Phantom without ghost

TL;DR

This paper explores three modified gravity models—Brans-Dicke, scalar-Einstein-Gauss-Bonnet, and F(R)—that realize the phantom regime without ghosts or instabilities, supporting gravitational modifications over exotic matter.

Contribution

It introduces ghost-free, stable modified gravity scenarios that achieve the phantom regime, addressing issues of instabilities in naive approaches.

Findings

Phantom regime can be realized without ghosts in modified gravity models.

The models are free of perturbative instabilities.

Gravitational modifications are favored over exotic matter for phantom behavior.

Abstract

The Nine-Year WMAP results combined with other cosmological data seem to indicate an enhanced favor for the phantom regime, comparing to previous analyses. This behavior, unless reversed by future observational data, suggests to consider the phantom regime more thoroughly. In this work we provide three modified gravitational scenarios in which we obtain the phantom realization without the appearance of ghosts degrees of freedom, which plague the naive approaches on the subject, namely the Brans-Dicke type gravity, the scalar-Einstein-Gauss-Bonnet gravity, and the $F(R)$ gravity, which are moreover free of perturbative instabilities. The phantom regime seems to favor the gravitational modification instead of the universe-content alteration.