Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Scattering cross-section under external magnetic field using the optical
  theorem
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
7
The categories of this paper are: hep-th