Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: "Espresso" Acceleration of Ultra-high-energy Cosmic Rays   We propose that ultra-high-energy (UHE) cosmic rays (CRs) above $10^{18}$eV
are produced in relativistic jets of powerful active galactic nuclei via an
original mechanism, which we dub "espresso" acceleration: "seed" galactic CRs
with energies $\lesssim 10^{17}$eV that penetrate the jet sideways receive a
"one-shot'" boost of a factor of $\sim\Gamma^2$ in energy, where $\Gamma$ is
the Lorentz factor of the relativistic flow. For typical jet parameters, a few
percent of the CRs in the host galaxy can undergo this process, and powerful
blazars with $\Gamma\gtrsim 30$ may accelerate UHECRs up to more than
$10^{20}$eV. The chemical composition of espresso-accelerated UHECRs is
determined by that at the Galactic CR knee and is expected to be
proton-dominated at $10^{18}$eV and increasingly heavy at higher energies, in
agreement with recent observations made at the Pierre Auger Observatory.

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The categories of this paper are: math
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
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The categories of this paper are: physics
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: hep-ex
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The categories of this paper are: alg-geom