Can we live in a self-tuning universe?

TL;DR

This paper explores the self-tuning brane scenario as a potential solution to the cosmological constant problem by modifying cosmological equations in extra-dimensional models, analyzing their observational viability.

Contribution

It investigates specific self-tuning models involving bulk scalar fields and their impact on cosmological evolution and observations.

Findings

Self-tuning models face difficulties matching observed cosmological evolution.

Modifications to Friedmann equations can remove vacuum energy effects.

Certain models struggle with observational constraints.

Abstract

The self-tuning brane scenario is an attempt to solve the cosmological constant problem in the context of extra dimensions. Rather than making the vacuum energy small, this approach proceeds by removing the gravitational effect of vacuum energy on the expansion of the universe. Such behavior is only possible through changing the Friedmann equation of conventional cosmology, and we discuss difficulties in obtaining cosmological evolution compatible with observation in this context. Specific models considered include a bulk scalar field coupling to the brane via a conformal transformation of the brane metric, and via a rescaling of the brane volume element.