Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Field-induced axion decay $a \to e^+ e^-$ in plasma   The axion decay $a \to e^+ e^-$ is investigated in the presence of a plasma
and an external magnetic field. The results demonstrate a strong catalyzing
influence of medium. The axion lifetime in the magnetic field of order
$10^{15}$ G and at the temperature of order 10 MeV is reduced to $10^4$ s.

2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
19
The categories of this paper are: eess
16
The categories of this paper are: stat
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin