Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Leptonic decay-constant ratio f_{K^+}/f_{pi^+} from lattice QCD with
  physical light quarks   A calculation of the ratio of leptonic decay constants f_{K^+}/f_{\pi^+}
makes possible a precise determination of the ratio of CKM matrix elements
|V_{us}|/|V_{ud}| in the Standard Model, and places a stringent constraint on
the scale of new physics that would lead to deviations from unitarity in the
first row of the CKM matrix. We compute f_{K^+}/f_{\pi^+} numerically in
unquenched lattice QCD using gauge-field ensembles recently generated that
include four flavors of dynamical quarks: up, down, strange, and charm. We
analyze data at four lattice spacings a ~ 0.06, 0.09, 0.12, and 0.15 fm with
simulated pion masses down to the physical value 135 MeV. We obtain
f_{K^+}/f_{\pi^+} = 1.1947(26)(37), where the errors are statistical and total
systematic, respectively. This is our first physics result from our N_f = 2+1+1
ensembles, and the first calculation of f_{K^+}/f_{\pi^+} from lattice-QCD
simulations at the physical point. Our result is the most precise lattice-QCD
determination of f_{K^+}/f_{\pi^+}, with an error comparable to the current
world average. When combined with experimental measurements of the leptonic
branching fractions, it leads to a precise determination of |V_{us}|/|V_{ud}| =
0.2309(9)(4) where the errors are theoretical and experimental, respectively.

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The categories of this paper are: nucl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: stat
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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: bayes-an
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The categories of this paper are: nlin
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The categories of this paper are: alg-geom
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The categories of this paper are: supr-con
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The categories of this paper are: patt-sol
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int