External Electromagnetic Field Research Articles

Radiation of High-Energy Gamma Quanta by Ultrarelativistic Electrons on Nuclei in Strong X-ray Fields

The possibility of radiation of high-energy gamma quanta with energies of the order of 100 GeV by ultrarelativistic electrons on nuclei in strong X-ray fields with intensities up to ∼1027Wcm−2 was theoretically studied. It is shown that this effect can be realized under special experimental conditions in the process of resonant spontaneous bremsstrahlung radiation of ultrarelativistic electrons on nuclei in an external electromagnetic field. These special experimental conditions determine the characteristic energy of the electrons. This characteristic energy should be significantly less than the energy of the initial electrons. Under these conditions, spontaneous gamma quanta are emitted in a narrow cone with energies close to the energy of the initial electrons. Moreover, the resonant differential cross-sections of such processes can exceed the corresponding differential cross-section without an external field by twenty orders of magnitude. The results obtained can explain the occurrence of high-energy gamma quanta near pulsars and magnetars.

New phenomena in laser-assisted leptonic decays of the negatively charged boson W −

The majority of studies and experiments performed at electron-positron colliders over the last two decades have focused on studying W and Z weak force-carrying bosons and accurately measuring all their properties, not only because they play an important role in establishing Standard Model theory and providing an accurate test of its predictions of particle interactions, but also because they are a unique tool for probing manifestations of the new physics beyond the standard model. Therefore, it would be particularly important to discuss some of the new phenomena and changes that can arise in these bosons when their decay occurs under an external electromagnetic field. In a recent paper, we investigated the laser effect on the final products of Z boson decay and found that laser had an unprecedented effect on branching ratios. In this work and within the standard Glashow-Weinberg-Salam model of electroweak interactions, we study theoretically the leptonic decay of the W −-boson in the presence of a circularly polarized electromagnetic field and we examine the laser effect, in terms of its field strength and frequency, on the leptonic decay rate and the phenomenon of multiphoton processes. The calculations are carried out using the exact relativistic wave functions of charged particles in an electromagnetic field. It was found that the laser significantly contributed to reducing the probability of W −-boson decay. We show that the laser-assisted decay rate is equal to the laser-free one only when the famous Kroll-Watson sum rule is fulfilled. The notable effect of the laser on the leptonic decay rate was reasonably interpreted by the well-known quantum Zeno effect or by the opening of channels other than leptonic ones to decay. This work will pave the way for an upcoming one to study the hadronic decay of the W −-boson and then explore the laser effect on its lifetime and branching ratios.

Externally driven plasma models as candidates for pulsar radio emission

ABSTRACT Coherent radio emission from pulsars originates from excited plasma waves in an ultra-relativistic and strongly magnetized electron–positron pair plasma streaming along the open magnetic field lines of the pulsar. Traditional coherent radio emission models have relied on instabilities in this pair plasma. Recently, alternative models have been suggested. These models appeal to direct coupling of the external electromagnetic field to the superluminal O-mode (lt2 mode) during the time-dependent pair cascade process at the polar gap. The objective of this work is to provide generic constraints on plasma models based on lt2 mode using realistic pulsar parameters. We find that the very short time-scale associated with pair cascades does not allow lt2 mode to be excited at radio frequencies and the impulsive energy transfer can only increase the kinetic spread (‘temperature’) of the pair plasma particles. Moreover, under homogeneous plasma conditions, plasma waves on both branches of O mode (i.e. superluminal lt2 and subluminal lt1) cannot escape the plasma. In the strongly magnetized pair plasma, only the extraordinary mode (t mode) can escape freely. We show that any generic fictitious mechanisms do not result in the wave electric field of t mode to have predominant orientation either parallel or perpendicular to the magnetic field plane as observed. Such fictitious mechanisms will inevitably lead to depolarization of signals and cannot account for the highly polarized single pulses observed in pulsars. We suggest coherent curvature radiation as a promising candidate for pulsar radio emission mechanism.

Constitutive relations of a chiral hadronic fluid

We study the role of nonabelian anomalies in relativistic fluids. To this end, we compute the local functional that solves the anomaly equations, and obtain analytical expressions for the covariant currents and the Bardeen–Zumino terms. We particularize these results to a background with two flavors, and consider the cases of unbroken and broken chiral symmetry. Finally, we provide explicit results for the constitutive relations of chiral nuclear matter interacting with external electromagnetic fields and in presence of chiral imbalance. We emphasize the nondissipative nature of the chiral electric effect.

Algebra of the Symmetry Operators of the Klein–Gordon–Fock Equation for the Case When Groups of Motions G3 Act Transitively on Null Subsurfaces of Spacetime

The algebras of the symmetry operators for the Hamilton–Jacobi and Klein–Gordon–Fock equations are found for a charged test particle, moving in an external electromagnetic field in a spacetime manifold on the isotropic (null) hypersurface, of which a three-parameter groups of motions acts transitively. We have found all admissible electromagnetic fields for which such algebras exist. We have proved that an admissible field does not deform the algebra of symmetry operators for the free Hamilton–Jacobi and Klein–Gordon–Fock equations. The results complete the classification of admissible electromagnetic fields, in which the Hamilton–Jacobi and Klein–Gordon–Fock equations admit algebras of motion integrals that are isomorphic to the algebras of operators of the r-parametric groups of motions of spacetime manifolds if (r≤4).

Axial-Current Anomaly in Euler Fluids.

We argue that a close analog of the axial-current anomaly of quantum field theories with fermions occurs in the classical Euler fluid. The conservation of the axial current (closely related to the helicity of inviscid barotropic flow) is anomalously broken by the external electromagnetic field as ∂_{μ}j_{A}^{μ}=2E·B, similar to that of the axial current of a quantum field theory with Dirac fermions, such as QED.

Algebras of integrals of motion for the Hamilton–Jacobi and Klein–Gordon–Fock equations in spacetime with four-parameter groups of motions in the presence of an external electromagnetic field

The algebras of the integrals of motion of the Hamilton–Jacobi and Klein–Gordon–Fock equations for a charged test particle moving in an external electromagnetic field in a spacetime manifold are found. The manifold admits four-parameter groups of motions that act nontransitively on the spacetime. All admissible electromagnetic fields for which such algebras exist are found. In the case of an arbitrary n-dimensional Riemannian space on which the groups of motions act, it is proved that the admissible field does not deform the algebra of symmetry operators of the free Hamilton–Jacobi and Klein–Gordon–Fock equations. In addition, the system of differential equations, which must be satisfied by the potentials of the admissible electromagnetic field, has been investigated for compatibility.

Higgs boson production and quark scattering amplitudes at high energy through the next-to-next-to-leading power in quark mass

We study the amplitudes of the quark scattering by an external electromagnetic field and of the light quark mediated Higgs boson production via gluon fusion in the high-energy limit. The asymptotic behavior of the quark form factors is obtained in the double-logarithmic approximation to all orders in strong coupling constant through mathcal{O}left({m}_q^3right) in the small quark mass expansion and the asymptotic formula is given in a closed analytic form. In the case of the two-gluon Higgs boson form factor we obtain a complete analytic result for the three-loop mathcal{O}left({m}_q^3right) double-logarithmic term while the all-order analysis is performed in the large-Nc limit of QCD and for the abelian gauge group. An estimate of the high-order high-power light quark mass effect in the Higgs boson production and decay is given.

Spinor Field Singular Functions in QED with Strong External Backgrounds

We construct and study singular functions in strong-field $QED$ with two external electromagnetic fields that represent principally different types of external backgrounds, the first one belongs to the class of so-called $t$-potential electric steps (electric-like fields that are switched on and off at initial and final time instants), and the second one belongs to the class of so-called $x$-potential electric steps (time-independent electric-like fields of constant direction that are concentrated in a restricted spatial area). As the first background ($T$-constant electric field) is chosen an uniform electric field which acts during a finite time interval $T$ , whereas as the second background ($L$-constant electric field) is chosen a constant electric field confined between two capacitor plates separated by a large distance $L$. For the both cases we find \textrm{in}- and \textrm{out}-solutions of the Dirac equation in terms of light cone variables. With the help of these solutions, we construct Fock-Schwinger proper-time integral representations for all the singular functions that provide nonperturbative (with respect to the external backgrounds) calculations of any transition amplitudes and mean values of any physical quantities. Considering calculations in the $T$-constant field and in the $L$-constant field as different regularizations of the corresponding calculations in the constant uniform electric field, we have demonstrated their equivalence for sufficiently large $T$ and $L$.

On the Equivalence of Causal Propagators of the Dirac Equation in Vacuum-Destabilising External Fields

In QED, an external electromagnetic field can be accounted for non-perturbatively by replacing the causal propagators used in Feynman diagram calculations with Green’s functions for the Dirac equation under the external field. If the external field destabilises the vacuum, then it is a difficult problem to determine which Green’s function is appropriate, and multiple approaches have been developed in the literature whose equivalence, in many cases, is not clear. In this paper, we demonstrate for a broad class of external fields that includes all that act for a finite time, that four Green’s functions used in the literature are equivalent: Schwinger’s “proper-time” propagator; the “causal propagator” used in the “Bogoliubov transformation” method based on the canonical quantization of the field operator; and two defined using analytic continuation from complexified parameters. To do so, we formulate Schwinger’s “proper-time quantum mechanics" as a Schrödinger wave mechanics, and use this to re-derive Schwinger’s expression for the propagator as a statement relating solutions of the inhomogeneous Dirac equation to those of the inhomogeneous “proper-time Dirac equation”. This is done by constructing direct integral spectral decompositions of the Hamiltonians of both equations, and deriving a form for solutions of the inhomogeneous Dirac equation in terms of these decompositions. We then show that all four propagators return solutions of the inhomogeneous Dirac equation that satisfy the same boundary condition, which under a physically reasonable assumption is sufficient to specify the solution uniquely.

Cracking features of asphalt mixtures under induced heating-healing

This research presents effects of induced heating-healing process on fracture properties and life extension of asphalt mixtures. Induced heating-healing technique is an innovative technique to repair damages and heal cracks in asphalt mixtures, implementing an external electromagnetic field to raise temperature of asphalt mixture. Temperature rising results in melting and flowing of asphalt binder between crack edges, healing cracks, and recovering internal strength of asphalt mixture lost during service life. Previous researchers considered different criteria to quantify induced healing efficiency in asphalt concrete, resulting in substantial differences. Nevertheless, conclusions presented by previous researchers are not comparable due to different materials, heating, healing, and testing conditions. Hence, a further study is needed to identify induced healing effectiveness based on asphalt mixtures form different binder grades. In this study, activated carbon modified and unmodified asphalt binders were utilized to prepare asphalt mixtures. Then, a cyclic heating-healing scenario under semi-circular bending (SCB) test was conducted at intermediate and low temperatures. Values of the fracture criteria (i.e., peak load, stress intensity factor, stiffness, strain energy, critical strain energy release rate, and fracture energy) were quantified at each cycle. Besides, extensions of fatigue and thermal fatigue lives obtained via induced healing process were characterized. Comparing results of modified and unmodified mixtures indicates that activated carbon significantly improves efficacy of induced healing. Additionally, induced healing process leads to different effects on different crack features. Moreover, induced healing efficiencies obtained based on fatigue and thermal fatigue extensions are approximately similar to that of peak load criterion. This study indicates that to evaluate effects of induced heating-healing process on improvement of different mechanical behaviors in asphalt mixtures over service life, corresponding crack property (criteria) needs to be considered.

Electromagnetic Field Evolution in Relativistic Heavy Ion Collision and Its Effect on Flow of Particles

We compute the electromagnetic fields generated in relativistic heavy-ion collisions using the iEBE-VISHNU framework. We calculated the incremental drift velocity from the four possible sources of electric force (coulomb, Lorentz, Faraday, and plasma-based) on the particles created. The effect of this external electromagnetic field on the flow harmonics of particles was investigated, and we found out that the flow harmonics values get suppressed and rouse in a non-uniform fashion throughout the evolution. More precisely, a maximum of close to 3% increase in elliptic flow was observed. We also found mass as the more dominant factor than charges for the change in flow harmonics due to the created electromagnetic field. On top of that, the magnetic field perpendicular to the reaction plane is found to be sizable, while the different radial electric forces were found to cancel out each other. Finally, we found out that the inclusion of electromagnetic field affects the flow of particles by suppressing or raising it in a non-uniform fashion throughout the evolution.

Theoretical Study of Light-Induced Crosslinking Reaction Between Pyrimidine DNA Bases and Aromatic Amino Acids

Low-lying electronic excited states and their relaxation pathways as well as energetics of the crosslinking reaction between uracil as a model system for pyrimidine-type building blocks of DNA and RNA and benzene as a model system for aromatic groups of tyrosine (Tyr) and phenylalanine (Phe) amino acids have been studied in the framework of density functional theory. The equilibrium geometries of the ground and electronic excited states as well as the crossing points between the potential energy surfaces of the uracil–benzene complex were computed. Based on these results, different relaxation pathways of the electronic excited states that lead to either back to the initial geometry configuration or the dimerization between the six-membered rings of the uracil–benzene complex have been identified, and the energetic conditions for their occurrence are discussed. It can be concluded that the DNA–protein crosslinking reaction can be induced by the external electromagnetic field via the dimerization reaction between the six-membered rings of the uracil–benzene pair at the electronic excited-state level of the complex. In the case of the uracil–phenol complex, the configuration of the cyclic adduct (dimerized) conformation is less likely to be formed.

Mitigation of Electro Magnetic Interference by Using C-Shaped Composite Cylindrical Device

The extremely low-frequency (ELF) and its corresponding electromagnetic field influences the yield of CMOS processes in the foundry, especially for high-end equipment such as scanning electron microscopy (SEM) systems, transmission electron microscopy (TEM) systems, focused ion beam (FIB) systems, and electron beam lithography (E-Beam) systems. There are several techniques to mitigate electromagnetic interference (EMI), among which active shielding systems and passive shielding methods are widely used. An active shielding system is used to generate an internal electromagnetic field to reduce the detected external electromagnetic field in electric coils with the help of the current. Although the active shielding system reduces the EMI impact, it induces an internal electromagnetic field that could affect the function of nearby tools and/or high-performance probes. Therefore, in this study, we have used a C-shaped cylindrical device combined with an active shielding system and passive shielding techniques to reduce EMI for online monitoring and to overcome the aforementioned issues. In this study, the active shielding system was wrapped with a permalloy composite material (i.e., a composite of nickel and iron alloy) as a tubular device. A C-shaped opening was made on the tubular structure vertically or horizontally to guide the propagation of the electromagnetic field. This C-shaped cylindrical device further reduced electromagnetic noise up to −5.06 dB and redirected the electromagnetic field toward the opening direction on the cylindrical device. The results demonstrated a practical reduction of the electromagnetic field.

Intergranular corrosion of AISI 347 stainless steel welds obtained under electromagnetic interaction of low intensity

The electromagnetic interaction of low intensity (EMILI) induced by the application of external electromagnetic fields of low intensity (EMFLI) during fusion welding of AISI 347 stainless steel improved the resistance to intergranular corrosion (RIGC). Microstructural observations and electrochemical methods were used to determine the metallurgical condition related to the enhanced RIGC. EMILI reduced the degree of sensitization (DOS) at the heat affected zone (HAZ) as compared to plain welds. EMILI induced Cr redistribution in the γ-matrix during welding, reducing the formation of δ-ferrite and minimizing Cr depletion.

Discrete hybrid Izhikevich neuron model: Nodal and network behaviours considering electromagnetic flux coupling

We analyse the dynamics of the improved discretised version of the well known Izhikevich neuron model under the action of external electromagnetic field. It is found that the improved three dimensional IZH map shows rich dynamics. With the variation of the electromagnetic field, period-doubling route to chaos in a repeating fashion is observed from the bifurcation diagram. Even the forward and backward continuation bifurcation diagram which do not completely overlap suggests that there is multistability in the system. The phenomenon of bistability (coexistence of periodic and chaotic attractors) is observed. The presence of periodic and chaotic attractor is aided by the maximal Lyapunov exponent diagram. The Lyapunov phase diagram of electromagnetic field and synapses current shows a large parameter region of chaotic and periodic behaviours with the presence of unbounded regions as well. The IZH map shows a plethora of spiking and bursting patterns such as mixed-mode patterns, tonic spiking, phasic spiking, steady spikes, regular spikes, spike bursting, periodic bursting, phasic bursting, chaotic firing etc with the variation of electromagnetic coupling strength and the synapses current. We also investigate the presence of chimera states in a ring-star, ring, star networks of IZH map neurons. Chimera states are found in the case of ring-star and ring network while synchronised clusters were found in the case of star network and are aided by the spatiotemporal plots, space-time plot, recurrence plots. The rich dynamics shown by the discretised IZH map makes it a promising research model to study about neurodynamics.

Mechanism analysis of magnetohydrodynamic control in hypersonic turbulent flow

Under the assumption of the low magnetic Reynolds number, the coupled model is established for the turbulent flow field and the externally applied magnetic field. The AUSMPW+ scheme and LUSGS method are used to solve turbulent magnetohydrodynamics (MHD) flow equations, in which the Spalart-Allmaras one-equation turbulence model is used. A series of numerical simulations over various geometry configurations, namely, a flat plate and a compression corner, is conducted by using an external electromagnetic field. Results show that the performance of MHD boundary layer flow control is determined mainly by the Lorentz force in the streamwise direction. With an external magnetic field used, the low velocity fluid in the boundary layer can decelerate and increase the static temperature locally. Moreover, the counter-flow Lorentz force always brings a negative effect on the turbulent skin friction coefficient, and the location for the MHD zone has a great influence on the control efficiency of the ramp-induced separation. A reasonable magnetic field layout scheme should be configured in practical engineering application.

Hybrid nonlinear resonance in Hamiltonian systems.

An electronic system in an atom can be considered Hamiltonian only at times shorter than the spontaneous relaxation time. However, this time is sufficient for resonant action on the electronic system and for the implementation of the resonance inherent in Hamiltonian systems. In practice, there may be a case when it is expedient to use a hybrid approach to study nonlinear resonance, in which the classical theory can be used to calculate the action-dependent nonlinear resonance frequency, and the quantum theory can be used to calculate its correction. The use of such a hybrid approach becomes necessary when the resonant value of the action does not exceed Planck's constant many times. It is shown in the work that if the external electromagnetic field has the form of a periodic series of light pulses with a high duty cycle, then the phenomenon of nonlinear hybrid resonance leads to the appearance of a line in the low-frequency region of the electronic spectrum. The broadening of this line is determined using the rms quantum fluctuations.

Modeling of Bound Electron Effects in Particle-in-Cell Simulation

To include the bound electron effects in particle-in-cell (PIC) simulation, we propose a model in which the response of the dipole components of partially ionized ions to external electromagnetic fields can be included. Instead of treating the macro-ion particle as a single particle without an internal structure, the ions are considered to have a structure composed of a central nucleus and a bounded electron cloud in our model. The two parts experience the interactions of both the external electromagnetic fields and the internal Coulomb fields. In this way, the laser scattering effects by a partially ionized medium can be modeled properly in the PIC simulation. The laser propagation in a neutral medium and the Bragg scattering of the laser in crystal structure have been simulated with a PIC code modified based on our model as the benchmark. Our model may find applications to study some interesting problems, such as the x-ray laser-driven wakefield acceleration in crystals, the x-ray laser-driven high energy density physics, and intense laser propagation in partially ionized nonlinear optical materials, etc.

SIMULATION OF THE P-I-N-STRUCTURES CHARACTERISTICS INTERACTING WITH HIGH-FREQUENCY ELECTROMAGNETIC RADIATION BY PERTURBATION THEORY METHODS

The mathematical model is proposed for the electron-hole plasma characteristics predicting of the active region (i-region) of p-i-n structures, taking into account the effect of the displacement current (induced by an external microwave electromagnetic field) on the formation of a space charge. The model is based on a singularly perturbed nonlinear boundary value problem for the system of the electron-hole current continuity equations and Poisson’s (the Poisson’s equation contains a naturally formed small parameter). The model nonlinear boundary value problem is reduced to a recurrent sequence of linear boundary value problems for determining of the electron-hole plasma concentrations and the electric potential distributions in the i-region by using asymptotic methods, in particular, the boundary layer method and complex amplitudes. The proposed mathematical model feature is that it reflects the role of the boundary layer in the p-i-n structure contact zones in the formation of a space charge and takes into account the effect of a displacement current caused by microwave radiation. An algorithm for predicting the charge carrier concentrations distribution in the electron-hole plasma is constructed. It is shown that an extraneous microwave field entails an additional increase in the stationary concentration of electrons and holes in the active region, against which the plasma concentration fluctuates at the microwave field frequency (the appearance of higher harmonics is not taken into account in the model). The effect of the growth of the concentration stationary component is more pronounced in the zones of p-i-, n-i-contacts. The proposed mathematical model and the developed algorithm for analyzing the problem posed are important for developers of microwave electronics semiconductor elements, in particular, p-i-n structures used for switching powerful electromagnetic fields and as protective devices for the input paths of radio engineering systems.