Avoiding the cosmological constant issue in a class of phenomenologically viable $F(R,{\cal G})$ theories

TL;DR

This paper explores specific $F(R,{ m f G})$ gravity models that naturally avoid the cosmological constant problem by ensuring de Sitter space as a stable attractor independent of vacuum energy.

Contribution

It identifies a class of phenomenologically viable $F(R,{ m f G})$ theories where de Sitter space is a stable attractor, circumventing the cosmological constant issue.

Findings

De Sitter space acts as a stable attractor in these models.

The models are free of ghosts and instabilities.

The Hubble rate is independent of vacuum energy.

Abstract

In this paper we investigate a class of phenomenologically viable $F(R,{\cal G})$ theories that are able to avoid the cosmological constant issue. While the absence of ghosts and other kinds of instability issues is of prime importance, other reasonable requirements such as vanishing effective (low curvature) cosmological constant, including the flat space as a stable vacuum solution, are also imposed on the viable models. These are free of the cosmological constant problem thanks to the following outstanding feature: the de Sitter space is an attractor of the asymptotic cosmological dynamics, with the resulting constant Hubble rate being unrelated both to the energy density of vacuum and to the low-curvature effective cosmological constant.