Dark Chiral Phase Transition Driven by Chemical Potential and its Gravitational Wave Test

TL;DR

This paper investigates how a large chemical potential in a dark-QCD sector induces a first-order chiral phase transition in the early universe, potentially generating detectable gravitational waves.

Contribution

It introduces a novel scenario where a large chemical potential drives a first-order dark-QCD phase transition, analyzed within the PNJL framework without KMT instanton effects.

Findings

Large chemical potential prolongs the phase transition duration.

The phase transition can produce gravitational waves detectable by space-based detectors.

The transition occurs at a temperature range between 1 GeV and 100 GeV.

Abstract

In this article, for the first time, we explore the scenario that the dark-QCD sector has a large chemical potential $\mu$ (on the order of magnitude of temperature) of dark quarks. It leads to a complex-valued Polyakov loop and tilts the partial confinement effect, driving the dark-QCD phase transition to a first-order one in the early universe. We present a toy model via the Affleck-Dine mechanism that could generate degenerate dark quarks. Our study, in the framework of PNJL, focuses on the dynamical impacts of a large chemical potential on the chiral phase transition without turning on the KMT instanton term. We plot the phase diagram of the dark-QCD in the chiral limit. The resulting first-order phase transition actually refers to a chiral phase transition, with the transition to the confinement vacuum being a cross-over. Following the phase diagram, we find that increasing $\mu$ can considerably prolong the duration of the phase transition and also the release of latent heat, which together make the cosmic dark-QCD phase transition at the critical temperature above 1 GeV and below 100 GeV produce gravitational wave signal in the intermediate frequency band, which is well probable in space detectors such as BBO