Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Relativistic nature of a magnetoelectric modulus of Cr_2O_3-crystals: a
  new 4-dimensional pseudoscalar and its measurement
14
The categories of this paper are: math-ph
2
The categories of this paper are: math
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics
28
The categories of this paper are: alg-geom
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn