Continuum Schwinger function methods for the strong-interaction bound-state problem are used to arrive at a unified set of parameter-free predictions for the semileptonic $K\to \pi$, $D\to \pi ,K$ and $D_s\to K$, $B_{(s)}\to \pi (K)$ transition form factors and the associated branching fractions. The form factors are a leading source of uncertainty in all such calculations: our results agree quantitatively with available data and provide benchmarks for the hitherto unmeasured $D_s\to K^0$, ${\overline{B}}_s\to K^{+}$ form factors. The analysis delivers a value of $|V_{cs}|=0.974(10)$ and also predictions for all branching fraction ratios in the pseudoscalar meson sector that can be used to test lepton flavour universality. Quantitative comparisons are provided between extant theory and the recent measurement of ${\mathcal{B}}_{B_s^0\to K^{-}{\mu }^{+}{\nu }_{\mu }}$. Here, further, refined measurements would be useful in moving toward a more accurate value of $|V_{ub}|$.

强相互作用边界状态问题的连续施温格函数方法用于为半轻子获得统一的无参数预测集 $钾\to \pi$, $D\to \pi ,钾$ 和 $D_{秒}\to 钾$, ${乙}_{(秒)}\to \pi (钾)$过渡形状因子和相关的支化分数。在所有此类计算中，形状因素是不确定性的主要来源：我们的结果在数量上与可用数据一致，并为迄今为止未测量的数据提供了基准$D_{秒}\to {钾}^0$, ${\overline{乙}}_{秒}\to {钾}^{+}$形式因素。该分析提供了一个价值$|{伏}_{C秒}|=0.974(10)$以及对可用于测试轻子风味普遍性的赝标量介子扇区中所有分支分数比率的预测。现有理论与最近的测量之间提供了定量比较${\mathcal{乙}}_{{乙}_{秒}^0\to {钾}^{-}{\mu }^{+}{\nu }_{\mu }}$. 在这里，进一步的精细测量将有助于获得更准确的值$|{伏}_{你乙}|$.