Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Extragalactic cosmic rays diffusing from two populations of sources   We consider the possibility of explaining the observed spectrum and
composition of the cosmic rays with energies above $10^{17}$ eV in terms of two
different extragalactic populations of sources in the presence of a turbulent
intergalactic magnetic field (including also a fading Galactic cosmic-ray
component). The populations are considered to be the superposition of different
nuclear species having rigidity dependent spectra. The first extragalactic
population is dominant in the energy range $10^{17}$ to $10^{18}$ eV and
consists of sources having a relatively large density ($> 10^{-3}$ Mpc$^{-3}$)
and a steep spectrum. The second extragalactic population dominates the cosmic
ray flux above few EeV, it has a harder spectral slope and has a high-energy
cutoff at few $Z$ EeV (where $eZ$ is the associated cosmic ray charge). This
population has a lower density of sources ($<10^{-4}$ Mpc$^{-3}$), so that the
typical intersource separation is larger than few tens of Mpc, being
significantly affected by a magnetic horizon effect that strongly suppresses
its flux for energies below $\sim Z$ EeV. We discuss how this scenario could be
reconciled with the values of the cosmic-ray source spectral indices that are
expected to result from the diffusive shock acceleration mechanism.

26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
8
The categories of this paper are: hep-ex
21
The categories of this paper are: adap-org
3
The categories of this paper are: physics