The Cosmological Constant Problem from a Brane-World Perspective

TL;DR

This paper examines the challenges in brane-world models addressing the cosmological constant problem, highlighting issues with singularities, fine-tuning, and the impact of bulk scalar fields on the effective cosmological constant.

Contribution

It identifies the limitations of singularity solutions, explores the effects of bulk scalar potentials, and discusses stability concerns in brane-world cosmological models.

Findings

Singularity solutions are inconsistent without fine-tuning.

Bulk scalar potentials can induce nonzero cosmological constants.

Classical solutions' stability is affected by quantum corrections.

Abstract

We point out several subtleties arising in brane-world scenarios of cosmological constant cancellation. We show that solutions with curvature singularities are inconsistent, unless the contribution to the effective four-dimentional cosmological constant of the physics that resolves the singularities is fine-tuned. This holds for both flat and curved branes. Irrespective of this problem, we then study an isolated class of flat solutions in models where a bulk scalar field with a vanishing potential couples to a 3-brane. We give an example where the introduction of a bulk scalar potential results in a nonzero cosmological constant. Finally we comment on the stability of classical solutions of the brane system with respect to quantum corrections.