Search results for "electrodynamics"

Compton scattering by a pion and off-shell effects

1994

We consider Compton scattering by a pion in the framework of chiral perturbation theory. We investigate off--shell effects in the s-- and u--channel pole diagrams. For that purpose we perform a field transformation which, in comparison with the standard Gasser and Leutwyler Lagrangian, generates additional terms at order $p^4$ proportional to the lowest--order equation of motion. As a result of the equivalence theorem the two Lagrangians predict the same Compton scattering S--matrix even though they generate different off--shell form factors. We conclude that off--shell effects are not only model--dependent but also representation--dependent.

Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at LowQ2Using the Virtual-Compton-Scattering Reaction

2006

Experimental details of a virtual Compton scattering (VCS) experiment performed on the proton at the MIT-Bates out-of-plane scattering facility are presented. The VCS response functions ${P}_{LL}\ensuremath{-}{P}_{TT}/\phantom{{P}_{TT}\ensuremath{\varepsilon}}\ensuremath{\varepsilon}$ and ${P}_{LT}$ have been measured at ${Q}^{2}=0.057\phantom{\rule{0.28em}{0ex}}{\mathrm{GeV}}^{2}/{c}^{2}$. The generalized electric and magnetic polarizabilities, $\ensuremath{\alpha}({Q}^{2})$ and $\ensuremath{\beta}({Q}^{2})$, and the mean-square electric polarizability radius$\ensuremath{\langle}{r}_{\ensuremath{\alpha}}^{2}\ensuremath{\rangle}$ are obtained from a dispersion analysis of the data. The resu…

Dynamical zero in ν¯e–e− scattering and the neutrino magnetic moment

2005

Abstract The Standard Model differential cross section for ν ¯ e – e − elastic scattering vanishes exactly, at lowest order, for forward electrons and incident ν ¯ e energy close to the rest energy of the electron. This dynamical zero is not induced by a fundamental symmetry of the Lagrangian but by a destructive interference between the left- and right-handed chiral couplings of the electron in the charged and neutral current amplitudes. We show that lowest-order analyses based on this favorable kinematic configuration are only mildly affected by the inclusion of the O ( α ) radiative corrections in the ν ¯ e – e − differential cross section, thus providing an excellent opportunity for the…

Proton-Hydrogen Charge Exchange and Elastic Scattering in the Faddeev Approach

2000

Results of the application of Faddeev-type integral equations to proton-hydrogen collisions are reported. The approach, realized in the impact parameter representation, incorporates the exact two-particle off-shell Coulomb T-matrices in all ‘triangle’ contributions to the effective potentials. Calculatedtotal and differential electron-transfer as well as differential elastic scattering cross sections show very good agreement with experiment, over a wide range of incident energies.

Fluctuations of the Casimir-Polder force between an atom and a conducting wall

2007

We consider the quantum fluctuations of the Casimir-Polder force between a neutral atom and a perfectly conducting wall in the ground state of the system. In order to obtain the atom-wall force fluctuation we first define an operator directly associated to the force experienced by the atom considered as a polarizable body in an electromagnetic field, and we use a time-averaged force operator in order to avoid ultraviolet divergences appearing in the fluctuation of the force. This time-averaged force operator takes into account that any measurement involves a finite time. We also calculate the Casimir-Polder force fluctuation for an atom between two conducting walls. Experimental observabili…

Laser Assisted Dirac Electron in a Magnetized Annulus

2021

We study the behaviour of a charge bound on a graphene annulus under the assumption that the particle can be treated as a massless Dirac electron. The eigenstates and relative energy are found in closed analytical form. Subsequently, we consider a large annulus with radius ρ∈[5000,10,000]a0 in the presence of a static magnetic field orthogonal to its plane and again the eigenstates and eigenenergies of the Dirac electron are found in both analytical and numerical form. The possibility of designing filiform currents by controlling the orbital angular momentum and the magnetic field is shown. The currents can be of interest in optoelectronic devices that are controlled by electromagnetic radi…

Electromagnetic field fluctuations near a dielectric-vacuum boundary and surface divergences in the ideal conductor limit

2012

We consider the electric and magnetic field fluctuations in the vacuum state in the region external to a half-space filled with a homogeneous non-dissipative dielectric. We discuss an appropriate limit to an ideal metal and concentrate our interest on the renormalized field fluctuations, or equivalently to renormalized electric and magnetic energy densities, in the proximity of the dielectric-vacuum interface. We show that surface divergences of field fluctuations arise at the interface in an appropriate ideal conductor limit, and that our limiting procedure allows to discuss in detail their structure. Field fluctuations close to the surface can be investigated through the retarded Casimir-…

Time-dependent Kohn-Sham approach to quantum electrodynamics

2010

We prove a generalization of the van Leeuwen theorem towards quantum electrodynamics, providing the formal foundations of a time-dependent Kohn-Sham construction for coupled quantized matter and electromagnetic fields. Thereby we circumvent the symmetry-causality problems associated with the action-functional approach to Kohn-Sham systems. We show that the effective external four-potential and four-current of the Kohn-Sham system are uniquely defined and that the effective four-current takes a very simple form. Further we rederive the Runge-Gross theorem for quantum electrodynamics.

A numerical model for coupled free surface and liquid metal flow calculation in electromagnetic field

2014

On the exhaust of electromagnetic drive

2016

Recent reports about propulsion without reaction mass have been met on one hand with enthusiasm and on the other hand with some doubts. Namely, closed metal cavities, when fueled with microwaves, have delivered thrust that could eventually maintain satellites on orbits using solar power. However, the measured thrust appears to be without any apparent exhaust. Thus the Law of Action-Reaction seems to have been violated. We consider the possibility that the exhaust is in a form that has so far escaped both experimental detection and theoretical attention. In the thruster's cavity microwaves interfere with each other and invariably some photons will also end up co-propagating with opposite pha…