Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Upper bounds on $f_D$ and $f_{D_s}$ from two-point correlation function
  in QCD   The correlation function of two pseudoscalar charmed quark currents with a
positive hadronic spectral density is employed to obtain upper bounds on the
decay constants of $D$ and $D_s$ mesons. Including all known terms of the
operator-product-expansion of this correlation function in QCD and taking into
account the estimated uncertainties, we obtain $f_{D}<230 $ MeV and
$f_{D_s}<270$ MeV. Comparison with the decay constants determined from $D\to l
\nu_l$ and $D_s\to l \nu_l$ measurements, reveals a tension between the bound
and current experimental value of $f_{D_s}$.

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The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs
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The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
16
The categories of this paper are: stat
32
The categories of this paper are: atom-ph
25
The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: cond-mat
14
The categories of this paper are: math-ph