Misc,
Effective Fluid Description of the Dark Universe
(Jul 31, 2017)
Abstract
We propose an effective anisotropic fluid description for a generic
IR-modified theory of gravity. In our framework, the additional component of
the acceleration commonly attributed to dark matter is explained as a radial
pressure generated by the reaction of the dark energy fluid to the presence of
baryonic matter. Using quite general assumptions we find the static,
spherically symmetric solution for the metric in terms of the Misner-Sharp mass
function and of the fluid pressure. At galactic scales, we correctly reproduce
the leading MOND-like \$łog( r)\$ and subleading \$(1/r)\,łog( r)\$ terms in the
weak-field expansion of the potential. Our description also predicts a tiny (of
order \$10^-6\$ for a typical spiral galaxy) Machian modification of the
Newtonian potential at galactic scales, which is controlled by the cosmological
acceleration \$a\_0\$.
