A weak lensing detection of a deviation from General Relativity on cosmic scales

We consider evidence for deviations from General Relativity (GR) in the growth of large scale structure, using two parameters, $\gamma$ and $\eta$, to quantify the modification. We consider the Integrated Sachs-Wolfe effect (ISW) in the WMAP Cosmic Microwave Background data, the cross-correlation between the ISW and galaxy distributions from 2MASS and SDSS surveys, and the weak lensing shear field from the Hubble Space Telescope's COSMOS survey along with measurements of the cosmic expansion history. We find current data, driven by the COSMOS weak lensing measurements, disfavors GR on cosmic scales, preferring $\eta<1$ at $1<z<2$ at the 98% significance level.