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

TL;DR

This paper investigates how modified gravity theories in the Palatini formalism affect large-scale structure formation, finding that relaxing dark matter assumptions can make these models compatible with observations.

Contribution

It demonstrates that relaxing the perfect, pressureless dark matter assumption allows viable f(R) gravity cosmologies to explain accelerated expansion.

Findings

Most models with cold dark matter are incompatible with observed matter power spectrum

Allowing dark matter pressure or imperfections makes some f(R) models consistent with data

Modified gravity models can mimic dark energy effects under relaxed dark matter assumptions

Abstract

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.