QED corrections to elastic electron-nucleus scattering beyond the first-order Born approximation

A potential for the vertex and self-energy correction is derived from the first-order Born theory. The inclusion of this potential in the Dirac equation, together with the Uehling potential for vacuum polarization, allows for a nonperturbative treatment of these QED effects within the phase-shift analysis. Investigating the 12C and 208Pb targets, a considerable deviation of the respective cross-section change from the Born results is found, which becomes larger with increasing momentum transfer. Estimates for the correction to the beam-normal spin asymmetry are also provided. For the 12C nucleus, dispersion effects are considered as well.Comment: 9 pages, 10 figure

ANTIBINDING OF ATOMIC ELECTRONS IN STRONG INHOMOGENEOUS MAGNETIC FIELDS

Abstract. The ground-state energy of heavy one-electron ions in an inhomogeneous locally bounded magnetic field is estimated by the variational principle. The ions are described by means of the pseudorelativistic Herbst/Chandrasekhar operator. Two classes of magnetic fields are considered which model a field-free region around the central charge. It is shown that for a certain size of this region the ground-state energy becomes positive and increases strongly with the magnetic field strength. This behaviour is in contrast to the two-dimensional case where electrons can be bound by such a field-free region. 1

Excitation of the electric pygmy dipole resonance by inelastic electron scattering

To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1$^-$ states in $^{140}$Ce by $(e,e')$ scattering for momentum transfers $q=0.1-1.2$~fm$^{-1}$ is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $(e,e')$ reactions is predominantly of transversal nature for scattering angles $\theta_e \approx 90^o-180^o$. Being thus mediated by the convection and spin nuclear currents, the $(e,e')$ like the $(\gamma,\gamma')$ reaction, may provide additional information to the one obtained from Coulomb- and hadronic excitations of the PDR in $(p,p')$, $(\alpha,\alpha')$, and heavy-ion scattering reactions. The calculations predict that the $(e,e')$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest $2^+_1$ state for the studied kinematics, but that they may become dominant at extreme backward angles.Comment: Prepared for the special issue of EPJA on the topic "Giant, Pygmy, Pairing Resonances and related topics" dedicated to the memory of Pier Francesco Bortigno