When hadrons become unstable: A novel type of non-analyticity in chiral extrapolations

Hadron masses show a specific dependence on the quark masses. Therefore, the variation of these masses can cause a resonance in a hadronic scattering amplitude to become a bound state. Consequently, the amplitude exhibits a non-analytic behavior at this transition. Crossed amplitudes, where the resonance can be exchanged in the t-channel, can be shown to exhibit the same phenomenon by s --> t analytic continuation. This entails possible kinks in lattice quark-mass extrapolations needed to compute hadronic observables. (C) 2011 Elsevier B.V. All rights reserved.