Using cosmic voids to distinguish f(R) gravity in future galaxy surveys
  We use properties of void populations identified in $N$-body simulations to
forecast the ability of upcoming galaxy surveys to differentiate models of f(R)
gravity from \lcdm~cosmology. We analyze multiple simulation realizations,
which were designed to mimic the expected number densities, volumes, and
redshifts of the upcoming Euclid satellite and a lower-redshift ground-based
counterpart survey, using the public {\tt VIDE} toolkit. We examine void
abundances, ellipicities, radial density profiles, and radial velocity profiles
at redshifts 1.0 and 0.43. We find that stronger f(R) coupling strengths
eliminates small voids and produces voids up to $\sim 20\%$ larger in radius,
leading to a significant tilt in the void number function. Additionally, under
the influence of modified gravity, voids at all scales tend to be measurably
emptier with correspondingly higher compensation walls. The velocity profiles
reflect this, showing increased outflows inside voids and increased inflows
outside voids. Using the void number function as an example, we forecast that
future surveys can constrain the modified gravity coupling strength to $\sim 3
\times 10^{-5}$ using voids.
