Improved description of the image-scattering phenomenology at low energies in covariant baryon chiral perturbation theory Original Research Article

We present a novel analysis of the image scattering amplitude in covariant baryon chiral perturbation theory up to image within the extended-on-mass-shell renormalization scheme and including the image explicitly in the image-counting. We take the hadronic phase shifts provided by partial wave analyses as basic experimental information to fix the low-energy constants. Subsequently, we study in detail the various observables and low-energy theorems related to the image scattering amplitude. In particular, we discuss the results and chiral expansion of the phase shifts, the threshold coefficients, the Goldberger–Treiman relation, the pion–nucleon sigma term and the extrapolation onto the subthreshold region. The chiral representation of the amplitude in the theory with the image presents a good convergence from very low energies in the subthreshold region up to energies above threshold and below the image peak, leading also to a phenomenological description perfectly consistent with the one reported by the respective partial wave analyses and independent determinations. We conclude that a model-independent and systematic framework to analyze image-scattering observables using directly experimental data shall be possible in covariant baryon chiral perturbation theory.