On chiral extrapolations of coupled-channel reaction dynamics for charmed mesons

We perform an analysis of QCD lattice data on masses of charmed meson with J^P = 0^- and J^P =1^- quantum numbers. The quark-mass dependence of the data set is used to gain information on the size of counter terms in the chiral Lagrangian formulated with open-charm mesons. Of particular interest are those counter terms that are active in the exotic flavour sextet channel. A chiral expansion scheme is developed and applied to the lattice data set. An accurate reproduction of the lattice data based on ensembles of PACS-CS, MILC, ETMC and HSC with pion and kaon masses smaller than 600 MeV is achieved. It is argued that a unique set of low-energy parameters is obtainable only if additional information from an HSC ensemble on some scattering phase shifts is included in our global fits. Based on such low-energy parameters we find a clear signal for a member of the exotic flavour sextet states in the pi D phase shift, between the eta D and bar K D_s thresholds. A striking dependence of such phase shifts on the values of the up, down and strange quarks is predicted.