2-PION EXCHANGE MECHANISM IN THE WEAK ISOSCALAR NUCLEON-INTERACTION

The P-odd isoscalar interaction in the NN system generated by two-pion exchange between nucleons is studied. The mechanism for this interact ion includes the emission and subsequent absorption of a pi meson by a nucleon, with the pion undergoing scattering on the second nucleon vi a P-odd exchange between these two processes. In the spirit of the vec tor-dominance model, the weak pi-N --> pi-N scattering occurs as a res ult of rho-meson exchange between the nucleon and the pi meson. At low energies of the NN system and, consequently, small momentum transfers , the weak pi-N scattering occurs practically as a contact interaction . Meanwhile, the range of the resulting weak NN interaction is determi ned by the peripheral nature of pi-meson emission by the nucleon and i s greater-than-or-equal-to 0.4 F. The main uncertainty in the calculat ion of the contribution of the two-pion exchange mechanism to the P-od d correlation is related to the poor knowledge of the constant describ ing the isoscalar P-odd interaction of the rho-meson with the axial nu cleon current. For realistic values of the latter the contribution of isoscalar two-pion exchange to the longitudinal analyzing power in low -energy pp scattering is congruent-to 10-15%.