Viable Palatini-f(R) cosmologies with generalized dark matter

Understand

We study the formation of large-scale structure in universes dominated by dark matter and driven to accelerated expansion by f(R) gravity in the Palatini formalism.

• If the dark matter is cold, practically all of these models are ruled out because they fail to reproduce the observed matter power spectrum.
• We point out that if the assumption that dark matter is perfect and pressureless at all scales is relaxed, nontrivial alternatives to a cosmological constant become viable within this class of modified gravity models.