Electromagnetic Dipole Research Articles

Helical Metal Nanoparticle Assemblies with Defects: Plasmonic Chirality and Circular Dichroism

Metal nanoparticle structures with a helical arrangement are able to create strong optical chirality and associated circular dichroism (CD). The CD effect in these chiral structures comes from the electromagnetic dipole–dipole interaction between nonchiral nanoparticles. In general, the calculated CD spectra are sensitive to the parameters. The shape of the CD spectrum depends on the helix pitch and radius and, sometimes, on the number of particles in a helix. Simulating several geometries, we were able to identify the sets of parameters for which the CD spectrum is very stable against defects or disorder. These results are important for designing novel nanocomposite materials with strong optical chirality in the visible wavelength region.

Spin electromagnetic field and dipole: A localized and quantized field

This paper investigates the structure of a spin electromagnetic (EM) field and its various physical properties. A spin EM field is an intrinsic mode of free space, which satisfies the spin equations derived from Maxwell equations. A spin mode has two basic properties: the spin along its axis and the localization of electromagnetic field. The source and EM structure of this electric and magnetic mode are described in detail in this paper. The distributed charge and current of a spin mode can be integrated to obtain the electric and magnetic moment, and they can be treated as the electromagnetic dipole. A spin mode possesses both wave and particle properties: a wave number, angular frequency and characteristic speed are its wave parameters; an intrinsic radius, energy and angular momentum are its dynamic parameters. The former is analogous to an EM resonant mode; the latter is similar to the behavior of a particle with intrinsic spin. There are two kinds of electric modes present, one can be expressed through a pair of charges, and the other can be expressed by a magnetic current. They both have the same electric moment, but have different divergence properties.

Long-Distance Dominance of theCPAsymmetry inB¯→Xs,dγDecays

We show that in the standard model the parametrically leading (by a factor $1/{\ensuremath{\alpha}}_{s}$) contribution to the inclusive $CP$ asymmetry in $\overline{B}\ensuremath{\rightarrow}{X}_{s,d}\ensuremath{\gamma}$ decays arises from a long-distance effect in the interference of the electromagnetic dipole amplitude with the amplitude for an up-quark penguin transition accompanied by soft gluon emission. Using model estimates for the associated hadronic parameter ${\stackrel{\texttildelow{}}{\ensuremath{\Lambda}}}_{17}^{u}$, we predict a value in the range $\ensuremath{-}0.6%<{\mathcal{A}}_{{X}_{s}\ensuremath{\gamma}}^{\mathrm{SM}}<2.8%$. In view of current experimental data, a future precision measurement of the flavor-averaged $CP$ asymmetry would signal the presence of new physics only if a value below $\ensuremath{-}2%$ was found. A cleaner probe of new physics is offered by the difference of the $CP$ asymmetries in charged versus neutral $\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ decays.

Nucleon toΔtransition form factors withNF=2+1domain wall fermions

We calculate the electromagnetic, axial, and pseudoscalar form factors of the nucleon to $\ensuremath{\Delta}(1232)$ transition using two dynamical light degenerate quarks and a dynamical strange quark simulated with the domain wall fermion action. Results are obtained at lattice spacings $a=0.114\text{ }\text{ }\mathrm{fm}$ and $a=0.084\text{ }\text{ }\mathrm{fm}$, with corresponding pion masses of 330 MeV and 297 MeV, respectively. High statistics measurements are achieved by utilizing the coherent sink technique. The dominant electromagnetic dipole form factor, the axial form factors and the pseudoscalar coupling are extracted to a good accuracy. This allows the investigation of the nondiagonal Goldberger-Treiman relation. Particular emphasis is given on the extraction of the subdominant electromagnetic quadrupole form factors and their ratio to the dominant dipole form factor, ${R}_{\mathrm{EM}}$ and ${R}_{\mathrm{SM}}$, measured in experiment.

Complete(O7,O8)contribution toB¯→XsγatO(αs2)

We calculate the set of O(alpha_s^2) corrections to the branching ratio and to the photon energy spectrum of the decay process B -> X_s gamma originating from the interference of diagrams involving the electromagnetic dipole operator O_7 with diagrams involving the chromomagnetic dipole operator O_8. The corrections evaluated here are one of the elements needed to complete the calculations of the B -> X_s gamma branching ratio at next-to-next-to-leading order in QCD. We conclude that this set of corrections does not change the central value of the Standard Model prediction for Br(B -> X_s gamma) by more than 1 %.

Level-set based topology optimization for electromagnetic dipole antenna design

This paper presents a level-set framework for a typical electromagnetic design problem of dipole antenna. In this study, the geometrical configuration of an antenna is represented by the zero-level contour of a higher-dimensional level-set function. The governing equation for the induced current flow on a metal surface is the Electric Field Integral Equation (EFIE), which takes into account the electric component of the incident wave. The design objective is formulated in terms of the surface current and incident electric field. The normal velocity of the level-set model, which reflects the sensitivity of the objective function, is derived from the adjoint variable method and shape derivative. By optimizing the objective function, the area with the highest current density, to which the voltage feeding should be applied, can be reshaped. The advantages of adopting the level-set technique for electromagnetic design lie in its capacity for capturing sophisticated topological changes and facilitation in mathematical representation of the design configuration. The demonstrative examples of dipole antenna design show that the level-set method results in a fairly smooth optimization process, where the vacuum/metal interface gradually attains its optimal configuration. A series of design cases with self-adjoint and non-self-adjoint sensitivity analyses are studied and compared to the benchmarking problems in dipole antenna.

LEPTOGENESIS: THE ELECTROMAGNETIC VERSION

In this work, we explore the possibility of leptogenesis beyond the standard Yukawa-mediated decays by considering a scenario where effective electromagnetic dipole operators that connect the light and heavy neutrinos play an important role. Through these operators, new decay channels for the postulated heavy neutrinos are opened up, and consequently, such L- and CP-violating processes can lead to the generation of the correct baryon asymmetry of the universe. In addition, it has been found that the relationship of the leptogenesis scale to the light neutrino masses is very similar to that for the standard leptogenesis setup.

BOUNDING THE ELECTROMAGNETIC AND WEAK DIPOLE MOMENTS OF THE TAU–LEPTON IN A SIMPLEST LITTLE HIGGS MODEL

From the total cross-section for the reaction e+e-→τ+τ-γ at the Z1 pole and in the framework of a simplest little Higgs model (SLHM), we get a limit on the characteristic energy scale of the model f, f ≥ 5.4 TeV , which in turn induces bounds on the electromagnetic and weak dipole moments of the tau–lepton. Our bounds on the electromagnetic moments are consistent with the bounds obtained by the L3 and OPAL collaborations for the reaction e+e-→τ+τ-γ. We also obtained bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI and ALEPH collaborations from the reaction e+e-→τ+τ-.

EMDPLER: A F77 program for modeling the EM response of dipolar sources over the non-magnetic layer earth models

A program EMDPLER coded in FORTRAN 77 is presented for modeling the electromagnetic (EM) response of a wide class of dipolar sources (namely, vertical magnetic dipole, horizontal magnetic dipole and horizontal electric dipole) over the layered earth model in induction ( f≤50 kHz) as well as higher frequency (50 kHz≤ f≤1000 kHz) regions. The program is based on a semi-analytical numerical approach for evaluating infinite integrals occurring in the expressions of EM field components. It is capable of computing the EM response with or without the displacement current factor for any arbitrary position of source and/or receiver either in air or on the surface of the model due to all the conventional EM dipole sources where other available algorithms fail due to one or other reasons. The program is well documented, easy to understand and amenable to modification for the user’s specification. The validity and accuracy of the program is demonstrated by computing the EM response of dipolar sources over homogeneous and multi-layer earth models, and comparing the computed results with those of published results in the literature. Response curves depict their characteristic variations. The computed results match very well with the published results for the induction region ( f≤50 kHz) and are extension of their characteristic variation in the higher frequency (50 kHz≤ f≤1000 kHz) region. The matching of computed results with the published results illustrates the validity of the program.

NEGATIVE REFRACTION OXIDE SUPERLATTICES

ABSTRACT A possible physical mechanism toward realizing negative refraction is theoretically discussed using an oxide-based r superlattice structure. In the superlattice configuration, phonon spectrum coupling among electromagnetic wave, dielectric dipole and magnetic moment vibration is used to realize both negative permeability and negative permittivity in a short frequency range after the resonance. Further material selection has been preliminarily discussed, and the focus will be the realization of such superlattice NIMs for optical frequencies.

Experimental Verification of Reversed Cherenkov Radiation in Left-Handed Metamaterial

By using a phased electromagnetic dipole array to model a moving charged particle, we experimentally verified a reversed Cherenkov radiation in the left-handed media in the frequency range from 8.1 to 9.5 GHz. Our results demonstrate the feasibility of new types of particle detectors and radiation generators.

Nucleon electromagnetic form factors in a quark–gluon core model

We study the nucleon electromagnetic form factors in a quark-gluon core model framework, which can be viewed as an extension of the Isgur-Karl model of baryons. Using this picture we derive nucleon electromagnetic dipole form factors at low Q^2 and the deviation from the dipole form at high Q^2, that are consistent with the existing experimental data.

The electromagnetic dipole radiation field through the Hamiltonian approach

The dipole radiation from an oscillating charge is treated using the Hamiltonian approach to electrodynamics where the concept of cavity modes plays a central role. We show that the calculation of the radiation field can be obtained in a closed form within this approach by emphasizing the role of coherence between the cavity modes, which is discarded in the calculation of the radiation power. We believe that this simple case can elucidate some basic questions students pose when introduced to quantum electrodynamics or perturbation theory in quantum mechanics.

Quadrupole polarizabilities of the pion in the Nambu–Jona-Lasinio model

The electromagnetic dipole and quadrupole polarizabilities of the neutral and charged pions are calculated in the Nambu–Jona-Lasinio model. Our results agree with the recent experimental analysis of these quantities based on dispersion sum rules. Comparison is made with the results from the chiral perturbation theory.

Fluorescence versus laser effect: Towards a unified theory

A single evolution equation is established to treat the mechanisms of fluorescence and the laser effect, using a mixed representation, classical for the electromagnetic field and quantum for the dipoles. The model approach takes advantage of the principle of conservation of energy for the system of electromagnetic field and dynamic dipole. A resulting nonlinear differential equation is derived and is shown to sustain two fixed points associated with fluorescence and laser emission. The existence of a pumping threshold is confirmed for the laser effect. In particular the pumping rate determines whether light will be emitted by fluorescence or by the laser effect, and there is no pumping that engenders fluorescence and laser emission simultaneously. The initial physical conditions, chosen to integrate the evolution equation in time, assume a nonvanishing electric polarization of the emitting dipole rather than a nonvanishing electromagnetic field. The distribution function accounting for the thermal fluctuations of the random initial polarization is also calculated.

Instantaneous-shape sampling for calculation of the electromagnetic dipole strength in transitional nuclei

Electromagnetic dipole absorption cross sections of transitional nuclei with large-amplitude shape fluctuations are calculated in a microscopic way by introducing the concept of instantaneous-shape sampling, which is based on slow shape dynamics as compared with fast dipole vibrations. The dipole strength is calculated by means of the quasiparticle random-phase approximation (QRPA) for the instantaneous shapes, the probability of which is obtained by means of the interacting boson approximation. The calculations agree well with the experimental photoabsorption cross sections near the nucleon emission threshold, but they underestimate it at low energies. The cumulative cross sections for the region below the threshold are a factor of 2 too low.

On the contribution of interference of electromagnetic and chromomagnetic dipole operators in the % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC % vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz % ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqipC0xg9qqqrpepC0xbb % L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe % pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam % aaeaqbaaGcbaGafmOqaiKbaebaaaa!3B84! $$ \bar B $$ → X s γ decay at O(α s 2 )

The contribution of c-quark loops into the interference of the electromagnetic and chromomagnetic dipole operators in the \( \bar B \) → Xsγ decay is calculated to O(αs2) within the framework of the Standard Model (SM). Several new calculation techniques, such as Laporta’s automated algorithm, the second order decomposition method, and Mellin-Barnes representation, have been used.

Gravitational eigenstates in weak gravity: I. Dipole decay rates of charged particles

The experimental demonstration that neutrons can reside in gravitational quantum stationary states formed in the gravitational field of the Earth indicates a need to examine in more detail the general theoretical properties of gravitational eigenstates. Despite the almost universal study of quantum theory applied to atomic and molecular states, very little work has been done to investigate the properties of the hypothetical stationary states that should exist in similar types of gravitational central potential wells, particularly those with large quantum numbers. In this first of a series of papers, we attempt to address this shortfall by developing analytic, non-integral expressions for the electromagnetic dipole state-to-state transition rates of charged particles for any given initial and final gravitational quantum states. The expressions are non-relativistic and hence valid provided the eigenstate wavefunctions do not extend significantly into regions of strong gravity. The formulae may be used to obtain tractable approximations to the transition rates that can be used to give general trends associated with certain types of transitions. Surprisingly, we find that some of the high angular momentum eigenstates have extremely long lifetimes and a resulting stability that belies the multitude of channels available for state decay.

The gravitational field of a radiating electromagnetic dipole

The principle purpose of this paper is to analyze in the context of general relativity the effects of electromagnetic radiation on a gravitational field. The basic outline is that we start from flat-space with a time-dependent electric and magnetic dipole solution of Maxwell's equations. This field, treated as first order, then acts as the source for a gravitational perturbation. First, from the flat-space version of the Bianchi identities, with the Maxwell stress tensor as the (second-order) source, the Weyl tensor is found as a field on the Minkowski background. From this Weyl tensor, we go on and find the spin coefficients and the full metric in this second-order approximation. The physical interpretation and meaning of many of the derived relations are discussed. In particular, we can identify the Bondi energy–momentum—given in terms of the Maxwell field—and their evolution. Of particular attractiveness is the observation of an angular momentum conservation law that comes directly from the asymptotic terms in the Bianchi identities. This law contains a flux term that is a confirmation of a classical E&M result but obtained directly from GR.

Electromagnetic leptogenesis

We present a new leptogenesis scenario, where the lepton asymmetry is generated by $CP$-violating decays of heavy electroweak singlet neutrinos via electromagnetic dipole moment couplings to the ordinary light neutrinos. Akin to the usual scenario where the decays are mediated through Yukawa interactions, we have shown, by explicit calculations, that the desired asymmetry can be produced through the interference of the corresponding tree-level and one-loop decay amplitudes involving the effective dipole moment operators. We also find that the relationship of the leptogenesis scale to the light neutrino masses is similar to that for the standard Yukawa-mediated mechanism.