Galaxy clustering constraints on deviations from Newtonian gravity at cosmological scales

In spite of the growing observational evidence for dark matter and dark energy in the universe, their physical nature is largely unknown. In fact, several authors have proposed modifications of Newton's law of gravity at cosmological scales to account for the apparent acceleration of the cosmic expansion. Inspired by such suggestions, we attempt to constrain possible deviations from Newtonian gravity by means of the clustering of SDSS (Sloan Digital Sky Survey) galaxies. To be specific, we assume a simple modification of Newton's law with an additional Yukawa-type term characterized by the amplitude alpha and the length scale lambda. Adopting spatially-flat universes dominated by cold dark matter and/or dark energy, we solve a linear perturbation equation for the growth of density fluctuations. In particular, we find an exact analytic solution for the Einstein-de Sitter case. Following the Peacock-Dodds prescription, we compute the nonlinear power spectra of mass fluctuations, perform a statistical comparison with the SDSS galaxy data, and derive constraints in the alpha-lambda plane; for instance, we obtain the constraints of -0.5 < alpha < 0.6 and -0.8 < alpha < 0.9 (99.7% confidence level) for lambda = 5h(-1) Mpc and 10h(-1) Mpc, respectively. We also discuss several future possibilities for improving our analysis.