Apparent Thermalization due to Plasma Instabilities in Quark-Gluon Plasma

Elliptic flow measurements and hydrodynamical modeling of heavy ion collisions at RHIC suggest that the quark-gluon plasma (QGP) "thermalizes" in a remarkably short time scale, about 0.6 fm/c. We argue that these measurements should be viewed as indicating fast isotropization, but not necessarily complete thermalization, of the non-equilibrium QGP. Non-Abelian plasma instabilities can drive local isotropization of an anisotropic QGP on a time scale which is faster than ordinary perturbative scattering processes. As a result, we argue that theoretical expectations based on weak coupling analysis are not necessarily in conflict with hydrodynamic modeling at RHIC, provided one recognizes the key role of non-Abelian plasma instabilities