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Color screening in cold quark matter

We compute---at finite quark chemical potentials---the color screening of cold quark matter at the one-loop level, comparing the normal, BCS-paired U(1)em (or Higgs) phase and a singlet phase with color-singlet condensate near the Fermi surface. The latter phase is computed using the example of two-color QCD with a color-singlet diquark condensate. In contrast to the normal and Higgs phases, neither electric nor magnetic screening masses appear in the singlet phase. The absence of a magnetic mass, within a perturbative framework, is a consequence of the proper treatment of gauge invariance. While at large momenta the gluon self-energies approach those in the normal phase, the medium contributions to the infrared region below a scale of the mass gap are substantially suppressed. Infrared gluons at low quark density in the singlet phase appear protected from medium effects, unless the quark-gluon vertices are significantly enhanced in the infrared.