Quark-loop effects in high-energy spin-flip processes

On the basis of the QCD model at large distances, we analyse the qbar-q-sea contribution to the spin effects in the s → ∞, t-fixed limit. It is shown that such effects lead to the spin-flip amplitude increasing as s. The magnitude of spin-flip and spin-non-flip amplitudes is estimated within simple non-perturbative models for quark and gluon propagators. The relative role of spin effects from the wavefunction and the elementary quark subprocess is also discussed. It is shown that the quark-sea effects in the scattering amplitude can reach 30-40% of the contribution of the simple two-gluon exchange at small momenta transfer. (author)