Unitarity Constraints on effective interaction in $\pi N$ scattering

Abstract

Positivity constraints are derived on pion-nucleon scattering amplitudes and their even-order derivatives inside the Mandelstam Triangle with the help of dispersion relations. Fairly interesting constraints are obtained on some of the low energy constants, by a combination of the chiral perturbation theory for heavy baryons and existing fitting results from available pion-nucleon phase shifts at intermediate energies.

Comments: version to appear in Phys. Lett. B. 6 pages