QCD over $T_c$: hadrons, partons and continuum

TL;DR

This paper offers a physical interpretation of the QCD phase transition, emphasizing the gradual shift from hadronic to partonic matter and highlighting the significant role of strongly correlated excitations up to three times the critical temperature.

Contribution

It introduces a spectral function-based picture of the QCD transition, accounting for the crossover nature and the persistence of hadronic contributions beyond the critical temperature.

Findings

Hadron resonance gas influences thermodynamics up to 3T_c

Strongly correlated excitations dominate intermediate regime

Quark-gluon plasma forms only above 3T_c

Abstract

In this paper we provide a physical picture for the QCD phase transition in terms of qualitative changes in the spectral functions. Our approach takes into account the crossover nature of this transition and counts for the observed strong correlation seen in higher order susceptibilities. We demonstrate that the hadron resonance gas, which alone describes the thermodynamics at temperatures $T<T_c$, will appreciably contribute to the total pressure until $T\leq 3T_c$. In this intermediate regime the QCD matter consists of strongly correlated excitations, interpretable as either hadrons or partons. As hadronic spectral peaks gradually vanish, the partonic excitations start to form a stand-alone quasiparticle gas. The conventional picture of a quark gluon plasma emerges only at $T\geq 3T_c$.