标题： $D$介子半轻子衰变形式因子在$q^2 = 0$ 显示英文标题

标题： $D$ meson Semileptonic Decay Form Factors at $q^2 = 0$

摘要： 我们讨论了在零动量转移下，使用MILC的$N_f = 2+1+1$HISQ格点系综在四个格点间距$a \approx 0.042, 0.06, 0.09$和0.12 fm，以及各种HISQ夸克质量（低至(简并)物理轻夸克质量）下，衰变$D\to\pi\ell\nu$和$D\to K \ell\nu$的向量形式因子$f_+^{\{\pi,K\}}$的初步结果。 我们使用运动学约束$f_+(q^2)= f_0(q^2)$在$q^2 = 0$处确定矢量流形因子，这来自于我们对标量电流的研究，得出的结果为$f_0(0)$。 结果在硬介子/奇夸克 SU(3) 重介子阶梯式$\chi$PT 和 Symanzik 有效理论的框架下外推到连续物理点。 我们的计算提高了现有格点 QCD 计算中在$q^2=0$处矢量流形因子的精度。 我们展示了使用我们对流形因子的初步结果以及最近的实验结果所得到的 CKM 矩阵元$|V_{cs}|$和$|V_{cd}|$的值，并讨论了这些值对第二行 CKM 归一性的意义。 显示英文摘要

摘要： We discuss preliminary results for the vector form factors $f_+^{\{\pi,K\}}$ at zero-momentum transfer for the decays $D\to\pi\ell\nu$ and $D\to K \ell\nu$ using MILC's $N_f = 2+1+1$ HISQ ensembles at four lattice spacings, $a \approx 0.042, 0.06, 0.09$, and 0.12 fm, and various HISQ quark masses down to the (degenerate) physical light quark mass. We use the kinematic constraint $f_+(q^2)= f_0(q^2)$ at $q^2 = 0$ to determine the vector form factor from our study of the scalar current, which yields $f_0(0)$. Results are extrapolated to the continuum physical point in the framework of hard pion/kaon SU(3) heavy-meson-staggered $\chi$PT and Symanzik effective theory. Our calculation improves upon the precision achieved in existing lattice-QCD calculations of the vector form factors at $q^2=0$. We show the values of the CKM matrix elements $|V_{cs}|$ and $|V_{cd}|$ that we would obtain using our preliminary results for the form factors together with recent experimental results, and discuss the implications of these values for the second row CKM unitarity.