K pi scattering in moving frames

We extend our study of the $K\pi$ system to moving frames and present an exploratory extraction of the masses and widths for the $K^{\ast }$ resonances by simulating $K\pi$ scattering in p-wave with $I=1\mathrm{/}2$ on the lattice. Using $K\pi$ systems with non-vanishing total momenta allows the extraction of phase shifts at several values of $K\pi$ relative momenta. A Breit-Wigner fit of the phase renders a $K^{\ast }(892)$ resonance mass and $K^{\ast }\to K\pi$ coupling compatible with the experimental numbers. We also determine the $K^{\ast }(1410)$ mass assuming the experimental $K^{\ast }(1410)$ width. We contrast the resonant $I=1\mathrm{/}2$ channel with the repulsive non-resonant $I=3\mathrm{/}2$ channel, where the phase is found to be negative and small, in agreement with experiment.