Kaon Energies in Dense Matter

We discuss the role of kaon-nucleon and nucleon-nucleon correlations in kaon condensation in dense matter. Correlations raise the threshold density for kaon condensation, possibly to densities higher than those encountered in stable neutron stars.Comment: RevTeX, 11 pages, 2 PostScript figures; manuscript also available, in PostScript form, at http://www.nordita.dk/locinfo/preprints.htm

Neutrino-pair bremsstrahlung by electrons in neutron star crusts

Neutrino-pair bremsstrahlung by relativistic degenerate electrons in a neutron-star crust at densities (10^9 - 1.5x10^{14}) g/cm^3 is analyzed. The processes taken into account are neutrino emission due to Coulomb scattering of electrons by atomic nuclei in a Coulomb liquid, and electron-phonon scattering and Bragg diffraction (the static-lattice contribution) in a Coulomb crystal. The static-lattice contribution is calculated including the electron band-structure effects for cubic Coulomb crystals of different types and also for the liquid crystal phases composed of rod- and plate-like nuclei in the neutron-star mantle (at 10^{14} - 1.5x10^{14} g/cm^3). The phonon contribution is evaluated with proper treatment of the multi-phonon processes which removes a jump in the neutrino bremsstrahlung emissivity at the melting point obtained in previous works. Below 10^{13} g/cm^3, the results are rather insensitive to the nuclear form factor, but results for the solid state near the melting point are affected significantly by the Debye-Waller factor and multi-phonon processes. At higher densities, the nuclear form factor becomes more significant. A comparison of the various neutrino generation mechanisms in neutron star crusts shows that electron bremsstrahlung is among the most important ones.Comment: 17 pages, 13 figures, LaTeX using aa.cls and epsf.sty. A&A, in pres

On Neutrino Emission From Dense Matter Containing Meson Condensates

We consider the rate at which energy is emitted by neutrinos from the dense interior of neutron stars containing a Bose condensate of pions or kaons. The rates obtained are larger, by a factor of 2, than those found earlier, and are consistent with those found for the direct Urca processes.Comment: RevTeX, 10 page

Kaon Zero-Point Fluctuations in Neutron Star Matter

We investigate the contribution of zero-point motion, arising from fluctuations in kaon modes, to the ground state properties of neutron star matter containing a Bose condensate of kaons. The zero-point energy is derived via the thermodynamic partition function, by integrating out fluctuations for an arbitrary value of the condensate field. It is shown that the vacuum counterterms of the chiral Lagrangian ensure the cancellation of divergences dependent on $\mu$, the charge chemical potential, which may be regarded as an external vector potential. The total grand potential, consisting of the tree-level potential, the zero-point contribution, and the counterterm potential, is extremized to yield a locally charge neutral, beta-equilibrated and minimum energy ground state. In some regions of parameter space we encounter the well-known problem of a complex effective potential. Where the potential is real and solutions can be obtained, the contributions from fluctuations are found to be small in comparison with tree-level contributions.Comment: 40 pages RevTeX, 3 epsf figure

Isospin Effects on Strangeness in Heavy-Ion Collisions

Kaon properties are studied within the framework of a fully covariant transport approach. The kaon-nucleon potential is evaluated in two schemes, a chiral perturbative approach and an effective One-Boson-Exchange model. Isospin effects are explicitly accounted for in both models. The transport calculations indicate a significant sensitivity of momentum distributions and total yields of $K^{0,+}$ isospin states on the choice of the kaon-nucleon interaction. Furthermore, isospin effects are rather moderate on absolute kaon yields, but appear on strangeness ratios. This is an important issue in determining the high density symmetry energy from studies of strangeness production in heavy-ion collisions.Comment: 15 papes, 5 figures. Accepted for publication in Nuclear Physic

Kaon Condensation in the Bound-State Approach to the Skyrme Model

We explore kaon condensation using the bound-state approach to the Skyrme model on a 3-sphere. The condensation occurs when the energy required to produce a $K^-$ falls below the electron fermi level. This happens at the baryon number density on the order of 3--4 times nuclear density.Comment: LaTeX format, 15 pages. 3 Postscript figures, compressed and uuencode

Rapid cooling of magnetized neutron stars

The neutrino emissivities resulting from direct URCA processes in neutron stars are calculated in a relativistic Dirac-Hartree approach in presence of a magnetic field. In a quark or a hyperon matter environment, the emissivity due to nucleon direct URCA processes is suppressed relative to that from pure nuclear matter. In all the cases studied, the magnetic field enhances emissivity compared to the field-free cases.Comment: 9 pages; Revtex; figure include

In-medium pion weak decay constants

In nuclear matter, the pion weak decay constant is separated into the two components $f_t, f_s$ corresponding to the time and space components of the axial-vector current. Using QCD sum rules, we compute the two decay constants from the pseudoscalar-axial vector correlation function in the matter $i \int d^4x~ e^{ip\cdot x} < \rho| T[{\bar d}(x) i \gamma_5 u (x)~ {\bar u}(0) \gamma_\mu \gamma_5 d (0)] | \rho>$. It is found that the sum rule for $f_t$ satisfies the in-medium Gell-Mann--Oakes--Renner (GOR) relation precisely while the $f_s$ sum rule does not. The $f_s$ sum rule contains the non-negligible contribution from the dimension 5 condensate $_N + {1\over 8} _N$ in addition to the in-medium quark condensate. Using standard set of QCD parameters and ignoring the in-medium change of the pion mass, we obtain $f_t =105$ MeV at the nuclear saturation density. The prediction for $f_s$ depends on values of the dimension 5 condensate and on the Borel mass. However, the OPE constrains that $f_s/f_t \ge 1$, which does not agree with the prediction from the in-medium chiral perturbation theory. Depending on the value of the dimension 5 condensate, $f_s$ at the saturation density is found to be in the range $112 \sim 134$ MeV at the Borel mass $M^2 \sim 1$ GeV$^2$.Comment: 19 pages including two postscript figures, substantially revise

Nonequilibrium Weak Processes in Kaon Condensation II - Kinetics of condensation ---

The kinetics of negatively charged kaon condensation in the early stages of a newly born neutron star is considered. The thermal kaon process, in which kaons are thermally produced by nucleon-nucleon collisions, is found to be dominant throughout the equilibration process. Temporal changes of the order parameter of the condensate and the number densities of the chemical species are obtained from the rate equations, which include the thermal kaon reactions as well as the kaon-induced Urca and the modified Urca reactions. It is shown that the dynamical evolution of the condensate is characterized by three stages: the first, prior to establishment of a condensate, the second, during the growth and subsequent saturation of the condensate, and the third, near chemical equilibrium. The connection between the existence of a soft kaon mode and the instability of the noncondensed state is discussed. Implications of the nonequilibrium process on the possible delayed collapse of a protoneutron star are also mentioned.Comment: 27 pages, incl. 8 eps figures, RevTe

Nonequilibrium Weak Processes in Kaon Condensation I --- Reaction rate for the thermal kaon process ---

We investigate the thermal kaon process,in which kaons are thermally produced via nucleon-nucleon collisions.This process is relevant to nonequilibrium dynamics of kaon condensation inside neutron stars.The reaction rates for these processes are calculated, and their temperature and density dependences are compared with those of other reaction rates.It is shown that the thermal kaon process is dominant over other relevant weak reactions throughout the nonequilibrium process, such as the kaon-induced Urca and the modified Urca reactions, and may control the entire evolution of the kaon condensate. The characteristic role of the soft and hard kaons during the evolution is explained, and implications for astrophysical phenomena are briefly discussed.Comment: 31 pages,incl.10 eps figures,RevTe