$D$-meson semileptonic form factors at zero momentum transfer in\n (2+1+1)-flavor lattice QCD

We present a calculation of the $D\\to K \\ell \\nu$ and $D\\to\\pi \\ell \\nu$\nsemileptonic form factors at $q^2=0$, which enable determinations of the CKM\nmatrix elements $\\lvert{V_{cs}}\\rvert$ and $\\lvert{V_{cd}}\\rvert$,\nrespectively. We use gauge-field configurations generated by the MILC\ncollaboration with four flavors of highly-improved staggered (HISQ) quarks,\nanalyzing several ensembles including those with physical pion masses and\napproximate lattice spacings ranging from 0.12~fm to 0.042~fm. We also use the\nHISQ action for the valence quarks. We employ twisted boundary conditions to\ncalculate the form factors at zero momentum transfer directly. We use\nheavy-light-meson chiral perturbation theory modified for energetic pions and\nkaons, and supplemented by terms to describe the lattice-spacing dependence, to\nobtain preliminary results at the physical point and in the continuum limit.\n

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