Research On Laser Assisted QED Processes

The main purpose of this thesis is to advance the understanding of the effects of laser field on relativistic processes in quantum electrodynamics.The Feynman diagram is a very important method to calculate the QED process.The Feyn-man rule is used to calculate the transition probability by drawing the Feynman diagram.In order to investigate the QED process in the laser field,we need to know the exact solution of the non-perturbation wave equation of the laser field modified charged particles,which is the formula of the laser-dressed fermion propagators.Volkov first proposed the exact solution of the electron motion e-quation in the plane electromagnetic wave.Based on this exact solution,we drew the Feynman diagram,and then replaced the free electron line with the laser dressed electron,and calculated the laser-assisted QED process.We analyzed three processes in this thesis.The first process is the scattering of an electron by a muon in the presence of a linearly polarized laser field,which is investigated in the first Born approximation.The theoretical results reveal the following:1)At medium and large scattering angles,many multiphoton processes occur during scattering,and these nonlinear phenomena may predict the resonant state of the electron and the muon formed in the collision process.2)The photoabsorption(inverse bremsstrahlung)dominates the photoemission(bremsstrahlung),causing the cross section to increase.3)When the laser polarization deviates from the incident direction,the laser-modified total cross section depends considerably on the azimuthal angle of the scattered electron.The dependence of the cross sec-tion on the field strength,polarization direction,and electron-impact energy are studied.The second process is the scattering of a positron by a muon in the pres-ence of a linearly polarized laser field.The theoretical results reveals:1)at large scattering angle,an amount of multiphoton processes take place in the course of scattering.The photon emission processes predominant the photon absorption ones.2)Some nonlinear phenomena about oscillations,dark angular windows,and asymmetry can be observed in angular distributions.We analyze the reason giving rise to "dark windows" and geometric asymmetry initially noted in the potential scattering.3)we also analyze the total differential cross section,the result shows that the larger the incident energy is,the smaller total differential cross section is.The reason of these new results are analysed.Finally,we inves-tigate the process of muon decay in a bichromatic laser field.The field has ? and 2?;,which are out of phase by an angle(?).We find the modification of the decay rate of the muon in the laser filed as a function of the phase angle(?).In chapter 1,Introduction.We introduced the research and development of quantum electrodynamic processes(QED),reviewed the research methods of QED,and the research and development of QED processes in various laser fields after the development of laser technology,such as the study of potential scatter-ing processes in laser fields,laser-assisted m(?)ller scattering etc.In chapter 2,The basic theory of quantum electrodynamic processes in laser fields.We discuss the interaction between charged particles and external field in classical theory and quantum theory,and analysis the energy of charged particles in an external field.The equations of motion of electrons in two-color laser field are discussed.The analysis of the quantum electrodynamics processes are presented.The laser ex-ternal field finally leads to the generalized Bessel function in the scattering cross section.The characteristics of the generalized Bessel function are discussed.The properties of the generalized Bessel function are discussed by the saddle point approximation method.In chapter 3,we investigate the laser-assisted relativistic scattering of an electron by a muon in frame of the Born approximation.The numerical calculation is carried out for the evaluation of the partial differential cross sections for multiphoton processes and for the cross section summed over all these processes.The nonlinear effects in the scattering process are given intu-itively,such as multiphoton processes and cut off characteristic phenomena.The multiphoton processes might predict the resonant state of the electron and the muon formed in the collision process.We calculate the total differential cross section in the medium intensity laser field,find that the cross-section dependen-cies on the field intensity,the frequency,the polarization direction,and on the electron-impact energy.We also investigate the recoil effect in relativistic scatter-ing of an electron from a freely movable muon.In chapter 4,we investigate the laser-assisted relativistic scattering of an electron by a muon in the frame of the Born approximation.A numerical calculation is performed to evaluate the partial differential cross sections of multiphoton processes and the cross section summed over all these processes.The nonlinear effects in the scattering process,such as multiphoton processes and characteristic cutoff phenomena,are given intuitively.The multiphoton processes might predict the resonant state of the electron and the muon formed in the collision process.We calculate the total differential cross section in a medium-intensity laser field and find that the cross section depends on the field intensity,frequency,polarization direction,and electron-impact energy.We also investigate the recoil effect in relativistic scattering of an electron from a freely movable muon.In chapter 5,muon decay in a bichromatic laser field.The field has ? and 2?,which are out of phase by an angle ?.We find the modification of the partial decay rate of the muon in the laser filed as a function of the phase angle ?.