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 Kπ scattering amplitudes as a function of the center-of-mass energy using Lüscher'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 √(3)2π/L; this includes 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 κ 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 κ-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) i] GeV at the lighter 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^* Kπ=5.02(26) and g_K^* Kπ=4.99(22), respectively.