Stealth Acceleration and Modified Gravity

TL;DR

This paper introduces a class of braneworld models that achieve late-time acceleration only in the presence of matter, called stealth-acceleration, with modified gravity effects emerging at late times.

Contribution

It constructs stable, asymmetric braneworld models with stealth-acceleration, analyzing their linear stability, graviton localization, and cosmological implications compared to LambdaCDM.

Findings

Models exhibit late-time acceleration only with matter presence.

Gravity is modified at late times due to quasi-localized graviton.

Identifies stable parameter regions and compares models to standard cosmology.

Abstract

We show how to construct consistent braneworld models which exhibit late time acceleration. Unlike self-acceleration, which has a de Sitter vacuum state, our models have the standard Minkowski vacuum and accelerate only in the presence of matter, which we dub ``stealth-acceleration''. We use an effective action for the brane which includes an induced gravity term, and allow for an asymmetric set-up. We study the linear stability of flat brane vacua and find the regions of parameter space where the set-up is stable. The 4-dimensional graviton is only quasi-localised in this set-up and as a result gravity is modified at late times. One of the two regions is strongly coupled and the scalar mode is eaten up by an extra symmetry that arises in this limit. Having filtered the well-defined theories we then focus on their cosmology. When the graviton is quasi-localised we find two main examples of acceleration. In each case, we provide an illustrative model and compare it to LambdaCDM.