Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The volume operator in loop quantum cosmology   We show that for basically all states, the evolution of the expectation value
of the volume operator in Wheeler-DeWitt and various homogenous isotropic loop
quantum comology (LQC) models ($k=0$, coupled to massless scalar field and
without cosmological constant) is ill-defined. The expectation value of the
volume operator become instantonously infinite during the evolution. The effect
is produced by a very long tail in the volume spectrum, that is however
semiclassically small and beyond reach of numerical simulations (that is why it
went unnoticed so far). This is not necessarily problem of theory but rather it
suggests that one should be extremely careful with unbounded observables.

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The categories of this paper are: q-alg
3
The categories of this paper are: physics
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
1
The categories of this paper are: cs
2
The categories of this paper are: math
22
The categories of this paper are: chao-dyn
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The categories of this paper are: atom-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga