Shear Viscosity of Multi-Component Systems: Theory and Application to Quark-Gluon Plasma

Shear viscosity is a property of fluids and plasmas that is sourced from the momentum transfer and interactions of the individual particles and molecules. One such plasma is the quark-gluon plasma: a state of matter from relativistic heavy-ion collisions consisting of deconfined quarks and gluons in a high-temperature and high-pressure setting. In this setting, the kinetic regime of the quarks and gluons (collectively the "partons") is ultra-relativistic, which is the kinematic regime only present for massless particles. Therefore, the partons are treated as massless, and their shared interactions depend on relativistic kinetic theory. However, the current treatment of the quark-gluon plasma is an effective gluon gas, assuming quarks only contribute in the degrees of freedom. In this book, the shear viscosity of a massless gas is expanded for N types for a general formalism. Then, this is applied to the quark-gluon plasma, where we insert quark contribution in the kinematics as well as in the degrees of freedom.