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High Energy Physics - Phenomenology, hep-ph,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO
Abstract:
The underlying physics of QCD phase transition in the early Universe remains
largely unknown due to its strong-coupling nature during the quark-gluon
plasma/hadron gas transition, yet a holographic model has been proposed to
quantitatively fit the lattice QCD data while with its duration of the
first-order phase transition (FoPT) left undetermined. At specific baryon
chemical potential, the first-order QCD phase transition agrees with the
observational constraint of baryon asymmetry. It therefore provides a scenario
for phase transition gravitational waves (GWs) within the Standard Model of
particle physics. If these background GWs could contribute dominantly to the
recently claimed common-spectrum red noise from pulsar timing array (PTA)
observations, the duration of this FoPT can be well constrained but disfavored
by the constraints from curvature perturbations. However, the associated
primordial black holes are still allowed by current observations. Therefore,
either the QCD phase transition is not described by our holographic model or
the other GW sources must be presented to dominate over the GWs from this FoPT.
