Cosmological constraints on $γ$-gravity models
In this paper we place observational constraints on the well-known $γ$-gravity $f(R)$ model using the latest cosmological data, namely we use the latest growth rate, Cosmic Microwave Background, Baryon Acoustic Oscillations, Supernovae type Ia and Hubble parameter data. Performing a joint likelihood analysis we find that the $γ$-gravity model is in very good agreement with observations. Utilizing the AIC statistical test we statistically compare the current $f(R)$ model with $Λ$CDM cosmology and find that they are statistically equivalent. Therefore, $γ$-gravity can be seen as a useful scenario toward testing deviations from General Relativity. Finally, we note that we find somewhat higher values for the $f(R)$ best-fit values compared to those mentioned in the past in the literature and we argue that this could potential alleviate the halo-mass function problem.