Cosmological constraints from the Hubble parameter onf(R) cosmologies

Abstract

Modified f(R) gravity in the Palatini approach has been recently applied in cosmology as a realistic alternative todark energy. In this regard, a number of authors have searched for observational constraints on severalf(R) gravity functional forms using mainly data from type Ia supernovae, cosmic microwavebackground (CMB) radiation and large scale structure. In this paper, considering ahomogeneous and isotropic flat universe, we use determinations of the Hubble functionH(z), which are based on a differential age method, to place bounds on the free parameters of thef(R) = R−β/Rn functional form.We also combine the H(z) data with constraints from baryon acoustic oscillations and CMB measurements, obtaining ranges of valuesfor n and β in agreement with other independent analyses. We find that, for some intervals ofn andβ, modelsbased on f(R) = R−β/Rn gravity in the Palatini approach, unlike the metric formalism, can produce a sequence ofradiation-dominated, matter-dominated, and accelerating periods without the need for darkenergy.