Nuclear chiral dynamics and phases of QCD

TL;DR

This paper reviews QCD phase diagrams from lattice and model approaches, emphasizing the importance of nuclear physics constraints and chiral effective field theory in understanding nuclear matter and phase transitions.

Contribution

It highlights the significance of nuclear physics constraints in modeling QCD phases and discusses nuclear chiral thermodynamics and the absence of a first-order chiral phase transition up to certain densities and temperatures.

Findings

No first-order chiral phase transition up to twice nuclear matter density

Nuclear chiral effective field theory accurately describes the hadronic phase

Constraints from neutron star observations inform the equation-of-state

Abstract

This presentation starts with a brief review of our current picture of QCD phases, derived from lattice QCD thermodynamics and from models based on the symmetries and symmetry breaking patterns of QCD. Typical approaches widely used in this context are the PNJL and chiral quark-meson models. It is pointed out, however, that the modeling of the phase diagram in terms of quarks as quasiparticles misses important and well known nuclear physics constraints. In the hadronic phase of QCD governed by confinement and spontaneously broken chiral symmetry, in-medium chiral effective field theory is the appropriate framework, with pions and nucleons as active degrees of freedom. Nuclear chiral thermodynamics is outlined and the liquid-gas phase transition is described. The density and temperature dependence of the chiral condensate is deduced. As a consequence of two- and three-body correlations in the nuclear medium, no tendency towards a first-order chiral phase transition is found at least up to twice the baryon density of normal nuclear matter and up to temperatures of about 100 MeV. Isospin-asymmetric nuclear matter and neutron matter are also discussed. An outlook is given on new tightened constraints for the equation-of-state of cold and highly compressed matter as implied by a recently observed two-solar-mass neutron star.