Hydrodynamic description of the baryon-charged quark-gluon plasma

TL;DR

This paper develops a (3+1)-dimensional relativistic hydrodynamic model incorporating baryon diffusion and critical fluctuations to better understand the quark-gluon plasma and locate the QCD critical point through heavy-ion collision simulations.

Contribution

It introduces the BEShydro code solving advanced hydrodynamic equations with baryon diffusion and extends hydrodynamics to include slow critical modes near the QCD critical point.

Findings

BEShydro models baryon diffusion effects on longitudinal dynamics.

Critical fluctuations influence phase diagram trajectories.

Coupling slow modes captures long-wavelength critical phenomena.

Abstract

One of the primary goals of nuclear physics is studying the phase diagram of Quantum Chromodynamics, where a hypothetical critical point serves as a landmark. A systematic model-data comparison of heavy-ion collisions at center-of-mass energies between 1 and 100 GeV per nucleon is essential for locating the critical point and the phase boundary between the deconfined quark-gluon plasma and the confined hadron resonance gas. At these energies the net baryon density of the system can be high and critical fluctuations can become essential in the presence of the critical point. Simulating their dynamical evolution thus becomes an indispensable part of theoretical modeling. In this thesis we first present the (3+1)-dimensional relativistic hydrodynamic code BEShydro, which solves the equations of motion of second-order Denicol-Niemi-Molnar-Rischke theory, including bulk and shear viscous components as well as baryon diffusion current. We then study the effects caused by the baryon diffusion on the longitudinal dynamics and on the phase diagram trajectories of fluid cells at different space-time rapidities of the system, and how they are affected by critical dynamics near the critical point. We finally explore the evolution of non-hydrodynamic slow processes describing long wavelength critical fluctuations near the critical point, by extending the conventional hydrodynamic description by coupling it to additional explicitly evolving slow modes, and their back-reaction to the bulk matter properties.