[en] Meson exchange currents play an important role in the description of observables in electron scattering. The authors use a relativistic model with pseudovector pion coupling to study the exchange current contributions, with emphasis on quasielastic kinematics. Starting with the Lagrangian for nucleons interacting with a scalar and vector mason along with pseudovector coupling to pions, they derive the one and two-body electromagnetic currents. They then calculate the longitudinal and transverse pieces of the quasielastic cross section for various nuclei and kinematics. The effects of meson exchange currents are found to be much more important in a relativistic model than in a non-relativistic one

[en] We present a comprehensive study of two-boson exchange (TBE) corrections in parity-violating electron-proton elastic scattering. Within a hadronic framework, we compute contributions from box (and crossed box) diagrams in which the intermediate states are described by nucleons and Delta baryons. The Delta contribution is found to be much smaller than the nucleon one at backward angles (small epsilon), but becomes dominant in the forward scattering limit (epsilon near 1), where the nucleon contribution vanishes. The dependence of the corrections on the input hadronic form factors is small for Q² < 1 GeV², but becomes significant at larger Q². We compute the nucleon and Delta TBE corrections relevant for recent and planned parity-violating experiments, with the total corrections ranging from -1% for forward angles to 1-2% at backward kinematics.

[en] We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q² region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization measurements, nonlinear epsilon contributions to the cross sections, and via e+p to e-p cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and gamma-Z interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.

[en] Within the framework of the relativistic Dirac-Hartree-Fock approach, the properties of nuclear matter and finite nuclei are studied based on a 'realistic' one-boson exchange interaction. With a minimal number of parameters fit to the saturation properties of nuclear matter one is able to give a resonably good account of the binding energies, single particle energies and density distributions of finite nuclei

[en] The particle-hole spectra of light nuclei are examined in the self-consistent random phase approximation based on fully relativistic Hartree and Hartree-Fock models for the nuclear ground state. The particle-hole interaction is completely prescribed by the ground-state calculation. It includes σ, ω, rho, and π meson exchanges, with σ and ω parameters adjusted to fit the bulk properties of nuclear matter. Differences between Hartree (no exchange) and Hartree-Fock (with exchange) predictions for the spectra are discussed

[en] The contributions of meson exchange currents are studied in the quasielastic region of the inclusive electron scattering cross section. Particular emphasis is placed on the importance of relativity in the analysis, and a relativistic Fermi gas model is employed. Significant effects are found in the transverse response function, while the longitudinal response is essentially unchanged. (orig.)

[en] Relativistic Hartree-Fock calculations are performed for ¹⁶O and ⁴⁰Ca nuclei. The exchange of photons, σ, ω, ρ and π mesons is considered, with coupling constants adjusted to saturate nuclear matter at the experimental binding energy and density. The binding energies, densities, RMS radii and single particle energies are compared with experiment and with those calculated in the Hartree approximation. (orig.)

[en] The effects of meson exchange currents, isobars and core polarisation on the magnetic form factor of ¹⁷O are investigated. A significant cancellation is found between second order core polarisation of the one-body operator and first order core polarisation of the two-body meson exchange operator. The importance of consistency to each order in perturbation theory is stressed and the relative magnitude of these different contributions is discussed. (orig.)

[en] The exact evaluation of one-loop corrections in a finite (1+1)-dimensional system is described. Scalar and vector (baryon) densities are calculated in a background of Gaussian scalar and vector potentials. The results are compared with a derivative expansion in inverse powers of the effective mass. Excellent agreement is found when derivative terms up to second order are retained

[en] A previous study of dense neutrino matter indicated that the behavior of such a system becomes nonperturbative at relatively low density under certain kinematic conditions. A detailed examination of the analysis indicates errors in the formulation and in some of the expressions used. We present a reformulation of the problem, and find no such physical effect