Resonances in coupled πK,ηK scattering from lattice QCD

Coupled-channel pi K and eta K scattering amplitudes are determined by studying the finite-volume energy spectra obtained from dynamical lattice QCD calculations. Using a large basis of interpolating operators, including both those resembling a q (q) over barq construction and those resembling a pair of mesons with relative momentum, a reliable excited-state spectrum can be obtained. Working at m(pi) = 391 MeV, we find a gradual increase in the J(P) =0(+) pi K phase shift which may be identified with a broad scalar resonance that couples strongly to pi K and weakly to eta K. The low-energy behavior of this amplitude suggests a virtual bound state that may be related to the. resonance. A bound state with J(P) = 1(-) is found very close to the pi K threshold energy, whose coupling to the pi K channel is compatible with that of the experimental K star(892). Evidence is found for a narrow resonance in J(P) = 2(+). Isospin-3/2 pi K scattering is also studied, and nonresonant phase shifts spanning the whole elastic scattering region are obtained.