28110065
Kaon production from hot and dense matter formed in heavy-ion collisions.
In heavy-ion collisions, kaons can be produced from baryon-baryon, meson-baryon, and meson-meson interactions. Simple meson-exchange models are introduced to study kaon production from these processes in the free space. These models are then extended to determine kaon production in hot, dense nuclear matter by taking into account the decreasing hadron masses as a result of the restoration of chiral symmetry and the condensation of kaons. We find that the cross sections for kaon production from all three processes are enhanced. In particular, the effect of decreasing hadron masses on kaon production from the meson-meson annihilation is most significant. In the hydrochemical model for heavy-ion collisions, we demonstrate that the observed enhancement of kaon yield in high-energy heavy-ion collisions can be explained if the medium effect is included.
119072699
Nuclear matter with Brown–Rho-scaled Fermi liquid interactions
Abstract We present a description of symmetric nuclear matter within the framework of Landau Fermi liquid theory. The low momentum nucleon–nucleon interaction V low - k is used to calculate the effective interaction between quasiparticles on the Fermi surface, from which we extract the quasiparticle effective mass, the nuclear compression modulus, the symmetry energy, and the anomalous orbital gyromagnetic ratio. The exchange of density, spin, and isospin collective excitations is included through the Babu–Brown induced interaction, and it is found that in the absence of three-body forces the self-consistent solution to the Babu–Brown equations is in poor agreement with the empirical values for the nuclear observables. This is improved by lowering the nucleon and meson masses according to Brown–Rho scaling, essentially by including a scalar tadpole contribution to the meson and nucleon masses, as well as by scaling g A . We suggest that modifying the masses of the exchanged mesons is equivalent to introducing a short-range three-body force, and the net result is that the Brown–Rho double decimation [G.E. Brown, M. Rho, Phys. Rep. 396 (2004) 1] is accomplished all at once.
120275311
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≥ 2M o 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 ∼ 3n o , (3) the Brown-Bethe maximum neutron-star mass M maX ≈1.5M ⊙ , and (4) Smolin's "cosmological natural selection" hypothesis.
117511063
The Physics of Supernovae and the Equation of State of Dense Nuclear Matter
The collapse of large stars leading to supernova explosions continues until the core reaches supranuclear densities. The large energy of SN(1987)A (Shelton) implies a soft equation of state, which makes it possible to transfer a large amount of energy from the core to the shock wave which carries through the explosion. At nuclear matter density the Landau forward scattering sum rule puts constraints on the Fermi liquid parameters strongly favouring a low-compression modulus. Whereas conventional nuclear physics calculations give a stiffer equation of state than required for supernovae at higher densities, it is pointed out that these do not include meson masses which decrease with increasing nuclear-matter density. This decrease in meson masses is implied by chiral symmetry. With decreasing meson masses the standard mechanism for saturation disappears, and saturation must be obtained from higher-order loops. These give the possibility, at least, of obtaining a low-compression modulus and soft equation of state at higher densities, because of their smooth dependence on density. In any case, this soft EOS seems to be required by the supernova explosion.
122541063
Relativistic effects in nuclear physics
Relativistic effects in nuclear physics are discussed. Very important effects stem from the lowering of the nucleon effective mass m* by the attractive scalar mean field. Spontaneous symmetry breaking by this field in the vacuum was originally responsible for the nucleon mass. Implications implied by the quark/gluon phase transition for this scalar mean field is discussed.
15066887
Renormalization group approach to neutron matter: quasiparticle interactions, superfluid gaps and the equation of state
Renormalization group methods can be applied to the nuclear many-body problem using the approach proposed by Shankar. We start with the two-body low momentum interaction Vlowk and use the RG flow from the particle–hole channels to calculate the full scattering amplitude in the vicinity of the Fermi surface. This is a new straightforward approach to the many-body problem which is applicable also to condensed matter systems without long-range interactions, such as liquid 3He. We derive the one-loop renormalization group equations for the quasiparticle interaction and the scattering amplitude at zero temperature. The RG presents an elegant method to maintain all momentum scales and preserve the antisymmetry of the scattering amplitude. As a first application we solve the RG equations for neutron matter. The resulting quasiparticle interaction includes effects due to the polarization of the medium, the so-called induced interaction of Babu and Brown. We present results for the Fermi liquid parameters, the equation of state of neutron matter and the 1S0 superfluid pairing gap.
39044560
Neutron halos in the Na isotopes.
The neutron and proton density distributions of the Na isotopes out to the proton and neutron drip lines are calculated in the spherical Hartree-Fock model with a wide variety of density-dependent Skyrme interactions. The results are compared to recent experimental data for the interaction cross sections and for the rms radii. We discuss the role of the deformed intruder states and the problems associated with predicting the location of the neutron drip line for this mass region. {copyright} {ital 1996 The American Physical Society.}
8824086
Isovector and isoscalar spin-flip excitations in even-even s-d shell nuclei excited by inelastic proton scattering.
Forward-angle cross sections for 1/sup +/ states have been measured in /sup 24,26/Mg, /sup 28/Si, and /sup 32/S by 201 MeV proton inelastic scattering. Comparisons are made with (..gamma..,..gamma..'), (e,e'), and (p,n) results. The measured strength is compared with microscopic distorted-wave Born approximation calculations using large-scale shell-model wave functions. Ratios of experimental to theoretical 1/sup +/ strengths are given. Almost no quenching is observed.
8977451
Isospin-mixing corrections for fp-shell Fermi transitions.
Isospin-mixing corrections for superallowed Fermi transitions in {ital fp}-shell nuclei are computed within the framework of the shell model. The study includes three nuclei that are part of the set of nine accurately measured transitions as well as five cases that are expected to be measured in the future at radioactive-beam facilities. We also include some new calculations for {sup 10}C. With the isospin-mixing corrections applied to the nine accurately measured {ital ft} values, the conserved-vector-current hypothesis and the unitarity condition of the Cabbibo-Kobayashi-Maskawa matrix are tested.
35977510
Quadrupole moments of sd-shell nuclei.
Shell-model calculations are presented for electric quadrupole moments of A = 17-39 nuclei. The shell-model wave functions, which span the complete 0d/sub 5/2/-ls/sub 1/2/-0d/sub 3/2/ model space in all instances, are obtained by diagonalizing an sd-shell Hamiltonian which consists of a fixed single-particle energy spectrum and a single set of two-body matrix elements scaled as a function of the mass number A. Results obtained with harmonic oscillator and Saxon-Woods single-particle radial wave functions and matched effective-charge models are presented for ground states of odd-even and doubly odd nuclei and for J/sup ..pi../ = 2/sup +/ first-excited states of doubly even sd-shell nuclei.
8485111
Direct evidence for the breakdown of the N = 8 shell closure in 12Be
Partial cross sections and corresponding momentum distributions have been studied in the one-neutron knockout reaction ( 12Be,11Be+gamma) on a 9Be target at 78 MeV/nucleon. The resulting spectroscopic factors for the only two bound states of 11Be are 0.42+/-0.06 ( 1/2(+)) and 0.37+/-0.06 ( 1/2(-)), where the errors are experimental only. This result shows that N = 8 is not a good closed shell in the neutron-rich 12Be and that the last neutron pair is two-thirds in the ( 1s(2)+0d(2)) intruder configuration.