Abstract. We show that inflation and current cosmic acceleration can be generated by a metric-affine f(R) gravity formulated in the Einstein conformal frame, if the gravitational Lagrangian L(R) contains both positive and negative powers of the curvature scalar R. In this frame, we give the equations for the expansion of the homogeneous and isotropic matter-dominated universe in the case , where α and β are constants. We also show that gravitational effects of matter in such a universe at very late stages of its expansion are weakened by a factor that tends to 3/4, and the energy density of matter scales the same way as in the ΛCDM model only when κ α.

PACS numbers: 04.50.-h, 98.80.−k

Print publication: Issue 6 (21 March 2006)
Received 8 October 2005, in final form 23 January 2006
Published 28 February 2006