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Description
Much of the physics in the cold-dense region in the QCD phase diagrams are characterised by the formation of Cooper pairs on the Fermi surface. In two-flavour symmetric quark matter, a phase transition is expected to occur into the two-flavour colour superconducting (2SC) phase. A key feature of this phase is that certain quarks remain ungapped due to repulsive colour-symmetric interactions. However, it is well established that Cooper pairs can still form via higher-order perturbative effects in large angular momentum channels, even when the bare interaction is repulsive. We investigate this possibility in QCD by analysing the renormalisation group (RG) equations for the quark-quark interaction vertex at extreme densities, where the perturbative expansion is valid. We find that the favoured partial wave is the 3P2 channel, analogous to the neutron superfluid phase at intermediate densities. However, the BCS gap for these colour-symmetric quark pairs remains small.