### Abstract

We compute the leptonic decay constants f_{D+}, f_{Ds}, and f_{K+}, and the quark-mass ratios m_{c}/m_{s} and m_{s}/m_{l} in unquenched lattice QCD. We use the MILC highly improved staggered quark (HISQ) ensembles with four dynamical quark flavors. Our primary results are f_{d+} = 212.6(0.4)(^{+1.0} _{-1.2}) MeV, f_{Ds} = 249.0(0.3)(^{+1.1} _{1. 5}) MeV, and f_{Ds}/f_{D+} = 1.1712(10)(^{+-29} _{-32}), where the errors are statistical and total systematic, respectively. We also obtain f_{K+}/f_{π}+ = 1.1956(10) (^{+-26} _{-18}), updating our previous result, and determine the quark-mass ratios m_{s}/m_{l} = 27.35(5)(^{+10} _{-7}) and m_{c}/m_{s} = 11.747(19)(^{+59} _{-43}). When combined with experimental measurements of the decay rates, our results lead to precise determinations of the CKM matrix elements |V_{us}| = 0.22487(51)(29)(20)(5), |V_{cd}| = 0.217(1)(5)(1) and |V_{cs}| = 1.010(5)(18)(6), where the errors are from this calculation of the decay constants, the uncertainty in the experimental decay rates, structure-dependent electromagnetic corrections, and, in the case of |V_{us}|, the uncertainty in |V_{ud}|, respectively.

Original language | English (US) |
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Article number | 382 |

Journal | Proceedings of Science |

Volume | Part F130500 |

State | Published - 2014 |

### ASJC Scopus subject areas

- General

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## Cite this

*Proceedings of Science*,

*Part F130500*, [382].