Growth of perturbations in nonlocal gravity with non-$\Lambda$CDM background

Understand

We re-analyze the nonlocal gravity model of Deser and Woodard which was proposed to account for the current phase of cosmic acceleration.

• We show that the growth of perturbations predicted by this nonlocal gravity model when its background evolution is fixed by some particular non-$\Lambda$CDM models can be substantially lower than when its background is fixed by $\Lambda$CDM.
• This can be seen when we consider the background expansion by a dark energy model with a slightly less negative equation of state with respect to cosmological constant.
• Our results hints towards a fact that the choice of the background expansion can play a crucial role how this nonlocal gravity model can fit the growth history data.