Multicomponent Superfluids and Superconductors in Dense Nuclear and Quark Matter

Matter at intermediate baryon densities and low temperatures is notoriously hard to tackle theoretically. Whereas lattice methods cannot cover more than rather small densities, perturbative methods are only applicable at much higher densities. The regime of intermediate chemical potential at low temperatures in the QCD-phase diagram is therefore out of reach of first-principle methods, thus we have to rely on stellar objects to investigate dense nuclear and quark matter at low temperatures. Compact stars can serve as a unique laboratory for this regime. Due to their fast rotation and high magnetic field, phenomena like hydrodynamic instabilities and the formation of vortices/flux tubes become of phenomenological interest. In this talk  I will show how these multicomponent systems can be investigated in a consistent multi-fluid treatment. By starting from a field-theoretical, bosonic model, the phase structure of a two-fluid system, e.g. consisting of superfluid neutrons and superconducting protons, is explored. By incorporating a gauge field and its coupling to one of the scalar fields, the influence of a super fluid on the magnetic phase structure of a superconductor can be studied. In the end I will discuss color superconducting quark matter, which can effectively be described as a multicomponent (color-)supercondcutor.