$B$- and $D$-meson leptonic decay constants from four-flavor lattice QCD
A. Bazavov, C. Bernard, N. Brown, C. DeTar, A. X. El-Khadra, E. Gámiz, Steven Gottlieb, U. M. Heller, J. Komijani, A. S. Kronfeld, J. Laiho, P. B. Mackenzie, E.… 展开作者
A. Bazavov, C. Bernard, N. Brown, C. DeTar, A. X. El-Khadra, E. Gámiz, Steven Gottlieb, U. M. Heller, J. Komijani, A. S. Kronfeld, J. Laiho, P. B. Mackenzie, E. T. Neil, J. N. Simone, R. L. Sugar, D. Toussaint, R. S. Van de Water
备注：
Errors related to the standard model prediction for the rare leptonic decays are fixed in the abstract and Eqs. (7.44), (7.45), and (8.3)
We calculate the leptonic decay constants of heavy-light pseudoscalar mesons with charm and bottom quarks in lattice quantum chromodynamics on four-flavor QCD gauge-field configurations with dynamical $u$, $d$, $s$, and $c$ quarks. We analyze over twenty isospin-symmetric ensembles with six lattice spacings down to $a\approx 0.03$~fm and several values of the light-quark mass down to the physical value $\frac{1}{2}(m_u+m_d)$. We employ the highly-improved staggered-quark (HISQ) action for the sea and valence quarks; on the finest lattice spacings, discretization errors are sufficiently small that we can calculate the $B$-meson decay constants with the HISQ action for the first time directly at the physical $b$-quark mass. We obtain the most precise determinations to-date of the $D$- and $B$-meson decay constants and their ratios, $f_{D^+} = 212.7(0.6)$~MeV, $f_{D_s} = 249.9(0.4)$~MeV, $f_{D_s}/f_{D^+} = 1.1749(16)$, $f_{B^+} = 189.4 (1.4)$~MeV, $f_{B_s} = 230.7(1.3)$~MeV, $f_{B_s}/f_{B^+} = 1.2180(47)$, where the errors include statistical and all systematic uncertainties. Our results for the $B$-meson decay constants are three times more precise than the previous best lattice-QCD calculations, and bring the QCD errors in the Standard-Model predictions for the rare leptonic decays $\overline{\mathcal{B}}(B_s \to μ^+μ^-) = 3.64(11) \times 10^{-9}$, $\overline{\mathcal{B}}(B^0 \to μ^+μ^-) = 1.00(3) \times 10^{-10}$, and $\overline{\mathcal{B}}(B^0 \to μ^+μ^-)/\overline{\mathcal{B}}(B_s \to μ^+μ^-) = 0.0273(9)$ to well below other sources of uncertainty. As a byproduct of our analysis, we also update our previously published results for the light-quark-mass ratios and the scale-setting quantities $f_{p4s}$, $M_{p4s}$, and $R_{p4s}$. We obtain the most precise lattice-QCD determination to date of the ratio $f_{K^+}/f_{π^+} = 1.1950(^{+16}_{-23})$~MeV.
Inclusive semi-leptonic B meson decay structure functions from lattice QCD
本文提出了一种非微扰计算包含半轻子B介子衰变的前向散射矩阵元的方法。通过对四点关联函数的格点量子色动力学计算，可以得到相应的强子非物理运动学结构函数。非物理运动学点可由物理微分衰减率解析延拓得到。在零反冲极限下，对B_s -> X_c l nu模进行了数值检验。我们使用2+1动力学夸克味产生的晶格系综。价粲夸克的质量被调谐到它的物理值，而底夸克的质量在（1.56-2.44）mc范围内变化。从数值结果中我们可以看出基态D_s^（*）介子的贡献以及激发态和连续态的贡献。
Leptonic Decays of Charged Pseudoscalar Mesons - 2015
本文综述了$π^\pm$、$K^\pm$、$D^{\pm}$、$D_s^\pm$和$B^\pm$赝标介子的纯轻子衰变物理。所测得的衰变率与组分夸克的相关弱相互作用CKM矩阵元和与介子中夸克和反夸克波函数重叠相关的强相互作用参数（称为衰变常数$f_P$）的乘积有关。用{ \it ab initio}格点QCD模拟方法，可以得到$π^\pm$、$K^\pm$、$D^{\pm}$、$D_s^\pm$和$B^\pm$介子的轻子衰变常数，理论不确定度可控，计算精度高.实验轻子衰变率测量和理论衰变常数计算相结合，使几个元素的CKM矩阵内的标准模型的确定。这些测定与半轻子衰变的结果是竞争性的，也是互补的，因为它们对不同的夸克变味电流敏感。它们也可以用来测试CKM矩阵的第一行和第二行的酉性。相反地，采用由么正性预测的CKM元素，可以推断出$f_P$的“实验”值，其可以与理论进行比较。这些提供了格点QCD方法的测试，假设新物理对轻子衰变的贡献在当前的精度水平上可以忽略不计。这篇评论是粒子数据组2016年版文章的基础，更新了参考文献中的版本。[1-3]中所述。
