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

Understand

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.