Mimicking Lambda with a spin-two ghost condensate

TL;DR

This paper introduces a higher-derivative braneworld gravity model with a spin-two ghost condensate that achieves stable late-time cosmic acceleration without a cosmological constant, matching observational bounds.

Contribution

It presents a novel gravity model that mimics Lambda and DGP features but remains stable and consistent with cosmological tests, using a ghost condensate mechanism.

Findings

Achieves stable acceleration without cosmological constant

Recovers four-dimensional gravity at subhorizon scales

No linearized instabilities in the model

Abstract

We propose a simple higher-derivative braneworld gravity model which contains a stable accelerating branch, in the absence of cosmological constant or potential, that can be used to describe the late time cosmic acceleration. This model has similar qualitative features to that of Dvali-Gabadadze-Porrati, such as the recovery of four-dimensional gravity at subhorizon scales, but unlike that case, the graviton zero mode is massless and there are no linearized instabilities. The acceleration rather is driven by bulk gravity in the form of a spin-two ghost condensate. We show that this model can be consistent with cosmological bounds and tests of gravity.