Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Topological Casimir effect in Maxwell Electrodynamics on a Compact
  Manifold   We study the Topological Casimir effect, in which extra vacuum energy emerges
as a result of the topological features of the theory, rather than due to the
conventional fluctuations of the physical propagating degrees of freedom. We
compute the corresponding topological term in quantum Maxwell theory defined on
a compact manifold. Numerically, the topological effect is much smaller than
the conventional Casimir effect. However, we argue that the Topological Casimir
Effect is highly sensitive to an external magnetic field, which may help to
discriminate it from the conventional Casimir effect. It is quite amazing that
the external magnetic field plays the role of the $\theta$ state, similar to a
$\theta$ vacuum in QCD, or $\theta=\pi$ in topological insulators.

21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs