标题： 轻夸克凝聚在重到轻的独占衰变中的主导作用 显示英文标题

标题： Dominance of the light-quark condensate in the heavy-to-light exclusive decays

摘要： Using the QCD {\it 混合} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit $M_b \rar \infty$, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive ($\bar B\rar \rho~(\pi)$ semileptonic as well as the $ B\rar \rho\gamma$ rare) decay--form factors are $universally$ dominated by the contribution of the soft light-quark condensate rather than that of the hard perturbative diagram. QCD-分析性$q^2$的形式因子行为是$q^2/M^2_b$的多项式，这在很大程度上模仿了通常的极点参数化，除了$A_1^B$形式因子的情况，其中存在与这种极形式显著的偏差。 形式因子的$M_b$依赖性从 HQET 和格点结果中预期的是被恢复的。 我们准确地提取出比值：$V^B(0)/A^B_1(0) \simeq A^B_2(0)/A^B_1(0) \simeq 1.11\pm 0.01$，以及$A^B_1(0)/F^B_1(0) \simeq 1.18 \pm 0.06$；结合“世界平均”值$f^B_+(0)$或/和$F^B_1(0)$，这些比值导致衰变率：\Gamma _{\bar B\rar \pi e\bar \nu } \simeq (4.3 \pm 0.7) 显示英文摘要

摘要： Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit $M_b \rar \infty$, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive ($\bar B\rar \rho~(\pi)$ semileptonic as well as the $ B\rar \rho\gamma$ rare) decay--form factors are $universally$ dominated by the contribution of the soft light-quark condensate rather than that of the hard perturbative diagram. The QCD-analytic $q^2$ behaviour of the form factors is a polynomial in $q^2/M^2_b$, which mimics quite well the usual pole parametrization, except in the case of the $A_1^B$ form factor, where there is a significant deviation from this polar form. The $M_b$-dependence of the form factors expected from HQET and lattice results is recovered. We extract with a good accuracy the ratios: $V^B(0)/A^B_1(0) \simeq A^B_2(0)/A^B_1(0) \simeq 1.11\pm 0.01$, and $A^B_1(0)/F^B_1(0) \simeq 1.18 \pm 0.06$; combined with the ``world average" value of $f^B_+(0)$ or/and $F^B_1(0)$, these ratios lead to the decay rates: $\Gamma_{\bar B\rar \pi e\bar \nu} \simeq (4.3 \pm 0.7)