Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Invisibility and PT Symmetry: A Simple Geometrical Viewpoint   We give a simplified account of the properties of the transfer matrix for a
complex one-dimensional potential, paying special attention to the particular
instance of unidirectional invisibility. In appropriate variables, invisible
potentials appear as performing null rotations, which lead to the
helicity-gauge symmetry of massless particles. In hyperbolic geometry, this can
be interpreted, via M\"{o}bius transformations, as parallel displacements, a
geometric action that has no Euclidean analogy.

12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
11
The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys