Some QED processes: Light-by-light and moeller scattering

We consider several applications of the simplest nonlinear QED phenomena described by the light-by-light (LBL) scattering tensor. Among the relevant processes we present the splitting of high energy photon in a Coulomb field, calculate the asymptotics of differential photon photon elastic scattering. We show that LBL mechanism of the four photon mode of neutral pion decay have a dominant role compared, for instance, with the quark loop Feynman amplitude contribution. The mechanisms of creation of two and three gluon jets at colliding electro-positron beams is analyzed. We calculate also the contribution of LBL mechanism to the ortho-positronium decay width. One Of the important application is the analytic calculation of the QED contribution to the anomalous magnetic moment of the muon arising from LBL mechanism realized through electron positron loops, which is enhanced by the logarithm of the ratio of muon to electron masses. The modification of the QED kernel, which takes into account the QED polarization operator is used to extract the pure strong interaction contribution. We consider as well the problem of the Coulomb law modification. At second part of review we consider Moeller scattering process and RC to it. We show that RC are in agreement with renormalization group approach and could be taken into account in form of Drell-Yan process cross-section.     

QED radiative corrections to impact factors

We consider radiative corrections to the electron and photon impact factors. The generalized eikonal representation for the e ⁺ e ^? scattering amplitude at high energies and fixed momentum transfers is violated by nonplanar diagrams. An additional contribution to the two-loop approximation appears from the Bethe-Heitler mechanism of fermion pair production with the identity of the fermions in the final state taken into account. The violation of the generalized eikonal representation is also related to the charge parity conservation in QED. A one-loop correction to the photon impact factor for small virtualities of the exchanged photon is obtained using the known results for the cross section of the e ⁺ e ^? production during photon-nuclei interactions.     

Processes with heavy ion collisions

Some Coulomb effects in heavy ion collisions are considered. Among them the process of muon and lepton pair creation, Coulomb and unitary corrections, statistics of multiple pair production. Effects of multiple photon exchange in process of lepton pair production by linearly polarized photon on nuclei are considered. This process is used for measuring the polarization of initial photon. Relativistic muon energy loss due to the light lepton pair production in the Coulomb field are calculated. Also we consider the effects of multiple photon exchange in elastic lepton scattering on unscreened atomic field and discuss the possible experimental testing.     

Electromagnetic radiation from QGP with chromo-magnetic monopoles

We consider the radiation of photons from quarks scattering on color-magnetic monopoles in the Quark-Gluon Plasma. The calculation is performed in the classical, non-relativistic approximation and results are compared to photon emission from Coulomb scattering of quarks, known to provide a significant contribution to the photon emission rates from the QGP. The present study is a first step towards understanding whether this scattering process can give a sizable contribution to dilepton production in heavy-ion collisions.     

Quantum photon emission from a moving mirror in the nonperturbative regime

We consider the coupling of the electromagnetic vacuum field with an oscillating perfectly-reflecting mirror in the nonrelativistic approximation. As a consequence of the frequency modulation associated to the motion of the mirror, low frequency photons are generated. We calculate the photon emission rate by following a nonperturbative approach, in which the coupling between the field sidebands is taken into account. We show that the usual perturbation theory fails to account correctly for the contribution of TM-polarized vacuum fluctuations that propagate along directions nearly parallel to the plane surface of the mirror. As a result of the modification of the field eigenfunctions, the resonance frequency for photon emission is shifted from its unperturbed value.     

Search for stimulated photon-photon scattering in vacuum

We have searched for stimulated photon scattering in vacuum at a center of mass photon energy of 0.8 eV. The QED contribution to this process is equivalent to four wave mixing in vacuum. No evidence for scattering was observed. The corresponding upper limit of the cross-section is . Received 29 September 1999     

Astrophysically relevant processes in Lorentz-violating QED

We consider quantum electrodynamics with violation of Lorentz in-variance. We calculate the rates of photon decay along with the cross sections of electron-positron pair production on background radiation and in the Coulomb field. The latter process is essential for detection of photon-induced air showers in the atmosphere. The results of this work are written in [1] in details.     

First-order radiative corrections to polarized muon decay spectrum

The first-order QED corrections to the polarized muon decay spectrum are considered. The exact dependence on electron and muon masses is kept. Numerical results are presented.     

Current tensor with a heavy photon for pair production by a longitudinally polarized electron

The electron current tensor for the scattering of a heavy photon on a longitudinally polarized electron accompanied with an additional electron-positron pair is considered. The contribution of soft and hard collinear and quasi-collinear pairs is taken into account. The full analysis of the spin-independent and spin-dependent parts of the electron current tensor is performed. The results allow us to calculate the corresponding contribution into the second-order radiative correction to cross sections for different processes with the next-to-leading accuracy.     

Azimuthal asymmetry in processes of nonlinear QED for linearly polarized photon

Cross sections of nonlinear QED processes (photon-photon scattering, photon splitting in a Coulomb field, and Delbrück scattering) are considered for linearly polarized initial photon. The cross sections have sizeable azimuthal asymmetry.     

New results in the theory of muonic atom formation in molecular hydrogen

Muonic atom formation in molecular hydrogen proceeds in two stages. In the first stage, the mu-molecular complex (abµe)^* is formed due to Coulomb capture of a muon by a hydrogen molecule (abee), and, in the second stage, the decay of the complex leads to exotic-atom formation. We consider various channels for the decay of the complex. The main competition channels are direct dissociation and Auger decay. The primary distribution of muonic atoms over quantum states and kinetic energy has been obtained taking into account the competition of the decay channels.     

CPT-violating effects in muon decay

We consider low-energy CPT-violating modifications in charged current weak interactions and analyze possible ramifications in muon and antimuon decays. We calculate the lifetime of muon and antimuon with these modifications, and from the result, put bounds on the CPT-violating parameters. Moreover, we elaborate on the muon and antimuon decay rate differentials in electron energy and spatial angle, which entail interesting phenomenological consequences presenting new ways to constrain CPT violation in charged lepton decays.     

Electroproduction of an electron-positron pair in a medium

The process of the electron-positron pair creation by a high-energy electron in a medium is analyzed. The spectral distribution over energies of created particles is calculated for the direct and cascade mechanisms of the process. The Coulomb corrections are included. The new formulation of the equivalent photon method is developed, which takes into account the influence of the multiple scattering. It is shown that the effects of multiple scattering can be quite effectively studied in the process under consideration. The text was submitted by the authors in English.     

Radiative muon pair production in high-energy electron-positron annihilation process

The lowest order radiative correction to the differential cross section of process of muon pair production with the emission of a hard photon at high energy electron-positron annihilation are calculated. Taking into account the emission of additional soft and hard photon, the cross section can be put in the form of the Drell-Yan process in leading logarithmical approximation. Applying the crossing transformation, we obtain the cross section of the radiative electron-muon high-energy scattering process. Virtual and soft photon emission contributions of the nonleading form are tabulated for several typical kinematical points. The limit of the small invariant mass of a muon pair is in agreement with our previous analysis.     

New method for calculating helicity amplitudes of jet-like QED processes for high-energy colliders

Inelastic QED processes, the cross sections of which do not drop with increasing energy, play an important role at high-energy colliders. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles , which yields the dominant contribution to their total cross sections. A new effective method is presented and applied to QED processes with emission of real photons to calculate the helicity amplitudes of these processes. Its basic idea is similar to the well-known equivalent-lepton method. Compact analytical expressions for those amplitudes up to are derived omitting only terms of the order of and higher order. The helicity amplitudes are presented in a compact form in which large compensating terms are already cancelled. Some common properties for all jet-like processes are found and we discuss their origin. Received: 19 December 2001 / Published online: 5 April 2002     

QED corrections to DIS cross section with tagged photon

We calculate the QED corrections to the deep inelastic scattering cross section with tagged photon at HERA, taking into account the leading and next-to-leading contributions. Different types of event selection are investigated. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 367–372 (25 September 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

激光电子散射中的最大可能增益

借鉴自由电子激光(FEL)发展之初Madey对自由电子激光器中受激辐射引起的增益的讨论,通过在激光场中的量子电动力学(QED)的模型中引入激光电子系统初态态密度以及由不确定的系统初态到确定光子末态的跃迁速率,推导了激光电子正碰过程中受激辐射至单一电磁模式产生的最大可能增益。采用成功得到X射线或γ射线光子的三个激光电子Compton背散射实验的实验参数计算了激光电子散射过程中的最大可能增益,与第一台X射线自由电子激光(XFEL)中的最大可能增益作比较,进而对激光电子散射作为激光光源的可行性进行评估。计算结果表明,现有的能够得到X射线光子或γ射线光子的激光电子散射实验中的最大可能增益远低于第一台XFEL中的。本工作未能找到合适的激光电子参数以获得比第一台XFEL中更高的最大可能增益,但是在入射电磁波位于射频波段范围内找到了能够实现较高增益的参数组合。     

Collapse and revivals of the photon field in a Landau-Zener process

We consider the evolution of a two-level system coupled to a photon field initially in a coherent state, as the energy of the two-level system is linearly varied through resonance with the photon field. At a fixed time after the resonance, the amplitude of the photon field is found to show a collapse and subsequent revivals as a function of rate of energy variation. Including decay of the photon field, we find that the observation of such collapse and revivals is near the technological limit of current cavity QED experiments but should be achievable.     

Higher order QED corrections to Bhabha scattering at low angles

We calculate the QED bremmstrahlung corrections beyond O() for small-angle scattering. These corrections are of vital importance for measuring the luminosity and consequently the total cross sections in LEP experiments. They are dominated by the second order leading-logarithmic contributions. We calculate them with the high technical precision 0.02% and we show that they depend strongly of the details of experiment cut-off. We propose a practical method of introducing the O(²) correction calculated in this paper into current procedures of the luminosity measurement at LEP. The remaining overall QED uncertainty is estimated to be 0.3%. This estimate includes 0.2% due to pure bremsstrahlung and 0.1% due to light pair production but does not include hadronic uncertainty in the photon vaccum polarization.     

QED in Krein Space Quantization

In this paper we consider the QED in Krein space quantization. We show that the theory is automatically regularized. The three primitive divergences integrals in usual QED are considered in Krein QED. The photon self energy, electron self energy and vertex function are calculated in this formalism. We show that these quantities are finite. The infrared and ultraviolet divergencies do not appear. We discuss that Krein space quantization is similar to Pauli-Villars regularization, so we have called it the “Krein regularization”.