Electrodynamic Calculations Research Articles

The orientation dependence of cavity-modified chemistry.

Recent theoretical studies have explored how ultra-strong light-matter coupling can be used as a handle to control chemical transformations. Ab initio cavity quantum electrodynamics calculations demonstrate that large changes to reaction energies or barrier heights can be realized by coupling electronic degrees of freedom to vacuum fluctuations associated with an optical cavity mode, provided that large enough coupling strengths can be achieved. In many cases, the cavity effects display a pronounced orientational dependence. Here, we highlight the critical role that geometry relaxation can play in such studies. As an example, we consider a recent work [Pavošević et al., Nat. Commun. 14, 2766 (2023)] that explored the influence of an optical cavity on Diels-Alder cycloaddition reactions and reported large changes to reaction enthalpies and barrier heights, as well as the observation that changes in orientation can inhibit the reaction or select for one reaction product or another. Those calculations used fixed molecular geometries optimized in the absence of the cavity and fixed relative orientations of the molecules and the cavity mode polarization axis. Here, we show that when given a chance to relax in the presence of the cavity, the molecular species reorient in a way that eliminates the orientational dependence. Moreover, in this case, we find that qualitatively different conclusions regarding the impact of the cavity on the thermodynamics of the reaction can be drawn from calculations that consider relaxed vs unrelaxed molecular structures.

Polarization dynamics in the paramagnet of a charged quark-gluon plasma

It is commonly understood that the strong magnetic field produced in heavy ion collisions is short-lived. The electric conductivity of the quark-gluon plasma is unable to significantly extend the lifetime of the magnetic field. We propose an alternative scenario to achieve this: with finite baryon density and spin polarization by the initial magnetic field, the quark-gluon plasma behaves as a paramagnet, which may continue to polarize the quark after fading of the initial magnetic field. We confirm this picture by calculations in both quantum electrodynamics and quantum chromodynamics. In the former case, we find a splitting in the damping rates of probe fermions with an opposite spin component along the magnetic field. In the latter case, we find a similar splitting in damping rate of the probe quark in quark-gluon plasma in both high and low density limits. The splitting provides a way of polarizing strange quarks by the quark-gluon plasma paramagnet consisting of light quarks, which effectively extends the lifetime of the magnetic field in heavy ion collisions. Published by the American Physical Society 2024

Electrodynamic calculation of the electric field of a printed ring antenna for microwave radiothermometry of the breast

Electrodynamic calculation of the electric field of a printed ring antenna for microwave radiothermometry of the breast

Synthesis of Antenna Array Radiation Pattern at Large Scanning Angles Using Genetic Algorithm

At present, in most modern communication systems, for example, in modern satellite terminals, the use of scanning beam antennas, i. e. antenna arrays is assumed. At the same time, at large scanning angles, the side lobe level (SLL) increases strongly and decrease in the gain is observed. In this regard, the problem of finding a procedure for synthesizing an amplitude-phase distribution (APD) with low SLL and high gain (G) at large scanning angles comes up. One of the ways to reduce SLL and compensate for the decrease in G is to synthesize the optimal APD (in terms of the maximum G and minimum SLL) using optimization algorithms. At the same time, taking into account the characteristics of the radiation pattern of the array emitters requires numerical electrodynamic calculation. The goal of this paper is to develop a procedure for the synthesis of APD with low SLL for linear and rectangular antenna arrays at various, including large, scanning angles and compensation for G reduction using a genetic algorithm and numerical electrodynamic calculation. The methods for studying the characteristics of antenna radiators are numerical electrodynamic modeling by the finite element method (FEM) in Ansys HFSS computer-aided design system and optimization of the APD for a given radiation pattern(RP) by a random search method using partial diagrams of antenna elements. The novelty is the combination of accurate numerical electrodynamic calculation of the RP of antenna elements and optimization search for APD for the synthesis of the required RP using partial diagrams. As a result, a procedure for APD synthesis of linear and uniform rectangular equidistant (for example, 8- and 64-element) antenna arrays has been developed, taking into account the exact electrodynamic characteristics of antenna elements and their mutual resistance. Radiation patterns were obtained taking into account the effect of neighboring elements, with the help of which, using a genetic algorithm, APDs on emitters were found at different scanning angles. The change in SLL and G of the antenna array is analyzed at different scanning angles using different APDs. The proposed algorithm allows to synthesize APD for a RP with low SLL and high G at scanning angles up to 40° for linear antenna array and up to 80° in the case of a uniform rectangular antenna array. The results of this work are relevant in the problems of radiation pattern synthesis, since the proposed solution provides a significant gain in the radiation pattern synthesis rate of APD of linear and rectangular antenna arrays, especially for systems with a large number of antenna elements. At the same time, it is possible to maintain a high G at large scanning angles, and achieve a significant reduction of SLL.

Resummation schemes for high-electric-charge objects leading to improved experimental mass limits

High-electric-charge compact objects (HECOs) appear in several theoretical particle physics models beyond the Standard Model, and are actively searched for in current colliders, such as the Large Hadron Collider at CERN. In such searches, mass bounds of these objects have been placed, using Drell-Yan and photon-fusion processes at tree level so far. However, such mass-bound estimates are not reliable, given that, as a result of the large values of the electric charge of the HECO, perturbative quantum electrodynamics calculations break down. In this work, we perform a Dyson-Schwinger resummation scheme (as opposed to lattice strong-coupling approach), which makes the computation of the pertinent HECO-production cross sections reliable, thus allowing us to extract improved mass bounds for such objects from ATLAS and MoEDAL searches. Published by the American Physical Society 2024

Zero-Quantum-Defect Method and the Fundamental Vibrational Interval of H_{2}^{+}.

The fundamental vibrational interval of H_{2}^{+} has been determined to be ΔG_{1/2}=2191.126 614(17) cm^{-1} by continuous-wave laser spectroscopy of Stark manifolds of Rydberg states of H_{2} with the H_{2}^{+} ion core in the ground and first vibrationally excited states. Extrapolation of the Stark shifts to zero field yields the zero-quantum-defect positions -R_{H_{2}}/n^{2}, from which ionization energies can be determined. Our new result represents a 4-order-of-magnitude improvement compared to earlier measurements. It agrees, within the experimental uncertainty, with the value of 2191.126 626 344(17)(100) cm^{-1} determined in nonrelativistic quantum electrodynamic calculations [V. Korobov, L. Hilico and J.-Ph. Karr, Phys. Rev. Lett. 118, 233001 (2017)PRLTAO0031-900710.1103/PhysRevLett.118.233001].

Fried-Yennie Gauge in Pseudo-QED.

The Fried-Yennie gauge is a covariant gauge for which the mass-shell renormalization procedure can be performed without introducing spurious infrared divergences to the theory. It is usually applied in calculations in regular Quantum Electrodynamics (QED), but it is particularly interesting when employed in the framework of pseudo-QED (PQED), where fermions are constrained to 2 + 1 dimensions while the dynamical fields interacting with these fermions live in the bulk of a 3 + 1 space. In this context, the gauge parameter can be adjusted to match the power of the external momentum in the denominator of the photon propagator, simplifying the infrared region without the need for a photon mass. In this work, we apply this machinery, for the first time, to PQED, generalizing the procedure to calculate the self energy in arbitrary dimensions, allowing, of course, for different dimensionalities of fermions and gauge fields.

Hyperfine structure in a vibrational quadrupole transition of ortho-H2

ABSTRACT A Lamb dip spectroscopic measurement of the Q(1) transition in the (2-0) overtone band of ortho- H 2 is performed with the ultra-sensitive NICE-OHMS intracavity absorption technique at 1238 nm . For the first time individual hyperfine components of a vibrational transition in H 2 are resolved, displaying a pattern of 4 overlapping components with singly isolated components at the red and blue side. Weak components at a line strength of 4.4 × 10 − 28 cm/molecule could be observed as a Lamb dip. Analysis yields a hyperfineless purely rovibrational transition frequency for the Q(1) (2-0) line in H 2 at unprecedented accuracy for any rovibrational transition in a molecular hydrogen isotopologue. Its frequency is 242,091,630,140 ( 9 ) kHz under the assumption that only a blue recoil component is observed. A 1.7σ deviation from the most advanced quantum electrodynamics calculations is obtained, forming a challenge for theory.

Molecular van der Waals Fluids in Cavity Quantum Electrodynamics.

Intermolecular van der Waals interactions are central to chemical and physical phenomena ranging from biomolecule binding to soft-matter phase transitions. In this work, we demonstrate that strong light-matter coupling can be used to control the thermodynamic properties of many-molecule systems. Our analyses reveal orientation dependent single molecule energies and interaction energies for van der Waals molecules. For example, we find intermolecular interactions that depend on the distance between the molecules R as R-3 and R0. Moreover, we employ ab initio cavity quantum electrodynamics calculations to develop machine-learning-based interaction potentials for molecules inside optical cavities. By simulating systems ranging from 12 H2 to 144 H2 molecules, we observe varying degrees of orientational order because of cavity-modified interactions, and we explain how quantum nuclear effects, light-matter coupling strengths, number of cavity modes, molecular anisotropies, and system size all impact the extent of orientational order.

Fully Electromagnetic Code KARAT Applied to the Problem of Aneutronic Proton–Boron Fusion

In this paper, the full electromagnetic code KARAT is presented in detail, the scope of which is a computational experiment in applied problems of engineering electrodynamics. The basis of the physical model used is Maxwell’s equations together with boundary conditions for fields, as well as material equations linking currents with field strengths. The Particle in Cell (PiC) method for the kinetic description of plasma is implemented in the code. A unique feature of the code KARAT is the possibility of the self-consistent modeling of inelastic processes, in particular, nuclear reactions, at each time step in the process of electrodynamic calculation. The aneutronic proton–boron nuclear reaction, accompanied by the release of almost only α-particles, is extremely in demand in medicine and, perhaps, in the future, will form the basis for obtaining “clean” nuclear energy. The results of a numerical simulation within the framework of the code KARAT of the key physical processes leading to the proton–boron fusion are presented and discussed both for laser-driven plasma and for a plasma oscillatory confinement scheme.

Measurement of Hyperfine Structure and the Zemach Radius in ^{6}Li^{+} Using Optical Ramsey Technique.

We investigate the 2^{3}S_{1}-2^{3}P_{J} (J=0, 1, 2) transitions in ^{6}Li^{+} using the optical Ramsey technique and achieve the most precise values of the hyperfine splittings of the 2^{3}S_{1} and 2^{3}P_{J} states, with smallest uncertainty of about 10kHz. The present results reduce the uncertainties of previous experiments by a factor of 5 for the 2^{3}S_{1} state and a factor of 50 for the 2^{3}P_{J} states, and are in better agreement with theoretical values. Combining our measured hyperfine intervals of the 2^{3}S_{1} state with the latest quantum electrodynamic (QED) calculations, the improved Zemach radius of the ^{6}Li nucleus is determined to be 2.44(2)fm, with the uncertainty entirely due to the uncalculated QED effects of order mα^{7}. The result is in sharp disagreement with the value 3.71(16)fm determined from simple models of the nuclear charge and magnetization distribution. We call for a more definitive nuclear physics value of the ^{6}Li Zemach radius.

Lamb Dip of a Quadrupole Transition in H_{2}.

The saturated absorption spectrum of the hyperfineless S(0) quadrupole line in the (2-0) band of H_{2} is measured at λ=1189 nm, using the NICE-OHMS technique under cryogenic conditions (72K). It is the first time that a Lamb dip of a molecular quadrupole transition has been recorded. At low (150-200W) saturation powers a single narrow Lamb dip is observed, ruling out an underlying recoil doublet of 140kHz. Studies of Doppler-detuned resonances show that the redshifted recoil component can be made visible for low pressures and powers, and prove that the narrow Lamb dip must be interpreted as the blue recoil component. A transition frequency of 252 016 361 164 (8)kHz is extracted, which is off by -2.6 (1.6)MHz from molecular quantum electrodynamical calculations therewith providing a challenge to theory.

Artificial Magnetic Conductors Based on Frequency Selective Surfaces

New band-passing frequency-selective surfaces (FSSs) are proposed and investigated. Formulas for calculating the modulus and phase of the reflection coefficient of artificial magnetic conductors are obtained based on the proposed FSSs. The comparison of the results of electrodynamic modeling and calculation by formulas is carried out. The possibility of expanding the operating frequency band is shown.

Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at {sqrt{s}}_{textrm{NN}} = 5.02 TeV

The first measurement of the e+e− pair production at low lepton pair transverse momentum (pT,ee) and low invariant mass (mee) in non-central Pb–Pb collisions at {sqrt{s}}_{textrm{NN}} = 5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|ηe| < 0.8) as a function of invariant mass (0.4 ≤ mee< 2.7 GeV/c2) in the 50–70% and 70–90% centrality classes for pT,ee< 0.1 GeV/c, and as a function of pT,ee in three mee intervals in the most peripheral Pb–Pb collisions. Below a pT,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The mee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the pT,ee spectra. The measured sqrt{leftlangle {p}_{textrm{T},textrm{ee}}^2rightrangle } of the excess pT,ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region.

The worldline formalism in strong-field QED

The worldline formalism provides an alternative to Feynman diagrams that has been found particularly useful for external-field calculations in quantum electrodynamics. Here I summarize its present range of applications, which includes Schwinger pair creation, photon splitting in constant fields and plane-wave backgrounds, as well as non-linear Compton scattering in constant fields.

Proton Electric Charge Radius from Lepton Scattering

A proton is a bound state of a strong interaction, governed by Quantum Chromodynamics (QCD). The electric charge radius of a proton, denoted by rEp, characterizes the spatial distribution of its electric charge carried by the quarks. It is an important input for bound-state Quantum Electrodynamic (QED) calculations of the hydrogen atomic energy levels. However, physicists have been puzzled by the large discrepancy between rEp measurements from muonic hydrogen spectroscopy and those from ep elastic scattering and ordinary hydrogen spectroscopy for over a decade. Tremendous efforts, both theoretical and experimental, have been dedicated to providing various insights into this puzzle, but certain issues still remain unresolved, particularly in the field of lepton scatterings. This review will focus on lepton-scattering measurements of rEp, recent theoretical and experimental developments in this field, as well as future experiments using this technique.

Computer Algebra Calculations in Supersymmetric Electrodynamics

We propose a new symbolic algorithm and a C++ program for generating and calculating supersymmetric Feynman diagrams for $$\mathcal{N} = 1$$ supersymmetric electrodynamics regularized by higher derivatives in four dimensions. According to standard rules, the program generates all diagrams that are necessary to calculate a specific contribution to the two-point Green function of matter superfields in the needed order, and then reduces the answer to the sum of Euclidean momentum integrals. At the moment, the program was used to calculate the anomalous dimension in $$\mathcal{N} = 1$$ supersymmetric quantum electrodynamics, regularized by higher derivatives, in the three-loop approximation.

Plasmoelectronic properties of self-assembled gold nanoparticles: impedance spectroscopy experiments combined with numerical simulations

Plasmoelectronics is a fast developing field driven by the combination of charge transport and surface plasmons in metal nanostructures. In this paper, we report on theoretical and experimental investigations of the plasmoelectronic properties of self-assembled monolayers of colloidal gold nanoparticles (NPs). A local plasmonic-electronic nanojunction is introduced, as the fundamental building block of a mesoscale electrical network, and serves as the beginning point for the development of a multiscale modeling strategy. The interparticle charge tunneling and accumulation account for the dynamical charge transport; the plasmoelectronic properties are implemented at the nanoscale using electrodynamic calculations based on the discrete dipole approximation (DDA) method. The electric characteristics of the macroscopic NP network are calculated using a numerical resolution of the current-bias equations based on Kirchhoff's laws. Disorder effects due to size and position fluctuations of the NPs within the network as well as dislocations and point defects in their spatial arrangement are taken into account. The effects of light excitation intensity and wavelength on the nanojunction photoconductance and on the macroscopic photoresistance of the NP network are addressed. In particular, plasmoelectronic conduction paths are extracted from the coupled DDA-Kirchhoff numerical simulations, and their statistical distribution is investigated as well as their dependence on path length. The theoretical results are compared with impedance spectroscopy measurements performed under optical excitation. We found a good agreement between the predicted impedance Nyquist plots and resonance properties, and the measurements. In particular, we were able to estimate the surface plasmon-assisted photoelectric conversion efficiency involving first neighbor NPs. We found that the photoconductance of a single nanojunction formed by a dimer of nearly touching NPs is around 18 nS/W/cm2 under resonant plasmonic excitation. The presented work provides insight into the photoinduced charge transport in self-assembled NP networks and opens the route to novel applications in the field of plasmoelectronics.

Calculated Estimation of the Displacement Current Density and its Influence on Electromagnetic Processes in a Metallic Conductor with an Alternating Current

The results of approximate calculations of the density δs(t) of the displacement current is(t) and the estimation of its influence on electromagnetic processes in the homogeneous non-magnetic metals (alloys) of a continuous cylindrical conductor of finite sizes (radius r0 and length l0&gt;&gt;r0) with an electric variable (pulse) axial current i0(t) of different amplitude and temporal parameters. The theoretical data obtained for the quantized (discrete) spatio-temporal distributions of standing longitudinal waves (half waves) of the displacement current is(t) at density δs(t) in the indicated conductor leads to the following conclusion. In the electrodynamic calculations of variable (pulse) electromagnetic processes that occur both in this conductor and in an electric circuit in it, it is possible to neglect the influence of longitudinal waves (half waves) of the displacement current is(t) at density δs(t) and of the displacement current is(t) itself at the practical field calculations. It is found that the waves (half waves) of the displacement current is(t) at density δs(t) and of the displacement current is(t) maintain solenoidality of the total electric current of ii(t) = i0(t)+is(t) in the conductor and its circuit. The calculations has shown that the displacement current is(t) and its density δs(t) in a non-magnetic metal (alloy) of the studied conductor do not lead to thermal (joule) energy losses.

Absolute measurement of the relativistic magnetic dipole transition in He-like sulfur

We have made an absolute, reference-free measurement of the $1s2s\phantom{\rule{0.28em}{0ex}}^{3}S_{1}\ensuremath{\rightarrow}1{s}^{2}\phantom{\rule{0.28em}{0ex}}^{1}S_{0}$ relativistic magnetic dipole transition in He-like sulfur. The highly charged sulfur ions were provided by an electron-cyclotron resonance ion source, and the x rays were analyzed with a high-precision double-crystal spectrometer. A transition energy of 2430.3685(97) eV was obtained and is compared to most advanced bound-state quantum electrodynamics calculations, providing an important test of two-electron QED effects and precision atomic structure methods in medium-$Z$ species. Thanks to the extremely narrow natural linewidth of this transition and to the large dispersion of the spectrometer at this energy, a complementary study is also performed to evaluate the impact of different silicon crystal atomic form-factor models in the transition-energy analysis. We find no significant dependence on the model used to determine the transition energy.