Onset of cavitation in the quark-gluon plasma

We study the onset of bubble formation (cavitation) in the quark-gluon plasma as a result of the reduction of the effective pressure from bulk-viscous corrections. By calculating velocity gradients in typical models for quark-gluon plasma evolution in heavy-ion collisions, we obtain results for the critical bulk viscosity above which cavitation occurs. Since present experimental data for heavy-ion collisions seems inconsistent with the presence of bubbles above the phase transition temperature of QCD, our results may be interpreted as an upper limit of the bulk viscosity in nature. Our results indicate that bubble formation is consistent with the expectation of hadronisation in low-temperature QCD.Comment: 12 pages, 2 figure

On Various Aspects of Ion Collisions Analyzed Via a Hydrodynamic Hybrid Approach

In this thesis, various theoretical results surrounding the quark--gluon plasma which is created in the ultrarelativistic collisions of ions are presented. The many-body, strong-coupling, and real-time characteristics of those collisions partially exclude first-principle quantum chromodynamics calculations, whereas the effective theory of hydrodynamics allows for a rather successful description of the quark--gluon plasma. A criterion of hydrodynamic stability is used to restrict the transport coefficient bulk viscosity. In addition, various collisional systems over a wide range of energy are successfully modeled for particle spectra, yields, flow coefficients, and HBT radii. Despite questions of hydrodynamic applicability to few-particle systems, there is reasonable agreement with experimental data for p+p collisions in this framework. Notably, the strong dependence on the bulk viscosity of simulation results for p+p collisions could help constrain this transport coefficient. All of those aspects solidify our quantitative understanding of the quark--gluon plasma produced in ion collisions