Current s-Quark Mass Corrections to the Form Factors of D-Meson Semileptonic Decays

The infinite mass effective theory, when a heavy quark mass tends to infinity, and Chiral perturbation theory at the quark level, based on the extended Nambu -- Jona -- Lasinio model with linear realization of chiral $U(3)\times U(3)$ symmetry, are applied to the calculation of current $s$ -- quark mass corrections to the form factors of the $D\to\bar K~e^+~\nu_e$ and $D\to\bar K^{\ast}~e^+~\nu_e$ decays. These corrections turn out to be quite significant, of the order of $7-20\%$. The theoretical results are compared with experimental data.