Transport theory for a two-flavor color superconductor

QCD with two light quark flavors at high baryonic density and low temperature is a color superconductor. The diquark condensate partially 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, linked to a quasiparticle behavior of the thermal excitations of the condensate. When solved in the collisionless limit and close to equilibrium, it gives rise to the ``hard superconducting loop'' (HSL) effective theory for the unbroken SU(2) gauge fields with momenta smaller than the gap. This theory describes Debye screening and Landau damping of the gauge fields in the presence of the diquark condensate. We also 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.