A modern view on exclusive reactions: selected topics at the interface between perturbative and non-perturbative QCD

A critical survey of recent developments in the description of exclusive reactions is given. An approach to nucleon distribution amplitudes and related properties is discussed, which makes use of QCD sum rules and the renormalization group. The behavior of helicity-conserving nucleon form factors in the spacelike region has been studied in detail, emphasizing the importance of a self-consistent treatment of endpoint contributions via a modified QCD factorization which takes into account Sudakov suppression of soft-gluon radiation. None of the considered observables is inconsistent with the data, although the leading perturbative contribution to the pion and nucleon form factors is small, calling for rather large K-factors and/or sizeable higher-twist contributions. (author)