Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: ALF gravitational instantons and collapsing Ricci-flat metrics on the K3
  surface   We construct large families of new collapsing hyperk\"ahler metrics on the K3
surface. The limit space is the quotient of a flat 3-torus by an involution.
Away from finitely many exceptional points the collapse occurs with bounded
curvature. There are at most 24 exceptional points where the curvature
concentrates, which always contains the 8 fixed points of the involution on the
3-torus. The geometry around these points is modelled by ALF gravitational
instantons: of dihedral type (Dk) for the fixed points of the involution on the
3-torus and of cyclic type (Ak) otherwise. The collapsing metrics are
constructed by deforming approximately hyperk\"ahler metrics obtained by gluing
ALF gravitational instantons to a background (incomplete) hyperk\"ahler metric
arising from the Gibbons-Hawking ansatz over a punctured 3-torus. As an
immediate application to submanifold geometry, we exhibit hyperk\"ahler metrics
on the K3 surface that admit a strictly stable minimal sphere which cannot be
holomorphic with respect to any complex structure compatible with the metric.

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The categories of this paper are: eess
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The categories of this paper are: astro-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-th
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The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: funct-an
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
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The categories of this paper are: gr-qc
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: cs
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The categories of this paper are: hep-th