  The statistical properties of dark matter halos, the building blocks of
cosmological observables associated with structure in the universe, offer many
opportunities to test models for cosmic acceleration, especially those that
seek to modify gravitational forces. We study the abundance, bias and profiles
of halos in cosmological simulations for one such model: the modified action
f(R) theory. In the large field regime that is accessible to current
observations, enhanced gravitational forces raise the abundance of rare massive
halos and decrease their bias but leave their (lensing) mass profiles largely
unchanged. This regime is well described by scaling relations based on a
modification of spherical collapse calculations. In the small field regime,
enhanced forces are suppressed inside halos and the effects on halo properties
are substantially reduced for the most massive halos. Nonetheless, the scaling
relations still retain limited applicability for the purpose of establishing
conservative upper limits on the modification to gravity.
