Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pion Observables and QCD   The nonperturbative, Dyson-Schwinger equation approach to solving QCD
provides a straightforward, microscopic description of dynamical chiral
symmetry breaking and confinement. It is an ideal tool for the study of pion
observables. This is illustrated via its application to the calculation of: the
$\pi$-$\pi$ scattering lengths $a_0^0$, $a_0^2$, $a_1^1$, $a_2^0$, $a_2^2$ and
associated partial wave amplitudes; the $\pi^0\rightarrow \gamma\gamma$ decay
width; and the charged pion form factor, $F_\pi(q^2)$.

23
The categories of this paper are: solv-int
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
6
The categories of this paper are: astro-ph
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs