Electromagnetic Dipole Research Articles

On the low-energy electromagnetic dipole modes in 151,153,155Sm Nuclei

The recently observed low-energy magnetic dipole (M1) and electric dipole (E1) excitations in deformed 151,153,155Sm are theoretically analysed. Rotational Invariant (RI-) and Translational-Galilean Invariant (TGI-) Quasiparticle Nuclear Model (QPNM) are used in the calculation of M1 and E1 properties, respectively. Both theories consider monopole pairing between nucleons, and the deformed Woods-Saxon potential is used as the mean-field potential. Pyatov's symmetry restoration procedure is applied in these models to eliminate the spurious modes from the intrinsic nuclear excitations. Model calculations show that although E1 transitions dominate the low-energy dipole spectra of 151,153,155Sm, many low-lying M1 transitions exist in these nuclei. It is shown that the most significant contribution to E1 and M1 excitation comes from ΔK=±1 transitions. The theory satisfactorily reproduces the gross features of low-lying dipole modes determined from the Oslo Method analysis of the experimental spectra.

All-dielectric meta-surface transmission-mode ultra-thin GaAs negative electron affinity photocathode

Transmission-mode (t-mode) GaAs negative electron affinity photocathodes (NEA-PCs) can be integrated with the optical focusing lenses and microchannel plates to produce high-quality electron beams and high-sensitive detectors. Quantum efficiency (QE) of ∼40% has been reported for the t-mode thick (>1000 nm) GaAs NEA-PCs. Nevertheless, practical applications of these devices have been seriously restricted by their long response time (tens of picoseconds). In this work, the all-dielectric meta-surfaces (ADMS) were designed as the light managers for the t-mode ultra-thin GaAs NEA-PCs. For the 500–850 nm waveband, high light absorption (>80%) can be obtained through coupling the electromagnetic dipole moments of ADMS into the leaky optical modes in 100 nm ultra-thin GaAs NEA-PC layer, which leads to enhanced QE higher than that of the thick ones, the response time less than 5 ps, and the mean transverse energy less than 60 meV, respectively. Given these properties, ADMS t-model ultra-thin NEA-PCs represent a promising photocathode to provide the high-brightness short-pulse spin-polarized electron beams and high-sensitive fast-response detectors for the electron accelerator and low-light-level photodetection applications, respectively.

Cost‐Effective Conductive Paste for Radiofrequency Devices Using Carbon‐Based Materials

With the increasing demand for compact, lightweight, cost‐effective, and high‐performance radiofrequency (RF) devices, the development of low‐profile antennas becomes crucial. This article presents a study of a novel carbon–cellulose‐based paste intended for screen printing RF devices. The investigation specifically explores the application of high‐reactivity carbon mixture (HRCM) particles as conductive fillers. The results demonstrate that optimal electrical conductivity values and discrete electromagnetic dipole performances can be achieved at lower concentrations of solid conductive material compared to conventional pastes, for similar applications. This offers benefits in terms of total cost, material consumption, and environmental impact. The paste formulation showcases a complex non‐Newtonian behavior, where yielding flow and thixotropicity are found to be independent and dependent on preshear conditions, respectively. This behavior can be attributed to the network orientation and rearrangement of filler structures within the paste system, which in turn are responsible for filler pattern uniformity and overall printing quality. Compared to traditional conductive materials, HRCM pastes are proven to be a viable alternative for RF devices fabrication, including printed Wi‐Fi antennas.

Tunable wideband terahertz absorber based on single-layer patterned graphene

In this study, we propose and validate a broadband terahertz perfect absorber. The absorber has a simple structure, which consists of a gold (Au) substrate, a TOPAS dielectric layer and a patterned graphene layer. By the simulations, a broad absorption band can be obtained with a high absorption above 90% between 3.31 THz and 7.15 THz, and the relative bandwidth reaches 73.4%. Meanwhile, the absorption higher than 99% is between 3.81 THz and 6.6 THz with a relative bandwidth of 53.6%. The mechanism of the surface excited plasma (SPP) and electromagnetic dipole resonance are responsible for its almost perfect broadband absorption. By changing the Fermi energy level of the graphene layer, the flexible broadband absorption spectra can be acquired. By varying the geometrical parameters of the structure, a wider spectral range of absorption wavelengths can be realized. For both TE and TM polarization, the absorption can remain above 90% over a wide range of incidence angles. Due to the independent tunability and high absorption of the proposed device, it has great potential applications in terahertz imaging, smart absorption, detectors and communications.

Measuring glitch recoveries and braking indices with Bayesian model selection

ABSTRACT For a selection of 35 pulsars with large spin-up glitches ($\Delta {\nu }/\nu \ge 10^{-6}$), which are monitored by the Jodrell Bank Observatory, we analyse 157 glitches and their recoveries. All parameters are measured consistently and we choose the best model to describe the post-glitch recovery based on Bayesian evidence. We present updated glitch epochs, sizes, changes of spin down rate, exponentially recovering components (amplitude and corresponding time-scale) when present, as well as pulsars’ second frequency derivatives and their glitch-associated changes if detected. We discuss the different observed styles of post-glitch recovery as well as some particularly interesting sources. Several correlations are revealed between glitch parameters and pulsar spin parameters, including a very strong correlation between a pulsar’s interglitch $|\ddot{\nu }|$ and $\dot{\nu }$, as well as between the glitch-induced spin-down rate change $\Delta \dot{\nu }_{\rm p}$ that does not relax exponentially and $\dot{\nu }$. We find that the ratio $\left|\Delta \dot{\nu }_{\mathrm{p}}/\ddot{\nu }\right|$ can be used as an estimate of glitch recurrence times, especially for those pulsars for which there are indications of a characteristic glitch size and interglitch waiting time. We calculate the interglitch braking index n and find that pulsars with large glitches typically have n greater than 3, suggesting that internal torques dominate the rotational evolution between glitches. The external torque, for example, from electromagnetic dipole radiation, could dominate the observed $\ddot{\nu }$ for the youngest pulsars ($\lesssim 10^{4}\,\,\mathrm{yr}$), which may be expected to display $n\sim 3$.

Graphene-based terahertz tunable double-broadband perfect absorber

The rapid advancement of terahertz(THz) technology has sparked significant interest in exploring tunable broadband functional devices. In this study, we propose an antisymmetric graphene skeletonized structure to achieve a terahertz double-broadband perfect absorber. This absorber consists of a gold (Au) substrate, a TOPAS dielectric layer and C4 regular antisymmetric-patterned graphene embedded in the polymer. It exhibits two unpolarized perfect absorbing broadbands through the resonance mechanisms of localized surface-isolated exciton resonance and electromagnetic dipole resonance. The results indicate high absorbance exceeding 90% across two distinct frequency ranges of 0.93–2.03 THz and 4.16–5.3 THz. The dual-broadband absorption feature stems from the pronounced aggregation effect of the “Hollow-out corner” on the electric field, enabling modulation of the second Harmonic while leaving the first Harmonic largely unaffected. The absorber’s response can be dynamically tuned through adjusting the Fermi energy level and structural parameters of graphene. Our design opens up possibilities for diverse applications in photodetectors, THz modulation, and stealth technologies.

Top quark anomalous couplings from top-pair tagged photoproduction at pe− colliders

We summarize the quantitative results of our analysis [1] of top-pair photoproduction in semileptonic mode in pe collisions at the LHeC and FCC-he. We define three photoproduction regions, based on the rapidity acceptance range of the electron tagger, that provide different degrees of sensitivity to top-quark effective couplings. We focus on the ttγ dipole couplings and the left-handed vector tbW coupling, for which we determine limits at both energies in the different photoproduction regions. Furthermore, we find that the LHeC and FCC-he will yield tight direct bounds on top dipole moments, greatly improving on current direct limits from hadron colliders, and direct limits on the tbW coupling as restrictive as those expected from the HL-LHC. We also consider indirect limits from b → sγ branching ratio and CP asymmetry, that are well known to be very sensitive probes of top electromagnetic dipole moments.

Soft scattering evaporation of dark matter subhalos by inner galactic gases

The large gap between a galactic dark matter subhalo’s velocity and its own gravitational binding velocity creates the situation that small subhalos can be evaporated before dark matter thermalize with baryons due to the low binding velocity. In case dark matter acquires an electromagnetic dipole moment, the survival of low-mass subhalos requires stringent limits on the photon-mediated soft scattering. The current stringent direct detection limits indicate for a small dipole moment, which lets DM decouple early and allows small subhalos to form. We calculate the DM kinetic decoupling temperature in the Early Universe and evaluate the smallest protohalo mass. In the late Universe, low-mass subhalos can be evaporated via soft collision by ionized gas and accelerated cosmic rays. We calculate the subhalos evaporation rate and show that subhalos lighter than 10^{-5}M_{odot } in the gaseous inner galactic region are subject to evaporation via dark matter’s effective electric and magnetic dipole moments below current direct detection limits, which potentially affects the low-mass subhalos distribution in the galactic center.

Tunable high-Q metasurface for terahertz optical switching and sensing

We designed a metasurface for sensing and optical switching using an E-shaped bulk Dirac semimetal (BDS). The numerical results show that an extremely narrow Fano resonance can be achieved when terahertz waves are incident on the metasurface. At the Fano resonance frequency, the directions of the currents on the E-shaped BDS point towards the centre part, resulting in direct cancellation of the net dipole moment and suppression of electromagnetic dipole radiation. Owing to the overlap of the LSPR and diffraction mode frequencies on the E-shaped BDS, strong coupling can be achieved, resulting in photon energy confinement into the lattice units. In terms of tunable performance, by changing the Fermi energy of the BDS, narrowband optical switching with a modulation depth of 92.9% can be realised. In terms of sensing performance, our design is capable of achieving a sensitivity of 0.7 THz/RIU and FOM of 1178. In addition, our design is easier to prepare in the future by only consisting of E-shaped BDS and silicon substrate. The proposed design opens up possibilities for the development of multifunctional and ultrasensitive terahertz sensors, filters, and optical switching.

Testing neutrino dipole portal by long-lived particle detectors at the LHC

We discuss the potential of using detectors aimed for searching long-lived particles (LLP) at the high-luminosity LHC run, to probe the neutrino dipole models. This is achieved by taking the heavy neutral leptons (HNL) of the models as candidates of the LLPs. Taking into account the dipole couplings to the weak bosons, d_{W,Z}, which control the production of the HNLs at the LHC, we discuss the reach on the electromagnetic dipole couplings, d_gamma , by searching for a single high-energy photon at LLP detectors. Four typical scenarios are considered in this paper, scenario A, B with d_{W}=0 or d_{Z}=0, and scenario C, D with d_{W,Z}gg d_gamma . We show the sensitivity on d_gamma , can be fairly different depending on the relations between the d_{W,Z} and d_gamma . And the LLP detectors can potentially extend the sensitivity on dipole couplings during the high-luminosity runs of the LHC in certain scenarios.

A theoretical analysis of the electromagnetic dipole response in odd-A thorium isotopes

A theoretical analysis of the electromagnetic dipole response in odd-A thorium isotopes

Searching the anomalous electromagnetic and weak dipole moments of the top quark at the bestest little Higgs model

Searching the anomalous electromagnetic and weak dipole moments of the top quark at the bestest little Higgs model

Geodesic completeness of a ring wormhole

In this work the possible geodesic completeness of an electromagnetic dipole wormhole is studied in detail. The space-time contains a curvature singularity and belongs to a class of solutions to the Einstein-Maxwell equations with a coupled scalar field. Specifically, a numerical analysis is performed to examine congruences of null geodesics that are directed toward the singularity. The results found here show that, depending on the strength of the coupling between the scalar and electromagnetic fields, the wormhole can be either geodesically incomplete or complete. We then focus on those wormholes that are geodesically complete and study the geometry of the neighborhood of their singularity using Kaluza-Klein theory in a five-dimensional space-time. This process allows us to provide a possible explanation of the completeness of geodesics despite unbounded curvature.

A Simple Correction to the Apparent Conductivity from Surface Magnetic Dipole Data

A method to improve the determination of apparent conductivities from near-surface electromagnetic dipole data should be simple and easy to implement and use in the field. With this objective, we present a simple correction to the apparent resistivity from surface magnetic dipole data. In contrast with the traditional approach that uses a truncated series to approximate the fields, the proposed method calculates the apparent conductivity by solving a minimization problem using the complete homogeneous half-space analytical solutions for the magnetic field of the dipole sources. In comparison with previous approaches to improve apparent conductivity estimation, this is an extremely simple solution, easily implemented and demanding almost negligible computer time and memory. To illustrate the method, applications to synthetic 2D data and real data are presented. The results show that the method can improve the responses of conductive zones which are difficult to perceive in the raw field data.

Continuous gravitational wave detection to understand the generation mechanism of fast radio bursts

ABSTRACT Since the unexpected discovery of fast radio bursts (FRBs), researchers have proposed varied theories and models to explain these phenomena. One such model that has recently been developed incorporates the so-called Gertsenshtein–Zel’dovich (GZ) effect, which states that when gravitational waves traverse a pulsar magnetosphere, a portion of the gravitational radiation is transformed into electromagnetic (EM) radiation. The observed properties of FRBs are consistent with the properties of this EM radiation, implying, remarkably, that the GZ effect can account for both repeating and non-repeating FRBs. If this model is correct, the pulsar’s properties should not change over time, and it would continue to emit both EM dipole and gravitational quadrupole radiation for a long period of time. This article targets the gravitational radiation produced by the pulsar mechanism and shows that several proposed gravitational wave detectors can detect these gravitational waves. If such detections are performed in the future from the location of FRBs, it might validate the GZ process for FRB production and potentially rule out several other theories of FRB generation.

Contribution of the electromagnetic dipole operator O7 to the B¯s→μ+μ− decay amplitude

We construct a factorization theorem that allows one to systematically include QCD corrections to the contribution of the electromagnetic dipole operator in the effective weak Hamiltonian to the ${\overline{B}}_{s}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay amplitude. We first rederive the known result for the leading-order QED box diagram, which features a double-logarithmic enhancement associated with the different rapidities of the light quark in the ${\overline{B}}_{s}$ meson and the energetic muons in the final state. We provide a detailed analysis of the cancellation of the related endpoint divergences appearing in individual momentum regions, and show how the rapidity logarithms can be isolated by suitable subtractions applied to the corresponding bare factorization theorem. This allows us to include in a straightforward manner the QCD corrections arising from the renormalization-group running of the hard matching coefficient of the electromagnetic dipole operator in soft-collinear effective theory, the hard-collinear scattering kernel, and the ${B}_{s}$-meson distribution amplitude. Focusing on the contribution from the double endpoint logarithms, we derive a compact formula that resums the leading-logarithmic QCD corrections.

Simulation of hyperfine-rotational spectrum of electromagnetic dipole transition rotation of BrF molecules

The transition dipole of the hyperfine-rotation spectrum of <i>J</i> = 1←0 within the vibronic ground (X<sup>1</sup>Σ, <i>v</i> = 0) state of BrF molecule is derived, and thus, the transition selection rules are summarized as follows: Δ<i>J =</i> ±1; Δ<i>F</i><sub>1</sub> = 0, ±1 and Δ<i>F </i>= 0, ±1, and those of Δ<i>F</i><sub>1</sub> = Δ<i>F</i> are intense while those of Δ<i>F</i><sub>1</sub> ≠ Δ<i>F</i> are weak. Some spectral lines result from both the electric dipole transition and nuclear magnetic dipole transition due to perturbations, however, the magnetic dipole transition only contributes about one-billionth in the spectral intensity. The spectral linewidth is determined to be about 18 kHz by calculating the spectral transition probability. The obtained spectral linewidth and relative intensities are consistent with the experimental results. Additionally, the hyperfine-rotation spectral positions are determined by diagonalizing the Hamiltonian matrix in the basis of |<i>JI</i><sub>1</sub><i>F</i><sub>1</sub><i>I</i><sub>2</sub><i>F</i><inline-formula><tex-math id="Z-20230210104836">\begin{document}$\rangle $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221957_Z-20230210104836.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221957_Z-20230210104836.png"/></alternatives></inline-formula>, which is also in good agreement with the experiments within 10<sup>–8</sup> (one-fiftieth of the spectral line width). Hence, the microwave hyperfine-rotation spectrum is simulated. In addition, we find that the nuclear spin-spin interaction not only slightly shifts the hyperfine-rotation spectral positions but also changes the sequence of the spectra. As to those unavailable constants of molecules, the fairly precise molecular constants can be achieved by quantum chemical calculation, say, by employing MOLPRO program, and then the simulated spectra can guide the spectral assignment. Besides the guidance of spectral assignment, our results are also helpful for other relevant applications such as in absolute single quantum state preparation.

Research on the electromagnetic and weak dipole moments of the tau-lepton at the Bestest Little Higgs Model

In this paper, using the Bestest Little Higgs Model (BLHM) we calculate at the one-loop level the contributions to the Anomalous Magnetic Dipole Moment (AMDM) and Anomalous Weak Magnetic Dipole Moment (AWMDM) of the tau-lepton. The implications from this model are studied, emphasizing the contributions of the new physics induced by the new scalar and vector bosons of the BLHM: S_i=H_0, A_0, phi ^{0}, eta ^{0}, sigma , H^{pm }, phi ^{pm }, eta ^{pm }, and V_i=Z', W'^{pm } because these quantify the new physics. With these new contributions, we estimated bounds on the real and imaginary parts of the AMDM and AWMDM of the tau-lepton. Our study complements other one-loop-level research performed on models beyond the Standard Model.

Broadband all-dielectric absorber based on supercell cylindrical metamaterials

Based on the cylindrical array microstructure of doped silicon, we propose an all-dielectric terahertz-band broadband absorber. First, we design an absorber with a cylindrical structure in a unit cell. Due to the electromagnetic dipole resonance characteristics, the absorber has an absorption efficiency of over 99.97% at a single frequency of 1.24 THz. In order to obtain wide-bandwidth angular absorption characteristics, we propose a kind of superstructure absorber with a single unit cell containing multiple cylinders with different diameters. The results show that the optimally designed absorber has wide-bandwidth angular absorption characteristics under different polarization states and different incident angles of terahertz waves. In order to further improve the absorption bandwidth, we propose a superimposed superstructure absorber. After optimized design, the absorption efficiency reaches more than 90% in the broadband frequency range of 1.42 THz–4.5 THz. At the same time, different structural parameters have different effects on the peak absorption efficiency.

Exclusive lepton pair production at the electron–ion collider

The two-photon exclusive production of lepton pairs at the Electron–Ion Collider will open interesting research directions thanks to a very high luminosity and clean experimental conditions. A survey of the scientific potential of such studies is reported. In particular, we consider unique measurements of the proton elastic electromagnetic form-factors and a possibility of studying the anomalous electromagnetic dipole moments of tau leptons.