Gluon condensate, modified gravity, and the accelerating Universe

TL;DR

This paper investigates how a specific nonanalytic modification to gravity, involving a gluon condensate, can produce an accelerating universe similar to our current cosmological observations, with an evolving dark energy component.

Contribution

It introduces a novel nonanalytic term in the gravitational action linked to a gluon condensate and explores its cosmological implications, leading to an accelerating universe model.

Findings

The model yields an accelerating universe resembling the present one.

The effective dark energy component's equation-of-state parameter approaches -1.

The approach provides a qualitative and quantitative match to observed cosmic acceleration.

Abstract

It has been suggested recently to study the dynamics of a gravitating gluon condensate q in the context of a spatially flat Friedmann-Robertson-Walker universe. The expansion of the Universe (or, more generally, the presence of a nonvanishing Ricci curvature scalar R) perturbs the gluon condensate and may induce a nonanalytic term \tilde{h}(R,q) in the effective gravitational action. The aim of this article is to explore the cosmological implications of a particular nonanalytic term \tilde{h} \propto \eta |R|^{1/2} |q|^{3/4}. With a quadratic approximation of the gravitating gluon-condensate vacuum energy density \rho_{V}(q) near the equilibrium value q_{0} and a small coupling constant \eta of the modified-gravity term \tilde{h}, an "accelerating universe" is obtained which resembles the present Universe, both qualitatively and quantitatively. The unknown component X of this model universe (here, primarily due to modified-gravity effects) has an effective equation-of-state parameter \bar{w}_{X} which is found to evolve toward the value -1 from above.