Vector mesons in dense matter

We will summarize the progress in understanding the changes in the vector meson spectral density in nuclear medium using the constraint equations obtained from the Borel transformed dispersion relation and QCD Operator Product Expansion. We will discuss the results for the scalar mass shift and dispersion effects (three momentum dependence) for the light quark system (,ω), the strange quark system (Φ) and the heavy quark system (J/ψ) in nuclear medium. For the light quark system, a nontrivvial change in the mass and width is expected, while the dispersion effects are found to be small. Existing model calculations for the dispersion effects are compared to the constraint equation in detail. Very small, but accurate mass shifts are obtained for the heavy quark system.     

Strange goings on in dense nucleonic matter

It has been suggested that charged pions form a Bose-Einstein condensate in baryonic matter at zero temperature and about twice nuclear density. In this letter it is shown that at somewhat higher densities one finds a charged kaon condensate, driven to a large extent by the “stgma term” interaction with baryons. Using the SU(3) × SU(3) chiral lagrangian to model meson-baryon interactions it is found that baryonic matter acquires a strangeness-per-baryon ratio approaching one at several times nuclear density. The relevance of kaon condensation as a route to strange matter and its role in neutron stars are discussed.     

Pseudoscalar neutral mesons in hot and dense matter

The behavior of neutral pseudoscalar mesons π⁰,η and η′ in hot and dense matter is investigated, in the framework of the three flavor Nambu–Jona-Lasinio model. Three different scenarios are considered: zero density and finite temperature, zero temperature and finite density in a flavor asymmetric medium with and without strange valence quarks, and finite temperature and density. The behavior of mesons is analyzed in connection with possible signatures of restoration of symmetries. In the high density region and at zero temperature it is found that the mass of the η′ increases, the deviation from the mass of the η being more pronounced in matter without strange valence quarks.     

Vector mesons in asymmetric nuclear matter

The propagation of a vector meson (ϱ and ω) in dense asymmetric nuclear matter (with the number density of protons and neutrons different) is studied. Of particular interest is the density dependence of the vector meson masses, as also their variation with the asymmetry parameter, mass splitting among the ϱ isospin multiplets and the change of the form of the ϱ meson self-energy or the polarization tensor (II_μν) when the p ↔ n symmetry is broken. Contributions of both the Fermi sea and Dirac vacuum have been considered. It is shown that while the density dependent dressing of the vector meson propagator lifts the dispersion characteristics into the region of instability, the Dirac vacuum on the other hand contributes with opposite sign, thereby enhancing the possibility of stable collective modes even for higher values of vector meson momenta. The role of tensor coupling on the dispersion characteristics is also presented.     

Superfluidity in dense nuclear matter

We discuss the onset of superfluidity in neutron stars, where the model of nuclear matter is realized in a high-density and asymmetry state. In particular, we present the study of the effects of microscopic three-body forces on the proton pairing in the ¹ S ₀ channel and neutron pairing in ³ PF ₁ channel for β-stable neutron star matter. It is found that the main effects of three-body forces are to shrink the domain of existence of the ¹ S ₀ below the threshold of the direct URCA process and to stretch the density range of the ³ PF ₁ pairing in a broad domain so to cover most part of the neutron-star core. The text was submitted by the authors in English.     

D-mesons in dense nuclear matter

The D-meson properties in dense nuclear matter are studied. The D-meson spectral density is obtained within the framework of a coupled-channel self-consistent calculation, assuming as bare meson-baryon interaction a separable potential. The resonance is generated dynamically in our coupled-channel model. The medium modifications of the D-meson properties due to Pauli blocking and the dressing of D-mesons, nucleons and pions are also studied. We conclude that the self-consistent coupled-channel process reduces the in-medium effects on the D-meson compared to previous literature which did not consider the coupled-channel structure.Received: 14 January 2005, Published online: 31 May 2005PACS: 14.40.Lb, 14.20.Gk, 21.65. + f     

Exotica in dense and cold nuclear matter

A method for creating and investigating, under laboratory conditions, droplets of superdense cold matter is proposed, neutron stars being the closest analog of this kind of matter in nature. Arguments in support of the statement that an implementation of respective experiments is possible are presented, and the mechanism of kinematical cooling of the droplets in question is clarified. Various trigger types are proposed for performing searches for various exotic multiquark states in cold superdense matter.     

Strange axial-vector mesons mixing angle

The masses of K ₁(³ P ₁) and K ₁(¹ P ₁) are considered in a nonrelativistic constituent quark model, and the absolute value of the K ₁(³ P ₁)- K ₁(¹ P ₁) mixing angle is determined to be about 59.29^°. The comparison of the theoretical predictions on the strong decay widths of K ₁(1270) and K ₁(1400) in the ³ P ₀ decay model as well as the production ratio of these two states in the τ decay between the available experimental data strongly favors that the K ₁(³ P ₁)- K ₁(¹ P ₁) mixing angle is about +59.29^°.     

Strange quark dynamics on hot dense matter under the extreme condition

Production and properties of φ-meson under the extreme hot dense matter which is formed in Au + Au collisions at RHIC energy have been briefly reviewed.The issues are focused on transverse momentum (p T ) spectra of φ,elliptic flow of φ,nuclear modification factor of φ,the ratio of Ω(p T )/φ(p T ) versus p T,the ratio of Ω(p T /3)/φ(p T /2) versus p T /n q,spin alignment of φ and the enhancement of φ etc.These observables give the significant information of the strange quark dynamics in hot dense matter under the extreme condition.     

Strange quark dynamics on hot dense matter under the extreme condition

Production and properties of φ-meson under the extreme hot dense matter which is formed in Au ＋ Au collisions at RHIC energy have been briefly reviewed.The issues are focused on transverse momentum （p T ） spectra of φ,elliptic flow of φ,nuclear modification factor of φ,the ratio of Ω（p T ）/φ（p T ） versus p T,the ratio of Ω（p T /3）/φ（p T /2） versus p T /n q,spin alignment of φ and the enhancement of φ etc.These observables give the significant information of the strange quark dynamics in hot dense matter under the extreme condition.     

Equation of state of dense nuclear matter

An equation of state for cold nuclear matter for the region of densities ρ_nm−4ρ_nm, where ρ_nm is empirical nuclear-matter density, is constructed. We begin from the detailed calculation of Day and Wiringa for the two-body interactions; these give a saturation density of ∼2ρ_nm. This density is brought down to ρ_nm by the addition of relativistic corrections. Additional binding is obtained from three-body forces. A reasonable picture is obtained with the Day-Wiringa compression modulus for the two-body calculation, but the picture can be further improved by choosing this to be smaller.Our equation of state is similar to that of Friedman and Pandharipande in the region of nuclear matter denstiy ρ_nm, but, due to higher-order terms in the loop correction, is substantially softer at high density. Basically what happens is that the many-body effects saturate with increasing density, leaving only the two-body interactions.With this equation of state, prompt supernova explosions are very powerful when the compression modulus of neutron-rich matter (twice as many neutrons as protons) is ∼150 MeV, which corresponds to K_nm ∼ 190 MeV for symmetric nuclear matter.Analysis shows that hot nuclear matter formed in heavy ion collisions demands a very stiff equation of state. We understand this as arising from the strong velocity dependence in the real part of the optical model potential which follows chiefly from the Lorentz character of the interactions, the vector mean field growing with increasing density and the scalar one decreasing. This gives a substantial repulsive contribution to the energy per particle and produces a stiff effective equation of state for several hundred MeV heavy-ion collisions. With increasing degree of equilibration the magnitude of the repulsive energy decreases since equilibration decreases the effective momentum. Given the strong velocity dependence in the interaction, the hot equation of state can be reconciled with the cool one.     

Recent progress on dense nuclear matter in skyrmion approaches

The Skyrme model provides a novel unified approach to nuclear physics. In this approach, single baryon, baryonic matter and medium-modified hadron properties are treated on the same footing. Intrinsic density dependence (IDD) reflecting the change of vacuum by compressed baryonic matter figures naturally in the approach. In this article, we review the recent progress on accessing dense nuclear matter by putting baryons treated as solitons, namely, skyrmions, on crystal lattice with accents on the implications in compact stars.     

Probing dense matter with strangeness production in nuclear collisions

Experiments on strangeness production in nucleus–nucleus collisions at SIS energies address fundamental questions of modern nuclear physics: the determination of the nuclear equation-of-state at high baryon densities and the properties of hadrons in dense nuclear matter. From the yields of K⁺ mesons measured in heavy-ion collisions a value for the nuclear compressibility of is extracted for nuclear densities around twice saturation density using different microscopic transport models. Both the yield of K⁺ mesons and their anisotropic azimuthal angular distribution (elliptic flow) exhibit strong evidence for a repulsive K⁺N potential. The yields of K⁺ and K⁻ mesons measured in proton–nucleus collisions can be reproduced by transport calculations assuming at saturation density a repulsive K⁺N potential of and an attractive K⁻N potential of .     

Propagation of mesons in asymmetric nuclear matter in a density-dependent coupling model

We study the propagation of the light mesons σ,ω,ρ, and a₀(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in β-equilibrium. The equation of state and the potential contribution to the symmetry coefficient arising from the mean-field approximation are investigated. Received: 16 October 2001 / Accepted: 10 January 2002     

The strangeness and charm of dense nuclear matter

Acta Physica Hungarica A) Heavy Ion Physics - The creation of strangeness and charm in nucleus-nucleus collisions at threshold beam energies is discussed as a probe for compressed baryonic matter....