Cosmological Dark Matter from a Bulk Black Hole

TL;DR

This paper explores a brane-world cosmology in a five-dimensional scalar-gravity background, proposing that a bulk black hole's effects can mimic dark matter, with implications for gravity and cosmological models.

Contribution

It introduces a novel mechanism where bulk black holes induce dark matter-like behavior in brane-world cosmology within a linear dilaton background.

Findings

The Friedmann equation includes a term acting as dark matter.

The model predicts only mild short-distance gravity corrections.

General models interpolate between dark radiation, dark matter, and dark energy.

Abstract

We study the cosmology of a three-brane in a specific five-dimensional scalar-gravity (i.e. soft-wall) background, known as the linear dilaton background. We discover that the Friedmann equation of the brane-world automatically contains a term mimicking pressureless matter. We propose to identify this term as dark matter. This dark matter arises as a projection of the bulk black hole on the brane, which contributes to the brane Friedmann equation via both the Weyl tensor and the scalar stress tensor. The nontrivial matter-like behavior is due to an exact cancellation between the Weyl and scalar pressures. We show that the Newtonian potential only receives a mild short-distance correction going as inverse distance squared, ensuring compatibility of the linear dilaton brane-world with observed 4D gravity. Our setup can be viewed as a consistent cosmological description of the holographic theories arising in the linear dilaton background. We also present more general scalar-gravity models where the brane cosmology features an effective energy density whose behavior smoothly interpolates between dark radiation, dark matter and dark energy depending on a model parameter.