K0⁎(800) as a companion pole of K0⁎(1430)

We study the light scalar sector up to 1.8 GeV by using a quantum field theoretical approach which includes a single kaonic state in a Lagrangian with both derivative and non-derivative interactions. By performing a fit to πK   phase shift data in the I=1/2I=1/2, J=0J=0 channel, we show that K0⁎(800) (or κ  ) emerges as a dynamically generated companion pole of K0⁎(1430). This is a result of investigating quantum fluctuations with one kaon and one pion circulating in the loops dressing K0⁎(1430). We determine the position of the poles on the complex plane in the context of our approach: for K0⁎(1430) we get (1.413±0.002)−i(0.127±0.003) (in GeV), while for κ   we get (0.746±0.019)−i(0.262±0.014) (in GeV). The model-dependence of these results and related uncertainties are discussed in the paper. A large-NcNc study confirms that K0⁎(1430) is predominantly a quarkonium and that K0⁎(800) is a molecular-like dynamically generated state.