Weak lensing by voids in modified lensing potentials
  We study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies,
which are examples of theories of gravity that modify the lensing potential. We
find voids in the dark matter and halo density fields of N-body simulations and
compute their lensing signal analytically from the void density profiles, which
we show are well fit by a simple analytical formula. In the Cubic Galileon
model, the modifications to gravity inside voids are not screened and they
approximately double the size of the lensing effects compared to GR. The
difference is largely determined by the direct effects of the fifth force on
lensing and less so by the modified density profiles. For this model, we also
discuss the subtle impact on the force and lensing calculations caused by the
screening effects of haloes that exist in and around voids. In the Nonlocal
model, the impact of the modified density profiles and the direct modifications
to lensing are comparable, but they boost the lensing signal by only $\approx
10\%$, compared with that of GR. Overall, our results suggest that lensing by
voids is a promising tool to test models of gravity that modify lensing.
