Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Torsion as electromagnetism and spin   We show that it is possible to formulate the classical Einstein-Maxwell-Dirac
theory of spinors interacting with the gravitational and electromagnetic fields
as the Einstein-Cartan-Kibble-Sciama theory with the Ricci scalar of the
traceless torsion, describing gravity, and the torsion trace acting as the
electromagnetic potential.

8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
23
The categories of this paper are: solv-int
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin