Non-perturbative Approach to Equation of State and Collective Modes of the QGP

TL;DR

This paper presents a non-perturbative T-matrix approach to study the quark-gluon plasma, revealing the transition from partonic to hadronic degrees of freedom and calculating key thermodynamic and transport properties.

Contribution

It introduces a self-consistent, non-perturbative T-matrix framework constrained by lattice QCD data to analyze the QGP's microscopic structure and equation of state.

Findings

Bound states dominate the low-temperature QGP EoS.

Parton quasiparticles dissolve near the pseudocritical temperature.

The QGP exhibits low viscosity and heavy-quark diffusion coefficients.

Abstract

We discuss a non-perturbative $T$-matrix approach to investigate the microscopic structure of the quark-gluon plasma (QGP). Utilizing an effective Hamiltonian which includes both light- and heavy-parton degrees of freedoms. The basic two-body interaction includes color-Coulomb and confining contributions in all available color channels, and is constrained by lattice-QCD data for the heavy-quark free energy. The in-medium $T$-matrices and parton spectral functions are computed selfconsistently with full account of off-shell properties encoded in large scattering widths. We apply the $T$-matrices to calculate the equation of state (EoS) for the QGP, including a ladder resummation of the Luttinger-Ward functional using a matrix-log technique to account for the dynamical formation of bound states. It turns out that the latter become the dominant degrees of freedom in the EoS at low QGP temperatures indicating a transition from parton to hadron degrees of freedom. The calculated spectral properties of one- and two-body states confirm this picture, where large parton scattering rates dissolve the parton quasiparticle structures while broad resonances start to form as the pseudocritical temperature is approached from above. Further calculations of transport coefficients reveal a small viscosity and heavy-quark diffusion coefficient.