The early onset of nuclear shadowing in photoabsorption at low photon energies $(\gtrsim 1$ GeV) has recently been interpreted as a possible signature of a decrease of the $\rho$ meson mass in nuclei. We show that one can understand this early onset within simple Glauber theory if one takes the negative real part of the $\rho N$ scattering amplitudes into account, corresponding to a higher effective mass of the $\rho$ meson in nuclear medium.

The Hamiltonian based on the U(6/12) graded algebra is considered. This is the most general CQF IBA-1 Hamiltonian for even-even nuclei, but it has a special form for odd nuclei. It is shown that although in general cases this Hamiltonian does not have a dynamical symmetry, however, a part of the eigenstates of the even and odd neighboring nuclei form the boson-fermion multiplets.

The antisymmetrization of the composite particles in cluster model calculations manifests itself in Pauli forbidden states (ghost states), if one restricts oneself to an undeformed cluster in the low-energy region. The resonating group method and the generating coordinate method rely on a property of the norm kernel, which introduces some of the ghost states. The norm kernel has been usually been calculated under the assumption that the inner wave functions have a simple Gaussian form. This is the first time that this assumption has been tested in a rigorous way. In the ${}^4\mathrm{He}+N$ system, we demonstrate a ghost state, which is calculated from a rigorous solution of Yakubovsky equations for the α particle. The ghost states calculated by rigorous and approximate methods turn out to have a very similar form. It is analytically proved that the trace of the norm kernel does not depend on the inner wave function we choose.

The level structure of the unbound nucleus ${}^{11}\mathrm{N}$ has been studied by ${}^{10}\mathrm{C}+p$ elastic resonance scattering in inverse geometry with the LISE3 spectrometer at GANIL, using a ${}^{10}\mathrm{C}$ beam with an energy of 9.0 MeV/nucleon. An additional measurement was done at the A1200 spectrometer at MSU. The excitation function above the ${}^{10}\mathrm{C}+p$ threshold has been determined up to 5 MeV. A potential-model analysis revealed three resonance states at energies ${1.27}_{-0.05}^{+0.18\mathrm{}}$ MeV $(\Gamma =1.44\mathrm{}\pm 0.2$ MeV), ${2.01}_{-0.05}^{+0.15\mathrm{}}$ MeV $(\Gamma =0.84\mathrm{}\pm 0.2$ MeV), and $3.75\pm 0.05$ MeV $(\Gamma =0.60\mathrm{}\pm 0.05$ MeV) with the spin-parity assignments $I^{\pi }={\frac{1}{2}}^{+},{\frac{1}{2}}^{-},{\frac{5}{2}}^{+},$ respectively. Hence, ${}^{11}\mathrm{N}$ is shown to have a ground state parity inversion completely analogous to its mirror partner ${}^{11}\mathrm{Be}.$ A narrow resonance in the excitation function at $4.33\pm 0.05$ MeV was also observed and assigned spin parity ${\frac{3}{2}}^{-}.$

High-spin states have been studied for the first time in the ${}^{94}\mathrm{Nb}$ nucleus with the reaction ${}^{82}\mathrm{Se}{(}^{19}\mathrm{F},\alpha 3n\gamma )$ at 68 MeV. A cascade of transitions has been observed, based on the ${\mathrm{}\left(6\right)\mathrm{}}^{+}$ ground state and extending up to 6.5 MeV excitation and spin of about 19.

We study the equation of state of kaon-condensed matter including the effects of temperature and trapped neutrinos. Several different field-theoretical models for the nucleon-nucleon and kaon-nucleon interactions are considered. It is found that the order of the phase transition to a kaon-condensed phase, and whether or not Gibbs’ rules for phase equilibrium can be satisfied in the case of a first order transition, depend sensitively on the choice of the kaon-nucleon interaction. To avoid the anomalous high-density behavior of previous models for the kaon-nucleon interaction, a new functional form is developed. For all interactions considered, a first order phase transition is possible only for magnitudes of the kaon-nucleus optical potential $\gtrsim 100\hspace{0.5em}\mathrm{MeV}.$ The main effect of finite temperature, for any value of the lepton fraction, is to mute the effects of a first order transition, so that the thermodynamics becomes similar to that of a second order transition. Above a critical temperature, found to be at least 30–60 MeV depending upon the interaction, the first order transition disappears. The phase boundaries in baryon density versus lepton number and baryon density versus temperature planes are delineated, which is useful in understanding the outcomes of proto-neutron star simulations. We find that the thermal effects on the maximum gravitational mass of neutron stars are as important as the effects of trapped neutrinos, in contrast to previously studied cases in which the matter contained only nucleons or in which hyperons and/or quark matter were considered. Kaon-condensed equations of state permit the existence of metastable neutron stars, because the maximum mass of an initially hot, lepton-rich proto-neutron star is greater than that of a cold, deleptonized neutron star. The large thermal effects imply that a metastable proto-neutron star’s collapse to a black hole could occur much later than in previously studied cases that allow metastable configurations.

Fission fragment angular distributions have been measured for ${}^{10}\mathrm{B}\left(\mathrm{spin}{=3\mathrm{}}^{+}\right),$ ${}^{11}\mathrm{B}(\mathrm{spin}{=3/2\mathrm{}}^{-}{)+}^{232}\mathrm{Th}$ reactions at projectile energies below and above the Coulomb barrier. The fragment anisotropies for the ${}^{11}\mathrm{B}{+}^{232}\mathrm{Th}$ system are found to be significantly larger than the statistical saddle point model (SSPM) predictions at sub-barrier energies, while for the ${}^{10}\mathrm{B}{+}^{232}\mathrm{Th}$ system the deviations from SSPM predictions are found to be much less. The present results indicate that the ground state spin of the projectile influences the fragment anisotropies at sub-barrier energies in a larger way than predicted by the statistical model with the inclusion of the M-state distributions. Calculations were carried out based on the entrance channel dependent K-states distribution and preequilibrium fission models, with inclusion of ground state spin of the projectiles, which are found to explain the variation of fission fragment anisotropies as a function of bombarding energy for both the systems.

Form factor measurements of $M2\mathrm{}$ and $M4\mathrm{}$ transitions to the lowest $J^{\pi }{=2\mathrm{}}^{-}$ and $4^{-}$ states, respectively, in ${}^{48}\mathrm{Ca}$ with inelastic electron scattering at $180°$ are reported for momentum transfers $q\simeq 0.4-0.8{\mathrm{fm}}^{-1}.$ These form factors complement previous measurements at higher $q$ which have been treated by Lallena [Phys. Rev. C 48, 344 (1993)], as a test case to derive information on in-medium modifications of the $\rho$-meson mass. He deduced within the random-phase approximation (RPA) an effective mass $m_{\rho }^{*}\simeq 0.9-0.95m_{\rho }$ assuming simultaneous scaling of the $\pi$ coupling constant (Brown-Rho scaling). The validity of the analysis is critically assessed by comparing the measured form factors to second random-phase approximation (SRPA) calculations with a $\pi +\rho$ exchange interaction. The dependence of the form factors on the choice of the interaction and corrections such as mesonic exchange currents (MEC) are found to be of comparable magnitude to effects from a dropping of $m_{\rho },$ and in-medium effects hence cannot be clearly inferred from the data. To quantify the latter would require first the construction of an interaction which is capable of describing simultaneously and optimally a large variety of low-energy nuclear properties in ${}^{48}\mathrm{Ca}.$ Remaining discrepancies in such a description could then be studied with the aim to single out in-medium effects of the type advocated by Lallena.

Two four-quasiparticle isomers, with $K^{\pi }{=12\mathrm{}}^{+}$ and ${(14\mathrm{}}^{+})$ and mean lives of 450(100) ns and $58\left(5\right)\mathrm{}\mu \mathrm{s},$ have been identified in ${}^{176}\mathrm{Lu},$ at excitation energies of 1515 and 1588 keV, respectively. The ${12}^{+}$ isomer exhibits a large number of K-forbidden decay branches, populating the rotational sequences based on the $K^{\pi }{=7\mathrm{}}^{-}$ ground state, two $K^{\pi }{=8\mathrm{}}^{+}$ states, and a $K^{\pi }{=4\mathrm{}}^{+}$ state from the $\nu \{{7/2}^{-}\left[514\right]\}\otimes \pi \{{1/2}^{-}\left[541\right]\}$ configuration. Most branches have decay rates that are consistent with normal K-hindrances except for the branch to the $K^{\pi }{=4\mathrm{}}^{+}$ band. It has an anomalously low hindrance factor, which is attributed to two-state mixing due to a near-degeneracy between the ${12}^{+}$ isomer and the ${12}^{+}$ member of this band. The implied mixing matrix element has a value of only 5 eV, showing explicitly that very small mixing matrix elements may be responsible for anomalous K-hindered decays.

The Thomas-Ehrman shift for ${}^{11}\mathrm{Be}$ and ${}^{11}\mathrm{N}$ mirror nuclei, which was recently observed as a differential energy shift between s and other orbital states, is investigated in terms of complex expectation values. In calculating the complex expectation values, we use a new method which was recently proposed within the framework of the complex scaling method. The physical origin of the energy shift can be understood by considering the effects of the s-wave halo and the Coulomb barrier top. These two effects are discussed as another proof of a halo in addition to the observation of large matter radii in the drip-line nuclei.

The $0_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_1^{+}$ excitation in the proton-rich nucleus ${}^{18}\mathrm{Ne}$ has been studied via intermediate energy heavy-ion scattering with a beam of this radioactive isotope. The observed $\gamma$-ray yields have been combined with coupled channels calculations of the inelastic scattering reactions to obtain the electromagnetic matrix element ${B(E2;0\mathrm{}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_1^{+}).\mathrm{}$ This result is combined with the corresponding results in the mirror nucleus ${}^{18}\mathrm{O}$ and the $T=1\mathrm{}$ states in the $N=Z$ nucleus ${}^{18}\mathrm{F}$ as a test of isospin purity.

The reactions ${}^{12}\mathrm{C}{+}^{116}\mathrm{Sn},$ ${}^{22}\mathrm{N}\mathrm{e}+\mathrm{A}\mathrm{g},$ ${}^{40}\mathrm{Ar}{+}^{100}\mathrm{Mo},$ and ${}^{64}\mathrm{Zn}{+}^{89}\mathrm{Y}$ have been studied at $47A\hspace{0.5em}\mathrm{MeV}$ projectile energy. For these reactions the most violent collisions lead to increasing amounts of fragment and light particle emission as the projectile mass increases. This is consistent with quantum molecular dynamics (QMD) model simulations of the collisions. Moving source fits to the light charged particle data have been used to gain a global view of the evolution of the particle emission. Comparisons of the multiplicities and spectra of light charged particles emitted in the reactions with the four different projectiles indicate a common emission mechanism for early emitted ejectiles even though the deposited excitation energies differ greatly. The spectra for such ejectiles can be characterized as emission in the nucleon-nucleon frame. Evidence that the ${}^3\mathrm{He}$ yield is dominated by this type of emission and the role of the collision dynamics in determining the ${}^3\mathrm{H}{/}^3\mathrm{He}$ yield ratio are discussed. Self-consistent coalescence model analyses are applied to the light cluster yields, in an attempt to probe emitter source sizes and to follow the evolution of the temperatures and densities from the time of first particle emission to equilibration. These analyses exploit correlations between ejectile energy and emission time, suggested by the QMD calculations. In this analysis the degree of expansion of the emitting system is found to increase with increasing projectile mass. The double isotope yield ratio temperature drops as the system expands. Average densities as low as $0.36{\rho }_0$ are reached at a time near $100\hspace{0.5em}\mathrm{fm}/c$ after contact. Calorimetric methods were used to derive the mass and excitation energy of the excited nuclei which are present after preequilibrium emission. The derived masses range from 102 to 116 u and the derived excitation energies increase from 2.6 to 6.9 MeV/nucleon with increasing projectile mass. A caloric curve is derived for these expanded $A\sim 110$ nuclei. This caloric curve exhibits a plateau at temperatures near 7 MeV. The plateau extends from $\sim 3.5$ to 6.9 MeV/nucleon excitation energy.

Properties of dense quark matter in and out of chemical equilibrium are studied within the SU(3) Nambu–Jona-Lasinio model. In addition to the four-fermion scalar and vector terms the model includes also the six-fermion flavor mixing interaction. First we study a new form of deconfined matter, meso-matter, which is composed of an equal number of quarks and antiquarks. It can be thought of as a strongly compressed meson gas where mesons are melted into their elementary constituents, quarks and antiquarks. Strongly bound states in this quark-antiquark matter are predicted for all flavor combinations of $q\overline{q}$ pairs. The maximum binding energy reaches up to 180 MeV per $q\overline{q}$ pair for mixtures with about 70% of strange $\left(s\overline{s}\right)$ pairs. Equilibrated baryon-rich quark matter with various flavor compositions is also studied. In this case only shallow bound states appear in systems with a significant admixture (about 40%) of strange quarks (strangelets). Their binding energies are quite sensitive to the relative strengths of scalar and vector interactions. The common property of all these bound states is that they appear at high particle densities when the chiral symmetry is nearly restored. Thermal properties of meso-matter as well as chemically equilibrated strange quark matter are also investigated. Possible decay modes of these bound states are discussed.

Several heavy ion experiments at SPS have measured azimuthal distributions of particles with respect to the reaction plane. These distributions are deduced from two-particle azimuthal correlations under the assumption that they result solely from correlations with the reaction plane. In this paper, we investigate other sources of azimuthal correlations: transverse momentum conservation, which produces back-to-back correlations, resonance decays such as $\overrightarrow{\Delta }p\pi ,$ HBT correlations, and final state interactions. These correlations increase with impact parameter: most of them vary with the multiplicity N like $1/N.$ When they are taken into account, the experimental results of the NA49 Collaboration at SPS are significantly modified. These correlations might also explain an important fraction of the pion directed flow observed by WA98. Data should be reanalyzed taking into account carefully these nonflow correlations.

A density-dependent relativistic mean field (DRMF) theory is extended to that at finite temperature and density, and the liquid-gas phase transition of warm nuclear matter is investigated. Our results are compared with those obtained from the Walecka’s mean field theory. The critical values of temperature, density, and pressure are calculated by the DRMF. The obtained critical temperature is $T_c=12.66\mathrm{}\hspace{0.5em}\mathrm{MeV}$ by using the parameter set A, which is in accord with recent experimental observation.

Small angle neutron-neutron correlations have been measured for the $E/A=45\mathrm{}\hspace{0.5em}\mathrm{MeV}{\hspace{0.5em}}^{58}\mathrm{Ni}{+}^{27}\mathrm{Al},{\hspace{0.5em}}^{\mathrm{nat}}\mathrm{Ni},$ and ${}^{197}\mathrm{Au}$ reactions. Two-neutron correlation functions, both integrated and gated on the total momentum of the neutron pair, have been constructed. In order to explain these data, a fraction of fast “dynamical” emission is needed in addition to slower evaporative emission. The overall emission time scale is shorter for the symmetric system, indicating that the dynamical component is stronger in this case.

In the context of simple models utilizing field transformations in Lagrangian field theories we discuss the impossibility of measuring off-shell effects in nucleon-nucleon bremsstrahlung, Compton scattering, and related processes. Our aim is to illustrate the general results using simple and familiar models. To that end we introduce a simple phenomenological Lagrangian describing nucleon-nucleon bremsstrahlung and perform an appropriate change of variables leading to different off-shell behavior in the nucleon-nucleon amplitude as well as the photon-nucleon vertex. As a result we obtain a class of equivalent Lagrangians, generating identical S-matrix elements, of which the original Lagrangian is but one representative. We make use of this property in order to show that what appears as an off-shell effect in an S-matrix element for one Lagrangian may originate in a contact term from an equivalent Lagrangian. By explicit calculation we demonstrate for the case of nucleon-nucleon bremsstrahlung as well as nucleon Compton scattering the equivalence of observables from which we conclude that off-shell effects cannot in any unambiguous way be extracted from an S-matrix element. Finally, we also discuss some implications of introducing off-shell effects on a phenomenological basis, resulting from the requirement that the description of one process be consistent with that of other processes described by the same Lagrangian.

The two-nucleon spectral function in nuclear matter is studied using correlated basis function perturbation theory, including central and tensor correlations produced by a realistic Hamiltonian. The factorization property of the two-nucleon momentum distribution into the product of the two single nucleon distributions shows up in an analogous property of the spectral function. The correlated model yields a two-hole contribution quenched with respect to the Fermi gas model, while the peaks acquire a quasiparticle width that vanishes as the two momenta approach the Fermi momentum $k_F.$ In addition, three-hole one-particle and more complicated intermediate states give rise to a background, spread out in energy and absent in the uncorrelated models. The possible connections with one- and two-nucleon emission processes are briefly discussed.

The problem of the final state interaction, in quasielastic ${(e,e}^{\prime })$ scattering at large $Q^2,$ is investigated by exploiting the idea that the ejected nucleon needs a finite amount of time to assume its asymptotic form. It is shown that when the dependence of the scattering amplitude of the ejected nucleon on its virtuality is taken into account, the final state interaction is decreased. The developed approach is simpler to implement than the one based on the color transparency description of the damping of the final state interaction, and is essentially equivalent to the latter in the case of the single rescattering term. The ${(e,e}^{\prime })$ process on the deuteron is numerically investigated and it is shown that, at $x=1,$ appreciable finite formation time effects at $Q^2$ of the order of $10\hspace{0.5em}(\mathrm{GeV}{/c)}^2$ are expected.

We investigate the rates of production and thermalization of ${\nu }_{\mu }$ and ${\nu }_{\tau }$ neutrinos at temperatures and densities relevant to core-collapse supernovae and protoneutron stars. Included are contributions from electron scattering, electron-positron annihilation, nucleon-nucleon bremsstrahlung, and nucleon scattering. For the scattering processes, in order to incorporate the full scattering kinematics at arbitrary degeneracy, the structure function formalism developed by Reddy, Prakash, and Lattimer [Phys. Rev. D $58,$ 013009 (1998)] and Burrows and Sawyer [Phys. Rev. C $58,$ 554 (1998)] is employed. Furthermore, we derive formulas for the total and differential rates of nucleon-nucleon bremsstrahlung for arbitrary nucleon degeneracy in asymmetric matter. We find that electron scattering dominates nucleon scattering as a thermalization process at low neutrino energies $({\varepsilon }_{\nu }\lesssim 10\hspace{0.5em}\mathrm{MeV}),$ but that nucleon scattering is always faster than or comparable to electron scattering above ${\varepsilon }_{\nu }\simeq 10\hspace{0.5em}\mathrm{MeV}.$ In addition, for $\rho \gtrsim {10}^{13}\hspace{0.5em}{\mathrm{g}\mathrm{}\mathrm{}\mathrm{cm}}^{-3},$ $T\lesssim 14\hspace{0.5em}\mathrm{MeV},$ and neutrino energies $\lesssim 60\hspace{0.5em}\mathrm{MeV},$ nucleon-nucleon bremsstrahlung always dominates electron-positron annihilation as a production mechanism for ${\nu }_{\mu }$ and ${\nu }_{\tau }$ neutrinos.