Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: QED effects in scattering processes involving atomic bound states:
  Radiative recombination   The standard S-matrix formulation cannot generally be used in the treatment
of atomic scattering processes, involving bound-state QED effects, due to the
special type of singularity that can here appear. This type of singularity can
be handled by means of methods designed for structure calculations. It is
essentially a consequence of the optical theorem that similar techniques can be
applied also in scattering processes. The optical theorem for free particles
gives a relation between the effective Hamiltonian and the cross section, a
relation that is valid also when bound states are present. We have found that
the method with the Covariant-evolution-operator/Green's operator that we have
developed primarily for structure problems can here be applied in a rather
straightforward manner. The new procedure is demonstrated for the case of
radiative recombination.

25
The categories of this paper are: patt-sol
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
30
The categories of this paper are: q-alg