Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-zone diffusion of electrons and positrons from Geminga explains the
  positron anomaly   The recent HAWC observations of very-high-energy $\gamma$-ray halo around
Geminga and Monogem indicate a very slow diffusion of cosmic rays, which
results in tiny contribution of positrons from these two pulsars to the local
flux. This makes the cosmic positron excess anomaly observed by PAMELA and
AMS-02 even more puzzling. However, from the Boron-to-Carbon ratio data one can
infer that the average diffusion coefficient in the Galaxy should be much
larger. In this work we propose a two-zone diffusion model that the diffusion
is slow only in a small region around the source, outside of which the
propagation is as fast as usual. We find that such a scenario can naturally
explain the positron excess data with parameters even more reasonable than that
in the conventional one-zone diffusion model. The reason is that during the
life time of Geminga ($\sim 300$ kyr) the electrons/positrons have propagated
too far away with a fast diffusion and lead to a low local flux. The slow
diffusion region in the two-zone model helps to confine the electrons/positrons
for a long time and lead to an enhancement of the local flux. So under the
constraint of the HAWC observations, pulsars are still the probable origin of
the cosmic-ray positron excess.

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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: stat
23
The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con