I=1/2 S-wave and P-wave Kπ scattering and the κ and K* resonances from lattice QCD

We present a lattice-QCD determination of the elastic isospin-1/2 S-wave and P-wave K pi scattering amplitudes as a function of the center-of-mass energy using Luscher's method. We perform global fits of K-matrix parametrizations to the finite-volume energy spectra for all irreducible representations with total momenta up to root 32 pi/L; this includes irreducible representations (irreps) that mix the S- and P-waves. Several different parametrizations for the energy dependence of the K-matrix are considered. We also determine the positions of the nearest poles in the scattering amplitudes, which correspond to the broad K resonance in the S-wave and the narrow K*(892) resonance in the P-wave. Our calculations are performed with 2 + 1 dynamical clover fermions for two different pion masses of 317.2(2.2) and 175.9(1.8) MeV. Our preferred S-wave parametrization is based on a conformal map and includes an Adler zero; for the P-wave, we use a standard pole parametrization including Blatt-Weisskopf barrier factors. The S-wave K-resonance pole positions are found to be [0.86(12) - 0.309(50) i] GeV at the heavier pion mass and [0.499(55) - 0.379 (66)] GeV at thelighter pion mass. The P-wave K* -resonance pole positions are found to be [0.8951(64) - 0.00250(21)i] GeV at the heavier pion mass and [0.8718(82) - 0.0130(11)i] GeV at the lighter pion mass, which corresponds to couplings of g(K*K pi) = 5.02(26) and g(K*K pi) = 4.99(22), respectively.