Methods Of Quantum Electrodynamics Research Articles

Intense interactions of molecules with a short-wavelength electromagnetic radiation field: I. The fundamentals of the nonadiabatic theory

The intense interactions between short-wavelength (SW) electromagnetic radiation with a wavelength λ ≥ 1 A and intensity up to 1014 W/cm2 and simple and polyatomic molecules are studied with the coherent excitations of high-lying Rydberg and autoionizing states taken into account. The Hamiltonian of a system “molecule + SW radiation” is obtained by using the methods of quantum electrodynamics. Conditions for the applicability of the dipole approximation to describe the interactions of molecules with radiation of the UV, VUV, XUV, and soft X-ray range are found. The fundamentals of the theory of resonance scattering of SW radiation from diatomic, triatomic, and symmetric-and asymmetric-top polyatomic molecules are outlined.

Radiation of dressed excitons in the semiconductor microcavity

In this paper, we introduced the dressed exciton model of the semiconductor micro-cavity device. In the semiconductor micro cavity of vertical-cavity surface-emission device, the excitons first coupled with the cavity through an intra-electromagnetic field and formed the dressed excitons. Then these dressed excitons decayed into the vacuum cavity optical mode, as a multiparticle process. Through the quantum electrodynamics method, the dipole emission density and system energy decayed equation were obtained. And it was predicted that the excitons decay into a very narrow mode when the exciton-cavity coupling becomes strong enough.

Evaluation of a Scattered Radiation Field in a Cluster Relevant for Multiple-Energy X-Ray Holography

We analyze theoretically multiple-energy X-ray holography (MEXH), a new tool for material structure determination, already tested experimentally, which utilizes synchrotron radiation to generate an electromagnetic scattering field at a specific target atom inside a material sample. In MEXH the target atom is considered as a detector, which indicates the electric field strength at its core via the measurement of the total intensity of fluorescence that the atom emits in all directions. The modulations of the intensity, upon varying the direction and the energy of the incident synchrotron radiation, are registered as a hologram which offers then the image of the environment surrounding the target atom. The purpose of this work is to determine theoretically the relevant physical quantity of the process, i.e. the electromagnetic field, at the target atom position. For this purpose we use methods of quantum electrodynamics (QED). We obtain formulas which are interpreted in terms of a holographic description of the process which can then have a direct experimental application through the MEXH method.

Excitation transfer in the vicinity of a dielectric surface

Using the quantum electrodynamics method, we present the resonance excitation transfer matrix element in the vicinity of a dielectric surface. Depending on the geometry and orientations of two dipoles, our results show that the excitation transfer can be suppressed or enhanced by the presence of the dielectric surface in comparison to that of the free space. Both near-zone and wave-zone limits are discussed.

Cerenkov radiation in anisotropic media by the methods of quantum electrodynamics

We examine the Cerenkov effect in a transparent anisotropic medium by the methods of quantum electrodynamics. We first show that in such a medium the electric field intensity is not transverse. By resolving the field we distinguish the contributions to the intensity of the radiation corresponding to the transverse and longitudinal components of the field. Focusing also on the role of the spin, we show that its effect is significant since the intensity can increase or decrease compared with that of a spinless particle.

Radiative corrections to two-photon exchange in elastic electron-proton and positron-proton scattering

The radiative corrections to the differential elastic electron (positron)—proton scattering cross section is determined in the fourth order in perturbation theory by quantum electrodynamics methods. The contribution from two-photon exchange is determined in the static approximation with subsequent recalculation for the center of mass system and with allowance for recoil of the proton. The electromagnetic structure of the proton is taken into account.

Mechanism for origination of a new kind of radiation during the channeling of relativistic electrons in a crystal

Singularities on the spontaneous radiation of relativistic electrons moving in the axial channeling mode in a crystal due to longitudinal electron vibrations are analyzed by quantum electrodynamics methods. A comparison is made with published experimental data.

Baryon resonance in a proton-electron-positron system

Quantum electrodynamics methods are used to calculate the effective annihilation section in the region of the resonant peak of an electron-positron pair for collision with a proton and subsequent formation of baryon resonance with an isospin I=1/2, spin and parity JP = 1/2− and J/P = 3/2−, with subsequent decay into a proton and a photon. Existence of baryon resonance with mass value close to 1650 MeV and quantum numbers I = 1/2 and JP = 3/2− is predicted, together with resonant spin values N (2700) and A (2160) with internal parities P = −1 equal to 13/2 and 7/2, respectively.

Mathematical modeling of the interaction of three particles

A composite material is a heterogeneous disperse body and its hardness is determined by internal chemical interatomic, intermolecular, claster, and structural interactions. The chemical intermolecular forces are determined by methods of quantum chemistry, and by methods of quantum electrodynamics when a more in-depth study of the nature of the relations is required. All of these methods are extremely complex; mathematical modeling, which makes it possible to obtain the required relationships and parameters by the fitting of experimental data is therefore used to solve engineering problems. One of these methods is the BornOppenheimer approximation [i].

Cooperative mean-frequency absorption: A two-beam two-photon process

It is shown that by a cooperative process involving virtual photon coupling between molecules, pairwise two-photon absorption can lead to molecular transitions associated with the mean of the laser frequencies in a two-beam experiment. The process is represented by A+A+ℏω1+ℏω2→A*+A*, and the selection rules are those normally applicable to two-photon absorption. The interaction may involve the excitation of chromophore pairs in polyatomic molecules, van der Waals molecules, or more usually discrete molecules in a gas or liquid. In the former case, however, dissymmetric juxtaposition of the chromophores produces a chirality which is manifest in a circular dichroism associated with the absorption process. The appropriate absorption rates are calculated using the methods of quantum electrodynamics, and the dependence on the separation of the interacting pair is examined in detail. Methods for observing the mean-frequency interaction are also outlined, and attention is drawn to a resonance condition which should appreciably enhance the absorption rate.

Application of graphical methods of spin algebras to limited CI approaches. I. Closed shell case

AbstractThe time independent diagrammatic technique based on the mathematical methods of quantum electrodynamics (second quantization, Wick's theorem, Feynman‐like diagrams) is combined with graphical techniques of spin algebras to derive general expressions for the matrix elements of spin independent one‐ and two‐particle operators between spin symmetry adapted ground, mono‐ and bi‐excited configurations of a closed shell system. Two coupling schemes are considered for bi‐excited states and their relative merits are discussed. Finally, the results are used to derive compact expressions for the coupling coefficients of the direct configuration interaction from molecular integrals (CIMI) method.

Theory of magnetic circularly polarized emission

A theory of magnetic circularly polarized emission (MCPE) based on the formalism and methods of quantum electrodynamics is developed for luminescent molecular systems. Differential transition probabilities for the (spontaneous) emission of left- and right-circularly polarized light are calculated and these quantities are related to the observables of MCPE spectroscopy. The emission intensity variables are further related to the emission analogs of the Faraday A, B, and C parameters. The influence of photoselection and reorientational relaxation (due to rotary Brownian motion) upon the MCPE observables is also considered. Results are obtained for two excitation–emission geometries—180° (head-on) and 90° (right angle). Explicit expressions are given for the A, B, and C Faraday parameters in both the orientationally relaxed limit (isotropic emitting sample) and the photoselected, frozen limit.

General theory of circularly polarized emission and magnetic circularly polarized emission from molecular systems

A theory of circularly polarized emission (CPE) based on the formalism and methods of quantum electrodynamics is developed for chiral luminescent molecular systems and for achiral luminescent molecular systems placed in a magnetic field. Differential transition probabilities for the (spontaneous) emission of left- and right-circularly polarized light are calculated and these quantities are related to the observables of CPE spectroscopy. The influence of photoselection and reorientational relaxation (due to rotary Brownian motion) upon the CPE observables (with and without an applied magnetic field) is considered. Expressions for emission anisotropy factors are derived and these factors are related to the molecular transition integrals which determine the CPE and total emission intensities. Results are obtained for two excitation–emission geometries—180° (head on) and 90° (right angle).

Radiation of an electron in an electric field. II

By the methods of quantum electrodynamics, the radiation of an electron moving in the field of a traveling electric wave is considered. It is shown that, in contrast to the classical case, the result given by quantum theory for the spectral-angular distribution of the radiant energy differs from the corresponding expression for an electron in a constant homogeneous electric field, even in the terms proportional to Planck's constant.

Tests of sum rules for photon total cross sections in quantum electrodynamics and mesodynamics

Sum rules for photon-hadron, photon-lepton and photon-photon total cross sections are tested using the perturbative methods of quantum electrodynamics and mesodynamics. Some possible modifications of the investigated sum rules are pointed out and discussed. Arguments are provided which support the validity of the Cabibbo-Radicati sum rule to all orders of the strong coupling constant in the “chiral” limit of a vanishing pion mass.

A radiation process in the passage of a heavy charged particle through an atom. I. Formulation

The author examines a process of radiative interaction between a fast moving, heavy, charged particle, N, and an atomic electron, e, moving with nonrelativistic velocities. Formulae for cross sections for the process in which the electron is left in a continuum final state after the interaction and emission of a photon, gamma , are presented. For collisions in which the heavy particle does not lose any sizeable fraction of its incident energy, the amplitudes are calculated by methods of quantum electrodynamics. Analysis of the results are presented for the limiting cases of: (a) soft photon emission; (b) forward scattering of the electron and/or photon; (c) scattering into a final state in which the initial momentum of N, and the final momenta of e and gamma are coplanar. Various useful kinematic constraints are pointed out and used in these analyses for limiting values of energies of N, e and gamma .

Axiomatic method in quantum electrodynamics

>A method in the theory of electromagnetic interactions is suggested, which is free from the infrared divergences. The method is based on the equations of the Bogolubov axiomatic approach in quantim fieid theory, from which the infrared divergences are removed. Exact consequences of the equations are discussed, such as the low energy theorems and dispersion relations in all orders with respect to the electromagnetic interaction. All the model-independent terms in the infrared asymptotics of the Green function of charged spinless particle are given out. (auth)

Polarization effects in electron scattering in the gravitational field of a rotating source

The polarization effects in electron scattering in a gravitational field with the Kerr metric are examined, and a formula is obtained for the deflection angle of a relativistic spin -1/2 particle in such a field by the methods of quantum electrodynamics.

Energy Straggling and Radiation Reaction for Magnetic Bremsstrahlung

When the average energy of the photon emitted by synchrotron radiation becomes appreciable compared to the energy of the particle, the particle will undergo straggling in its energy loss, which in turn broadens the radiation spectrum. The energy distributions of particles and the emitted photons are calculated using the method of quantum electrodynamics. The results are presented together with effects due to classical radiative reaction for experimental test. The significance of energy straggling in astrophysics is discussed briefly.

Spin effects in the theory of synchrotron radiation due to the motion of an electron in a medium

The methods of quantum electrodynamics are used here to show that the presence of a medium does substantially modify certain spin effects during superoptical motion of an electron in a magnetic field. It is found, specifically, that the fundamental state becomes unstable while the first excited state loses its metastable character. Expressions are derived for the lifetime of the fundamental and of the first excited state respectively. The radiation intensity of the two principal polarization components is also analyzed, as a function of the spin orientation.