Transition rate and gravitational wave spectrum from first-order QCD phase transitions

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Abstract
We investigate the gravitational wave spectrum induced by first-order quantum chromodynamics (QCD) phase transitions, e.g., the confinement-deconfinement phase transition of the pure gluon system and the chiral phase transitions in the quark-meson model and Polyakov quark-meson model. The gravitational wave power spectra are sensitive to the phase transition rate β / H . All QCD models predict a relatively large phase transition rate in the order of β / H ∼ 10 4 at high temperature region, and the produced gravitational waves lie in the peak frequency region of 10 − 4 – 0.01 Hz , corresponding to an energy spectrum in the range of 10 − 8 – 10 − 7 , which can be detected by LISA and Taiji. If a high baryon density region is generated through Affleck-Dine baryogenesis or other mechanisms, the baryon chemical potential significantly reduces the phase transition rate, which will drop to the order of β / H ∼ 10 1 , thus leading to the production of nanohertz gravitational waves. Furthermore, there exists a critical quark chemical potential with zero phase transition rate β / H = 0 , indicating that the false vacuum will not decay, which supports the formation of primordial quark nuggets in the early Universe.
Funding Information
  • National Natural Science Foundation of China (12235016, 12221005)
  • Chinese Academy of Sciences (XDB34030000)

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