Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Unitarity constraints on neutral pion electroproduction   At large virtuality $Q^2$, the coupling to the vector meson production
channels provides us with a natural explanation of the surprisingly large cross
section of the neutral pion electroproduction recently measured at Jefferson
Laboratory, without destroying the good agreement between the Regge pole model
and the data at the real photon point. Elastic rescattering of the $\pi^0$
provides us with a way to explain why the node, that appears at $t\sim -0.5$
GeV$^2$ at the real photon point, disappears as soon as $Q^2$ differs from
zero.

17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
19
The categories of this paper are: eess
18
The categories of this paper are: econ
16
The categories of this paper are: stat
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci