Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Einstein-Dirac theory on gauge-natural bundles   We present a clear-cut example of the importance of the functorial approach
of gauge-natural bundles and the general theory of Lie derivatives for
classical field theory, where the sole correct geometrical formulation of
Einstein (-Cartan) gravity coupled with Dirac fields gives rise to an
unexpected indeterminacy in the concept of conserved quantities.

4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con