Onset of collective flow due to Weibel instabilities*

Since the local momentum density is highly anisotropic at the early stage of an ultra-relativistic nuclear collision, it is expected that Weibel instabilities will generate color currents with a characteristic (preferentially transverse) wave vector. As demonstrated first by Amp{\'e}re, different currents repel and in the SU(3) plasma there is therefore a net tendency for the Weibel currents to experience a mutual repulsion. This feature is phenomenologically important since the associated increase of the pressure provides a mechanism for the early development of collective flow. For the purpose of establishing a framework for examining this effect, we have extended our earlier work to encompass the evolving correlation function for the local momentum density. Starting from the fluctuations in a free gas of gluons, quarks and anti-quarks, we treat the self-consistent feed-back of the amplified chromodynamic fields on the phase-space densities.