Relativistic Hartree approach with exact treatment of vacuum polarization for finite nuclei

We study the relativistic Hartree approach with the exact treatment of the vacuum polarization in the Walecka sigma-omega model. The contribution from the vacuum polarization of nucleon-antinucleon field to the source term of the meson fields is evaluated by performing the energy integrals of the Dirac Green function along the imaginary axis. With the present method of the vacuum polarization in finite system, the total binding energies and charge radii of 16O and 40Ca can be reproduced. On the other hand, the level-splittings in the single-particle level, in particular the spin-orbit splittings, are not described nicely because the inclusion of vacuum effect provides a large effective mass with small meson fields. We also show that the derivative expansion of the effective action which has been used to calculate the vacuum contribution for finite nuclei gives a fairly good approximation.Comment: 15 pages, 8 figure

Loop corrections and the K-matrix formalism

We propose a new model that combines the rigor of full-fledged loop calculations in field theory with the simplicity of the K-matrix formalism for channel-coupling effects. We show, for one example, the equivalence of this new model, the renormalized Im-K-matrix (RIK) model, with a more standard approach in which nonperturbative loop corrections are calculated. In the RIK model an analytic continuation of the K-matrix formalism is combined with a renormalization procedure to arrive at a scattering amplitude that obeys low-energy theorems and is also an analytic function in the complex momentum plane

Dibaryon resonance and two-photon bremsstrahlung in pp scattering

The signature of a possible dibaryon state is studied in two-photon production in proton-proton scattering, that is, in the process pp -> D gamma -> 2 gamma NN. We have investigated the effects on the cross section for cases in which the dibaryon has spin 0(+/-). Special attention is paid to interference of the dibaryon signal with that of the two-photon bremsstrahlung process