Gluon exchange and p_{T} distribution
  It is shown that even if a quark q is on the mass shell, the quark q' created via vacuum pair production in the process q -> h + q' has wide distribution for its spacelike virtuality, and so at the end of daughter string (q'\bar{q}) there is a parton having wide distributed spacelike virtuality. However, the essence of the parton model is to regard a high energy hadron-like cluster as a collection of quasifree partons. Therefore we use a set of some principles of string model, formulated, for example, by Andersson and Nilsson, that gluons move like localised particles carrying energy momentum between quark and antiquark at the endpoints of string, and so we take into account they go on the mass shell before the break of daughter string occurs. It is stressed, the gluons carry also transverse momentum which could be connected with spacelike virtuality of quark at the end of string. Some approximations to describe the gluon exchange are studied and results of Monte Carlo calculations for antiproton-proton interactions are given. 
Vladimir Lugovoi