Brane-$f(R)$ gravity and dark matter

TL;DR

This paper explores how brane-$f(R)$ gravity can explain dark matter phenomena by deriving a modified virial theorem, analyzing galaxy rotation curves, light deflection, and radar delay without invoking dark matter particles.

Contribution

It introduces a geometric mass approach in brane-$f(R)$ gravity to account for galaxy cluster mass discrepancies and derives exact solutions for galaxy rotation curves using conformal symmetry.

Findings

Geometric mass explains virial mass discrepancy

Galaxy rotation curves tend to a constant velocity at large radii

Light deflection and radar delay are consistent with observations

Abstract

The collision-free Boltzmann equation is used in the context of brane-$f(R)$ gravity to derive the virial theorem. It is shown that the virial mass is proportional to certain geometrical terms appearing in the Einstein field equations and contributes to gravitational energy and that such a geometric mass can be attributed to the virial mass discrepancy in a cluster of galaxies. In addition, the galaxy rotation curves are studied by utilizing the concept of conformal symmetry and notion of conformal Killing symmetry. The field equations may then be obtained in an exact parametric form in terms of the parameter representing the conformal factor. This provides the possibility of studying the behavior of the angular velocity of a test particle moving in a stable circular orbit. The tangential velocity can be derived as a function of the conformal factor and integration constants, resulting in a constant value at large radial distances. Relevant phenomenon such as the deflection of light passing through a region where the rotation curves are flat and the radar echo delay are also studied.