Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Angular momentum of the physical electron   The angular momentum of the physical electron, modelled as a Dirac fermion
coupled to the electromagnetic field, is found to be hbar/2, the same as that
of a bare Dirac fermion and independent of the size of the electric charge.

30
The categories of this paper are: q-alg
16
The categories of this paper are: stat
3
The categories of this paper are: physics
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
31
The categories of this paper are: ao-sci