Singularities and accumulation of singularities of πN scattering amplitudes

Abstract It is demonstrated that for the isospin I = 1/2 πN scattering amplitude, T =1/2 ( s , t ), s = m N 2 − π / and $s={m}_{N}^{2}+2{m}_{\pi }^{2}$?> + are two accumulation points of poles on second sheet complex plane, hence singularities ). For =3/2 point plane. The proof valid up to all orders chiral expansions.