Weak lensing by galaxy troughs with modified gravity
  We study the imprints that theories of gravity beyond GR can leave on the
lensing signal around line of sight directions that are predominantly
halo-underdense (called troughs) and halo-overdense. To carry out our
investigations, we consider the normal branch of DGP gravity, as well as a
phenomenological variant thereof that directly modifies the lensing potential.
The predictions of these models are obtained with N-body simulation and
ray-tracing methods using the ECOSMOG and Ray-Ramses codes. We analyse the
stacked lensing convergence profiles around the underdense and overdense lines
of sight, which exhibit, respectively, a suppression and a boost w.r.t. the
mean in the field of view. The modifications to gravity in these models
strengthen the signal w.r.t. $\Lambda{\rm CDM}$ in a scale-independent way. We
find that the size of this effect is the same for both underdense and overdense
lines of sight, which implies that the density field along the overdense
directions on the sky is not sufficiently evolved to trigger the suppression
effects of the screening mechanism. These results are robust to variations in
the minimum halo mass and redshift ranges used to identify the lines of sight,
as well as to different line of sight aperture sizes and criteria for their
underdensity and overdensity thresholds.
