Isotropization of a rotating and longitudinally expanding ${\phi }^4$ scalar system

We present numerical simulations for the evolution of an expanding system of massless scalar fields with quartic coupling. By setting a rotating, non-isotropic initial configuration, we compute the energy density, the transverse and longitudinal pressures and the angular momentum of the system. We compare the time scales associated with the isotropization and the decay of the initial angular momentum due to the expansion, and show that even for fairly large initial angular momentum, it decays significantly faster than the pressure anisotropy.