A Lower Growth Rate from Recent Redshift Space Distortion Measurements than Expected from Planck

Abstract

We perform a meta-study of recently published Redshift Space Distortion (RSD) measurements of the cosmological growth rate, f(z) \sigma_8(z). We analyse the latest results from the 6dFGS, BOSS, LRG, WiggleZ and VIPERS galaxy redshift surveys, and compare the measurements to expectations from Planck. In this Letter we point out that the RSD measurements are consistently lower than the values expected from Planck, and the relative scatter between the RSD measurements is lower than expected. A full resolution of this issue may require a more robust treatment of non-linear effects in RSD models, although the trend for a low \sigma_8 agrees with recent constraints on \sigma_8 and \Omega_m from Sunyaev-Zeldovich cluster counts identified in Planck.