Propagator in the instanton background and instanton induced processes in scalar model

The cross section of the multiparticle scattering processes in the non-perturbative sector of the scalar -lambda * phi^4 model is studied within the semiclassical approximation. For this purpose the exact formula for the residue of the propagator in the instanton background is derived. The exponent of the cross section is calculated at small energies both analytically and numerically in the leading and next-to-leading orders in energy. The results are in agreement with the numerical calculations of ref.[1].