Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Searching for the dark sector in two-body anti-muon decay with the
  polarization of monochromatic positrons   The $\mu^+ \to e^+ X$ decay, where $X$ is a dark sector boson, provides one
of the strongest available bounds on the scale of dark sector interactions. The
$X$ boson can be an axion or a dark photon. We show that the concurrent
determination of the anti-muon and positron polarizations makes possible to
distinguish with a confidence level of 99% between the two dark sector portals
with as few as 6 observed events in the case of the massless dark photon.
Instead, the massive spin-1, dimension 4 dark portal cannot be distinguished
from the axion-like case. We also discuss the possibility that the $X$ boson be
a massive spin-2 particle.

25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
30
The categories of this paper are: q-alg
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
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The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs