Evidence for departure from ΛCDM with LSS

Abstract

We investigate the growth index parameter γand the time variation of the gravitational constant G_{eff} by using the currently available growth function f(z) data at different redshifts, with and without scaling to the fiducial ΛCDM model. We inquire the four different models of γincluding a constant γ. From a χ^2 minimization, we constrain the parameter spaces of models and show that ΛCDM model is excluded by 1-σlevel from current f(z) data. G_{eff} is different from the Newton's gravitational constant G_{N} in modified gravity theories and interestingly, the current data shows that G_{eff} \neq G_{N} at z \gtrsim 0.2 \sim 0.3 at 3-σlevel. From these, we conclude that Einstein's General Relativity with ΛCDM is ruled out by 99% confidence level from large scale structure observations.