Non-perturbative dynamics in gauge and scalar systems. A challenge to kinetic theory

We report of a universality class for longitudinally expanding systems, encompassing strongly correlated non-Abelian plasmas and scalar field theories in an intermediate range of momenta. This poses further challenges to our understanding of the thermalization process in the high-energy limit of heavy-ion collisions, like a puzzling evolution of the longitudinal to transverse pressure ratio in non-Abelian plasmas. In scalar theory, we show that the same behavior can be understood from non-trivial infrared dynamics related to a nonthermal fixed point.