Electromagnetic Dipole Research Articles

Virtual O( alpha s) corrections to the inclusive decay b-->s gamma.

We present in detail the calculation of the $O({\ensuremath{\alpha}}_{s})$ virtual corrections to the matrix element for $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$. In addition to the one-loop virtual corrections of the electromagnetic and color dipole operators ${O}_{7}$ and ${O}_{8}$, we include the important two-loop contribution of the four-Fermi operator ${O}_{2}$. By applying the Mellin-Barnes representation to certain internal propagators, the result of the two-loop diagrams is obtained analytically as an expansion in $\frac{{m}_{c}}{{m}_{b}}$. These results are then combined with existing $O({\ensuremath{\alpha}}_{s})$ bremsstrahlung corrections in order to obtain the inclusive rate for $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$. The new contributions drastically reduce the large renormalization scale dependence of the leading logarithmic result. Thus, a very precise standard model prediction for this inclusive process will become possible once the corrections to the Wilson coefficients are also available.

Geophysical variables and behavior: LXXX. Periodicities and energetic characteristics of a strobe-light luminosity during a geomagnetic storm.

A videotape of a "strobe-light" luminosity that occurred in northern Ontario for several minutes during the evening of 6 October, 1994, at the time of a geomagnetic storm, was analyzed frame by frame. Brightness of the flashes decreased over the time of the observation. The interflicker intervals displayed phase-shifted periodicities that would be compatible with a rotating electromagnetic dipole and with the observations of the witnesses. The time of the occurrence and the dynamics of the luminosity were consistent with the predictions of the tectonic strain hypothesis.

Electromagnetic Response of Horizontal Magnetic Dipole over Inhomogeneous. Earth Model with Linear Conductivity Variation.

The problem of calculating the electromagnetic (em) field response ofa horizontal magnetic dipole placed over a multi layer earth model with one of the layers having linear variation of conductivity with depth is formulated. Analytical solutions are obtained for the three layer earth model having linear variation of conductivity in the intermediate transition layer, for the case of quasi-static approximation. Computations are performed for the absolute-amplitude ratio, i.e. the ratio of the absolute amplitude of the field component over a multi-layer model and the corresponding component over a homogeneous half space possessing the conductivity of the top layer. The effects of transition layer thickness and conductivity contrast between the top and bottom layers are investigated by computing these ratios as a function of numerical distance. The results depict characteristic dependence of the em response on conductivity inhomogeneity.

Electromagnetic dipole response of 11Li in a solvable three-body model

The electric dipole response of the halo nucleus 11Li is calculated in a hyperspherical three-body formulation, for an n− 9Li potential which has a low-lying s-wave virtual state. Strength concentrations at lower energies are found but no narrow resonances. There is close correspondence with MSU and RIKEN experimental data.

Electromagnetic properties of neutrinos and pion radiative decay.

We investigate the implications of neutrino electromagnetic dipole moments for the radiative decay $\pi \rightarrow e \nu \gamma$. We show that the dominant new effect comes from the interference between the amplitude of the process with the photon emitted by the neutrino and the structure dependent standard amplitude. Such interference takes place only if the massive neutrino is a Majorana fermion. Moreover, since electric and magnetic dipole moments give rise to contributions with opposite signs, future experiments might be able to distinguish between them.

Terahertz electromagnetic radiation from quantum wells

The observation of terahertz electromagnetic dipole radiation from quantum well structures has finally proven the existence of charge oscillations in semiconductors associated with wave packet dynamics. This article closely examines the physics behind the emission of terahertz electromagnetic radiation from excitonic charge oscillations in such quantum well structures, points out similarities and differences between the various generation schemes, and discusses the various relaxation mechanisms involved. Finally, we show how both amplitude and phase of charge oscillations and the corresponding terahertz emission can be manipulated using phase-locked optical pulses.

A dipole-type intracavitary hyperthermic applicator with a metallic reflector: experiments and theoretical analysis.

A water-cooled electromagnetic (EM) dipole, for intracavitary hyperthermia, embodying a metallic reflector to give directional characteristics to the SAR and then to the heating pattern in the biological tissue, is considered. The influence of the reflector on the SAR deposition has been theoretically modelled with an EM analysis which uses the method of moments (MOM). A thermal model, based on the heat transfer equation, is used to predict temperature distribution, which exhibits a directivity related to the angular extension of the reflector. Experiments have been carried out in a polyacrylamide phantom. The temperature distribution detected with a liquid crystal sheet shows fairly good agreement with theoretical predictions.

Can accretion onto isolated neutron stars produce γ-ray bursts?

THE isotropy and flat count spectrum of γ-ray bursts revealed by the BATSE detector on the Compton Gamma-Ray Observatory1 have led to suggestions that the burst sources are an extended galactic halo of high-velocity neutron stars2,3We show here that if slow accretion onto these neutron stars from the interstellar medium is to be the origin of γ-ray bursts, the accretion physics is very different from what applies for local, low-velocity neutron stars4,5. For halo neutron stars with high magnetic fields and velocities (v > 190 km s–1), electromagnetic dipole radiation pressure prevents accretion unless the period is longer than tens of seconds; the centrifugal barrier will then prevent accretion until the period reaches several thousand seconds. For periods as long as this, accretion may proceed through Kelvin–Helmholtz instability at the magnetopause boundary. At interstellar densities and neutron-star magnetic fields of ∼1012 G, the accretion rate by this process can be much larger than the Bondi–Hoyle (hydrodynamic) accretion rate, but is still well below what is needed for slow-accretion burst models. We conclude that slow accretion onto high-velocity neutron stars in the halo cannot be the origin ofγ-ray bursts.

Accurate Matching of electromagnetic dipole data with CT and MR images

Interpretation of EEG (electroencephalography) or MEG (magnetoencephalography) derived three-dimensional dipole localizations is hampered by poor visualization. This paper describes a method for combining dipole data with structural image data of the same patient. To ensure high precision this method utilizes external markers that are easy to apply. These markers can achieve subslice accuracy and can even be used to pinpoint reference points outside the scanned volume. Accurate matching is thus provided even in standard imaging protocols employing thick slices and/or large interslice gaps. The results of the matching method are presented in 2D and 3D visualizations. The hybrid images facilitate the interpretation of dipole localizations with respect to the patient's anatomy.

Dirac field in the five-dimensional Kaluza-Klein theory

The authors consider the five-dimensional Kaluza-Klein theory with a Dirac field coupled to the metric field. As a result, the authors obtain a four-dimensional Einstein-Maxwell-Dirac theory with an extra CP violating term. The resultant anomalous electromagnetic dipole moment of the electron is of the order of magnitude of about 10-31 e cm, and may not be detectable by present experimental techniques. However, the mass of the charged Dirac particle is found to be of the order of the Planck mass (10-7 g), so that the Kaluza-Klein theory containing spin-1/2 particles must be rejected.

Core mass at the helium flash from observations and a new bound on neutrino electromagnetic properties

Existing measurements of the bolometric magnitudes of the brightest red giants in 26 globular clusters are used to determine the brightness difference between the tip of the red giant branch (on average found to be 0.1 mag brighter than the brightest red giant) and RR Lyrae stars. The metallicity variation of the result agrees perfectly with theoretical predictions. In conjunction with previous determinations of the number ratio of horizontal-branch versus red giant stars, with statistical parallax determinations of RR Lyrae absolute luminosities, and with theoretical predictions based on the Sweigart and Gross evolutionary sequences, this result yields an allowed range for a hypothetical core mass variation relative to the standard results of (0.009 + or - 0.012) solar mass. If neutrinos had anomalous electromagnetic dipole moments, the increased energy loss near the helium flash would lead to an increased core mass. Constraints on neutrino electromagnetic properties are determined from the color-magnitude diagrams of the globular clusters.

Refractive index of polarizable fluids: Numerical results from the mean spherical approximation solution

The numerical solution of the MSA (mean spherical approximation) for a fluid of polarizable particles interacting via the electromagnetic dipole radiation field is presented. The effects of this interaction are studied for molecules with polarizabilities both independent and dependent on frequency. Imaginary and real parts of the refractive index are evaluated, and their behaviors in connection with the absorption bands are determined. Finally, time-correlation and response functions have been evaluated.

High-brightness electron-beam generation and transport

Experimental results for a high-brightness electron-beam source are compared to results of numerical and analytic calculations. The 4-MV, 5-kA beam is generated from a velvet cathode and focused by a solenoidal magnet. Data for the diode impedance and the beam focusing length and spot size agree well with numerical simulations. The minimum spot size is consistent with a normalized Lapostolle emittance of 0.12 cm rad, yielding a brightness of 3.5×108 A/m2 rad2 . Transverse beam oscillations are observed in streak photographs and are thought to be caused by electromagnetic dipole modes in the diode cavity. The oscillation amplitude is significantly reduced by making the current rise more slowly.

Acceleration by pulsar winds in binary systems

view Abstract Citations (73) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Acceleration by Pulsar Winds in Binary Systems Harding, Alice K. ; Gaisser, T. K. Abstract In the absence of accretion torques, a pulsar in a binary system will spin down due to electromagnetic dipole radiation, and the spin-down power will drive a wind of relativistic electron-position pairs. Winds from pulsars with short periods will prevent any subsequent accretion but may be confined by the companion star atmosphere, wind, or magnetosphere to form a standing shock. This paper investigates the possibility of particle acceleration at such a pulsar wind shock and the production of VHE and UHE gamma-rays from interactions of accelerated protons in the companion star's wind or atmosphere. It is found that, in close binaries containing active pulsars, protons will be shock accelerated to a maximum energy dependent on the pulsar spin-down luminosity. If a significant fraction of the spin-down power goes into particle acceleration, these systems should be sources of VHE and possibly UHE gamma-rays. The application of the pulsar wind model to binary sources such as Cygnus X-3 is discussed, as well as the possibility of observing VHE gamma-rays from known binary radio pulsar systems. Publication: The Astrophysical Journal Pub Date: August 1990 DOI: 10.1086/169009 Bibcode: 1990ApJ...358..561H Keywords: Binary Stars; Electromagnetic Radiation; Electron-Positron Pairs; Pulsars; Relativistic Effects; Stellar Winds; Magnetic Dipoles; Particle Acceleration; Standing Waves; Astrophysics; GAMMA RAYS: GENERAL; PARTICLE ACCELERATION; PULSARS; RADIATION MECHANISMS; STARS: BINARIES; STARS: WINDS full text sources ADS | data products SIMBAD (9)

Neutrino mass physics

It is shown that, even if right-handed currents exist, the observation of ν → ν oscillation would imply not only that neutrinos are their own antiparticles but also that they have mass. If neutrinos are their own antiparticles, then there can be large CP-violating effects in the leptonic sector even if only two of the lepton generations mix appreciably. However, the nature of the CP-violating signals can be constrained by CPT invariance. In general, neutrinos can have transition electromagnetic dipole moments, and, if they are not their own antiparticles, non-transition moments as well. The role of neutrino-electron scattering in bounding these moments, and the implications for radiative neutrino decay, and for the solar neutrino flux, are discussed.

Level spectra, electromagnetic moments and transition rates and spectroscopic factors for odd rhodium isotopes in the coriolis coupling model

Properties of low-lying positive- and negative-parity states of 97,99,101,103,105,107,109Rh at low excitation energies have been analyzed in terms of a Coriolis coupling model. The model can account for the general trend of the level schemes for states of both parties. In particular, the 9 2 , 7 2 , and 5 2 triplet near the ground state, the occurrence of multiple 13 2 and at least one 15 2 and 19 2 state of positive parity are reasonably reproduced by the model. Similarly, 1 2 ground-state spin followed by a ( 3 2 , 5 2 ) doublet, and one or more 13 2 and 17 2 states of negative parity are adequately understood in terms of the model. The calculated electromagnetic dipole and quadrupole moments and magnetic dipole and electric quadrupole transition rates are in broad agreement with the observed ones. This is achieved without the use of any effective charge. The general trend of observed spectroscopic factors for pick-up reactions is in agreement with the calculated ones. The results are presented as a function of deformation. Because of the sparsity of data on many of these isotopes, no attempt has been made to find the best fit for each isotope individually. Since the model can reasonably reproduce the general trend of level schemes, electromagnetic properties and spectroscopic factors, one may conclude that the Coriolis coupling model provides a good description of the nuclear properties of these isotopes.

Towards the in situ measurement of the remanent magnetization of oceanic basalts

SUMMARY Recent developments in electromagnetic double dipole devices make these systems convenient for both magnetic susceptibility and resistivity measurements. The coupling of such an electromagnetic logging tool with a magnetic probe supplying the three components of the total magnetic field in the well, allows in siru determination of magnetic parameters. This paper shows how to (i) interpret the raw data in terms of magnetic susceptibility and resistivity of the surrounding medium (ii) determine the horizontal and vertical components of the total magnetization, and (iii) separate the remanent magnetization which seems to be possible at many points of the logging.

Statistical E1 and M1 gamma strength functions from heavy-ion, xn gamma data.

A statistical model analysis of heavy-ion, xn\ensuremath{\gamma} data puts constraints on the electromagnetic dipole strength functions at low energies, ${E}_{\ensuremath{\gamma}}$\ensuremath{\sim}0.5--4 MeV. The M1 strength is inferred to be up to an order of magnitude smaller than at the higher energies of neutron capture gamma rays. The analysis supports the Kadmensky-Markushev-Furman shape of the E1 strength function, with a low-energy tail of the giant resonance that is suppressed relative to the shape based on a Lorentzian. The data considered include the yrast feeding pattern in the N=92 isotones $^{160}\mathrm{Er}$, $^{162}\mathrm{Yb}$, and $^{164}\mathrm{Hf}$, and in $^{152}\mathrm{Dy}$ up to spin 60\ensuremath{\Elzxh}.

Quantum mechanics of the Einstein–Hopf model

The Einstein–Hopf model for the thermodynamic equilibrium between the electromagnetic field and dipole oscillators is considered within the framework of quantum mechanics. Essential to the consistency of the theory is the fluctuation–dissipation theorem connecting the radiation reaction with the zero-point electromagnetic field. The well-known ’’particle’’ term in the Einstein fluctuation formula is shown to be aconsequence of the quantum-mechanical zero-point oscillations of the field and the dipole radiators. Both the wave and particle aspects of the fluctuation formula are interpreted in terms of the fundamental absorption and emission processes.

Relativity of the metric

Although the form of the metric is invariant for arbitrary coordinate transformations, the magnitudes of the elements of the metric are not invariant. For Cartesian coordinates these elements are equal to one and are on the diagonal. Such a unitary metric can also apply to arbitrary coordinates, but only for a coordinate system inhabitant (CSI), to whom these coordinates would appear to be Cartesian. The meaning for a non-Euclidean metric consequently appears to be a simple coordinate system transformation for the appropriate CSI. The conversion of arbitrary coordinates to the flat Cartesian ones can be accomplished by a sequence of isomorphic mappings linking the arbitrary coordinates to the flat Cartesian ones. This is shown for two, three, and four-dimensional spaces. It is also applied to toroidal metrics and fluidfilled spaces for toroidal vortices that are discontinuous, half-wavelength, electromagnetic dipole field distributions. A number of other applications are discussed.