Second-order weak lensing from modified gravity

TL;DR

This paper investigates second-order corrections in weak gravitational lensing within scalar-tensor theories, finding these effects are generally negligible, supporting weak lensing as a reliable mass tracer in cosmology despite modifications to gravity.

Contribution

It provides a systematic analysis of second-order weak lensing effects in scalar-tensor theories, demonstrating their small impact and reinforcing the robustness of weak lensing as a cosmological tool.

Findings

Second-order corrections are typically negligible in scalar-tensor theories.

Weak lensing remains a reliable mass tracer despite potential gravity modifications.

Non-Gaussianities from nonlinearities are minimal within the studied framework.

Abstract

We explore the sensitivity of weak gravitational lensing to second-order corrections to the spacetime metric within a cosmological adaptation of the parameterized post-Newtonian framework. Whereas one might expect nonlinearities of the gravitational field to introduce non-Gaussianity into the statistics of the lensing convergence field, we show that such corrections are actually always small within a broad class of scalar-tensor theories of gravity. We show this by first computing the weak lensing convergence within our parameterized framework to second order in the gravitational potential, and then computing the relevant post-Newtonian parameters for scalar-tensor gravity theories. In doing so we show that this potential systematic factor is generically negligible, thus clearing the way for weak lensing to provide a direct tracer of mass on cosmological scales for a wide class of gravity theories despite uncertainties in the precise nature of the departures from general relativity.