Improved description of the πNπN-scattering phenomenology at low energies in covariant baryon chiral perturbation theory

• The chiral series shows a better convergence than previous analyses.
• Improved prediction of the πNπN scattering phenomenology.
• This analysis connects reliably the subthreshold and physical regions for the first time using ChPT.
• Extraction of an accurate value of σπNσπN from experimental data.
• σπNσπN extracted is compatible with related phenomenology.

We present a novel analysis of the πNπN scattering amplitude in covariant baryon chiral perturbation theory up to O(p3)O(p3) within the extended-on-mass-shell renormalization scheme and including the Δ(1232) explicitly in the δδ-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 πNπN 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 Δ presents a good convergence from very low energies in the subthreshold region up to energies above threshold and below the Δ(1232) 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 πNπN-scattering observables using directly experimental data shall be possible in covariant baryon chiral perturbation theory.