Chiral Dynamics and S-wave contributions in Semileptonic $D_s/B_s$ decays into ${\pi }^{+}{\pi }^{-}$

Yu-Ji Shi, Wei Wang

In this work, we study the semileptonic decay modes $B_s^0\to {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$ and $D_s^{+}\to {\pi }^{+}{\pi }^{-}{\ell }^{+}\nu$ in the kinematics region where the ${\pi }^{+}{\pi }^{-}$ system has a invariant m…