Hard exclusive electroproduction of pions

We investigate the exclusive electroproduction of π+ mesons from nucleons. To leading-twist, leading-order αs accuracy, the corresponding production amplitude can be decomposed into pseudovector and pseudoscalar parts. Both can be expressed in terms of quark double distribution functions of the nucleon. While the pseudovector contribution is connected to ordinary polarized quark distributions, the pseudoscalar part can be related to one-pion t-channel exchange. We observe that the pseudovector part of the production amplitude is important at xBj<0.1. On the other hand, for 0.1<xBj<0.4, contributions from one-pion exchange dominate. (orig.)