2 0 1 5 ) 3 3 8 D-meson semileptonic form factors at zero momentum transfer in ( 2 + 1 + 1 )-flavor lattice QCD

We present a calculation of the D→K`ν and D→ π`ν semileptonic form factors at q2 = 0, which enable determinations of the CKM matrix elements |Vcs| and |Vcd |, respectively. We use gaugefield configurations generated by the MILC collaboration with four flavors of highly-improved staggered (HISQ) quarks, analyzing several ensembles including those with physical pion masses and approximate lattice spacings ranging from 0.12 fm to 0.042 fm. We also use the HISQ action for the valence quarks. We employ twisted boundary conditions to calculate the form factors at zero momentum transfer directly. We use heavy-light-meson chiral perturbation theory modified for energetic pions and kaons, and supplemented by terms to describe the lattice-spacing dependence, to obtain preliminary results at the physical point and in the continuum limit.