Galactic rotation curves in brane world models

TL;DR

This paper investigates whether brane world models, which include extra-dimensional effects, can explain galactic rotation curves traditionally attributed to dark matter, showing good agreement with observational data.

Contribution

It provides an analytical model for galactic rotation curves in brane world scenarios and tests its fit to observed galaxy data, proposing an alternative to dark matter.

Findings

Brane world effects can replicate dark matter in galactic dynamics.

The model fits observed rotation curves within 1σ confidence level.

Extra-dimensional models are viable alternatives to dark matter.

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.