Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ghost D-branes   We define a ghost D-brane in superstring theories as an object that cancels
the effects of an ordinary D-brane. The supergroups U(N|M) and OSp(N|M) arise
as gauge symmetries in the supersymmetric world-volume theory of D-branes and
ghost D-branes. A system with a pair of D-brane and ghost D-brane located at
the same location is physically equivalent to the closed string vacuum. When
they are separated, the system becomes a new brane configuration. We generalize
the type I/heterotic duality by including n ghost D9-branes on the type I side
and by considering the heterotic string whose gauge group is OSp(32+2n|2n).
Motivated by the type IIB S-duality applied to D9- and ghost D9-branes, we also
find type II-like closed superstrings with U(n|n) gauge symmetry.

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The categories of this paper are: funct-an
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The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: supr-con
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: astro-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: econ