Universal Efimovian three-body potential “deeply" affected by narrow Feshbach resonances

We analyse the change in the hyperradial Efimovian three-body potential as the two-body interaction is tuned from the broad to narrow Feshbach resonance regime, where experimental data has revealed a shift of the three-body parameter away from the universal value $\left|a_−\right| = −9.7 r_{\mathrm{vdW}}$ . To this end we develop a model separable two-body interaction which takes into account the full zero-energy behaviour of the multichannel wave function. We find that the short-range suppression of the three-body wave function characteristic for single-channel models remains universal also for narrow resonances, whilst the change in the three-body parameter originates from a strong decrease in the potential depth. From an analysis of the underlying spin structure we argue that this behaviour may be attributed to the dominance of the two-body interaction in the resonant channel compared to other background interactions.