Chiral loop contribution to D-->K*l nu.

Abstract

Light vector mesons are included in the heavy meson chiral Lagrangian in the leading order in momentum expansion. Tree-level form factors in ${D}^{+}\ensuremath{\rightarrow}{\overline{K}}^{0*}{e}^{+}{\ensuremath{\nu}}_{e}$ are found at the order of $O({k}^{1})$, and the coefficients of $\frac{1}{{m}_{Q}}$ terms are fixed by requiring reparametrization invariance of the heavy meson chiral Lagrangian and the weak current. Then, chiral loop contributions [$O({k}^{2})$] to $D\ensuremath{\rightarrow}{K}^{*}l\ensuremath{\nu}$ are considered. The imaginary part of the $K\ensuremath{\pi}$ loop contribution is finite and therefore unambiguously calculable, leading to the lower bounds on the form factors and the partial decay rate in ${D}^{+}\ensuremath{\rightarrow}{\overline{K}}^{0*}{e}^{+}{\ensuremath{\nu}}_{e}$. Under a reasonable assumption, one finds ${g}^{2}<0.5$ is preferred where $g$ is the ${D}^{*}D\ensuremath{\pi}$ coupling.