Infrared renormalons and higher-twist contribution in proton ?proton and photon-photon inclusive collisions

In this thesis, we calculate the contribution of the higher?twist Feynman diagrams to the large?pT inclusive single pion production cross section in hadron?hadron and photon? photon collisions in case of the frozen coupling and running coupling approaches within holographic QCD. The structure of infrared renormalon singularities of the higher?twist subprocess cross section and the Borel sum for it are found. We compared the resummed higher?twist cross sections with the ones obtained in the framework of the frozen coupling approach and leading?twist cross section. Key Words: Differential cross section, Infrared renormalon singularities, The contribution of the higher?twist.