Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The reaction $^2H(\gamma,\pi^0)np$ in the threshold region   Neutral pion photoproduction on the deuteron in the inelastic channel is
studied in the threshold region from 142 to 160 MeV. The calculation is based
on the use of the diagrammatic approach. Contributions from the pole diagrams,
one-loop diagrams both with $n$-$p$ and $\pi$-$N$ rescattering as well as
two-loop diagrams with simultaneous inclusion of these rescattering mechanisms
are taken into account. We have found a reasonable agreement with a very simple
calculation by J.C. Bergstrom et al. [Phys. Rev. C 57 (1998) 3203]. It is shown
that the `effective' electric dipole deuteron amplitude $E_d$ is negative in
agreement with a prediction of ChPT. We conclude that a deviation of about 20%
from a ChPT prediction for $E_d$ discovered in an experiment on coherent
$\pi^0$ photoproduction off the deuteron cannot be attributed to inadequate
estimates of inelastic channel contributions. We suggest that $\pi$-$N$
rescattering is responsible for the deviation of the free-nucleon $p_1$
threshold amplitude from the value measured in that experiment

25
The categories of this paper are: patt-sol
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th