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

TL;DR

A metastudy of recently published redshift space distortion measurements of the cosmological growth rate, f(z)σ8(z), pointing out that the RSD measurements are consistently lower than the values expected from Planck, and the relative scatter between the R SD measurements is lower than expected.

Abstract

We perform a meta-study of recently published Redshift Space Distortion (RSD) measurements of the cosmological growth rate, f(z) σ_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 σ_8 agrees with recent constraints on σ_8 and Ω_m from Sunyaev-Zeldovich cluster counts identified in Planck.

Figures (1)

• Figure 1: Comparing models to recent measurements of $f(z)\sigma_{8}(z)$. We are plotting results for the LRG$_{200}$ data set. The open markers are the original published values from the RSD measurements, and the filled markers are after accounting for the Alcock-Paczynski effect in going from WMAP to Planck cosmology. The measurement error bars are at the 1 standard deviation uncertainty level. The dashed red line illustrates the expected growth rate from $\Lambda$CDM with Planck parameters, with the 1 and 2 standard deviation uncertainty illustrated with the shaded bands. The solid blue line and corresponding blue shaded regions illustrates the best fit to the RSD data with the gravitational slip model. We note that almost all the measurements include our best fit model at the 1 standard deviation uncertainty level, which is reflected in the low $\chi^{2}$ in Table \ref{['tab:GrowthRateResults']}. The one standard deviation range of the model (the darker blue band) is narrower than the typical one standard deviation uncertainty on any of the measurements because the fit has been calculated from the several independent measurements.