The light scalar $K_{0}^{\ast}(700)$ in the vacuum and at nonzero temperature

Abstract

There is mounting evidence toward the existence of a light scalar kaon $\kappa\equiv$ $K_{0}^{\ast}(700)$ with quantum numbers $I(J^{P})=\frac{1}{2}(0^{+}).$ Here, we recall the results of an effective model with both derivative and non-derivative terms in which only one scalar kaonic field is present in the Lagrangian (the standard quark-antiquark ,,seed\textquotedblright\ state $K_{0}^{\ast}(1430)$): a second \textquotedblleft companion\textquotedblright\ pole $K_{0}^{\ast}(700)$ emerges as a dynamically generated state. A related question is the role of $K_{0}^{\ast}(700)$ at nonzero $T$: since it is the lightest scalar strange state, one would naively expect that it is relevant for $\pi$ and $K$ multiplicities. However, a repulsion in the $\pi K$ channel with $I=3/2$ cancels its effect.