NANOGrav Signal from First-Order Confinement/Deconfinement Phase Transition in Different QCD Matters

TL;DR

This paper explores how first-order confinement/deconfinement phase transitions in various QCD matter could generate the stochastic gravitational wave signals observed by NANOGrav, emphasizing flavor dependence and potential cosmological sources.

Contribution

It demonstrates that certain QCD phase transitions, specifically involving heavy static quarks or finite baryon chemical potential, could explain the NANOGrav signal, unlike gluon confinement.

Findings

NANOGrav signal may originate from confinement/deconfinement transitions in heavy static quarks.

Transitions with finite baryon chemical potential are potential sources.

Gluon confinement is unlikely to produce the observed signal.

Abstract

Recently, an indicative evidence of a stochastic process, reported by the NANOGrav Collaboration based on the analysis of 12.5-year pulsar timing array data which might be interpreted as a potential stochastic gravitational wave signal, has aroused keen interest of theorists. The first-order color charge confinement phase transition at the QCD scale could be one of the cosmological sources for the NANOGrav signal. If the phase transition is flavor dependent and happens sequentially, it is important to find that what kind of QCD matter in which the first-order confinement/deconfinement phase transition happens is more likely to be the potential source of the NANOGrav signal during the evolution of the universe. In this paper, we would like to illustrate that the NANOGrav signal could be generated from confinement/deconfinement transition in either heavy static quarks with a zero baryon chemical potential, or quarks with a finite baryon chemical potential. In contrast, the gluon confinement could not possibly be the source for the NANOGrav signal according to the current observation. Future observation will help to distinguish between different scenarios.