Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Reconciling the diffuse Galactic gamma-ray and the cosmic ray spectra   Most of the diffuse Galactic GeV gamma-ray emission is produced via
collisions of cosmic ray (CR) protons with ISM protons. As such the observed
spectra of the gamma-rays and the CRs should be strongly linked. Recent
observations of Fermi-LAT exhibit a hardening of the gamma-ray spectrum at
around a hundred GeV, between the Sagittarius and Carina tangents, and a
further hardening at a few degrees above and below the Galactic plane. However,
standard CR propagation models that assume a time independent source
distribution and a location independent diffusion cannot give rise to a
spatially dependent CR (and hence gamma-ray) spectral slopes. Here we consider
a dynamic spiral arm model in which the distribution of CR sources is
concentrated in the (dynamic) spiral arms, and we study the effects of this
model on the $\pi^0$-decay produced gamma-ray spectra. Within this model, near
the Galactic arms the observed gamma-ray spectral slope is not trivially
related to the CR injection spectrum and energy dependence of the diffusion
coefficient. We find unique signatures that agree with the Fermi-LAT
observations. This model also provides a physical explanation for the
difference between the local CR spectral slope and the CR slope inferred from
the average gamma-ray spectrum.

31
The categories of this paper are: ao-sci
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
10
The categories of this paper are: q-bio
7
The categories of this paper are: hep-th
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th