# Meson Retardation in the Two-Body Problem

## M. Schwamb and H. Arenhövel

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Institut für Kernphysik, J.J.-Becherweg 45, D-55099 Mainz, Germany
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The basic motivation for the incorporation of meson retardation in the
theoretical description of hadronic and electromagnetic reactions on the
two-nucleon system is the failure of conventional static approaches in
describing deuteron photodisintegration in the Delta-resonance region [1].
Therefore, a model for hadronic and electromagnetic reactions on the
two-nucleon system has been developed [2-5] which is based on retarded
interactions and currents and which can be applied to any reaction on
the two-nucleon system for excitation energies up to about 500 MeV in
which not more than one pion is produced or absorbed. It is based on
meson, nucleon and Delta-degrees of freedom where for technical reasons
maximal one meson is allowed to be present explicitly.

The results of this approach for NN-scattering as well as the
electromagnetic breakup of the deuteron are discussed. Moreover, we
consider the role of two-body contributions (MEC and hadronic backscattering)
for the GDH-sum rule on the deuteron in the Delta-region.

### References

- P. Wilhelm and H. Arenhövel, Phys. Lett. B 318, 410 (1993)
- M. Schwamb, H. Arenhövel, P. Wilhelm and Th. Wilbois, Phys. Lett.
B 420, 255 (1998)
- M. Schwamb and H. Arenhövel, Nucl. Phys. A 690, 647 (2001)
- M. Schwamb and H. Arenhövel, Nucl. Phys. A 690, 682 (2001)
- M. Schwamb and H. Arenhövel, nucl-th/0105033, Nucl. Phys. A, in
print