Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: pi+pi- Atom in Chiral Theories   We review the existing theoretical approaches to the study of the observables
of hadronic atoms. In the relativistic perturbative approach based on the
Bethe-Salpeter equation and Chiral Perturbation Theory we derive the general
expression for the pi+pi- atom lifetime. The lowest-order correction to the
relativistic Deser-type formula for the atom width is predicted to be 6.1\pm
3.1 %.

30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
1
The categories of this paper are: cs
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th