$a_0(980)$ revisited

Abstract

Light scalar hadrons can be understood as dynamically generated resonances. These arise as `companion poles' in the propagators of quark-antiquark seed states when accounting for meson-loop contributions to the self-energies of the latter. Along this line, we extend previous calculations of Törnqvist and Roos and of Boglione and Pennington, where the resonance $a_0(980)$ appears as companion pole in the propagator of $a_0(1450)$ which is predominantly a quark-antiquark state. We also construct an effective Lagrangian where $a_0(1450)$ couples to pseudoscalar mesons with both non-derivative and derivative interactions. Computing the one-loop self-energy, we demonstrate that the propagator has two poles: a companion pole corresponding to $a_0(980)$ and a pole of the seed state $a_0(1450)$. The positions of these poles are in quantitative agreement with experimental data.

14 pages, 2 figures, 1 table

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