Maximal symmetry and metric-affine f(R) gravity

The affine connection in a spacetime with a homogenous and isotropic subspace is derived using the properties of maximally symmetric tensors. The number of degrees of freedom in metric-affine gravity is thereby considerably reduced while the theory allows spatio-temporal torsion and remains non-metric. The Ricci tensor and scalar are calculated in terms of the connection and the field equations derived for the Einstein-Hilbert as well as for f(R) Lagrangians. By considering specific forms of f(R), we demonstrate that the resulting Friedmann equations in the so-called Palatini formalism without torsion and metric-affine formalism with maximal symmetry are in general different in the presence of matter.