Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Evolution of superhigh magnetic fields of magnetars   In this paper, we consider the effect of Landau levels on the decay of
superhigh magnetic fields of magnetars. Applying ${}^3P_2$ anisotropic neutron
superfluid theory yield a second-order differential equation for a superhigh
magnetic field $B$ and its evolutionary timescale $t$. The superhigh magnetic
fields may evolve on timescales $\sim (10^{6}-10^{7})$ yrs for common
magnetars. According to our model, the activity of a magnetar may originate
from instability caused by the high electron Fermi energy.

3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
16
The categories of this paper are: stat
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The categories of this paper are: cs
18
The categories of this paper are: econ