Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Effective Field Theory Approach to Pionium   The various dynamical scales below the pion mass involved in $\pi^{+}$
$\pi^{-}$ atoms are sequentially integrated out using non-relativistic
effective field theory techniques. This allows us to systematically organise
the corrections to the energy levels and decay width. We present our results in
terms of a single unknown constant which may be obtained by matching to the
Chiral Lagrangian with electromagnetic interactions at two loops.

34
The categories of this paper are: chem-ph
17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
26
The categories of this paper are: bayes-an
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat