Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: $\eta^{(')}\to\pi^+\pi^-\gamma^{(\ast)}$ in large-$N_c$ chiral
  perturbation theory   We present a calculation of the decays
$\eta^{(')}\to\pi^+\pi^-\gamma^{(\ast)}$ at the one-loop level up to and
including next-to-next-to-leading order (NNLO) in large-$N_c$ chiral
perturbation theory. The numerical evaluation of the results is performed
successively at LO, NLO, and NNLO, fitting the relevant low-energy constants to
the available experimental data. We discuss the widths and decay spectra of
$\eta^{(')}\to\pi^+\pi^-\gamma$ as well as $\eta^{(')}\to\pi^+\pi^-l^+l^-$,
with $l=e,\ \mu$.

25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga