Nuclear Superconductivity in Compact Stars: BCS Theory and Beyond

This chapter provides a review of microscopic theories of pairing in nuclear systems and neutron stars. Special attention is given to the mean-field BCS theory and its extensions to include effects of polarization of the medium and retardation of the interactions. Superfluidity in nuclear systems that exhibit isospin asymmetry is studied. We further address the crossover from the weak-coupling BCS description to the strong-coupling BEC limit in dilute nuclear systems. Finally, within the observational context of rotational anomalies of pulsars, we discuss models of the vortex state in superfluid neutron stars and of the mutual friction between superfluid and normal components, along with the possibility of type-I superconductivity of the proton subsystem.