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

Using the QCD {\it hybrid} (moments-Laplace) sum rule, we show $semi$-$analytically$ that, in the limit $M_b\text{rar}\mathrm{\infty }$, the $q^2$ and $M_b$ behaviours of the heavy-to-light exclusive ($\bar{B}\text{rar}\rho (\pi )$ semileptonic as well as the $B\text{rar}\rho \gamma$ 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 $q^2\mathrm{/}{M}_b^2$, 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$A^B_1(0)/F^B_1(0) \simeq 1.18 \pm 0.06$;combinedwiththe\mathrm{‘}\mathrm{‘}worldaverage\mathrm{"}valueof$f^B_+(0)$or\mathrm{/}and$F^B_1(0)$,theseratiosleadtothedecayrates:$\Gamma_{\bar B\rar \pi e\bar \nu} \simeq (4.3 \pm 0.7)