Transport theory for a two-flavor color superconductor.

QCD with two light-quark flavors at high baryonic density is a color superconductor. The diquark condensate breaks the SU(3) gauge symmetry down to an SU(2) subgroup. We study thermal fluctuations of the superconductor for temperatures below the gap. These are described by a simple transport equation. In the collisionless limit and close to equilibrium, it gives rise to the "hard superconducting loop" effective theory for the SU(2) gauge fields. This theory describes Debye screening and Landau damping of the gauge fields in the presence of the diquark condensate. We explain how our effective theory follows to one-loop order from quantum field theory. Our approach provides a convenient starting point for the computation of transport coefficients of the two-flavor color superconductor.