Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Two-Nucleon System beyond the Pion Threshold   A model is developed for the hadronic and electromagnetic interaction in the
two-nucleon system above pion threshold in the framework of meson, nucleon and
$\Delta$ degrees of freedom. It is based on time-ordered perturbation theory
and includes full meson retardation in potentials and exchange currents as well
as loop contributions to the nucleonic one-body current. Results for some
selected processes are discussed.

24
The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio