Equation of state with kaon condensates and neutron stars

Abstract

Kaon condensation in dense neutron star matter is investigated on the basis of current algebra and PCAC (partially conserved axial-vector current). Second-order perturbation effects are incorporated naturally within framework, which are necessary to be consistent with KN scattering data, but we find it hardly affects K − condensation. The excitation energy of kaons in a nuclear medium is examined by combining the framework with a relativistic mean-field theory. Next we obtain the equation of state of the K −-condensed phase in neutron star matter, and clarify characteristic features of the system. There can occur a first-order phase transition from the normal phase to the K −-condensed one. Subsequently bulk structure of kaon-condensed neutron stars is studied. Softening of the equation of state due to kaon condensation has a large influence on the internal structure of the neutron star. As a dynamical property associated with the first-order phase transition, the energy release due to a collapse from a metastable configuration to a stable kaon-condensed one is estimated. Its implications for the gamma-ray bursts are briefly mentioned.