Chiral Dynamics Predictions for ${\eta }^{\mathrm{\prime }}\to \eta \pi \pi$

We study the decay ${\eta }^{\mathrm{\prime }}\to \eta \pi \pi$ in two different chiral invariant approaches: Large-$N_c$ Chiral Perturbation Theory (ChPT) and Large-$N_c$ Resonance Chiral Theory (RChT). We analyze the Dalitz plot and the invariant mass spectra. We also compare the relevance of the isoscalar and isovector channels in these approaches. While the predictions of Large-$N_c$ ChPT at next-to-leading order slightly disagree with the measured decay width (showing the need for final state interactions and higher order local contributions), a reasonable agreement is obtained for the case of RChT. Forthcoming experimental analyses at Bonn, Frascati, J"ulich and Mainz will decide among the different frameworks.