A first nonperturbative and unitary treatment of multichannel systems with anomalous thresholds based on realistic potentials is presented. We consider the isospin one-half example system, with $D\pi$, $D\eta$, $D_s\overline{K}$, $D^{*}\pi$, $D^{*}\eta$, $D^{*}\overline{K}$ coupled channels in the $J^P=1^{-}$ partial wave, chosen such that various phenomena that come with the opening of an anomalous threshold can be illustrated in a stepwise procedure by a suitable variation of up, down and strange quark masses. We use a set of low-energy constants in the chiral Lagrangian that were adjusted to a large set of lattice QCD results. The six phase shifts and inelasticity parameters are presented for various choices of the pion mass. For a pion mass of 150 MeV there are no anomalous thresholds encountered. The small change from 150 MeV to 145 MeV pion mass causes a dramatic impact of the anomalous threshold on the phase shifts showing that our results are highly relevant for the extrapolation of lattice QCD calculations toward the physical pion mass.

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• Effective field theory
• Lattice field theory
• Nonperturbative effects in field theory
• Particle interactions
• Phase shift
• Phenomenology
• Quantum chromodynamics
• Resummation methods
• Scattering amplitudes