2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/189697We consider a modified gravity theory, f(R)=R-a/R^n+bR^m, in the metric formulation, which has been suggested to produce late time acceleration in the Universe, whilst satisfying local fifth-force constraints. We investigate the parameter range for this theory, considering the regimes of early and late-time acceleration, Big Bang Nucleosynthesis and fifth-force constraints. We conclude that it is difficult to find a unique range of parameters for consistency of this theory.Replaced to match version published in Phys. Rev. D. - corrected references and minor typos. 26 pages, revtex, 10 eps figures, 1 diagramHigh Energy Physics - TheoryAstrophysicsGeneral Relativity and Quantum Cosmologytext