Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Small $x$ Contributions to the Structure Function $F_L(x,Q^2)$   The gluon contributions to $F_L(x,Q^2)$ in ${\cal O}(\alpha_s)$ are
calculated taking into account the transverse momentum of the initial state
parton. In comparison with collinear factorization $F_L(x,Q^2)$, is not
affected at large $x$ but takes smaller values in the small $x$ range. The
onset of the $k_{\perp}$ effect is a function of $Q^2$.

27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
22
The categories of this paper are: chao-dyn
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
1
The categories of this paper are: cs