Jet momentum broadening and gluon emission rates during the pre-hydrodynamic stages in heavy-ion collisions

Jets are a promising tool to probe the initial nonequilibrium stages in heavy-ion collisions, before a hydrodynamic description of the quark-gluon plasma has become applicable. Jet-medium interactions are typically encoded in a single medium function, the elastic collision kernel, which is often used in a harmonic approximation using the jet quenching parameter $hat q$. In this talk, I will present first results for this collision kernel from QCD kinetic theory during the initial pre-hydrodynamic stages in heavy-ion collisions. In particular, we find that small-momentum exchange processes are enhanced as compared to thermal equilibrium, and that the small-distance form of the related dipole cross section is reduced, leading to a reduction of jet quenching during the initial stages. Finally, I will present results for the gluon splitting rate in the AMY formalism, which is used in QCD kinetic theory simulations in a particular isotropic approximation. Our results indicate that this particular approximation leads to quantitatively and qualitatively different rates during the initial stages, with potential yet unexplored impact for kinetic theory simulations. Our results may lead to a better understanding and more realistic modeling of jet quenching during the initial stages.