Exploring the limits of hydrodynamic simulations of relativistic heavy-ion collisions

Hydrodynamic simulations of ultrarelativistic heavy-ion collisions have been remarkably successful at explaining experimental data, usually invoking non-zero values of both shear and bulk viscosities to do so. Bulk viscosity is a negative contribution to the kinematic pressure, meaning that large bulk viscosities can possibly lead to negative net kinematic pressure. Unlike cavitation in the standard sense, in relativistic heavy-ion collisions this is not observed to lead to nucleation or bubble formation: a process that is not possible when phase change happens with a smooth crossover. We also demonstrate that net negative kinematic pressure does not necessarily lead to inward flow of fluid. Finally, we explore the phenomenological consequences of imposing the condition that kinematic pressure always stay positive, and we consider observables like mean-p_T and v_n in AA collisions.