High-energy phase diagrams with charge and isospin axes under heavy-ion collision and stellar conditions

Abstract

We investigate the phase transition from hadron to quark matter in the general case without the assumption of chemical equilibrium with respect to weak decays. The effects of net strangeness on charge and isospin fractions, chemical potentials, and temperature are studied in the context of the Chiral Mean Field (CMF) model that incorporates chiral symmetry restoration and deconfinement. The extent to which these quantities are probed during deconfinement in conditions expected to exist in protoneutron stars, binary neutron-star mergers, and heavy-ion collisions is analyzed quantitatively via the construction of 3-dimensional phase diagrams.

Deconfinement phase transition under chemical equilibrium

“…To identify the position of the phase transition region, we vary, for each temperature T and charge or isospin fraction (Y Q or Y I ), the Gibbs free energy per baryon of the system̃until we find a discontinuity in the order parameters. The free energy, by definition, is the same on the hadronic and quark sides of the deconfinement phase transition and can be used to calculate the baryon chemical potential B on each side of the coexistence region, either fixing the charge or isospin fraction in the system (Aryal et al 2020):…”

“…To identify the position of the phase transition region, we vary, for each temperature T and charge or isospin fraction ( Y Q or Y I ), the Gibbs free energy per baryon of the system until we find a discontinuity in the order parameters. The free energy, by definition, is the same on the hadronic and quark sides of the deconfinement phase transition and can be used to calculate the baryon chemical potential μ B on each side of the coexistence region, either fixing the charge or isospin fraction in the system (Aryal et al 2020): where the charge fraction , the isospin fraction , and the strangeness fraction are defined as the respective quantum numbers divided by the number of baryons in the system. Note that if we had imposed zero net strangeness (which we did not do in this work), the relation between isospin fraction and charge fraction would be trivial, Y Q = Y I + 1/2.…”

“…To calculate the chemical equilibrium lines, for each temperature, we have calculated the μ Q , I necessary to fulfill the standard chemical equilibrium equations (see appendix A of Aryal et al 2020) with the additional constraints related to the introduction of leptons, μ Q = − μ electron and Y Q = Y lepton . The chemical equilibrium lines do not exactly touch the fixed Y Q regions.…”

“…In this work, we will revisit the results concerning three-dimensional QCD phase diagrams derived and presented in Aryal et al (2020) and further investigated in Dexheimer et al (2020a) to include, for the first time, chemically equilibrated matter lines for the deconfinement phase transition. We choose to show only phase diagrams built assuming that strangeness is not conserved ( S = 0) in order to describe astrophysical scenarios.…”

The Effect of Charge, Isospin, and Strangeness in the QCD Phase Diagram Critical End Point

“…In the past, this formalism was used to simulate particle multiplicities, rapidity distributions, and flow in heavy-ion collisions [100] and the differences among stellar matter vs. matter produced in heavy-ion collisions in the vicinity of the deconfinement coexistence line, drawing analogies with the nuclear liquid-gas phase diagram [96]. More recently, we used this formalism to construct three-dimensional QCD phase diagrams up to a temperature T = 160 MeV, the other two axes being the chemical potential (µ B or μ), and either the charge or isospin fractions [101]. In this work, we go further by extending coexistence lines all the way to the respective critical end points and discussing the effects of different conditions on the relative position of the critical end points.…”