Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Degenerations of K3, Orientifolds and Exotic Branes   A recently constructed limit of K3 has a long neck consisting of segments,
each of which is a nilfold fibred over a line, that are joined together with
Kaluza-Klein monopoles. The neck is capped at either end by a Tian-Yau space,
which is non-compact, hyperkahler and asymptotic to a nilfold fibred over a
line. We show that the type IIA string on this degeneration of K3 is dual to
the type I$'$ string, with the Kaluza-Klein monopoles dual to the D8-branes and
the Tian-Yau spaces providing a geometric dual to the O8 orientifold planes. At
strong coupling, each O8-plane can emit a D8-brane to give an O8$^*$ plane, so
that there can be up to 18 D8-branes in the type I$'$ string. In the IIA dual,
this phenomenon occurs at weak coupling and there can be up to 18 Kaluza-Klein
monopoles in the dual geometry. We consider further duals in which the
Kaluza-Klein monopoles are dualised to NS5-branes or exotic branes. A 3-torus
with $H$-flux can be realised in string theory as an NS5-brane wrapped on
$T^3$, with the 3-torus fibred over a line. T-dualising gives a 4-dimensional
hyperkahler manifold which is a nilfold fibred over a line, which can be viewed
as a Kaluza-Klein monopole wrapped on $T^2$. Further T-dualities then give
non-geometric spaces fibred over a line and can be regarded as wrapped exotic
branes. These are all domain wall configurations, dual to the D8-brane. Type
I$'$ string theory is the natural home for D8-branes, and we dualise this to
find string theory homes for each of these branes. The Kaluza-Klein monopoles
arise in the IIA string on the degenerate K3. T-duals of this give exotic
branes on non-geometric spaces.

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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: q-alg
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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The categories of this paper are: cond-mat
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: astro-ph
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The categories of this paper are: nlin
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The categories of this paper are: hep-ph
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph