Color deconfinement and subhadronic matter: phase states and the role of constituent quarks

Abstract

Contents 1. Introduction 2. Retrospect, heuristic considerations, and QCD 3. The phase plane: the current outlook 4. Theoretical models 4.1 Lattice calculations; 4.2 Bag model; 4.3 Interim results: what do the theoretical models teach us? 5. Man-made subhadronic matter? 5.1 A general view of the process; 5.2 The direct phase transition scenario, QGP -> H: pro and contra; 5.3 The scenario with two phase transitions, QGP -> QπK -> H: advantages and problems; 5.4 Dilepton (e + e~-pairs) production Concluding remarks ReferencesAbstract. Major aspects of the subhadronic state of nuclear matter populated with deconfined color particles are reviewed. At high and even at rather low nuclear collision energies, this is expected to be a short-term quark-gluon plasma (QGP), but, seemingly, not only this. Emphasis is put on the self-consistency requirement that must be imposed on any phenomenological description of the evolution of a hot and dense nuclear medium as it expands (cools down) to the point where the final scattering of secondary particles starts. The view is argued and analyzed that massive constituent quarks should then play a major role at a certain cooling stage. A hypothesis is discussed regarding the existence of an intermediate stage (a valon plasma), allowing a consistent explanation of data on the mid-rapidity yields of various kinds of hadrons and direct dileptons (e + e -pairs) in high-energy heavy-ion collisions.

Hadron production and phase changes in relativistic heavy-ion collisions

“…The conceivable explanation of the fit result below 30 A GeV is presence, at the high baryon density arising at large µ B , of a constituent quark plasma [95]. Even if the perturbative QCD quark phase is reached at high temperature, in expansion-cooling the system encounters the valon (word derived from 'valance' quark) phase in which the color quark bonds are broken, but chiral symmetry restoration is not completed, with quarks of mass m u,d ≃ 340 MeV and m s ≃ 500 MeV being the only active degrees of freedom.…”

QCD against black holes of a star mass?

“…Nearly outside of the phase transition "boundary" (which is, actually, not a boundary but rather an extended spherical layer), the energy density of HPh substance made of closely packed neutrons approaches the value ε n vac |, what refers to a ≃ 1, in eq.s (2,3). This is just about the total density because the QCD vacuum condensate tends to zero.…”

“…Below, we consider two conceivable scenarios of this phase transition [1,2,3] -the hard scenario, when the HPh transforms at some fixed density (pressure) directly (stepwise) into the current quark state (this is the "conventional" phase transition), and the soft one, which admits an intermediate state in between (a kind of crossover). The latter asks for the notion of deconfined dynamical quarks (valons) -quasi-particles of non-fixed mass, which diminishes along with the density (pressure) increase.…”

Increasing effective intensity of soft strong interactions

“…However, these two scales Λ QCD and Λ χ may have different values [6] and spontaneous chiral symmetry breaking becomes responsible for formation of a core in a hadron. A proton structure can be imagined then as a hard ball placed in the hadron central region coated by a thick but fragile peripheral matter [7].…”