Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Orbital Angular Momentum Parton Distributions in Quark Models   At the low energy, {\sl hadronic}, scale we calculate Orbital Angular
Momentum (OAM) twist-two parton distributions for the relativistic MIT bag
model and for non-relativistic quark models. We reach the scale of the data by
leading order evolution in perturbative QCD. We confirm that the contribution
of quarks and gluons OAM to the nucleon spin grows with $Q^2$, and it can be
relevant at the experimental scale, even if it is negligible at the hadronic
scale, irrespective of the model used. The sign and shape of the quark OAM
distribution at high $Q^2$ may depend strongly on the relative size of the OAM
and spin distributions at the hadronic scale. Sizeable quark OAM distributions
at the hadronic scale, as proposed by several authors, can produce the dominant
contribution to the nucleon spin at high $Q^2$.

23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn