Nonpartonic effects in pion electroproduction in the HERMES kinematical region

The presentation is concerned with higher twist corrections of nonpartonic origin to semi-inclusive observables in the kinematical region relevant for the HERMES experiment. We demonstrate a strong impact of the VDM-like interaction and the exclusive production of ${\rho }^0$ meson on the extraction of the $\bar d

• \bar u$ asymmetry from charged pion DIS multiplicities. We also show that it is the exclusive-${\rho }^0$ channel which accounts for the experimentally observed effect of the excess of charged over neutral pions produced at large $z$.