The successful hydrodynamical description of the strongly interacting matter created in ultrarelativistic heavy-ion collisions implies that the system reaches sufficient degree of isotropy within 0.2-1fm after the collision. During the transient equilibration phase the system initially consists of overoccupied gluon fields which can be described using classical Yang-Mills theory. Due to expansion the occupation number of the system falls, and when the occupation numbers become of the order 1 the system can no longer be described using classical theory, and kinetic theory description is needed. The classical theory has an overlapping range of validity with kinetic theory. This means that the combination of the two can be used to track the evolution of the system until sufficient hydrodynamization has been reached.
We work in the interface of classical Yang-Mills theory and kinetic theory by studying the quasiparticle excitations of the classical theory. We extract the quasiparticle mass using different methods in 3 and 2 spatial dimensions. The different methods agree within 50%. We also study the spectral function of the classical theory using linear response analysis. The spectral function contains a Lorentzian contribution, indicating the existence of quasiparticles in the system. We also extract the momentum dependence of the damping rate of the quasiparticles for the first time.