Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quark Orbital-Angular-Momentum Distribution in the Nucleon   We introduce gauge-invariant quark and gluon angular momentum distributions
after making a generalization of the angular momentum density operators. From
the quark angular momentum distribution, we define the gauge-invariant and
leading-twist quark {\it orbital} angular momentum distribution $L_q(x)$. The
latter can be extracted from data on the polarized and unpolarized quark
distributions and the off-forward distribution $E(x)$ in the forward limit. We
comment upon the evolution equations obeyed by this as well as other orbital
distributions considered in the literature.

12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
17
The categories of this paper are: q-fin
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The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
6
The categories of this paper are: astro-ph