Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Novel multi-lepton signatures of dark sectors in light meson decays   We point out kaon decays to multiple charged leptons as a novel probe of
light dark particles $X$. Previously neglected channels, such as $K^+\to \pi^+
\left(XX \to 2(e^+e^-)\right)$, $K_L\to \pi^0 \left( XX \to 2(e^+e^-)\right)$,
and $K_S\to \left(XX \to 2(e^+e^-)\right)$ may have very large rates, exceeding
not only the Standard Model expectations but also possible backgrounds, such as
Dalitz decays of neutral pions. We apply this idea to dark sector models where
the production of dark Higgses or heavy neutral leptons leads to final states
with several visible dark photons. We also investigate a recently proposed
model of an MeV-scale QCD axion, where the rates for kaon decays to multiple
axion states are large due to the non-linear interactions of the axion with the
light mesons. In addition, we point out new probes of this axion in pion
decays, such as the single production of $a$ in $\pi^+ \to \nu \left((e^+)^*
\to e^+ a\to e^+e^+e^-\right)$, double production in pion capture $\pi^-+(p
\text{ or D})\to aa + (n\text{ or }nn) \to 2(e^+e^-) + (n\text{ or }nn)$, as
well as $\pi^0 \to aaa\to 3(e^+e^-)$. The latter decay is fixed at
$\mathcal{B}(\pi^0\to a a a) = 1.0 \times 10^{-3}$ for a $17$ MeV axion.

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The categories of this paper are: nucl-th
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The categories of this paper are: funct-an
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The categories of this paper are: ao-sci
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: atom-ph
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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: patt-sol