Structure formation in the Deser-Woodard nonlocal gravity model: a reappraisal
In this work, we extend previous analyses of the structure formation in the $f(\Box^{-1}R)$ model of nonlocal gravity proposed by Deser and Woodard (DW), which reproduces the background expansion of $Λ$CDM with no need of a cosmological constant nor of any dimensional constant beside Newton's one. A previous analysis based on redshift-space distortions (RSD) data concluded that the model was ruled out. In this work we revisit the issue and find that, when recast in a localized model, the DW model is not ruled out and actually gives a better fit to RSD data than $Λ$CDM. At the same time, the model predicts a slightly lower value of $σ_{8}$ than $Λ$CDM, in agreement with recent estimates based on lensing. We also produce analytical approximations of the two modified gravity functions and of $fσ_{8}(z)$ as a function of redshift. Finally, we also show how much the fit depends on initial conditions when these are generalized with respect to a standard matter-dominated era.