We construct an updated and extended compilation of growth rate data based on recent Redshift Space Distortion ( RSD ) measurements .
The dataset consists of 34 datapoints and includes corrections for model dependence .
In order to minimize overlap and maximize the independence of the datapoints we also construct a subsample of this compilation ( a ‘ Gold ’ growth dataset ) which consists of 18 datapoints .
We test the consistency of this dataset with the best fit Planck15/ \Lambda CDM parameters in the context of General Relativity ( GR ) using the evolution equation for the growth factor \delta ( a ) with a w CDM background .
We find tension at the \sim 3 \sigma level between the best fit parameters w ( the dark energy equation of state ) , \Omega _ { 0 m } ( the matter density parameter ) and \sigma _ { 8 } ( the matter power spectrum normalization on scales 8 h ^ { -1 } Mpc ) and the corresponding Planck15/ \Lambda CDM parameters ( w = -1 , \Omega _ { 0 m } = 0.315 and \sigma _ { 8 } = 0.831 ) .
We show that the tension disappears if we allow for evolution of the effective Newton constant , parametrized as G _ { \textrm { eff } } ( a ) / G _ { \textrm { N } } = 1 + g _ { a } ( 1 - a ) ^ { n } - g _ { a } ( 1 - a ) ^ { 2 n } with n \geq 2 where g _ { a } and n are parameters of the model , a is the scale factor and z = 1 / a - 1 is the redshift .
This parametrization satisfies three important criteria : a ) positive energy of graviton ( G _ { \textrm { eff } } > 0 ) , b ) consistency with Big Bang Nucleosynthesis constraints ( G _ { \textrm { eff } } ( a \ll 1 ) / G _ { \textrm { N } } = 1 ) and c ) consistency with Solar System tests ( G _ { \textrm { eff } } ( a = 1 ) / G _ { \textrm { N } } = 1 and G _ { \textrm { eff } } ^ { \prime } ( a = 1 ) / G _ { \textrm { N } } = 0 ) .
We show that the best fit form of G _ { \textrm { eff } } ( z ) obtained from the growth data corresponds to weakening gravity at recent redshifts ( decreasing function of z ) and we demonstrate that this behavior is not consistent with any scalar-tensor Lagrangian with a real scalar field .
Finally , we use MGCAMB to find the best fit G _ { \textrm { eff } } ( z ) obtained from the Planck CMB power spectrum on large angular scales and show that it is a mildly increasing function of z , in 3 \sigma tension with the corresponding decreasing best fit G _ { \textrm { eff } } ( z ) obtained from the growth data .