The state of Regge pion exchange calculations for high-energy reactions is reviewed. Experimental evidence is summarized to show that {i) the pion trajectory has a slope similar to that of other trajectories; {ii) the pion exchange contribution can dominate contributions of higher trajectories up to quite a large energy; {iii) many two-body cross sections with large pion contributions can be fit only by models which allow for kinematical conspiracy at t = 0. The theory of kinematic conspiracy is reviewed for two-body amplitudes, and calculations of the conspiring pion -Pomeron cut discussed. The author then summarizes recent work on pion exchange in Reggeized Deck models for multiparticle final states, with emphasis on the predictions of various models {with and without resonances) for phases of the partial wave amplitudes. CONTENTS V. Refe Foreword Is the Pion a Normal Beggeon'? A. What do we expect? B. Extraction of trajectories for negative t C. Trajectory at positive t D. C ouplings Calculation of Pion Exchange in Two-Body Reactions A. Behavior at large t .
B. Kinematics of reactions with spin at small t:Conspiracy and evasion C. Behavior at low t creasing number of situations in nuclear physics in which one-pion exchange effects similar to those known in particle physics appear. It is hoped that our review of the role of the cut or absorption corrections will prove helpful in analyzing these lower-energy situations.Calculations of pion exchange in multiparticle final states should then reflect the properties of the pion learned from two-body interactions. They must also properly include the constraints of unitarity and analyticity. These constraints are rather more complex for muliibody reactions than for two-body reactions; as a result it is only within the past few years that theoretical work has really grappled with the phase of the multibody amplitude. This work is summarized in Sec. IV.Section V essays an overview of the situation.