Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extracting black-hole rotational energy: The generalized Penrose process   In the case involving particles the necessary and sufficient condition for
the Penrose process to extract energy from a rotating black hole is absorption
of particles with negative energies and angular momenta. No torque at the
black-hole horizon occurs. In this article we consider the case of arbitrary
fields or matter described by an unspecified, general energy-momentum tensor
$T_{\mu \nu}$ and show that the necessary and sufficient condition for
extraction of a black hole's rotational energy is analogous to that in the
mechanical Penrose process: absorption of negative energy and negative angular
momentum. We also show that a necessary condition for the Penrose process to
occur is for the Noether current (the conserved energy-momentum density vector)
to be spacelike or past directed (timelike or null) on some part of the
horizon. In the particle case, our general criterion for the occurrence of a
Penrose process reproduces the standard result. In the case of relativistic
jet-producing "magnetically arrested disks" we show that the negative energy
and angular-momentum absorption condition is obeyed when the Blandford-Znajek
mechanism is at work, and hence the high energy extraction efficiency up to
$\sim 300\%$ found in recent numerical simulations of such accretion flows
results from tapping the black hole's rotational energy through the Penrose
process. We show how black-hole rotational energy extraction works in this case
by describing the Penrose process in terms of the Noether current.

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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: supr-con
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex