Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Geometry and topology of complete Lorentz spacetimes of constant
  curvature   We study proper, isometric actions of nonsolvable discrete groups Gamma on
the 3-dimensional Minkowski space R^{2,1} as limits of actions on the
3-dimensional anti-de Sitter space AdS^3. To each such action is associated a
deformation of a hyperbolic surface group Gamma_0 inside O(2,1). When Gamma_0
is convex cocompact, we prove that Gamma acts properly on R^{2,1} if and only
if this group-level deformation is realized by a deformation of the quotient
surface that everywhere contracts distances at a uniform rate. We give two
applications in this case. (1) Tameness: A complete flat spacetime is
homeomorphic to the interior of a compact manifold. (2) Geometric degeneration:
A complete flat spacetime is the rescaled limit of collapsing AdS spacetimes.

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The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
3
The categories of this paper are: physics
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex