0 value is somewhat greater (within ∼ 1.8σ uncertainty), from the derived value of [57], Ω m0 = 0.272 ± 0.003 4 .…”

“…With respect to other recent studies, our best fit values of γ are in agreement, within 1σ errors, to that of [57] (see also [58]) who found γ = 0.597 ± 0.046, using a combined statistical analysis of expansion and growth data (SNIa/BAOs/CMB shift /f σ 8 ). However, our joint Ω m0 value is somewhat greater (within ∼ 1.8σ uncertainty), from the derived value of [57], Ω m0 = 0.272 ± 0.003 4 . For comparison, in Figure 3 we also display the combined (Ω m0 , γ) likelihood contours (see green dotted lines) of [57].…”

“…However, our joint Ω m0 value is somewhat greater (within ∼ 1.8σ uncertainty), from the derived value of [57], Ω m0 = 0.272 ± 0.003 4 . For comparison, in Figure 3 we also display the combined (Ω m0 , γ) likelihood contours (see green dotted lines) of [57]. It is evident that the combined analysis of the growth data with the LRGs clustering provides strong constraints on the growth parameter γ, which implies that this method works equally well with that of the joint SNIa/BAOs/CMB shift /f σ 8 .…”

“…Following the considerations discussed in the previous section and for the sake of simplicity the "cosmo-gravity" vector becomes ) values (solid points) given in section 3.1. Finally, the green dotted curves are the SNIa/BAOs/CMB shift /f σ 8 joint likelihood contours provided by [57]. [57,58] 0.560 ± 0.03 −0.10 ± 0.11 Our study…”

“…The bottom panels show the joint statistical results. Finally, the green dotted curves are the SNIa/BAOs/CMB shift /f σ 8 joint likelihood contours provided by [57].…”