Light meson gas in the QCD vacuum and oscillating Universe

TL;DR

This paper presents a phenomenological model of a meson gas in the QCD vacuum, linking thermodynamics with cosmology, and suggests the universe may have experienced oscillations during the QCD epoch.

Contribution

It introduces a novel effective quantum-field theoretical model for the hadron gas and explores its implications for cosmological evolution during the QCD transition.

Findings

Universe could oscillate during the QCD epoch

QCD transition affects cosmological evolution

Model connects hadron physics with early universe dynamics

Abstract

We have developed a phenomenological effective quantum-field theoretical model describing the "hadron gas" of the lightest pseudoscalar mesons, scalar {\sigma}-meson and {\sigma}-vacuum, i.e. the expectation value of the {\sigma}-field, at finite temperatures. The corresponding thermodynamic approach was formulated in terms of the generating functional derived from the effective Lagrangian providing the basic thermodynamic information about the "meson plasma + QCD condensate" system. This formalism enables us to study the QCD transition from the hadron phase with direct implications for cosmological evolution. Using the hypothesis about a positively-definite QCD vacuum contribution stochastically produced in early universe, we show that the universe could undergo a series of oscillations during the QCD epoch before resuming unbounded expansion.