The effect of modified gravity on weak lensing

We study the effect of modified gravity on weak lensing in a class of scalar-tensor theory that includes f(R)f(R) gravity as a special case. These models are designed to satisfy local gravity constraints by having a large scalar-field mass in a region of high curvature. Matter density perturbations in these models are enhanced at small redshifts because of the presence of a coupling Q   that characterizes the strength between dark energy and non-relativistic matter. We compute a convergence power spectrum of weak lensing numerically and show that the spectral index and the amplitude of the spectrum in the linear regime can be significantly modified compared to the ΛCDM model for large values of |Q||Q| of the order of unity. Thus weak lensing provides a powerful tool to constrain such large coupling scalar-tensor models including f(R)f(R) gravity.