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 \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 1.18\pm 0.04, A^B_1(0)/f^B_+(0) \simeq 1.64 \pm 0.06, and A^B_1(0)/F^B_1(0) \simeq 1.19 \pm 0.03; 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 (3.6 \pm 0.6)