Phenomenology of the Modified Newtonian Dynamics and the Concordance Cosmological Scenario

Abstract

After reviewing the modified Newtonian dynamics (MOND) proposal, we advocate that the associated phenomenology may actually not result from a modification of Newtonian gravity, but from a mechanism of "gravitational polarization" of some dipolar medium playing the role of dark matter. We then build a relativistic model within standard general relativity to describe (at some phenomenological level) the dipolar dark matter polarizable in a gravitational field. The model naturally involves a cosmological constant, and is shown to reduce to the concordance cosmological scenario (Lambda-CDM) at early cosmological times. From the mechanism of gravitational polarization, we recover the phenomenology of MOND in a typical galaxy at low redshift. Furthermore, we show that the cosmological constant Lambda scales like a0^2, where a0 is the constant MOND acceleration scale, in good agreement with observations.

8 pages; to appear in the Proceedings of the "43rd Rencontres de Moriond", La Thuile (Italy), March 2008, edited by J. Dumarchez, Y. Giraud-Heraud and J. Tran Thanh Van