Dispersive analysis of the $ππ$ and $πK$ scattering data

We present a data-driven analysis of the S-wave $ππ\to ππ\,(I=0,2)$ and $πK \to πK\,(I=1/2, 3/2)$ reactions using the partial-wave dispersion relation. The contributions from the left-hand cuts are parametrized using the expansion in a suitably constructed conformal variable, which accounts for its analytical structure. The partial-wave dispersion relation is solved numerically using the $N/D$ method. The fits to the experimental data supplemented with the constraints from chiral perturbation theory at threshold and Adler zero give the results consistent with Roy-like (Roy-Steiner) analyses. For the $ππ$ scattering we present the coupled-channel analysis by including additionally the $K\bar{K}$ channel. By the analytic continuation to the complex plane, we found poles associated with the lightest scalar resonances $σ/f_0(500)$, $f_0(980)$, and $κ/K_0^*(700)$. For all the channels we also performed the fits directly to the Roy-like (Roy-Steiner) solutions in the physical region, in order to minimize the $N/D$ uncertainties in the complex plane and to extract the most constrained Omnès functions.

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