Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The volume operator in covariant quantum gravity   A covariant spin-foam formulation of quantum gravity has been recently
developed, characterized by a kinematics which appears to match well the one of
canonical loop quantum gravity. In particular, the geometrical observable
giving the area of a surface has been shown to be the same as the one in loop
quantum gravity. Here we discuss the volume observable. We derive the volume
operator in the covariant theory, and show that it matches the one of loop
quantum gravity, as does the area. We also reconsider the implementation of the
constraints that defines the model: we derive in a simple way the boundary
Hilbert space of the theory from a suitable form of the classical constraints,
and show directly that all constraints vanish weakly on this space.

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The categories of this paper are: comp-gas
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
11
The categories of this paper are: hep-lat
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The categories of this paper are: nucl-ex
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The categories of this paper are: supr-con
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
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The categories of this paper are: eess
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The categories of this paper are: bayes-an
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The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph