Kaon Condensation Research Articles

Nuclear symmetry energy effects in finite nuclei and neutron star

Within a relativistic mean-field model with nonlinear isoscalar–isovector coupling, we explore the possibility of constraining the density dependence of nuclear symmetry energy from a systematic study of the neutron skin thickness of finite nuclei and neutron star properties. We find the present skin data supports a rather stiff symmetry energy at subsaturation densities that corresponds to a soft symmetry energy at supranormal densities. Correlation between the skin of 208Pb and the neutron star masses and radii with kaon condensation has been studied. We find that 208Pb skin estimate suggest star radii that reveals considerable model dependence. Thus precise measurements of neutron star radii in conjunction with skin thickness of heavy nuclei could provide significant constraint on the density dependence of symmetry energy.

Multi-K¯hypernuclei

Relativistic mean-field calculations of multi-K hypernuclei are performed by adding K{sup -} mesons to particle-stable configurations of nucleons, {lambda} and {xi} hyperons. For a given hypernuclear core, the calculated K separation energy B{sub K} saturates with the number of K mesons for more than roughly 10 mesons, with B{sub K} bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the K-meson densities peak, similarly to what was found for multi-K nuclei. The calculations demonstrate that particle-stable multistrange (N,{lambda},{xi}) configurations are stable against strong-interaction conversions {lambda}{yields}NK and {xi}{yields}NKK, confirming and strengthening the conclusion that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter.

Double-strangeness production with antiprotons

The production of double-strangeness by antiproton annihilation in nuclei will be an exciting way to investigate whether the formation of deeply bound antikaonic nuclear clusters occurs. The existence of deeply bound antikaonic nuclear clusters is a lively debated problem in hadron physics today, which can be solved only experimentally. At CERN with the Antiproton Decelerator (AD) and in future with the new FAIR facility at Darmstadt low energy antiprotons are available to perform this type of experiments. The use of antiprotons for the production of double-strangeness was recently discussed by Weise and Kienle and indeed, it would be very challenging to produce and study such “double-strange nuclei” in the view of the prediction of Akaishi and Yamazaki that double-antikaon bound nuclear systems with strangeness (S = − 2) will be formed with binding energies up to 200–300 MeV. Such binding energies might result in an increase of the average density to more than 3 times the average nuclear density. If such dense systems are created, conditions in the phase diagram might be reached where phase transition to kaon condensation or colour superconductivity will occur at low temperature.

Overview of $\boldsymbol{\bar{K} N}$ and $\boldsymbol{\bar{K}}$ -nucleus dynamics

The main features of coupled-channel \({\bar K}N\) dynamics near threshold and its repercussions in few-body \(\bar K\)-nuclear systems are briefly reviewed highlighting the I = 1/2 \({\bar K}NN\) system. For heavier nuclei, the extension of mean-field calculations to multi-\(\bar K\) nuclear quasibound states is discussed focusing on kaon condensation.

Multi- $\bar K$ configurations and the limit of kaon condensation

Our recent relativistic mean-field (RMF) calculations of multi - \(\bar K\) nuclei are briefly reviewed. I discuss the saturation pattern of the \(\bar K\) separation energy \(B_{\bar K}\) and nuclear densities on increasing the number of antikaons embedded in the nuclear medium. Saturation appears to be a robust feature of multi-\(\bar K\) nuclei. Because \(B_{\bar K}\) generally does not exceed 200 MeV, it is unlikely that kaon condensation occurs in strong-interaction self-bound strange hadronic matter. Last, I present our calculations of self-bound strange systems made out of neutrons and \({\bar K}^0\) mesons.

Kaon-Nucleus Interaction Studied through the in-flight [formula omitted] Reactions

We studied the K ¯ -nucleus interaction by the ( K − , N ) reactions on 12C and 16O. An appreciable strength observed in a bound region indicates that the K ¯ -nuclear potential is strongly attractive. Potential depth was derived by comparing with the theoretical calculations. It is −190 MeV for the C ( K − , n ) 12 −160 MeV for the C ( K − , p ) 12 , and −180 MeV for the O ( K − , n ) 16 reaction and −160 MeV for the O ( K − , p ) 16 respectively. Our data suggest that the K ¯ -nucleus potential is sufficiently deep to realize kaon condensation in the core of neutron stars.

Kaon condensation in the color–flavor-locked phase of quark matter, the Goldstone theorem, and the 2PI Hartree approximation

At very high densities, QCD is in the color–flavor-locked phase, which is a color-superconducting phase. The diquark condensates break chiral symmetry in the same way as it is broken in vacuum QCD and gives rise to an octet of pseudo-Goldstone bosons and a superfluid mode. The lightest of these are the charged and neutral kaons. For energies below the superconducting gap, the kaons are described by an O ( 2 ) × O ( 2 ) -symmetric effective scalar field theory with chemical potentials. We use this effective theory to study Bose-condensation of kaons and their properties as functions of the temperature and the chemical potentials. We use the 2-particle irreducible effective action formalism in the Hartree approximation. The renormalization of the gap equations and the effective potential is studied in detail and we show that the counterterms are independent of temperature and chemical potentials. We determine the phase diagram and the medium-dependent quasiparticle masses. It is shown that the Goldstone theorem is satisfied to a very good approximation. The effects of imposing electric charge neutrality is examined as well.

Dynamic migration of rotating neutron stars due to a phase transition instability

Using numerical simulations based on solving the general relativistic hydrodynamic equations, we study the dynamics of a phase transition in the dense core of isolated rotating neutron stars, triggered by the back bending instability reached via angular momentum loss. In particular, we investigate the dynamics of a migration from an unstable configuration into a stable one, which leads to a mini-collapse of the neutron star and excites sizeable pulsations in its bulk until it acquires a new stable equilibrium state. We consider equations of state with softening at high densities, a simple analytic one with a mixed hadron-quark phase in an intermediate pressure interval and pure quark matter at very high densities, and a microphysical one that has a first-order phase transition, originating from kaon condensation. Although the marginally stable initial models are rigidly rotating, we observe that during the collapse (albeit little) differential rotation is created. We analyze the emission of gravitational radiation, which in some models is amplified by mode resonance effects, and assess its prospective detectability by interferometric detectors. We expect that the most favorable conditions for dynamic migration exist in very young magnetars. We find that the damping of the post-migration pulsations strongly depends on the character of the equation of state softening. The damping of pulsations in the models with the microphysical equation of state is caused by dissipation associated with matter flowing through the density jump at the edge of the dense core. If at work, this mechanism dominates over all other types of dissipation, like bulk viscosity in the exotic-phase core, gravitational radiation damping, or numerical viscosity.

Multi-antikaonic nuclei in relativistic mean-field theory

Properties of multi-antikaonic nuclei (MKN), where several numbers of ${K}^{\ensuremath{-}}$ mesons are bound, are studied in the relativistic mean-field model, combined with chiral dynamics for the kaonic part of the thermodynamic potential. The density profiles for nucleons and ${K}^{\ensuremath{-}}$ mesons, the single particle energy of the ${K}^{\ensuremath{-}}$ mesons, and binding energy of the MKN are obtained. The effects of the $\overline{K}\text{\ensuremath{-}}\overline{K}$ interactions on these quantities are discussed in comparison with other meson ($\ensuremath{\sigma}$, $\ensuremath{\omega}$, and $\ensuremath{\rho}$)-exchange models. It is shown that the $\overline{K}\text{\ensuremath{-}}\overline{K}$ interactions originate from two contributions: One is the contact interaction between antikaons inherent in chiral symmetry, and the other is the one generated through coupling between the ${K}^{\ensuremath{-}}$ and meson mean fields. Both effects of the $\overline{K}\text{\ensuremath{-}}\overline{K}$ repulsive interactions become large on the ground state properties of the MKN as the number of the embedded ${K}^{\ensuremath{-}}$ mesons increases. A relation between the multi-antikaonic nuclei and kaon condensation in infinite and uniform matter is mentioned.

Hot Nuclear Matter Equation of State and Finite Temperature Kaon Condensation

We perform a systematic calculation of the equation of state of asymmetric nuclear matter at finite temperature within the framework of the Brueckner–Hartree–Fock approach with a microscopic three-body force. When applying it to the study of hot kaon condensed matter, we find that the thermal effect is more profound in comparison with normal matter, in particular around the threshold density. Also, the increase of temperature makes the equation of state slightly stiffer through suppression of kaon condensation.

Pion and kaon condensations in three-flavor random matrix theory

We study the QCD phase structure in a three-flavor random matrix model with symmetries of QCD formulated at finite temperature and nonzero chemical potentials of baryon number, isospin, and strangeness. We numerically investigate the phase diagram in the chemical potential plane at zero temperature with finite quark masses. We find a rich phase structure separated by both first and second order phase transition lines, which qualitatively agrees with the predictions of effective chiral models and Nambu-Jona-Lasinio models. The phases are characterized by the chiral condensates of three flavors, pion and kaon condensates.

Kaon condensation in the linear sigma model at finite density and temperature

Basing on the Cornwall-Jackiw-Tomboulis effective action approach we formulate a theoretical formalism for studying kaon condensation in the linear sigma model at finite density and temperature. We derive the renormalized effective potential in the Hartree-Fock approximation, which preserves the Goldstone theorem. This quantity is then used to consider physical properties of kaon matter.

NON-UNIFORM STRUCTURE OF MATTER AND THE EQUATION OF STATE

We investigate the non-uniform structures and the equation of state (EOS) of nuclear matter in the context of the first-order phase transitions (FOPT) such as liquid-gas phase transition, kaon condensation, and hadron-quark phase transition. During FOPT the mixed phases appear, where matter exhibits non-uniform structures called "Pasta" structures due to the balance of the Coulomb repulsion and the surface tension between two phases. We treat these effects self-consistently, properly taking into account of the Poisson equation and the Gibbs conditions. Consequently, they make the EOS of the mixed phase closer to that of Maxwell construction due to the Debye screening. This is a general feature of the mixed phase consisting of many species of charged particles.

EXOTIC PHASES IN NEUTRON STARS

The appearance of exotic phases in neutron stars is studied. The possible transition from hadron to quark phase is studied within the density dependent mass quark model, and the kaon condensation within the Nelson and Kaplan model. In both cases a microscopic approach is adopted for dense hadron matter. From the study of the possible coexistence between the two phases it is found that the hybrid phase may strongly hinder the onset of kaon condensation.

Kaon condensation with lattice QCD

Kaon condensation may play an important role in the structure of hadronic matter at densities greater than that of nuclear matter, as exist in the interior of neutron stars. We present the results of the first lattice QCD investigation of kaon condensation obtained by studying systems containing up to 12 negatively charged kaons. Surprisingly, the properties of the condensate that we calculate are remarkably well reproduced by leading order chiral perturbation theory. In our analysis, we also determine the three-kaon interaction from the multi-kaon systems and update our results for pion condensates.

Publisher’s Note: Kaon Condensation, Black Holes, and Cosmological Natural Selection [Phys. Rev. Lett.101, 091101 (2008)

Received 2 September 2008DOI:https://doi.org/10.1103/PhysRevLett.101.119901©2008 American Physical Society

Kaon Condensation, Black Holes, and Cosmological Natural Selection

It is argued that a well-measured double neutron-star binary in which the two neutron stars are more than 4% different from each other in mass or a massive neutron star with mass M > or approximately 2M(middle dot in circle) would put in serious doubt or simply falsify the following chain of predictions: (1) a nearly vanishing vector meson mass at chiral restoration, (2) kaon condensation at a density n-3n0, (3) the Brown-Bethe maximum neutron-star mass Mmax approximately 1.5M(middle dot in circle), and (4) Smolin's "cosmological natural selection" hypothesis.

Kaon condensation in neutron stars in relativistic mean field theory with isovector-scalar channel interaction

We study the properties of neutron stars involving antikaon condensation with three different models in the framework of relativistic mean field (RMF) approximation theory: the Glendenning-Moszkowski (GM) model, the Zimanyi-Moszkowski (ZM) model, and the hybrid derivative coupling (HD) model. We take the isovector-scalar (\ensuremath{\delta}-meson) channel interaction into account in our calculations and find that large mass neutron stars with kaon condensation can exist if the kaon optical potential is appropriately weak. The \ensuremath{\delta}-meson channel interaction has a significant influence on the property of neutron stars and the effects are a little different for the three models.

Deconfinement phase transition in hybrid neutron stars from the Brueckner theory with three-body forces and a quark model with chiral mass scaling

We study the properties of strange quark matter in equilibrium with normal nuclear matter. Instead of using the conventional bag model in quark sector, we achieve the confinement by a density-dependent quark mass derived from in-medium chiral condensates. In nuclear matter, we adopt the equation of state from the Brueckner-Bethe-Goldstone approach with three-body forces. It is found that the mixed phase can occur, for a reasonable confinement parameter, near the normal nuclear saturation density and goes over to pure quark matter at about 5 times the saturation. The onset of mixed and quark phases is compatible with the observed class of low-mass neutron stars, but it hinders the occurrence of kaon condensation.

Multi-K¯nuclei and kaon condensation

We extend previous relativistic mean-field (RMF) calculations of multi-$\overline{K}$ nuclei, using vector boson fields with SU(3) PPV coupling constants and scalar boson fields constrained phenomenologically. For a given core nucleus, the resulting $\overline{K}$ separation energy ${B}_{\overline{K}}$, as well as the associated nuclear and $\overline{K}$-meson densities, saturate with the number \ensuremath{\kappa} of $\overline{K}$ mesons for $\ensuremath{\kappa}g{\ensuremath{\kappa}}_{\mathrm{sat}}~10$. Saturation appears robust against a wide range of variations, including the RMF nuclear model used and the type of boson fields mediating the strong interactions. Because ${B}_{\overline{K}}$ generally does not exceed 200 MeV, it is argued that multi-$\overline{K}$ nuclei do not compete with multihyperonic nuclei in providing the ground state of strange hadronic configurations and that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter. Last, we explore possibly self-bound strange systems made of neutrons and ${\overline{K}}^{0}$ mesons, or protons and ${K}^{\ensuremath{-}}$ mesons, and study their properties.