Minimal color-flavor-locked-nuclear interface - art. no. 074017

At nuclear matter density, electrically neutral strongly interacting matter in weak equilibrium is made of neutrons, protons, and electrons. At suffic iently high density, such matter is made of up, down, and strange quarks in the color-flavor-locked (CFL) phase, with no electrons. As a function of i ncreasing density (or, perhaps, increasing depth in a compact star) other p hases may intervene between these two phases, which are guaranteed to be pr esent. The simplest possibility, however, is a single first order phase tra nsition between CFL and nuclear matter. Such a transition, in space, could take place either through a mixed phase region or at a single sharp interfa ce with electron-free CFL and electron-rich nuclear matter in stable contac t. Here we construct a model for such an interface. It is characterized by a region of separated charge, similar to an inversion layer at a metal-insu lator boundary. On the CFL side, the charged boundary layer is dominated by a condensate of negative kaons. We then consider the energetics of the mix ed phase alternative. We find that the mixed phase will occur only if the n uclear-CFL surface tension is significantly smaller than dimensional analys is would indicate.