We perform a rigorous analysis of the πK scattering at an unphysical pion mass 391 MeV using the Roy-Steiner equations, which satisfy unitarity, analyticity, and crossing symmetry, for the first time. Stable solutions of the Roy-Steiner equations with different quantum numbers of isospin and angular momentum are obtained in the elastic energy region, by taking inputs from the πK lattice data in the inelastic region, the lattice data from the crossed ππ→KK¯ channels, the masses of f0(500) and K* at the same pion mass from previous study, and the Regge model. Predictions on the elastic πK scattering phase shifts and the K0*(700) pole content are made. Contrary to the virtual pole scenario obtained using the K-matrix method in the literature, we find that lightest strange scalar meson K0*(700) remains a broad resonance at mπ=391 MeV. The cross-channel dynamics is found to play a crucial role in deriving the proper pole position.
Cao et al. (Fri,) studied this question.