Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Origin and propagation of the highest energy cosmic rays   In this lecture I give an overview of shock acceleration, interactions of
high energy cosmic rays with, and propagation through, the background
radiation, and the resulting electron-photon cascade. I argue that while the
origin of the highest energy cosmic rays is still uncertain, it is not
necessary to invoke exotic models such as emission by topological defects to
explain the existing data. It seems likely that shock acceleration at
Fanaroff-Riley Class II radio galaxies can account for the existing data.
However, new cosmic ray data, as well as better estimates of the extragalactic
radiation fields and magnetic fields will be necessary before we will be
certain of the origin of the highest energy particles occurring in nature.

30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
1
The categories of this paper are: cs
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: acc-phys
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
13
The categories of this paper are: quant-ph