Locating quark deconfinement by the observational data on neutron stars and isospin QCD

Oleksii Ivanytskyi (University of Wroclaw)

I discuss the location of quark deconfinement in cold QCD matter at finite baryon and isospin densities and show that quark degrees of freedom can onset as early as at two saturation densities. In the baryon rich case typical for the interiors of neutron stars the recently proposed three-flavor nonlocal NJL model of quark matter with the scalar attractive, vector repulsive and diquark pairing interaction channels is used to construct a large set of asymptotically conformal hybrid quark-hadron equations of state applied to the physics-informed Bayesian analysis of the observational data. The most probable hybrid equations of state are statistically preferred over the purely hadronic baseline on the level of one-two orders of magnitude. This suggests that quark cores may exist in all observed neutron stars with the most probable onset density at about two saturation densities and the onset mass even below one solar mass. Such early deconfinement is explained using a toy-model based energetical criterion of quark deconfinement, which shows that the quark onset density strongly depends on isospin asymmetry. More specifically, the onset density in symmetric matter can be two-three times the onset density in neutron stars. This answers the question why in neutron stars deconfinement occurs at rather small densities, while under the heavy ion collision conditions its traces are not reliably detected up to the highest densities of the proton flow data. To estimate the density of quark deconfinement in isospin QCD I consider a simple confining model of pions existing as the lowest energy P-state of in-medium three-dimensional harmonic oscillator. According to the experimentally established pion charge radius, the model predicts that under the conditions of cold isospin QCD the quark onset density can be even lower than two nuclear saturation densities. This estimate is used as an input for the recently proposed quarkyonic picture of isospin QCD. It is based on a field-theory inspired model of quark-antiquark-pion matter with nonlocal vector-isovector repulsion among pions and (anti)quarks. The quark substructure of pions, which is one of the key elements of the model, is accounted for within the one-loop no-sea approximation and is shown to be crucial to provide the agreement with the existing data of numerical simulation of discrete space-time lattices.

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The colloquium will be streamed but not recorded.
Zoom link: https://uni-frankfurt.zoom.us/j/2848286010?pwd=VmtCY1RCc1hpVStKd0RibFBpc1IzZz09
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