Alexander Velytsky
PhD in Physics

A Model Study of the Deconfining Phase Transition

The study of the deconfining phase transition or crossover is important for the understanding of properties of nuclear matter and the quark gluon plasma. Heavy ion collisions experiments are capable of creating conditions necessary for deconfinement. The dynamics of this process and not only its equilibrium properties are of interest. In this project non-equilibrium aspects of rapid heating and cooling of the QCD vacuum are studied in a model framework. The $3$-D Potts model with an external magnetic field is an effective model of QCD. It is studied by means of Monte Carlo simulations. Other models are used to understand the influence of the strength of the phase transition. In our investigations these systems are temperature driven through a phase transition or a rapid crossover using updating procedures in the Glauber universality class. We study hysteresis cycles with different updating speeds and quench simulations. Qualitatively this should reveal the physics of non-equilibrium configurations. A number of observables is measured during the simulations: Thermodynamical quantities such as the internal energy and the magnetization, properties of Fortuin-Kasteleyn clusters and structure functions. Comparing with equilibrium data we conclude that the Monte Carlo dynamics is capable of creating a spinodal decomposition, which dominates the statistical properties of configurations. A slowing down of the equilibration in the ordered phase due to the competition of different magnetization domains is observed. This could lead to a situation where the system does not fully equilibrize in the available time. Spinodal decomposition of the Polyakov loops may lead to an enhancement of low momentum degrees of freedom. If this scenario is realized by Nature, this may be observed in experiments as an increase in the low energy gluon production.