K pi form factors, final state interactions and D+ -> K- pi+ pi+ decays

We present a model for the decay $D^+\to K^-\pi^+\pi^+$. The weak interaction part of this reaction is described using the effective weak Hamiltonian in the factorisation approach. Hadronic final state interactions are taken into account through the $K\pi$ scalar and vector form factors fulfilling analyticity, unitarity and chiral symmetry constraints. Allowing for a global phase difference between the $S$ and $P$ waves of $-65^\circ$, the Dalitz plot of the $D^+\to K^-\pi^+\pi^+$ decay, the $K\pi$ invariant mass spectra and the total branching ratio due to $S$-wave interactions are well reproduced.