Probing Newton’s constant on vast scales: Dvali-Gabadadze-Porrati gravity, cosmic acceleration, and large scale structure

The nature of the fuel that drives today's cosmic acceleration is an open andtantalizing mystery. The braneworld theory of Dvali, Gabadadze, and Porrati(DGP) provides a context where late-time acceleration is driven not by someenergy-momentum component (dark energy), but rather is the manifestation of theexcruciatingly slow leakage of gravity off our four-dimensional world into anextra dimension. At the same time, DGP gravity alters the gravitational forcelaw in a specific and dramatic way at cosmologically accessible scales. Wederive the DGP gravitational force law in a cosmological setting for sphericalperturbations at subhorizon scales and compute the growth of large-scalestructure. We find that a residual repulsive force at large distances givesrise to a suppression of the growth of density and velocity perturbations.Explaining the cosmic acceleration in this framework leads to a present dayfluctuation power spectrum normalization sigma_8 <= 0.8 at about the two-sigmalevel, in contrast with observations. We discuss further theoretical worknecessary to go beyond our approximations to confirm these results.Comment: 21 pages, 3 figures. References adde