Testing Modified Gravity with Cosmic Shear
  We use the cosmic shear data from the Canada-France-Hawaii Telescope Lensing
Survey to place constraints on $f(R)$ and {\it Generalized Dilaton} models of
modified gravity. This is highly complimentary to other probes since the
constraints mainly come from the non-linear scales: maximal deviations with
respects to the General-Relativity + $\Lambda$CDM scenario occurs at $k\sim1 h
\mbox{Mpc}^{-1}$. At these scales, it becomes necessary to account for known
degeneracies with baryon feedback and massive neutrinos, hence we place
constraints jointly on these three physical effects. To achieve this, we
formulate these modified gravity theories within a common tomographic
parameterization, we compute their impact on the clustering properties relative
to a GR universe, and propagate the observed modifications into the weak
lensing $\xi_{\pm}$ quantity. Confronted against the cosmic shear data, we
reject the $f(R)$ $\{ |f_{R_0}|=10^{-4}, n=1\}$ model with more than 99.9%
confidence interval (CI) when assuming a $\Lambda$CDM dark matter only model.
In the presence of baryonic feedback processes and massive neutrinos with total
mass up to 0.2eV, the model is disfavoured with at least 94% CI in all
different combinations studied. Constraints on the $\{ |f_{R_0}|=10^{-4},
n=2\}$ model are weaker, but nevertheless disfavoured with at least 89% CI. We
identify several specific combinations of neutrino mass, baryon feedback and
$f(R)$ or Dilaton gravity models that are excluded by the current cosmic shear
data. Notably, universes with three massless neutrinos and no baryon feedback
are strongly disfavoured in all modified gravity scenarios studied. These
results indicate that competitive constraints may be achieved with future
cosmic shear data.
