Estimates of elementary cross sections for dielectron production in pN and pd reactions are presented. Throughout, we use the vector dominance model for all hadron-hadron-photon vertices. The Δ,η Dalitz decays and bremsstrahlung appears as dominant sources of dielectrons. We show that the recently observed strong enhancement from 2 of the ratio of dielectron production from pd to pp collision at low energy E∼1.0–1.3 GeV may be understood by a different threshold behavior of eta production in proton-proton and proton-neutron collisions. Relying on a realistic deuteron wave function we estimate the energy dependence of the ratio and find qualitative agreement with new experimental results.

A general procedure for constructing front form, one boson exchange models for the two-nucleon system is developed. The procedure entails the construction of a mass-square operator which when used in conjunction with a free spin operator leads to an exactly Poincaré invariant model. An exchange model involving π, η, ρ, ω, δ, and σ mesons is constructed, and calculations of nucleon-nucleon phase shifts and deuteron properties are carried out. A comparison with the Bonn B potential, and a fit to a recent nucleon-nucleon phase shift analysis are presented.

A careful reanalysis is done of the contribution to ${\mathit{K}}^{+}$-nucleus scattering from the interaction of the kaon with the virtual pion cloud. The usual approximations made in the evaluation of the related kaon self-energy are shown to fail. We also find new interaction mechanisms which provide appreciable correlations to the kaon self-energy. Some of these contribute to the imaginary part below the pion creation threshold. The inclusion of these new mechanisms in the inelastic part of the optical potential produces a significant improvement in the differential and total ${\mathit{K}}^{+}$ nuclear cross sections. Uncertainties remain in the dispersive part of the optical potential.

This microscopic abrasion-ablation model approximates primary fragment cross sections using the Glauber interaction probabilities of the individual nucleon orbitals. It estimates the excitation energy distribution of the primary fragments using the density of hole states left by the abraded nucleons. The secondary (observable) cross sections are obtained by taking into account the statistical decay of each primary fragment over its entire range of excitation energy. The agreement with experimental data is good for light projectiles but deteriorates with increasing mass of the projectile, due to the increasing importance of secondary collisions of the abraded nucleons with the rest of the projectile.

Effects of the delta-isobar (Δ) mixing on the spin-isospin response functions in finite nuclei are studied in the quasielastic region. A method to calculate the response function for a finite system composed of nucleon (N) and Δ is formulated in a ring approximation. It is designed to treat the Δ-related Landau-Migdal parameters ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$, ${\mathrm{g}}_{\mathrm{\Delta }\mathrm{\Delta }}^{\prime }$ and the nucleon parameter ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$, independently, so that the universality ansatz, ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$=${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$=${\mathrm{g}}_{\mathrm{\Delta }\mathrm{\Delta }}^{\prime }$, is removed. We calculated the isovector spin-longitudinal and -transverse response functions, ${\mathrm{R}}_{\mathrm{L}}$ and ${\mathrm{R}}_{\mathrm{T}}$, with and without the Δ mixing. Inclusion of Δ enhances ${\mathrm{R}}_{\mathrm{L}}$ but reduces ${\mathrm{R}}_{\mathrm{T}}$ for ordinary interactions. Dependence of ${\mathrm{R}}_{\mathrm{L},\mathrm{T}}$ on ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$ and ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$ is investigated. Decomposition into the process-decomposed response functions, ${\mathrm{R}}^{\left[\mathrm{NN}\right]}$, ${\mathrm{R}}^{\left[\mathrm{N}\mathrm{\Delta }\right]}$, and ${\mathrm{R}}^{\left[\mathrm{\Delta }\mathrm{\Delta }\right]}$, is very elucidative to see the Δ effects, which are found to be mainly governed by ${\mathrm{R}}^{\left[\mathrm{N}\mathrm{\Delta }\right]}$ and sensitive to ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$. The isovector spin-transverse response function ${\mathrm{R}}_{\mathrm{T}}^{(\mathrm{e},\mathrm{e}\prime )}$ obtained by (e,e′) is calculated by various effective interactions and compared to each other as well as experimental data.

We investigate the π-nucleon interaction in nuclear matter around √s =1.5 GeV by examining dynamical modifications of ${\mathit{N}}^{\mathrm{*}}$ resonances microscopically. The pion production through the πΔ channel is suppressed appreciably in nuclear matter because the pion produced is strongly distorted through a Δ formation with a neighboring nucleon. This effect makes the width of N(1520) smaller and the mass larger in nuclear medium than in free space, and the πN ${\mathit{D}}_{13}$-wave amplitude loses much of its inelasticity. A similar situation arises with N(1535) and the πN ${\mathit{S}}_{11}$-wave amplitude because the ηN channel is suppressed by Pauli blocking of the nucleus that accompanies η. The total widths of ${\mathit{N}}^{\mathrm{*}}$ in nuclear medium, however, could be larger than in free space because of their spreading potentials.

Collective transverse momentum flow of nucleons and fragments in intermediate energy ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{27}$Al collisions is calculated with the antisymmetrized molecular dynamics (AMD). The observed flow and its balance energy are reproduced well by calculation with the Gogny force which corresponds to the soft equation of state (EOS) of nuclear matter. The calculated absolute value of the fragment flow is larger than that of the nucleon flow in the negative flow region, which can be explained by the existence of two components of flow. In addition to many similarities, the difference in the deuteron flow is found between ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${+}^{12}$C and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$${+}^{27}$Al collisions, and its origin is investigated by studying the production mechanism of light fragments. We also investigate the dependence of the flow of nucleons and fragments on the stochastic collision cross section and the effective interaction, and conclude that the stiff EOS without momentum dependence of the mean field is not consistent with the experimental data.

Predictions from the relativistic quantum molecular dynamics (RQMD) model are systematically compared to recently published charged hadron distributions of AGS Experiment 802 for central Si+Au collisions at 14.6A GeV/c, taking into account both the experimental trigger condition and acceptance. The main features of the data, including ${\mathit{K}}^{+}$ production, can be understood quantitatively to better than 20% within the framework of the model, although several discrepancies are found, most importantly for the proton spectra.

The rapidity distribution of thermal photons emitted from a hadronizing quark-gluon plasma is obtained with initial conditions locally determined from the hadronic rapidity density and assuming a longitudinal scaling expansion as in Bjorken hydrodynamics. The corresponding results for direct (QCD) photons and for decay photons are also obtained. The rapidity distributions of the three types of photons are found to be quite different and may help identify the most favorable window in the momentum space for identification for the quark-gluon plasma

Recent experiments on pion correlations, interpreted as interferometric measurements of the collision zone, are compared with models that distinguish a prehadronic phase and a hadronic phase. The models include prehadronic longitudinal expansion, conversion to hadrons in local kinetic equilibrium, and rescattering of the produced hadrons. We find that the longitudinal and outward radii are surprisingly sensitive to the algorithm used for two-body collisions. The longitudinal radius measured in collisions of 200 GeV/nucleon sulfur nuclei on a heavy target requires the existence of a prehadronic phase which converts to the hadronic phase at densities around 0.8–1.0 GeV/${\mathrm{fm}}^3$. The transverse radii cannot be reproduced without introducing more complex dynamics into the transverse expansion.

The dynamics of an idealized, infinite, MIT-type flux tube is followed in time as the interior evolves from a pure gluon field to a q¯q plasma. We work in color U(1). q¯q pair formation is evaluated according to the Schwinger mechanism using the results of Brink and Pavel. The motion of the quarks toward the tube end caps is calculated by a Boltzmann equation including collisions. The tube undergoes damped radial oscillations until the electric field settles down to zero. The electric field stabilizes the tube against pinch instabilities; when the field vanishes, the tube disintegrates into mesons. There is only one free parameter in the problem, namely the initial flux tube radius, to which the results are very sensitive. Among various quantities calculated is the mean energy of the emitted pions.

Within the finite-density QCD sum-rule approach we investigate the self-energies of Σ hyperons propagating in nuclear matter from a correlator of Σ interpolating fields evaluated in the nuclear matter ground state. We find that the Lorentz vector self-energy of the Σ is similar to the nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the Σ is also close to the corresponding value for nucleon; however, this prediction is sensitive to the strangeness content of the nucleon and to the assumed density dependence of certain four-quark condensate. The scalar and vector self-energies tend to cancel, but not completely. The implications for the couplings of Σ to the scalar and vector mesons in nuclear matter and for the Σ spin-orbit force in a finite nucleus are discussed.

We consider Compton scattering by a pion in the framework of chiral perturbation theory. We investigate off-shell effects in the s- and u-channel pole diagrams. For that purpose we perform a field transformation which, in comparison with the standard Gasser and Leutwyler Lagrangian, generates additional terms at order ${\mathit{p}}^4$ proportional to the lowest-order equation of motion. As a result of the equivalence theorem the two Lagrangians predict the same Compton scattering S-matrix even though they generate different off-shell form factors. We conclude that off-shell effects are not only model dependent but also representation dependent.

A suggestion is made for distinguishing 2N and 6q short-range correlations within the deuteron. The suggestion depends upon observing high momentum backward nucleons emerging from inelastic electromagnetic scattering from a deuteron target. A simple model is worked out to see the size of effects that may be expected.

The neutrinoless double beta decay of ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ is studied in a shell-model framework. Inclusion of the recoil terms in the hadronic currents is found to be essential in giving the right order of magnitude for the coupling constant between left and right currents. Short-range correlations and nucleon-size effects are also examined. The comparison of calculations in the full and truncated pf shell spaces indicates that the process is not very sensitive to nuclear-structure details. Assuming a mass of 1 eV for the electron neutrino the calculated half-life for the (${\mathrm{\beta }}^{\mathrm{-}}$${\mathrm{\beta }}^{\mathrm{-}}$${)}_{0\nu }$ mode is ${\mathit{T}}_{1/2}^{(0\mathrm{}\nu )}$≃${10}^{25}$ yr.

The cross section of the ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$(n,α${)}^{30}$Si reaction was measured in a neutron energy spectrum yielding the stellar rate for a thermal energy of kT=25 keV. For the ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$(n,p${)}^{36}$S reaction, the experiment was performed in the neutron energy range from 10 to 260 keV. Our new result for ${}_{}{}^{33}{}_{}{}^{}\mathrm{S}$ resolves the problem of a large discrepancy between two previous experiments. In case of ${}_{}{}^{36}{}_{}{}^{}\mathrm{Cl}$ it could be shown that the (n,α) channel is negligibly small compared to the (n,p) reaction at s-process conditions. The present results are used for a detailed discussion of a possble s-process origin of the rare neutron-rich isotope ${}_{}{}^{36}{}_{}{}^{}\mathrm{S}$.

We present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which we designate Argonne ${\mathit{v}}_{18}$. The model has a charge-independent part with 14 operator components that is an updated version of the Argonne ${\mathit{v}}_{14}$ potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen pp and np scattering database, low-energy nn scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a ${\mathrm{\chi }}^2$ per datum of 1.09 for 4301 pp and np data in the range 0–350 MeV.

The influence of two-proton capture reactions on long-lived waiting point isotopes near the proton drip line is discussed for the rp-process reaction flow. These reactions are characterized by two successive proton captures, where the first reaction product is unstable against proton emission, but the second reaction results in a particle stable nucleus. The reactions which have this character and involve long-lived waiting points in the rp process are ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$(2p,γ${)}^{17}$Ne, ${}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}$(2p,γ${)}^{20}$Mg, and ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$(2p,γ${)}^{40}$Ti. Their rates are presented and compared with the rates of alpha-induced reactions for stellar conditions at high temperatures and densities. We find that the two-proton captures on ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{Ne}$ can only compete for unrealistically high densities, but that ${}_{}{}^{38}{}_{}{}^{}\mathrm{Ca}$(2p,γ${)}^{40}$Ti can act as an efficient reaction link at conditions typical for x-ray bursts on neutron stars.

In-beam γ-ray spectroscopic studies of ${}_{}{}^{182}{}_{}{}^{}\mathrm{Hg}$ have revealed five new bands. The $2^{+}$ state of the prolate band has been identified at an energy of 548.6 keV and is higher than in ${}_{}{}^{184}{}_{}{}^{}\mathrm{Hg}$. A two parameter band mixing calculation results in an interaction energy of 83 keV between the prolate $2^{+}$ and the oblate $2^{+}$ states. Several additional new bands are seen including some which are interpreted as quadrupole vibrational bands built on the excited prolate minimum.

Requiring the translational invariance in the nonrelativistic description of the weak decay of hypernuclei, we investigate its effects on an asymmetry in the angular distribution of the pion emitted from the polarized${\mathrm{-}}_{\mathrm{\Lambda }}^3$H decay.