Strange phases in neutron star matter

Abstract

Neutron stars are produced in nature as the remnants of core-collapse supernovae. Their masses lie in the range 1--2 M⊙ and they possess radii of order 10 km, yielding central densities of several times the density of nuclear matter at saturation. At these extreme densities, the usual degrees of freedom of low-energy matter (neutrons, protons, and electrons) will be supplemented by more exotic components. In particular, matter containing strange quarks is expected to appear beyond some critical density in the form of hyperons, negative kaons, or perhaps three-flavor quark matter. After reviewing relevant background material, in this thesis we focus on the possibility of a first-order phase transition to a state containing a condensate of negative kaons. We calculate the importance of finite-size effects in a kaonic-nuclear charge-separated mixed phase. ("Finite-size effects" here refers to surface-tension-induced pressure differences between the two phases and Debye screening corrections to the charged particle distributions.) We then discuss the question of when and how the kaonic phase is nucleated during the formation of a neutron star. The results of nucleation rate calculations are presented and analyzed in detail, including a discussion of the implications to the interpretation of observational data. Finally, we turn to an alternative form in which kaons may appear in high-density matter. This involves the condensation of kaon-like mesons in a background of flavor-symmetric superconducting quark matter. We present the results of a stability analysis designed to identify whether a homogeneous or a heterogeneous condensate is energetically favored. We conclude by summarizing the new work presented, discussing its limitations, and indicating directions for future work.