Two Boson Exchange And Annihilation Effects

The high precise measurements and experiments play more and more important roles in particle physics and atomic physics.To extract the physical quantities from the precise ex-perimental data sets,the corresponding precise and reliable theoretical calculations are neces-sary.Until now,the masses of charmonium,the form factors of elemental constituents such as pion and proton are still attractive issues in current Quantum Chromodynamics(QCD).The two-boson-exchange effects should be considered carefully when we investigate these physical quantities.Concretely,based on the current experimental measurements and the development of theoretical research,we focus on the following subjects in this thesis:1.The nonrelativistic asymptotic behaviors of the transitions q(?)(¹S₀)?2g?q(?)(¹S₀) and q(?)(³P_J)?2g?q(?)(³P_J).For the¹S₀channel,the imaginary part of the results after applying the on-shell conditions are comparable with the known nonrelativistic QCD (NRQCD)results in the leading order of?_s,and the real part of the results can be used to estimate the mass shift of the¹S₀heavy quarkonia due to the 2g annihilation effect.As for the³P_Jchannel,we take the momenta of quarks and antiquarks on shell,the imaginary parts of the results can also reproduce the NRQCD results,while the real parts have IR divergence.After absorbing the IR divergence by the amplitude of(?)q?1g?(?)q,the final results can be used to estimate the mass shifts of the³P_Jheavy quarkonia due to the effect of 2g annihilation.2.The two-photon-exchange(TPE)effect in ep?en?⁺.In the pion dominance approx-imation and the limit m_e?0,the TPE contribution to the amplitude can be described by a scalar function.We calculate TPE contributions to the amplitude and the unpolar- ized differential cross section with only elastic intermediate state is considered.The TPE corrections to the separated cross sections?_{L,T,LT,T T}are also analyzed.3.The dispersion relations on the TPE effect in the elastic ep scattering based on several toy interactions.After analysing the possible kinematical singularities,the asymptotic behaviors and the branch cuts of the TPE amplitudes,we obtain some exact relations between the dispersion relation method and the hadronic model method.To get the same results,these two methods should be modified respectively to general forms.The new general forms automatically and correctly include the contributions due to the meson-exchange effect,the contact interactions and the off-shell effect.