Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A first look at transition amplitudes in (2+1)-dimensional causal
  dynamical triangulations   We study a lattice regularization of the gravitational path integral--causal
dynamical triangulations--for (2+1)-dimensional Einstein gravity with positive
cosmological constant in the presence of past and future spacelike boundaries
of fixed intrinsic geometries. For spatial topology of a 2-sphere, we determine
the form of the Einstein-Hilbert action supplemented by the
Gibbons-Hawking-York boundary terms within the Regge calculus of causal
triangulations. Employing this action we numerically simulate a variety of
transition amplitudes from the past boundary to the future boundary. To the
extent that we have so far investigated them, these transition amplitudes
appear consistent with the gravitational effective action previously found to
characterize the ground state of quantum spacetime geometry within the
Euclidean de Sitter-like phase. Certain of these transition amplitudes
convincingly demonstrate that the so-called stalks present in this phase are
numerical artifacts of the lattice regularization, seemingly indicate that the
quantization technique of causal dynamical triangulations differs in detail
from that of the no-boundary proposal of Hartle and Hawking, and possibly
represent the first numerical simulations of portions of temporally unbounded
quantum spacetime geometry within the causal dynamical triangulations approach.
We also uncover tantalizing evidence suggesting that Lorentzian not Euclidean
de Sitter spacetime dominates the ground state on sufficiently large scales.

19
The categories of this paper are: eess
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
21
The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph