Consistency of coupled-channel effects between off-shell and on-shell chiral models

Determine whether the coupled-channel effects in the S = −1 meson–baryon system behave consistently when computed using fully off-shell covariant unitarized chiral effective field theory up to next-to-leading order versus when computed using the on-shell approximation, particularly in the context of femtoscopic correlation functions for K−p and related coupled channels.

Background

The paper develops a fully off-shell covariant unitarized chiral effective field theory (UχEFT) for S = −1 meson–baryon scattering up to next-to-leading order and compares it to the widely used on-shell approximation. While many scattering observables and correlation functions are similar across schemes, notable differences appear near threshold at NLO.

In analyzing K−p femtoscopic correlation functions, the authors find that the near-threshold discrepancy between off-shell and on-shell results stems from different fitted scattering lengths rather than explicit off-shell effects. However, they note that the consistency of coupled-channel effects across these two dynamical frameworks has not been established, leaving an open question relevant to interpreting femtoscopy data and constraining coupled-channel dynamics.

References

Furthermore, whether the coupled-channel effects behave consistently across these two dynamical models remains an open question.

— Off-shell Chiral Dynamics in the $Λ(1405)$ Resonance and $K^-p$ Femtoscopic Correlations  (2604.00791 - Xie et al., 1 Apr 2026) in Section III.C, Femtoscopic correlation functions

Our findings indicate that either something is missing in the model, particularly in relation with the calculation of the correlation function, or that the data sets on CF and invariant mass spectra may have some incompatibility.

— Enigmatic properties of $Ξ(1620)$ and $Ξ(1690)$  (2608.27236 - Veloso et al., 27 Aug 2026) in Section 3, subsection “Comparison of model results with the available experimental data”