Unitarity constraints on effective interaction in πN scattering

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.