Large-$N_{\rm c}$ Pole Trajectories of the Vector Kaon $K^{\ast }(892)$ and of the Scalar Kaons $K_{0}^{\ast }(800)$ and $K_{0}^{\ast }(1430)$

Abstract

We study the spectral functions, the poles and their trajectories for increasing $N_{c}$ of the vector kaon state $K^{\ast}(892),$ characterized by $I(J^{P})=\frac{1}{2}(1^{-})$, and of the scalar kaons $K_{0}^{\ast}(800)$ and $K_{0}^{\ast}(1430),$ characterized by $I(J^{P})=\frac{1}{2}(0^{+})$. To this end, we use relativistic QFT's Lagrangians with both derivative and non-derivative terms. In the vector kaonic sector the spectral function is well approximated by a Breit-Wigner function: there is one single peak and, correspondingly, a single pole in the complex plane. On the contrary, in the scalar sector, although the Lagrangian contains only one scalar kaonic field, we find two poles, one corresponding to a standard quark-antiquark ,,seed\textquotedblright state $K_{0}^{\ast}(1430),$ and one to a \textquotedblleft companion\textquotedblright dynamically generate pole $K_{0}^{\ast}(800)$. The latter does not correspond to any peak in the scalar kaonic spectral function, but only to an enhancement in the low-energy regime.