Weak Lensing Probes of Modified Gravity

TL;DR

This paper investigates how different modified gravity theories affect weak lensing signals, proposing methods to distinguish these effects from dark energy models and highlighting the potential for future surveys to detect such deviations.

Contribution

It compares predictions of three modified gravity models on weak lensing observables and introduces a test to isolate matter-potential relations from growth factors.

Findings

Modified gravity models produce distinguishable weak lensing signals.

Future surveys can detect these signals with high significance.

Weak lensing provides a stronger signature than ISW effect for modified gravity.

Abstract

We study the effect of modifications to General Relativity on large scale weak lensing observables. In particular, we consider three modified gravity scenarios: f(R) gravity, the DGP model, and TeVeS theory. Weak lensing is sensitive to the growth of structure and the relation between matter and gravitational potentials, both of which will in general be affected by modified gravity. Restricting ourselves to linear scales, we compare the predictions for galaxy-shear and shear-shear correlations of each modified gravity cosmology to those of an effective Dark Energy cosmology with the same expansion history. In this way, the effects of modified gravity on the growth of perturbations are separated from the expansion history. We also propose a test which isolates the matter-potential relation from the growth factor and matter power spectrum. For all three modified gravity models, the predictions for galaxy and shear correlations will be discernible from those of Dark Energy with very high significance in future weak lensing surveys. Furthermore, each model predicts a measurably distinct scale dependence and redshift evolution of galaxy and shear correlations, which can be traced back to the physical foundations of each model. We show that the signal-to-noise for detecting signatures of modified gravity is much higher for weak lensing observables as compared to the ISW effect, measured via the galaxy-CMB cross-correlation.