Galactic rotation curves in brane world models

Abstract

In the braneworld scenario the four dimensional effective Einstein equation has extra source terms, which arise from the embedding of the 3-brane in the bulk. These non-local effects, generated by the free gravitational field of the bulk, may provide an explanation for the dynamics of the neutral hydrogen clouds at large distances from the galactic center, which is usually explained by postulating the existence of the dark matter. In the present paper we consider the asymptotic behavior of the galactic rotation curves in the brane world models, and we compare the theoretical results with observations of both High Surface Brightness and Low Surface Brightness galaxies. For the chosen sample of galaxies we determine first the baryonic parameters by fitting the photometric data to the adopted galaxy model; then we test the hypothesis of the Weyl fluid acting as dark matter on the chosen sample of spiral galaxies by fitting the tangential velocity equation of the combined baryonic-Weyl model to the rotation curves. We give an analytical expression for the rotational velocity of a test particle on a stable circular orbit in the exterior region to a galaxy, with Weyl fluid contributions included. The model parameter ranges for which the $\chi^2$ test provides agreement (within 1$\sigma$ confidence level) with observations on the velocity fields of the chosen galaxy sample are then determined. There is a good agreement between the theoretical predictions and observations, showing that extra-dimensional models can be effectively used as a viable alternative to the standard dark matter paradigm.Comment: to be published in MNRAS, 17 pages, 31 figures, version including corrections on the proo

Extending the geometric deformation: New black hole solutions

“…In this extra-dimensional context, the exterior r > R of a spherically symmetric self-gravitating system of radius R will be filled with a Weyl fluid of effective density U and anisotropy P µν . This fluid has interesting phenomenological consequences, and indeed may be used to explain some issues associated with the gravitational interaction beyond the Solar System scales [69]- [71].…”

“…where the expressions in Eqs. (14) and (20) have been used in the field equations (5) and (6). Therefore, according to Eq.…”

The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology

“…But, MOG must effectively become Milgromian on galaxy scales. In addition, it has been shown that flat rotation curves of galaxies can be accounted for without DM by brane-world models (Gergely et al 2011) as well as by f(R)-gravity models (Capozziello et al 2009) whereby lensing constraints are also being studied in these and other theories.…”

Null fluid collapse in brane world models

“…Specifically, several classes of static, spherically-symmetric, solutions of the vacuum field equations on the brane have been obtained [64][65][66][67]. As a possible physical application of these solutions the behavior of the angular velocity, v tg , of test particles in stable circular orbits has been considered [66][67][68][69][70][71]. The general form of the solution, together with the specific values of the two, arbitrary, constants of integration, uniquely determines the rotational velocity of the particle.…”