Identifying the QCD Phase Transitions via the Gravitational Wave Frequency

TL;DR

This paper explores how gravitational wave frequencies from oscillating neutron stars and strange quark stars can reveal QCD phase transitions, highlighting differences in mode frequencies that could be detected observationally.

Contribution

It demonstrates that $g$-mode frequencies are significantly lower in strange quark stars compared to neutron stars, providing a potential observational signature of QCD phase transitions.

Findings

$g$-mode frequencies are about ten times lower in SQSs than NSs.

$f$- and $p$-mode frequencies are much higher than $g$-mode frequencies.

Gravitational waves can potentially identify QCD phase transitions in dense matter.

Abstract

We investigate the nonradial oscillations of newly born neutron stars (NSs) and strange quark stars (SQSs). This is done with the relativistic nuclear field theory with hyperon degrees of freedom employed to describe the equation of state for the stellar matter in NSs, and with both the MIT bag model and the Nambu--Jona-Lasinio model adopted to construct the configurations of the SQSs. We find that the gravitational-mode ($g$-mode) eigenfrequencies of newly born SQSs are about one order of magnitude lower than those of NSs, which is independent of models implemented to describe the equation of state for the strange quark matter. Meanwhile the eigenfrequencies of the other modes of nonradial oscillations, e.g., fundamental ($f$)- and pressure ($p$)-modes, are much larger than those of the $g$-mode. In the light of the first direct observation of gravitational waves, it is promising to employ the gravitational waves to identify the QCD phase transition in high density strong interaction matter.