Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Causality in Spin Foam Models   We compute Teitelboim's causal propagator in the context of canonical loop
quantum gravity. For the Lorentzian signature, we find that the resultant power
series can be expressed as a sum over branched, colored two-surfaces with an
intrinsic causal structure. This leads us to define a general structure which
we call a ``causal spin foam''. We also demonstrate that the causal evolution
models for spin networks fall in the general class of causal spin foams.

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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: solv-int
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The categories of this paper are: astro-ph
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The categories of this paper are: physics
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The categories of this paper are: nucl-th
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The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: eess