Instability of Boost-invariant hydrodynamics with a QCD inspired bulk viscosity

TL;DR

This paper investigates the stability of boost-invariant hydrodynamics with QCD-inspired bulk viscosity, revealing that near the critical temperature the system becomes unstable and may fragment into droplets, providing insights into QGP freeze-out.

Contribution

It demonstrates that a peak in bulk viscosity around Tc causes the hydrodynamic solution to become unstable, suggesting a mechanism for QGP freeze-out and potential early universe transitions.

Findings

Background solution 'freezes' at Tc with high instability.

Inhomogeneous modes grow rapidly, tearing the system into droplets.

Implications for QGP freeze-out and early universe phase transitions.

Abstract

We solve the relativistic Navier-Stokes equations with homogeneous boost-invariant boundary conditions, and perform a stability analysis of the solution. We show that, if the bulk viscosity has a peak around $T_c$ as inferred from QCD-based arguments, the background solution "freezes" at $T_c$ to a nearly constant temperature state. This state is however highly unstable with respect to certain inhomogeneous modes. Calculations show that these modes have enough time to blow up and tear the system into droplets. We conjecture that this is how freeze-out occurs in the QGP created in heavy ion collisions, and perhaps similar transitions in the early universe.