Charmed and light pseudoscalar meson decay constants from four-flavor lattice QCD with physical light quarks

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 using the experimentally determined value of f(pi+) for normalization. We use the MILC highly improved staggered quark ensembles with four dynamical quark flavors-up, down, strange, and charm-and with both physical and unphysical values of the light sea- quark masses. The use of physical pions removes the need for a chiral extrapolation, thereby eliminating a significant source of uncertainty in previous calculations. Four different lattice spacings ranging from a approximate to 0.06 to 0.15 fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are f(D+) = 212.6(0.4) ((+1.0)(-1.2)) MeV, f(Ds) = 249.0(0.3) ((+1.0)(-1.5)) MeV, and f(Ds)/f(D+) = 1.1712(10)((+29)(-32)), where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately 2- 4 times smaller than those of the most precise previous lattice calculations. We also obtain f(K+)/f(pi+) = 1.1956d10_d_26 - 18_, updating our previous result, and determine the quark- mass ratios ms= ml 27.35d5_d_10 - 7 _ and mc= ms 11.747d19_d_59 - 43_. When combined with experimental measurements of the decay rates, our results lead to precise determinations of the CabibboKobayashi- Maskawa matrix elements jVusj 0.22487d51_d29_d20_d5_, jVcdj 0.217d1_d5_d1_ and jVcsj 1.010d5_d18_d6_, 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 jVusj, the uncertainty in jVudj, respectively.