Magnetic Monopoles Research Articles

Electromagnetic energy transfer processes in effective electro-magneto dynamics of axions

Oscillating and dissipative energy exchange between the electromagnetic and axion fields is investigated in an effective electro-magneto dynamical (EEMD) model theory, implying the coexistence of axions with hypothetic magnetic charges. An exact formula is presented for the energy transfer between the electromagnetic and axionic sectors. In a first example, we compute analytically the homogeneously oscillating electric and magnetic field configurations generated by the combined action of a constant static magnetic field and a periodically oscillating axion condensate. In the second example, the electromagnetic radiative energy loss of a gravitationally bound axion configuration is computed in the EEMD model. As a result, an asymptotic [Formula: see text] temporal increase of the clump size is found also in EEMD.

Conformal hairy black holes of quartic quasi-topological gravity with power-Yang–Mills source

We study higher dimensional hairy black holes of quartic quasi-topological gravity in the framework of non-abelian power-Yang–Mills theory. It is shown that real solutions of the gravitational field equations exist only for positive values of quartic quasi-topological coefficient. Depending on the values of the mass, conformal coupling constants, quasi-topological coefficients, Yang–Mills magnetic charge, and nonlinearity parameter, they can be interpreted as black holes with one horizon, at most three horizons and naked singularity. It is also shown that the solution associated with these black holes has an essential curvature singularity at the centre r=0. Thermodynamic and conserved quantities for these hairy black holes are computed and we show that the first law has been verified. We also check thermodynamic stability in both canonical and grand canonical ensembles. In addition to this, we also formulate new power-Yang–Mills hairy black hole solutions in pure quasi-topological gravity. The physical and thermodynamic properties of these black holes are discussed as well. It is concluded that unlike Yang–Mills black holes without scalar hair there exist stability regions for the power-Yang–Mills hairy black holes in grand canonical ensemble. Finally, we discuss the thermodynamics of horizon flat power-Yang–Mills rotating black branes and analyze their thermodynamic and conserved quantities by using the counter-term method inspired by AdS/CFT correspondence.

Gravitational capture of magnetic monopoles by primordial black holes in the early universe

It is intriguing to ask whether the existence of primordial black holes (PBHs) in the early universe could significantly reduce the abundance of certain stable massive particles (SMP) via gravitational capture, after which the PBHs evaporate before BBN to avoid conflict with stringent bounds. For example, this mechanism is relevant to an alternative solution of the monopole problem proposed by Stojkovic and Freese, in which magnetic monopoles produced in the early universe are captured by PBHs, thus freeing inflation from having to occur during or after the corresponding phase transitions that produced the monopoles. In this work, we reanalyze the solution by modelling the capture process in the same way as the coexisting monopole annihilation. A subtle issue which is not handled properly in the previous literature is the choice of an effective capture cross section for diffusive capture. We model this aspect properly and justify our treatment. A monochromatic PBH mass function and a radiation-dominated era before PBH evaporation are assumed. We find that for Pati-Salam monopoles corresponding to a symmetry breaking scale between 1010 GeV and 1015 GeV, the capture rate is many orders of magnitude below what is needed to cause a significant reduction of the monopole density. Within our assumptions, we also find that the magnetic charge that is large enough to make an extremal magnetic black hole cosmologically stable cannot be obtained from magnetic charge fluctuation via monopole capture. The large magnetic charged required by cosmological stability can nevertheless be obtained from magnetic charge fluctuation at PBH formation, and if later the monopole abundance can be reduced significantly by some non-inflationary mechanism, long-lived near-extremal magnetic black holes of observational relevance might result.

Constraints, symmetry transformations and conserved charges for massless Abelian 3-form theory

We demonstrate the existence of the first-class constraints on the massless Abelian 3-form theory which generate the classical gauge symmetry transformations for this theory in any arbitrary D-dimension of spacetime. We write down the explicit expression for the generator in terms of these first-class constraints. Using the celebrated Noether theorem, corresponding to the gauge symmetry transformations, we derive the Noether conserved current and conserved charge. The latter is connected with the first-class constraints of the theory in a subtle manner as we demonstrate clearly in our present investigation. We comment on the first-class constraints within the framework of Becchi-Rouet-Stora-Tyutin (BRST) formalism where the conserved (anti-)BRST charges are the generalizations of the above generator for the classical gauge symmetry transformation. The standard Noether conserved (anti-)BRST charges are found to be non-nilpotent. We derive the nilpotent versions of the (anti-)BRST charges. One of the interesting observations of our present endeavor is the result that only the nilpotent versions of the conserved (anti-)BRST charges lead to the annihilation of the physical states by the operator form of the first-class constraints at the quantum level which is consistent with the Dirac quantization condition for the systems that are endowed with any kind of constraints. We comment on the existence of the Curci-Ferrari (CF) type restrictions from different theoretical angles, too.

Diode type unidirectional conduction in Hall measurement of magnetic honeycomb lattice

Artificial magnetic honeycomb lattice is emerging as a new platform for spintronics research applications, as evidenced from recent findings of magnetic diode effect and collective magnetic switching phenomena in different lattice geometries. In this report, we present Hall measurements on thermally tunable artificial magnetic honeycomb lattice. Experimental investigation using detailed Hall probe measurements reveals diode-type unidirectional conduction in both longitudinal and Hall resistances. The unidirectional conduction persists to low temperature but remains unaffected to modest application of perpendicular magnetic field. The behavior can be understood in terms of topological magnetic charges that arise on the vertices of honeycomb lattice and affect electrical transport properties. The experimental finding can be utilized for the design of spintronic logic devices.

Magnetic monopole becomes dyon in topological insulators

Magnetic monopole becomes dyon in topological insulators

Strain-controlled spin transport in a two-dimensional (2D) nanomagnet

Semiconductors with controllable electronic transport coupled with magnetic behaviour, offering programmable spin arrangements present enticing potential for next generation intelligent technologies. Integrating and linking these two properties has been a long standing challenge for material researchers. Recent discoveries in two-dimensional (2D) magnet shows an ability to tune and control the electronic and magnetic phases at ambient temperature. Here, we illustrate controlled spin transport within the magnetic phase of the 2D semiconductor CrOBr and reveal a substantial connection between its magnetic order and charge carriers. First, we systematically analyse the strain-induced electronic behaviour of 2D CrOBr using density functional theory calculations. Our study demonstrates the phase transition from a magnetic semiconductor → half metal → magnetic metal in the material under strain application, creating intriguing spin-resolved conductance with 100% spin polarisation and spin-injection efficiency. Additionally, the spin-polarised current–voltage (I–V) trend displayed conductance variations with high strain-assisted tunability and a peak-to-valley ratio as well as switching efficiency. Our study reveals that CrOBr can exhibit highly anisotropic behaviour with perfect spin filtering, offering new implications for strain engineered magneto-electronic devices.

4D Einstein-Gauss-Bonnet black hole in Power-Yang-Mills field: a shadow study

We consider a static black hole immersed in the Power-Yang-Mills field in four-dimensional Einstein-Gauss-Bonnet gravity and investigate the effect of various parameters on the radius of the photon sphere. The modified form of the Newman-Janis algorithm is used for obtaining a rotating black hole solution in this gravity. Further, we try to explore the influence of the Yang-Mills magnetic charge Q with power q, Gauss-Bonnet parameter α, and spin a on the horizon radius. The geodesic equations are constructed by incorporating the Hamilton-Jacobi formalism. The radial component of the geodesic equations gives the effective potential which is further used in deriving the mathematical structure for the shadows by using Bardeen's procedure for a fixed observer at infinity. The shadows are calculated and plotted in terms of two celestial coordinates for an equatorial observer. It is observed that all the parameters have a very significant effect on the shadow and related physical observables. We also obtain the constraint values for the spin, magnetic charge, and Gauss-Bonnet parameters, using the shadow size of supermassive black holes Sagittarius A* and M87* from the EHT observations for the cases of q = 0.6 and q = 0.9. It is shown that there are upper and lower bounds for the charge and spin of M87* at q = 0.6, while only the upper bounds for the charge and spin of Sagittarius A*. Finally, we investigate the energy emission rate in the Hawking radiation around the 4D Einstein-Gauss-Bonnet black hole in the Power-Yang-Mills field.

A Planar Electromagnetic Actuator With Passive Adsorption for CubeSats Transport in a Weightless Environment

A planar electromagnetic actuator (PEA) with passive adsorption is proposed to transport multiple miniature satellites (CubeSats) in a weightless environment. It can realize reliable mover adsorption to the track and fast 2-Dof translational motion, even under the interference of external acceleration. Compared with the conventional layout of permanent magnets (PMs), the PEA with the structure of Halbach array can achieve higher force density. The magnetic equivalent circuits (MEC) method is applied to reveal the mechanism of electromagnetic performance improvement. An accurate electromagnetic force model is developed by combining the MEC and mirror magnetic charge methods to consider the positive effects of yokes on the PM operating point and airgap magnetic field distribution for PEAs with large airgaps. The influence of main structural parameters on adsorption and driving performances is analyzed. A kinetic model is derived to predict the mover velocity. A PEA prototype has been manufactured and tested to experimentally validate the improved models, electromagnetic performance, and motion characteristics.

Pairwise helicity in higher dimensions

Studies of scattering amplitudes for electric and magnetic charges have identified previously overlooked multiparticle representations of the Poincaré group in four dimensions. Such representations associate nontrivial quantum numbers (known as pairwise helicities) with asymptotically separated pairs of particles, and thus cannot be described as tensor products of one-particle states. We extend this construction to sources and spacetimes of higher dimension. We first establish the dynamical origin of pairwise helicity in [Formula: see text]-form electrodynamics coupled to mutually nonlocal branes. We then interpret this pairwise helicity as a quantum number under an SO(2) pairwise little group associated with pairs of distinct branes. We further characterize the “higher” little groups that could in principle be used to induce multiparticle or multi-brane representations of the Lorentz group.

Generalized half-dyon in SU(2) Yang–Mills–Higgs theory

In this paper, we report on generalized half-dyon solutions in SU(2) Yang–Mills–Higgs theory, namely Type I and Type II solutions. These solutions are constructed by considering [Formula: see text]-winding number [Formula: see text], electric charge parameter [Formula: see text] and Higgs self-coupling constant [Formula: see text]. They represent system of magnetic charge [Formula: see text] ([Formula: see text]) and electric charge [Formula: see text] that lies along the negative (positive) [Formula: see text]-axis. Fundamental properties, such as total energy, electric charge, dipole moment, are explored and discussed.

Analysis of output characteristics of wireless power transfer system based on LCC/S-S hybrid compensation structure

PurposeTo simplify the circuit design and control complexity of the magnetic coupling resonant wireless charging system, the radio energy transmission constant current and constant voltage charging is realized.Design/methodology/approachThe purpose of this study is to simplify the circuit design and control complexity of the magnetic coupling resonance wireless charging system, in order to achieve constant current and constant voltage charging for wireless energy transmission. First, the principle of LCC/S-S compensation structure is analyzed, and the equivalent mathematical model is established; then, the system characteristics under constant current and constant voltage mode are analyzed, and the design method of system parameters is given; finally, a simulation and experimental system is built to verify the correctness and feasibility of the theoretical analysis.FindingsThe results show that the proposed hybrid topology can achieve a constant current output of 2 A and a constant voltage output of 30 V under variable load conditions, and effectively suppress the current distortion problem under light load conditions. The waveform distortion rate of the inverter current is reduced from 33.97% to 10.45%.Originality/valueBy changing the high-order impedance characteristics of the compensation structure, the distortion of the current waveform under light load is suppressed, and the overall stability and efficiency of the system are improved.

Computational analysis of thin-shell with scalar field for class of new black hole solutions in metric-affine gravity

The aim of this study is to investigate the geometric structure of a thin-shell within the context of metric-affine gravity. To accomplish this, we employ a cut and paste approach to match the inner Minkowski spacetime and an outer newly calculated class of black hole solutions in metric-affine gravity. These solutions are Reissner–Nordström-like black holes with shear, spin, dilation, electric, magnetic charges, and a cosmological constant. Using the Klein–Gordon equation of motion, we analyze the dynamics of the thin-shell configuration under both massive and massless scalar fields. We find that the scalar field affects thin-shell dynamics and can lead to interesting effects such as dynamics and stability configurations. We demonstrate that the linearized radial perturbation approach employing a phantom-like equation of state, such as quintessence, dark energy, and phantom energy, reveal stable configurations of the thin-shell located beyond the expected position of the event horizon of the exterior manifold. We also find that the stability of the thin-shell depends strongly on the parameters of the black hole solutions. Our results shed light on the dynamics of thin-shells in the context of metric affine gravity with scalar fields and provide new insights into the behavior of black hole solutions in this theory. It is concluded that the thin-shell composed of quintessence and dark energy shows the more stable configuration for the choice of Reissner-Nordström-like black holes with shear, spin, and dilation charges.

A resolution of the monopole problem in the Rh = ct Universe

Spontaneous symmetry breaking in grand unified theories is thought to have produced an exceedingly large number of magnetic monopoles in the early Universe. In the absence of suppression or annihilation, these very massive particles should be dominating the cosmic energy budget today, but none has ever been found. Inflation was invented in part to dilute their number, thereby rendering their density undetectable by current instruments. Should the inflationary paradigm not survive, however, the ensuing disagreement between theory and observation would constitute a cosmological ‘monopole problem’ and create further tension for any extension to the standard model of particle physics. But as is also true for all horizon problems, a monopole overabundance emerges only in cosmologies with an initial period of deceleration. We show that the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the Rh=ct universe completely eliminates all such anomalies rather trivially and naturally, without the need for an inflated expansion. We find that the monopole energy density today would be completely undetectable in Rh=ct. Evidence continues to grow that the zero active mass condition from general relativity ought to be an essential ingredient in ΛCDM.

Artificial Magnetic Tripod Ice.

We study the collective behavior of interacting arrays of nanomagnetic tripods. These objects have six discrete moment states, in contrast to the usual two states of an Ising-like moment. Our experimental data demonstrate that triangular lattice arrays form a "tripod ice" that exhibits charge ordering among the effective vertex magnetic charges, in direct analogy to artificial kagome spin ice. The results indicate that the interacting tripods have effective moments that act as emergent local variables, with strong connections to the well-studied Potts and clock models. In addition, the tripod moments display a tendency toward a nearest neighbor alignment in our thermalized samples that separates this system from kagome spin ice. Our results open a path toward the study of the collective behavior of nonbinary moments that is unavailable in other physical systems.

Exact multicentered static point charge source distributions in the Born–Infeld theory of nonlinear electromagnetism and presence of electric and magnetic currents

Exact multicentered solutions to the governing equations of the Born–Infeld nonlinear theory of electrodynamics describing distributions of electric, magnetic, and dyonic point charge sources are constructed explicitly for the first time. The method of construction may effectively be adapted to obtain such solutions in generalized theories as well. As a consequence, the solutions unveil that, in order to achieve a balance between such multicentered electric or magnetic point charge distribution in equilibrium, a static magnetic or electric current must be present, resulting in non-conservativeness of the induced electric or magnetic intensity field, respectively and universally. Moreover, it is also shown that the methods of construction and conclusions drawn in the multicentered situation may be extended to obtain exact solutions and similar conclusions, explicitly, in the situation of continuously distributed charge source problems.

Rotating Bardeen black hole surrounded by perfect fluid dark matter as a particle accelerator

We study the event horizon of a rotating Bardeen black hole surrounded by perfect fluid dark matter and the black hole as a particle accelerator. The black hole is represented by four parameters: mass M, rotation parameter a, dark matter parameter α and magnetic charge g. It is interesting that when we determine the values of magnetic charge g and dark matter parameters α we can get a critical rotation parameter a E and then we get a contour plane with Δ = 0 taking three parameters as coordinates. We also derive the effective potential of the particle and the center-of-mass (CM) energy of the two particles outside the black hole by using the motion equations of the particle in the equatorial plane of the black hole. We find that the CM energy depends not only on the rotation parameter a, but also on the parameters g and α. We discuss the CM energy for two particles colliding at the black hole horizon in the extreme and non-extreme cases, respectively. It is found that the CM energy can become arbitrarily high when the angular momentum of one of the two particles is the critical angular momentum under the background of extreme black holes and there is no such result for non-extreme black holes, because the particles do not reach the black hole horizon when the angular momentum of the particles is critical angular momentum. Therefore, we prove that the rotating Bardeen black hole surrounded by perfect fluid dark matter can be used as a particle accelerator.

Observational appearance of Kaluza–Klein black holes

The optical properties of rotating black holes in Kaluza–Klein theory described by the total mass, spin, and electric and magnetic charges are investigated in detail. Using a developed general relativistic ray-tracing code to calculate the motion of photons, shadows of Kaluza–Klein black holes are generated. The properties of the shadow and the light deflection angle around these black holes are also studied in order to put constraints on the parameters of Kaluza–Klein black holes using M87* shadow observations. The possibility of imposing constraints on Kaluza–Klein black holes using shadow observations is investigated. Moreover, we find that small charges (electric and magnetic) of the black hole can meet these constraints. We conclude that with the current precision of the M87* black hole shadow image observation by the EHT collaboration, the shadow observations of Kaluza–Klein black holes are indistinguishable from that of the Kerr black hole. Much better observational accuracy than the current capabilities of the EHT collaboration are required in order to place verified constraints on the parameters of modified theories of gravity in the strong field regime.

Applicability of the 0–1 test for chaos in magnetized Kerr–Newman spacetimes

The dynamics of electrically neutral or charged particles around a magnetized Kerr–Newman black hole immersed in an external electromagnetic field can be described by a dimensionless Hamiltonian system. This Hamiltonian is given an appropriate time transformation, which allows for construction of explicit symplectic integrators. Selecting one of the integrators with good accuracy, long-term stabilized Hamiltonian error behavior and less computational cost, we employ the 0–1 binary test correlation method to distinguish between regular and chaotic dynamics of electrically neutral or charged particles. The correlation method is almost the same as the techniques of Poincaré map and fast Lyapunov indicators in identifying the regular and chaotic two cases. It can well describe the dependence of the transition from regularity to chaos on varying one or two dynamical parameters. From a statistical viewpoint, chaos occurs easily under some circumstances with an increase of the external magnetic field strength and the particle electric charge and energy or a decrease of the black hole spin and the particle angular momentum. A small change of the black hole electric charge does not very sensitively affect the dynamics of neutral particles. With the black hole electric charge increasing, positively charged particles do not easily yield chaotic motions, but negatively charged particles do. On the other hand, the effect of a small change of the black hole magnetic charge on the dynamical transition from order to chaos has no universal rule.

Static magnetic signature of a ghost-ship propulsor system as a composite ferromagnetic medium

In this paper, it is shown that the static magnetic signature of a propulsor belonging to a ghost ship, whose hull is made of fiberglass, can be calculated by regarding it as a composite ferromagnetic medium. The calculation of the magnetic signature in the static regime is carried out using finite-element method simulations and according to a simple analytical model based on the concepts of volume averaged magnetization arising from a source magnetic field, volume averaged permeability, surface magnetic charges, and the demagnetization tensor applied to a composite magnetic medium. Using targeted simulations, it is demonstrated that the magnetostatic field of demagnetizing nature forming inside the propulsor almost cancels the contribution of the volume averaged magnetization. From the interplay between the numerical simulations and the analytical model, the elements of the demagnetization tensor in the region filled by the propulsor are locally calculated, and their role in determining the localization effects of the magnetic signature is discussed. By replacing the original ferromagnetic materials with weakly ferromagnetic ones, it is shown that, in the underwater region outside the propulsor, the magnetic signature drop is 64%. This analysis suggests an experimental way to use a simple passive method to minimize the magnetic signature of a propulsor as an alternative to more complex and time-consuming methods, such as the deperming and degaussing methods, widely employed to reduce the magnetic signature of ships and underwater objects in military applications.