The cosmological dark sector as a scalar $\sigma$-meson field

TL;DR

This paper demonstrates that a classical chiral symmetry breaking in a low-energy effective sigma-model can produce a dark energy component that scales with the Hubble parameter, aligning with cosmological observations.

Contribution

It shows that the dark sector behavior, including decaying dark energy and dark particle creation, emerges at the classical level from a sigma-model, linking QCD vacuum effects to cosmology.

Findings

Dark energy scales linearly with the Hubble parameter.

Homogeneous creation of non-relativistic dark particles occurs.

The sigma mass scale determines creation rate and horizon properties.

Abstract

Previous quantum field estimations of the QCD vacuum in the expanding space-time lead to a dark energy component scaling linearly with the Hubble parameter, which gives the correct figure for the observed cosmological term. Here we show that this behaviour also appears at the classical level, as a result of the chiral symmetry breaking in a low energy, effective $\sigma$-model. The dark sector is described in a unified way by the $\sigma$ condensate and its fluctuations, giving rise to a decaying dark energy and a homogeneous creation of non-relativistic dark particles. The creation rate and the future asymptotic de Sitter horizon are both determined by the $\sigma$ mass scale.