Electron-positron pair production in time-dependent potentials is considered. We find that the particle production distribution probability shows interesting resonance structures. Some numerical applications to heavy ion collisions are made.

Aiming at exploring microscopic dynamics responsible for the dissipative large-amplitude collective motion, the dynamic response and correlation functions are introduced within the general theory of nuclear coupled-master equations. The theory is based on the microscopic theory of nuclear collective dynamics which has been developed within the time-dependent Hartree-Fock (TDHF) theory for disclosing the complex structure of the TDHF manifold. A systematic numerical method for calculating the dynamic response and correlation functions is proposed. By performing numerical calculation for a simple model Hamiltonian, it is pointed out that the dynamic response function gives important information in understanding the large-amplitude dissipative collective motion which is described by an ensemble of trajectories within the TDHF manifold.

The direct nuclear reaction (N,N’π) on light nuclei is investigated using an intermediate isobar model. Cross sections for this exclusive reaction are calculated in distorted-wave approximation, for an incident nucleon of energy 300–800 MeV scattering from a closed-shell target, where the final nucleon and pion are detected in coincidence. The residual nucleus is assumed to be in a particle-hole state of arbitrary angular momentum and isospin. This reaction permits a small momentum transfer to the nucleus (1 ${\mathrm{fm}}^{\mathrm{-}1}$) so the nuclear structure is relatively well known. We study the dependence of these cross sections on several factors. The greatest sensitivity is to the self-energy of the intermediate meson. By considering different spin and parity nuclear final states, the nucleus is used as a spin-isospin filter allowing one to select certain amplitudes and study them independently. As an example, a detailed numerical study of the coincidence reaction on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is carried out. Such coincidence experiments may be useful for studying various aspects of the production and propagation of mesons and isobars in nuclei.

The dynamical polarization potential corresponding to a simple and tractable, but physically meaningful, two-channel model is derived and examined, with particular attention to its analytic properties. This enables us to illustrate explicitly the emergence of the general dispersive and retardation features expected from the imposition of causality. The energy dependence of the potential, and the associated nonlocality in time expressed by its Fourier transform, are explored. A new theorem is proposed for the asymptotic behavior of the Fourier transforms.

The entropy per nucleon (S/A) has been extracted for the Au [(150–800)A MeV] + Au reaction by using the phase I setup of the 4π facility at GSI, Darmstadt. The entropy has been obtained from the comparison of various observables characterizing the dM/dZ fragment multiplicity distributions, extending up to Z∼15, with those calculated with the quantum statistical model. It is the first time that S/A values are determined by considering the full ensemble of charged products detected in the reaction. Consistent values of S/A are found from different methods. These entropy values are shown to be fairly independent of the volume of the ‘‘participant’’ region considered. They are somewhat lower than those extracted in earlier works but are in good agreement with hydrodynamic calculations and suggest a low viscosity for the hot and dense nuclear matter.

Inclusive quasielastic neutrino (antineutrino) reactions on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at intermediate energies (50<E<400 MeV) are studied to investigate the effects of the nuclear medium on the total cross section and the energy spectrum of the outgoing leptons. The calculations are done in the local density approximation and various nuclear effects like Pauli blocking, Fermi motion, and strong-interaction renormalizations due to the presence of nucleons are taken into account. The corrections due to Coulomb effects are included which have been hitherto neglected in inclusive reactions. The results presented here are applicable to the inclusive reactions with neutrino beams planned to look for neutrino oscillations in the Los Alamos experiments or the experiments with underground detectors looking for atmospheric or solar flare neutrinos.

Dependences of the azimuthal and target asymmetries in the breakup of polarized deuterons by unpolarized electrons on the choice of the deuteron electromagnetic (EM) current model and final-state interaction (FSI) effects are investigated. Possibilities for separation of the structure functions which determine these observables are discussed. Results of the calculations are compared with available data. It has been shown that FSI plays an important role in formation of the asymmetries. In the quasifree region some of them depend considerably on the neutron electric form factor and on the spin-orbit EM interaction with nucleon. The tensor target asymmetries ${\mathit{T}}_{20}$ and ${\mathit{T}}_{22}$ calculated for ${}_{}{}^2{}_{}{}^{}\to$(e,pn)e’ under kinematic conditions of the experiment with the electron storage ring VEPP-3 in Novosibirsk have been found to be very sensitive to the meson exchange current contributions.

Sub-barrier fusion has often been studied by linearizing couplings to nuclear structure for calculational convenience. Using a Green function technique and the interacting boson model, we are able to include couplings to all orders. After renormalizing the coupling strengths, we find that couplings to all orders lead to improved agreement with data for the fusion cross section and distribution of barriers, compared to the linear couplings.

We investigate the processes leading to phase-space equilibration of parton distributions in nuclear interactions at collider energies. We derive a set of rate equations describing the chemical equilibration of gluons and quarks including medium effects on the relevant QCD transport coefficients, and discuss their consequences for parton equilibration in heavy ion collisions.

Large discrepancies have been observed between measured electromagnetic dissociation (ED) cross sections and the predictions of the semiclassical Weizäcker-Williams-Fermi (WWF) method. In this paper, the validity of the semiclassical approximation is examined. The total cross section for electromagnetic excitation of a nuclear target by a spinless projectile is calculated in first Born approximation, neglecting recoil. The final result is expressed in terms of correlation functions and convoluted densities in configuration space. The result agrees with the WWF approximation to leading order (unretarded electric dipole approximation), but the method allows an analytic evaluation of the cutoff, which is determined by the details of the electric dipole transition charge density. Using the Goldhaber-Teller model of that density, and uniform charge densities for both projectile and target, the cutoff is determined for the total cross section in the nonrelativistic limit, and found to be smaller than values currently used for ED calculations. In addition, cross sections are calculated using a phenomenological momentum space cutoff designed to model final state interactions. For moderate projectile energies, the calculated ED cross section is found to be smaller than the semiclassical result, in qualitative agreement with experiment.

Excited muonic atoms in the actinide region may induce prompt fission. Following atomic muon capture, some of the inner-shell transitions proceed by inverse internal conversion, i.e., the excitation energy of the muonic atom is transferred to the nucleus. In particular, the (E2:3d→1s) muonic transition energy is close to the peak of the isoscalar giant quadrupole resonance in actinide nuclei which exhibits a large fission width. Prompt fission in the presence of a bound muon allows us to study the dynamics of large-amplitude collective motion. We solve the time-dependent Dirac equation for the muonic spinor wave function in the Coulomb field of the fissioning nucleus on a three-dimensional lattice and demonstrate that the muon attachment probability to the light fission fragment is a measure of the nuclear energy dissipation between the outer fission barrier and the scission point.

At medium energies the distorted-wave Born approximation provides a much less reliable description of transfer reactions induced by composite projectiles. While use of the Johnson-Soper adiabatic method includes the dominant contributions from three-body breakup channels, recent experimental data have suggested the need for additional theoretical refinements. The use of Weinberg or Sturmian states provides a framework within which the adiabatic theory can be improved systematically. The results of the Weinberg states method are presented for the ${}_{}{}^{66}{}_{}{}^{}\mathrm{Zn}$(d,p${)}^{67}$Zn (g.s.; 5/$2^{\mathrm{-}}$; l=3) reaction at 88.2 MeV incident energy. The implementation of the method is shown to reduce the three-body transfer reaction calculation to a very small coupled-channels problem. For the reaction in question, the method introduces significant corrections to the adiabatic method which agree qualitatively with earlier calculations using the quasiadiabatic method.

Calculations for the kaon capture, electron pair, and hyperon (Y) production reactions, p(${\mathit{K}}^{\mathrm{-}}$,${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$)Y, are made for Y=Λ, ${\mathrm{\Sigma }}^0$, and Λ(1405) using our previously developed crossing and duality constrained electroproduction model. Because there is no constraint on the minimum 4-momentum transferred by the timelike photon (${\mathit{q}}^2$≥2${\mathit{M}}_{\mathit{e}}^2$∼0), we observe that the low-lying ρ, ω, and φ vector mesons are kinematically accessible, producing up to four orders of magnitude enhancement in the theoretical hyperon production cross section. We also discuss the significance and utility of this dramatic enhancement for investigating several important topics of current interest.

Within the finite-temperature relativistic mean field theory models (linear and nonlinear) and using the local density approximation, the statistical properties and stability of hot nuclei are investigated. It is found that the nonlinear model presents higher thermal response than the linear model. The critical temperature is found to be about 9 MeV for the linear model and about 8 MeV for the nonlinear one. The value of the energy level density parameter obtained by the nonlinear model is found to be of the order of 0.11 ${\mathrm{MeV}}^{\mathrm{-}1}$, in good agreement with the empirical value ≃0.12 ${\mathrm{MeV}}^{\mathrm{-}1}$. The linear model gives smaller values. The nonrelativistic limit of the linear model indicates that the relativistic treatment increases the excitation.

Parity nonconserving nuclear forces induce electromagnetic currents and nuclear moments of the wrong parity (e.g., anapole moment). The interaction between atomic electrons and these currents is considered taking into account finite nuclear size and relativistic effects. The formula has been derived which allows one to separate the atomic and nuclear problems. The result can be approximately expressed as the interaction of an electron with a pointlike nuclear anapole moment times a correction factor [1-0.3(Zα${)}^2$]. As an illustration we use a simple model to calculate the distribution of the parity-violating electromagnetic current, magnetic field, and vector potential.

Two-photon intensity interferometry is used to probe the dynamics of quarks and gluons in a high-energy nucleus-nucleus collision. A (1+1)-dimensional expansion of the plasma according to Bjorken hydrodynamics as well as a (3+1)-dimensional expansion, both with a first-order phase transition, are considered. The correlation of high transverse-momentum photons is sensitive to the details of the space-time evolution of the high density QCD plasma. The so-called ‘‘longitudinal’’ and ‘‘outward’’ correlations are found to be dramatically affected by the transverse expansion of the system.

Studies of the closed core response to a perturbation in the Dirac Hamiltonian (due to an out-of-core baryon) are extended to particle-hole states in nuclear matter. Both isoscalar nucleon-particle–nucleon-hole states and Λ-particle–nucleon-hole hypernuclear states are considered. Core-response effects on the nuclear baryon current and the vector and scalar densities are studied, using both a perturbative treatment and linear response theory. While no essentially new physical insight is encountered by considering particle-hole states, there are many new and interesting applications. In particular, we mention applications to hypernuclei, meson-nucleus (especially ${\mathit{K}}^{+}$) interactions, meson photoproduction on nuclei, nuclear reactions, and nuclear transitions in inelastic scattering and weak interactions in nuclei. We point out interest in core-response effects related to nuclear transitions, where new physical insight is expected.

The decisive role played by the interaction between the kaon and the delta isobar in describing ${\mathit{K}}^{+}$-nucleon data above pion threshold is demonstrated.

We calculate order-${\mathrm{\alpha }}_{\mathit{s}}$ color magnetic corrections to the valence quark distributions of the proton using the Los Alamos potential model wave functions. The spin-spin interaction breaks the model SU(4) symmetry, providing a natural mechanism for the difference between the up and down distributions. For a value of ${\mathrm{\alpha }}_{\mathit{s}}$ sufficient to produce the N-Δ mass splitting, we find up and down quark distributions in reasonable agreement with experiment.

The scattering from thorium of electrons emitted in the decay of ${}_{}{}^{90}{}_{}{}^{}\mathrm{Y}$ is studied. Coincidence spectra of electrons and positrons in the energy region 210–420 keV were measured. In contrast with what has been the case in studies of the corresponding positron scattering, no anomaly was observed.