Transport coefficients in quantum chromodynamics

Relativistic kinetic theory provides a transport equation for classical, spinless, colored particles in a non-Abelian external field. The methods used in the literature to find the transport coefficients for quark and gluon systems are reviewed. Most authors use the relaxation time approximation of the Boltzmann equation to compute the transport coeffiecients, but this method has shortcomings in mixtures. The Chapman Enskog (CE) method is used to solve the classical transport equations for quarks and gluons for the transport coefficients. The differential cross sections describing the particle interaction are obtained from the lowest order scattering diagrams of quantum chromodynamics. A pure quark sytem, a pure gluon system and a quark antiquark mixture are studied. For mixtures of quarks, antiquarks and gluons, the shear viscosity, heat conductivity and cross-coefficients are found. The coefficients pertaining to quark antiquark mixtures, namely the termal diffusion, diffusion and Dufour coefficient, the viscosities and heat conductivity are obtained and the conductivity of a quark antiquark mixture in an external field is computed. In the CE method, the transport coefficients depend naturally on a logarithmic factor due to the divergent scattering cross-sections, reflecting the plasma shielding effects. This logarithm is evaluated by relating it to typical plasma parameters. The results are applied to the quark-gluon phase in the early universe and ultra-relativistic heavy ion collisions. A comparison of the quark-gluon to pion transport coefficients at the quark-hadron phase transition shows that the latter are ∼ 103 smaller. Dissipative effects increase the plasma lifetime, resulting in a longer high energy density and a temperature plasma phase. 25 figs., 9 tabs., 89 refs