Kaon Condensation Research Articles

Meson current in the color-flavor-locked phase

We study the stability of the color-flavor-locked (CFL) phase of dense quark matter with regard to the formation of a nonzero Goldstone boson current. We show that an instability appears in the vicinity of the point ${\ensuremath{\mu}}_{s}=\ensuremath{\Delta}$ which marks the appearance of gapless fermion modes in the CFL phase. Here, ${\ensuremath{\mu}}_{s}={m}_{s}^{2}/(2\ensuremath{\mu})$ is the shift in chemical potential due to the strange quark mass and $\ensuremath{\Delta}$ is the gap in the chiral limit. We show that in the Goldstone boson current phase all components of the magnetic screening mass are real. In this work we do not take into account homogeneous kaon condensation. We study the effects of an instanton induced interaction of the magnitude required to suppress kaon condensation.

Finite size effects on kaonic “pasta” structures

Non-uniform structures of mixed phases at the first-order phase transition to charged kaon condensation are studied using a density functional theory within the relativistic mean field model. Including electric field effects and applying the Gibbs conditions in a proper way, we numerically determine density profiles of nucleons, electrons and condensed kaons. Importance of charge screening effects is elucidated and thereby we show that the Maxwell construction is effectively justified. Surface effect is also studied to figure out its effect on the density profiles.

Strangeness Condensation by Expanding about the Fixed Point of the Harada-Yamawaki Vector Manifestation

Building on, and extending, the result of a higher-order in-medium chiral perturbation theory combined with renormalization group arguments and a variety of observations of the vector manifestation of Harada-Yamawaki hidden local symmetry theory, we obtain a surprisingly simple description of kaon condensation by fluctuating around the "vector manifestation" fixed point identified to be the chiral restoration point. Our development establishes that strangeness condensation takes place at approximately 3n0 where n0 is nuclear matter density. This result depends only on the renormalization-group (RG) behavior of the vector interactions, other effects involved in fluctuating about the bare vacuum in so many previous calculations being irrelevant in the RG about the fixed point. Our results have major effects on the collapse of neutron stars into black holes.

Neutrino emissivity under neutral kaon condensation

Neutrino emissivity from neutron star matter with neutral kaon condensate is considered. It is shown that a new cooling channel is opened and that all previously known channels acquire greater emissivity reaching the level of the direct URCA cycle in normal matter.

Meson Supercurrent State in High-Density QCD

The ground state of three flavor quark matter at asymptotically large density is believed to be the color-flavor-locked (CFL) phase. At nonasymptotic density the effect of the nonzero strange quark mass cannot be neglected. If the strange quark mass exceeds m(s) approximately m(u)(1/3)delta(2/3), the CFL state becomes unstable toward the formation of a neutral kaon condensate. Recently, several authors discovered that for m(s) approximately (2deltap(F))(1/2) the CFL state contains gapless fermions, and that the gapless modes lead to an instability in current-current correlation functions. Using an effective theory of the CFL state, we demonstrate that this instability can be resolved by the formation of a meson supercurrent, analogous to Migdal's p-wave pion condensate. This state has a nonzero meson current that is canceled by a backflow of gapless fermions.

Interplay between kaon condensation and hyperons in high density matter(Hadrons at finite density)

Interplay between kaon condensation and hyperons in high density matter(Hadrons at finite density)

Kaon Condensation a la Vector Manifestation(Hadrons at finite density)

Kaon Condensation a la Vector Manifestation(Hadrons at finite density)

Kaon condensation in a Nambu–Jona-Lasinio model at high density

We demonstrate a fully self-consistent microscopic realization of a kaon-condensed colour-flavour locked state (CFLK0) within the context of a mean-field NJL model at high density. The properties of this state are shown to be consistent with the QCD low-energy effective theory once the proper gauge neutrality conditions are satisfied, and a simple matching procedure is used to compute the pion decay constant, which agrees with the perturbative QCD result. The NJL model is used to compare the energies of the CFLK0 state to the parity even CFL state, and to determine locations of the metal/insulator transition to a phase with gapless fermionic excitations in the presence of a non-zero hypercharge chemical potential and a non-zero strange quark mass. The transition points are compared with results derived previously via effective theories and with partially self-consistent NJL calculations. We find that the qualitative physics does not change, but that the transitions are slightly lower.

Kaon condensation in the quark-meson coupling model and compact stars

The properties of neutron stars, consisting of a crust of hadrons and an internal part of hadrons and kaon condensate, are calculated within the quark-meson-coupling model. We considered stars with nucleons only in the hadron phase and also stars with hyperons as well. The results are compared with the ones obtained from the nonlinear Walecka model for the hadronic phase.

Kaon condensation and lambda–nucleon loop in the relativistic mean-field approach

The possibility of kaon condensation in high-density symmetric nuclear matter is investigated including both s- and p-wave kaon–baryon interactions within the relativistic mean-field (RMF) theory. Above a certain density, we have a collective K ¯ s state carrying the same quantum numbers as the antikaon. The appearance of the K ¯ s state is caused by the time component of the axial-vector interaction between kaons and baryons. It is shown that the system becomes unstable with respect to condensation of K– K ¯ s pairs. We consider how the effective baryon masses affect the kaon self-energy coming from the time component of the axial-vector interaction. Also, the role of the spatial component of the axial-vector interaction on the possible existence of the collective kaonic states is discussed in connection with Λ-mixing effects in the ground state of high-density matter. Implications of K K ¯ s condensation for high-energy heavy-ion collisions are briefly mentioned.

Thermal kaon production in relativistic heavy-ion collisions

We study kaon production in hot and dense hypernuclear matter with a conserved zero total strangeness and a conserved small negative isospin charge fraction in order to make our results relevant to relativistic heavy-ion collisions. The baryons and kaons are treated as MIT bags in the context of the modified quark–meson coupling model. They interact with each other via the scalar mesons σ, σ ∗ and the vector mesons ω, ϕ as well as the isovector meson ρ. We adopt realistic sets of hyperon–hyperon interactions based on several versions of the Nijmegen core potential models. Our results indicate that the hyperons as well as the kaons are produced abundantly when the temperature increases and approaches the critical temperature for the phase transition to a quark–gluon plasma. Moreover we find that the kaons are only produced thermally and we find no kaon condensation in the regime explored by relativistic heavy-ion collisions.

Pycnonuclear reactions in dense stellar matter

We discuss pycnonuclear burning of highly exotic atomic nuclei in deep crusts of neutron stars, at densities up to 1e13 g/cc. As an application, we consider pycnonuclear burning of matter accreted on a neutron star in a soft X-ray transient (SXT, a compact binary containing a neutron star and a low-mass companion). The energy released in this burning, while the matter sinks into the stellar crust under the weight of newly accreted material, is sufficient to warm up the star and initiate neutrino emission in its core. The surface thermal radiation of the star in quiescent states becomes dependent of poorly known equation of state (EOS) of supranuclear matter in the stellar core, which gives a method to explore this EOS. Four qualitatively different model EOSs are tested against observations of SXTs. They imply different levels of the enhancement of neutrino emission in massive neutron stars by (1) the direct Urca process in nucleon/hyperon matter; (2) pion condensates; (3) kaon condensates; (4) Cooper pairing of neutrons in nucleon matter with the forbidden direct Urca process. A low level of the thermal quiescent emission of two SXTs, SAX J1808.4-3658 and Cen X-4, contradicts model (4). Observations of SXTs test the same physics of dense matter as observations of thermal radiation from cooling isolated neutron stars, but the data on SXTs are currently more conclusive.

Neutron star cooling

The impact of nuclear physics theories on cooling of isolated neutron stars is analyzed. Physical properties of neutron star matter important for cooling are reviewed such as composition, the equation of state, superfluidity of various baryon species, neutrino emission mechanisms. Theoretical results are compared with observations of thermal radiation from neutron stars. Current constraints on theoretical models of dense matter, derived from such a comparison, are formulated.

Kaonic nuclei probed by the in-flight [formula omitted] reaction

Kaonic nuclei are observed by the ( K − , n ) reaction. The spectra indicate that the kaon nuclear potential is strongly attractive which seems to contradict many theoretical predictions. It suggests that kaon condensation is taking place in the core of neutron stars.

Kaon condensation in hyperonic matter and properties of neutron stars

The equation of state (EOS) of kaon condensation in hyperonic matter, where hyperons ( Λ , Σ − ) are mixed in the ground state of neutron-star matter, is investigated. P-wave kaon–baryon interactions are included as well as s-wave ones by the use of effective chiral Lagrangian. It is shown that kaon condensates appear with finite momentum, stemming from the attractive p-wave kaon–baryon interactions. However, in the fully-developed phase, the s-wave kaon–baryon interactions control the EOS, and kaon condensation becomes of an s-wave type at higher density. Due to a considerable softening of the EOS caused by both hyperon-mixing and kaon condensates, the energy of the system has a local minimum, which leads to a metastable configuration of self-bound kaon-condensed star in addition to a usual kaon-condensed star obtained by Maxwell's construction.

Mixed-phase induced core-quakes and the changes in neutron-star parameters

We present approximate formulae describing the changes in neutron star parameters caused by the first-order phase transition to an ``exotic'' state (pion or kaon condensate, quark matter) resulting in formation of a mixed-phase core. The analytical formulae for the changes in radius, moment of inertia and the amount of energy released during the core-quake are derived using the theory of linear response of stellar structure to the core transformation. Numerical coefficients in these formulae are obtained for two realistic EOSs of dense matter. The problem of nucleation of the exotic phase as well as possible astrophysical scenarios leading to a core-quake phenomenon is also discussed.

Structured mixed phase at charged kaon condensation

Non-uniform structures of the mixed phase at the first-order phase transition to the charged kaon condensation are studied using the density functional theory within the relativistic mean-field model. Including the electric field effects and applying Gibbs conditions in a proper way, we numerically determine density profiles of nucleons, electrons and condensed kaons. The importance of the charge screening effects is elucidated and thereby we show that the Maxwell construction is effectively justified.

Equation of state, neutron stars and exotic phases

The role of the equation of state in the structure of neutron stars is summarized. At densities beyond a few times the normal nuclear saturation density, the neutron-proton-electron sea can be supplemented with more exotic matter, usually involving strangeness, such as hyperons, kaon or pion condensates, and deconfined quark matter. In the case of a boson condensate or deconfined quark matter, the exotic matter may form a mixed-phase region with the hadronic matter. Global aspects of neutron stars, such as radii, moments of inertia and the maximum mass, can be related to specific properties of matter at selected density ranges. Recent observations of isolated neutron stars and pulsars in binaries are beginning to yield significant constraints on structural properties of neutron stars and hence on the properties and composition of neutron-rich nuclear matter.

NJL-model description of Goldstone boson condensation in the color–flavor locked phase

A schematic NJL-type model is employed to investigate kaon and pion condensation in deconfined quark matter in the color–flavor locked (CFL) phase, explicitly referring to quark degrees of freedom. To that end we allow for non-vanishing pseudoscalar diquark condensates in addition to the scalar ones which constitute the CFL phase. Color neutrality is ensured by the appropriate choice of color chemical potentials. The dependence of the free energy in the Goldstone condensed phases on quark masses and charge chemical potentials is found to be in good qualitative—in most cases also quantitative—agreement with the predictions obtained within the effective Lagrangian approach.

Pion and kaon condensation in a 3-flavor Nambu–Jona-Lasinio model

We analyze the phase diagram of a 3-flavor Nambu--Jona-Lasinio model at finite temperature $T$ and chemical potentials ${\ensuremath{\mu}}_{u},{\ensuremath{\mu}}_{d},{\ensuremath{\mu}}_{s}$. We study the competition of pion and kaon condensation and we propose a physical situation in which kaon condensation could be led only by light quark finite densities.