Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hard diffraction in hadron--hadron interactions and in photoproduction   Hard single diffractive processes are studied within the framework of the
triple--Pomeron approximation. Using a Pomeron structure function motivated by
Regge--theory we obtain parton distribution functions which do not obey
momentum sum rule. Based on Regge-- factorization cross sections for hard
diffraction are calculated. Furthermore, the model is applied to hard
diffractive particle production in photoproduction and in $p\bar{p}$
interactions.

35
The categories of this paper are: mtrl-th
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat