Dilatonic ghost condensate as dark energy

TL;DR

This paper proposes a stable, ghost scalar field dark energy model within string theory, demonstrating conditions for cosmological scaling solutions and addressing quantum stability issues.

Contribution

It introduces a ghost condensate dark energy model with higher-order derivatives ensuring stability and derives conditions for scaling solutions in dilaton-dark matter systems.

Findings

A viable phantom dark energy model without quantum instability.

Conditions for cosmological scaling solutions derived.

Rapidly increasing coupling leads to stable late-time acceleration.

Abstract

We explore a dark energy model with a ghost scalar field in the context of the runaway dilaton scenario in low-energy effective string theory. We address the problem of vacuum stability by implementing higher-order derivative terms and show that a cosmologically viable model of ``phantomized'' dark energy can be constructed without violating the stability of quantum fluctuations. We also analytically derive the condition under which cosmological scaling solutions exist starting from a general Lagrangian including the phantom type scalar field. We apply this method to the case where the dilaton is coupled to non-relativistic dark matter and find that the system tends to become quantum mechanically unstable when a constant coupling is always present. Nevertheless, it is possible to obtain a viable cosmological solution in which the energy density of the dilaton eventually approaches the present value of dark energy provided that the coupling rapidly grows during the transition to the scalar field dominated era.