An accurate fitting function for scale-dependent growth rate in Hu-Sawicki f ( R ) gravity

We present a simple fitting formula for the scale-dependent growth rate of Hu-Sawicki model in f(R) modified gravity. We compare the accuracy of the fitting function against numerical results and report achieving a sub-percent maximum error for all different studied cases. The validity of the fitting function is tested against a wide range of scales, 10−4≤k≤5[Mpc−1], for various redshift values in the range of z∈[0.0,3.0] and different |fR0| values. This formula is useful in producing predictions for cosmological probes that are sensitive to growth rate such as redshift space distortions, galaxy-galaxy correlation function, peculiar velocity statistics and pairwise velocities of galaxy clusters.