2007/05/31 by Baojiu Li, John D. Barrow, David F. Mota
Physics and Astronomy · #Black Holes and Theoretical Physics #Classical mechanics #Cosmological constant #Cosmology #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #Gravitation #Lambda #Mathematical physics #Omega #Perturbation (astronomy) #Perturbation theory (quantum mechanics) #Physics #Quantum mechanics #astro-ph #gr-qc #hep-ph
paper · pdf · doi:10.1103/physrevd.76.044027
published as Phys.Rev.D76:044027,2007 · 10 pages, 4 figures. Referenes updated; to appear in Phys. Rev. D
arxiv created 2007/07/17 · openalex publication_date 2007/08/30 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We consider the cosmology where some function f(G) of the Gauss-Bonnet term G is added to the gravitational action to account for the late-time accelerating expansion of the universe. The covariant and gauge invariant perturbation equations are derived with a method which could also be applied to general f(R,RabRab,RabcdRabcd) gravitational theories. It is pointed out that, despite their fourth-order character, such f(G) gravity models generally cannot reproduce arbitrary background cosmic evolutions; for example, the standard \ensuremathΛCDM paradigm with \ensuremathΩDE=0.76 cannot be realized in f(G) gravity theories unless f is a true cosmological constant because it imposes exclusionary constraints on the form of f(G). We analyze the perturbation equations and find that, as in the f(R) model, the stability of early-time perturbation growth puts some constraints on the functional form of f(G), in this case \ensuremath∂2f/\ensuremath∂G2<0. Furthermore, the stability of small-scale perturbations also requires that f not deviate significantly from a constant. These analyses are illustrated by numerically propagating the perturbation equations with a specific model reproducing a representative \ensuremathΛCDM cosmic history. Our results show how the f(G) models are highly constrained by cosmological data.