A quarkyonic matter model: rapid stiffening driven by quark saturation

Abstract Quarkyonic matter is a state of matter in dense QCD whose bulk thermodynamics is dominated by quarks, while low-energy excitations remain confined. This picture leads to a crossover description from baryonic matter to quark matter, which is triggered by the saturation of quark states in dense matter ( quark saturation ). The crossover driven by the quark saturation accompanies rapid growth in pressure but moderate increase in energy density, resulting in a characteristic peak in the sound speed. Such a rapid stiffening is consistent with constraints inferred from neutron star observations. The quark saturation can occur at a few times nuclear saturation density, which is smaller than the density at which the baryon cores of ∼ 0.5 – 0.8 fm spatially overlap. In this contribution we discuss an ideal model of quarkyonic matter, the IdylliQ model, and we explicitly describe how the baryon and quark occupation probabilities are related, and explain how stiffening of matter occurs. The model is further applied to charge neutral matter including hyperons, and it is shown that the statistical constraints at quark level induce effective repulsion among different baryon species, mitigating the hyperon softening problem in neutron star physics.