Abstract
We propose an effective anisotropic fluid description for a generic infrared-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, and a microscopic description of the fluid in terms of a Bose–Einstein condensate of gravitons, we find the static, spherically symmetric solution for the metric in terms of the Misner–Sharp mass function and the fluid pressure. At galactic scales, we correctly reproduce the leading MOND-like log(r) and subleading (1/r)log(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.
Highlights
One of the most intriguing puzzles of contemporary fundamental physics is the origin of the dark components of matter and energy in our universe [1,2,3,4]
Our description predicts a tiny Machian modification of the Newtonian potential at galactic scales, which is controlled by the cosmological acceleration
We have proposed an effective fluid description in a general relativity (GR) framework for an infrared-modified theory of gravity
Summary
One of the most intriguing puzzles of contemporary fundamental physics is the origin of the dark components of matter and energy in our universe [1,2,3,4]. We will not address the problem of explaining the origin of DE, the existence of which we take for granted and which we describe by means of a DE fluid component with vacuum equation of state εDE = −pDE = 3 H2/(8 π GN) For small velocities, such a system is approximately described by a static, spherically symmetric geometry, whose physical content is effectively represented by an anisotropic fluid. We will employ a microscopic description in terms of a corpuscular picture, in which the DE fluid component is given by a Bose–Einstein condensate of gravitons [36,37], whereas the back-reaction effects are carried by gravitons in the non-condensed phase of the fluid This will give us a way to relate the pressure causing the dark force to the Newtonian acceleration originating from the presence of baryonic matter. At such scales, we will find a tiny Machian correction to the Newtonian potential depending on the position of the cosmological horizon
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