Unquenching the meson spectrum: a model study of excited rho resonances

Quark models taking into account the dynamical effects of hadronic decay often produce very different predictions for mass shifts in the hadron spectrum. The consequences for meson spectroscopy can be dramatic and completely obscure the underlying confining force. Recent unquenched lattice calculations of mesonic resonances that also include meson-meson interpolators provide a touchstone for such models, despite the present limitations in applicability. On the experimental side, the $\rho(770)$ meson and its several observed radial recurrences are a fertile testing ground for both quark models and lattice computations. Here we apply a unitarised quark model that has been successful in the description of many enigmatic mesons to these vector $\rho$ resonances and the corresponding $P$-wave $\pi\pi$ phase shifts. This work is in progress, with encouraging preliminary results.