Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Establishing The GZK Cutoff With Ultra High Energy Tau Neutrinos   The cosmic ray spectrum has been shown to extend well beyond 10^20 eV. With
nearly 20 events observed in the last 40 years, it is now established that
particles are accelerated or produced in the universe with energy near 10^21
eV. In all production models neutrinos and photons are part of the cosmic ray
flux. In acceleration models (bottom-up models), they are produced as
secondaries of the possible interactions of the accelerated charged particle,
in direct production models (top-down models) they are a dominant fraction of
the decay chain. In addition, hadrons above the GZK threshold energy will also
produce, along their path in the Universe, neutrinos and photons as secondaries
of the pion photo-production processes. Therefore, photons and in particular
neutrinos, are very distinctive signatures of the nature and distribution of
the potential sources of ultra high energy cosmic rays. In the following we
expose the identification capabilities of the Auger observatories. In the
hypothesis of nu_mu-->nu_tau oscillations with full mixing, special emphasis is
placed on the observation of tau neutrinos, with which Auger is able to
establish the GZK cutoff as well as to provide a strong and model independant
constraint on the top-down sources of ultra high energy cosmic rays.

29
The categories of this paper are: funct-an
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
7
The categories of this paper are: hep-th
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
4
The categories of this paper are: cond-mat