Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-Body Dirac Equations from Relativistic Constraint Dynamics with
  Applications to QED and QCD Bound-States and to N-N Scattering   The formulation of relativistic two-body bound state wave equations and the
study of their relationship to quantum field theory began with work by
Eddington and Gaunt in 1928. However, the large variety of approaches attempted
in recent years shows that this problem still has no generally agreed-upon
solution. We describe here a recent approach resulting from " Two-Body Dirac
Equations" (emerging from Dirac's Relativistic Constraint Dynamics) that
satisfies many of the requirements one would demand of a treatment of the
relativistic two-body problem. We use its applications to QED bound states such
as positronium, QCD quarkonia, and the nucleon-nucleon scattering problem to
demonstrate the advantages of the approach.

16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys