Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The effect of photon-axion-like particle conversions in galaxy clusters
  on very high energy {\gamma}-ray spectra   Very high energy (VHE, energy >~ 100 GeV) {\gamma}-rays originating from
extragalactic sources interact with low energy photons of background radiation
fields and produce electron-positron pairs. Alternatively, in the presence of
ambient magnetic fields, they can convert into hypothetical axion-like
particles (ALPs), pseudo-scalar spin-0 bosons, predicted by extensions of the
standard model. These particles propagate unimpeded over cosmological
distances. Here, the effect of photon-ALP oscillations in magnetic fields of
galaxy clusters and the Milky Way on VHE {\gamma}-ray spectra is studied. It is
shown that this mechanism can lead to a substantial enhancement of the VHE flux
and a spectral hardening, thus effectively reducing the opacity of the Universe
to VHE {\gamma}-rays.

16
The categories of this paper are: stat
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
9
The categories of this paper are: nlin
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
35
The categories of this paper are: mtrl-th
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci