The domain of validity of fluid dynamics and the onset of cavitation in ultrarelativistic heavy ion collisions

TL;DR

This paper investigates how large bulk viscosity in QCD matter can cause negative pressure and cavitation during ultrarelativistic heavy ion collisions, affecting the stability of the quark-gluon plasma.

Contribution

It estimates the critical bulk viscosity needed for cavitation to occur in hydrodynamic simulations of heavy ion collisions at LHC energies.

Findings

Bulk viscosity can induce negative pressure in QGP.

Cavitation onset depends on the magnitude of bulk viscosity.

Simulations identify viscosity thresholds for cavitation.

Abstract

If the bulk viscosity of QCD matter is large, the effective pressure of the hot and dense matter created in ultrarelativistic heavy ion collisions can become negative, leading to instabilities in the evolution of the plasma. In the context of heavy ion collisions, this effect is sometimes referred to as cavitation. In this contribution we discuss the onset of cavitation in event-by-event hydrodynamic simulations of ultrarelativistic heavy ion collisions at LHC energies. We estimate how large the bulk viscosity of the QGP has to be in the QCD (pseudo) phase transition region in order for the effective pressure of the system to actually become negative.