Coulomb Field Research Articles

Effects of gravity in extra dimensions in atomic phenomena

We use the difference between theory and experiment for energy intervals in simple atomic systems (hydrogen, muonium, positronium and deuteron) to find limits on the size of extra space dimensions in the Arkani-Hamed - Dimopoulos - Dvali model for gravitation potential on short distances. As an additional experimental fact we use absence of the small size gravitational bound states of elementary particles. We demonstrate that the perturbation theory approach does not work and more reliable results are obtained by solving the Dirac equations for an electron in Coulomb and gravitational fields. These results probe smaller distances than distance between nuclei in molecules and the limits are significantly stronger than the limits on the size of extra dimensions obtained using spectra of hydrogen molecules.

Semiclassical strong-field theory of phase delays in ω−2ω above-threshold ionization

Phase and time delays of atomic above-threshold ionization were recently experimentally explored in an $\omega -2\omega$ setting [Zipp et al, Optica 1, 361 (2014)]. The phases of wavepackets ejected from argon by a strong $2\omega$ pulse were probed as a function of the relative phase of a weaker $\omega$ probe pulse. Numerical simulations solving the time-dependent Schr\"{o}dinger equation (TDSE) displayed a sensitive dependence of the doubly differential momentum distribution on the relative phase between the $\omega$ and $2\omega$ fields. Moreover, a surprisingly strong variation of the extracted phase delays on the intensity of the probe pulse was found. We present a semiclassical strong-field description of the phase delays in the emission of electrons in an $\omega -2\omega$ setting and apply it to atomic hydrogen. Non-perturbative effects in both the $2\omega$ pump and the $\omega$ probe field are included. The semiclassical description allows tracing phase delays to path interferences between emission during different points in time of emission within the temporal unit cell of the two-color laser field. We find good agreement between the semiclassical saddle-point approximation, the full strong field approximation (SFA), and previous results applicable in the perturbative limit of probe fields. We show that the RABBIT-like perturbative description of phase delays breaks down for stronger fields and higher-energy electron emission. In this regime, characterization of the ionization signal requires an entire ensemble of phase delays {$\delta_i(E)$} with $i=1,2,\ldots$ the difference in photon numbers of the strong $2\omega$ field involved in the interfering paths. Comparison between SFA and TDSE calculations reveals the influence of the Coulomb field even in this strong-field scenario.

Improved Electrical Performance of InAlN/GaN High Electron Mobility Transistors with Post Bis(trifluoromethane) Sulfonamide Treatment

An enhancement of the electrical performance of the InAlN/GaN high electron mobility transistors (HEMTs) is demonstrated by the incorporation of post bis(trifluoromethane) sulfonamide (TFSI) treatment. The surface treatment of TFSI solution results in the increase of 2DEG electron mobility from 1180 to 1500 cm2/Vs and thus a reduction of on-state resistance and an increase in transconductance. The results indicate that the positive charge of H+ will decrease the polarization charges of the InAlN barrier under the access region due to the converse piezoelectric effect, leading to the reduced polarization Coulomb field (PCF) scattering in InAlN/GaN HEMT. This offers a possible way to improve the electron mobility and device performance of InAlN/GaN HEMTs for further application.

Threshold effect on the femtosecond laser-induced periodic subwavelength structure: An analytical approach

For linearly polarized femtosecond laser-induced periodic nanostructures on a metal surface, the underlying physics of self-formation patterns is yet to be fully explained. We demonstrated here that the stabilized periodic interface electrostatic field (Coulomb field) arising from the surface phase-locking resonant dominates the self-formation of ripple structures. The kinetics of ultrafast laser ablation on solid surface were discussed. The threshold fluence and upper limit fluence for self-formation of ripple structures were calculated. The underlying mechanisms were clarified with both simulation and experimental results. Analytical formula for the interspace between ripples (i.e., wavelength of surface Langmuir wave) was developed. As illustrated by the experimental results, the competition of the two ablation mechanisms, namely surface Coulomb ablation and direct ultrafast laser ablations, was shown to result in distinct structuring patterns for a typical Gaussian pulse laser irradiation on the target surface at the appropriate laser energy fluence.

Ultrafast visualization of an electric field under the Lorentz transformation

In special relativity, four-vectors, such as space–time, energy–momentum and electromagnetic potential vectors, follow the Lorentz transformation. The transformations of space–time and energy–momentum vectors have been tested by time dilation and rest mass energy experiments, respectively. However, the Lorentz transformation of electromagnetic potentials has never been directly demonstrated in experiments due to the limitations of the diagnostics. Here we show the spatiotemporal electric-field profiles around a highly energetic electron beam with a subpicosecond temporal resolution obtained by a terahertz technique based on electro-optic sampling. We observe the Coulomb field contraction in the propagation direction of the beam under the Lorentz transformation. After passing the beam through a metallic plate, we investigate the birth of the Coulomb field around it and follow the spatiotemporal evolution of the spherical wavefront, which is derived by the Liénard–Wiechert potentials. The measured electric-field profile in the far propagation distance is experimentally confirmed to coincide with the calculation of the Liénard–Wiechert potentials and the Lorentz transformation. Our ultrafast measurement of a spatiotemporal relativistic electric field provides both additional experimental evidence of special relativity and a platform for detailed experimental research of energetic charged particle beams and electromagnetic radiation physics.

Mu2e Crystal Calorimeter Readout Electronics: Design and Characterisation

The Mu2e experiment at Fermi National Accelerator Laboratory will search for the charged-lepton flavour-violating neutrinoless conversion of negative muons into electrons in the Coulomb field of an Al nucleus. The conversion electron with a monoenergetic 104.967 MeV signature will be identified by a complementary measurement carried out by a high-resolution tracker and an electromagnetic calorimeter, improving by four orders of magnitude the current single-event sensitivity. The calorimeter—composed of 1348 pure CsI crystals arranged in two annular disks—has a high granularity, 10% energy resolution and 500 ps timing resolution for 100 MeV electrons. The readout, based on large-area UV-extended SiPMs, features a fully custom readout chain, from the analogue front-end electronics to the digitisation boards. The readout electronics design was validated for operation in vacuum and under magnetic fields. An extensive radiation hardness certification campaign certified the FEE design for doses up to 100 krad and 1012 n1MeVeq/cm2 and for single-event effects. A final vertical slice test on the final readout chain was carried out with cosmic rays on a large-scale calorimeter prototype.

Photoproduction of e+e− pair in a Coulomb field near the threshold

We consider the electron-positron pair production by a photon in Coulomb field near threshold. We obtain the analytical results for the particle energy spectrum and angular distribution exactly in the parameter Ze2/ħv. We show that Furry-Sommerfeld-Maue approximation for the wave functions used by Nishina, Tomonaga and Sakata in Ref. [1] is not sufficient and leads to wrong results.

Celestial holography on Kerr-Schild backgrounds

We explore the celestial holography proposal for non-trivial asymptotically flat backgrounds including the Coulomb field of a static and spinning point charge, their gravitational counterparts described by the Schwarzschild and Kerr metrics, as well as the Aichelburg-Sexl shockwave and spinning shockwave geometries and their electromagnetic cousins. We compute celestial two-point amplitudes on these Kerr-Schild type backgrounds which have the desirable feature, due to the presence of an external source, that they are non-vanishing for general operator positions and are not constrained by the kinematic delta functions of flat space celestial CFT correlators. Of particular interest is the case of shockwave backgrounds where the two-point scattering amplitude of massless scalars can be interpreted as a standard CFT three-point correlator between two massless asymptotic states and a conformal primary shockwave operator. We furthermore show that the boundary on-shell action for general backgrounds becomes the generating functional for tree-level correlation functions in celestial CFT. Finally, we derive (conformal) Faddeev-Kulish dressings for particle-like backgrounds which remove all infrared divergent terms in the two-point functions to all orders in perturbation theory.

Spin-Dependent Electron–Electron Interaction in Rashba Materials

We review the effects of the pair spin-orbit interaction (PSOI) in Rashba materials. The PSOI is the electron-electron interaction component that depends on the spin and momentum of the electrons. Being produced by the Coulomb fields of interacting electrons, it exists already in vacuum, but becomes orders of magnitude larger in materials with the giant Rashba effect. The main nontrivial feature of the PSOI is that it is attractive for electrons in certain spin configurations tied to their momentum and competes with the Coulomb repulsion of the electrons. Under certain conditions attainable in modern low-dimensional structures the PSOI prevails. The resulting attraction between electrons leads to the formation of bound electron pairs, the binding energy of which can be controlled by electrical means. In many-electron systems the PSOI results in the instabilities of the uniform ground state with respect to the density fluctuations, which develop on different spatial scales, depending on the geometry of the electric fields that produce the PSOI. If the PSOI is not too strong the electronic system is stable, but its collective excitations reveal the highly unusual spin-charge structure and spectrum, which manifest themselves in the frequency dependence of the dynamic conductivity.

Influence of the ZrO2 gate dielectric layer on polarization coulomb field scattering in InAlN/GaN metal–insulator–semiconductor high-electron -mobility transistors

An InAlN/GaN MIS-HEMT with ZrO2 gate dielectric layer and a Schottky-gate InAlN/GaN HEMT were fabricated. Subsequently, the influence of ZrO2 gate dielectric layer on polarization Coulomb field (PCF) scattering in InAlN/GaN MIS-HEMT was studied. Compared with InAlN/GaN HEMT, the ZrO2 gate dielectric layer in InAlN/GaN MIS-HEMT results in fewer additional polarization charge and higher two-dimensional electron gas density at the same gate-source voltage (VGS) conditions. Also, we established that both of these factors weaken PCF scattering intensity. However, the InAlN/GaN MIS-HEMT has a larger gate swing. Therefore, there is a smaller VGS was applied during regular operation of device. When the VGS is small, PCF scattering is the strongest scattering and play non-negligible impact in the size of total electron mobility. This study provides a new theoretical foundation for further enhancing the performance of InAlN/GaN MIS-HEMTs.

On quantum and classical treatments of radiative recombination

The quantum-mechanical solution to the problem of radiative recombination of an electron in a Coulomb field, obtained in the approximation of the smallness of the electron coupling with the radiation field, has been known for a long time. However, in astrophysics, the classical approach, which does not explicitly use this smallness, is sometimes used to describe similar processes in systems of magnetic monopoles or self-interacting dark matter particles. The importance of such problems is determined by the fact that recombination processes play a crucial role in the evolution of the large-scale structure of the Universe. Therefore, of particular interest is the fact that the classical and quantum expressions for the recombination cross section differ significantly in magnitude. It is shown that the applicability of quantum and classical approaches to radiative recombination is closely related to the radiated angular momentum and its quantization. For situations where the classical approach is not suitable, a semi-classical approach based on the angular momentum quantization is proposed, in some respects an alternative to the well-known semi-classical Kramers' approach.

Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions

In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at sqrt{s_text {NN}} = 2.4 GeV. We show that the low-m_t region (m_t < 0.2 GeV/c^2) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a A_{text {part}}^{2/3} scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields.

Contribution of Liénard–Wiechert potential to the broadening of spectral lines by electron collisions in plasmas

In this work, we have calculated the relativistic collision operator representing the line broadening, by collision with free electrons, of isolated lines emitted by hydrogen-like ions (Ly-α line 2p 2P3/2o→1s 2S1/2) of hydrogenic ions FeXXVI, CrXXIV, and CoXXVII in the temperature range of 108 to 5×109 K and electron densities of 1021 to 1026cm−3. To accomplish this task, we have considered the fine structure of these ions and taking into account the relativistic effects related to the free electrons. Specifically, two relativistic effects are considered: the electric field of Liénard–Wiechert, created by the free electron at the emitter ion, and the modification of the hyperbolic trajectory due to the dependent mass on the free electron velocity. The average over the velocities of the free electrons is accomplished by using the Maxwell–Juttner distribution, which is more adequate for the fast (relativistic) electrons. The results are compared to the classical case (when the electric field is the Coulomb's field) to Doppler broadening and to some experimental results (K. Koyama and M. G. Haines) available in the literature. It turns out that, at high temperatures and high densities, the Stark broadening by the relativistic electrons overcomes the Doppler broadening.

Electron correlations due to pair spin–orbit interaction in 2D electron systems

We show that the pair spin–orbit interaction (PSOI) created by the Coulomb fields of interacting electrons leads to the appearance of an unconventional correlated electronic state in two-dimensional materials with the large Rashba effect. The effect manifests itself at sufficiently strong PSOI as a sharp peak in the structure factor, indicating a tendency to form a striped structure with a spatial scale determined by the competition between the Coulomb repulsion and the PSOI-induced attraction of electrons. Above the critical value of PSOI, the system becomes unstable with respect to the charge density fluctuations on this scale.

Global dynamical analysis of an electronic spin–orbit coupling system

By means of a canonical generalized momentum and a canonical conjugate spin variable, a complete canonical Hamiltonian formalism is designed to describe a coulomb field with electronic spin–orbit coupling in a semi-classical and non-relativistic way. After this operation, unlike the existing Lagrange formulation, the concepts of hidden momentum, hidden angular momentum and spin kinetic energy are not used in the canonical formalism. Besides, it is easy to find that there are four first integrals involving the conserved total energy and the conserved total angular momentum vector in an 8-dimensional phase space of the system. In this sense, the global dynamics is typically integrable, regular and non-chaotic, and each orbit in the phase space is a quasi-periodic 4-dimensional Kolmogorov-Arnold-Moser(KAM) torus.

The Global Form of Flavor Symmetries and 2-Group Symmetries in 5d SCFTs

2-group symmetries arise when 1-form symmetries and 0-form symmetries of a theory mix with each other under group multiplication. We discover the existence of 2-group symmetries in 5d \mathcal{N}=1𝒩=1 abelian gauge theories arising on the (non-extended) Coulomb branch of 5d superconformal field theories (SCFTs), leading us to argue that the UV 5d SCFT itself admits a 2-group symmetry. Furthermore, our analysis determines the global forms of the 0-form flavor symmetry groups of 5d SCFTs, irrespective of whether or not the 5d SCFT admits a 1-form symmetry. As a concrete application of our method, we analyze 2-group symmetries of all 5d SCFTs, which reduce in the IR, after performing mass deformations, to 5d \mathcal{N}=1𝒩=1 non-abelian gauge theories with simple, simply connected gauge groups. For rank-1 Seiberg theories, we check that our predictions for the flavor symmetry groups match with the superconformal and ray indices available in the literature. We also comment on the mixed `t Hooft anomaly between 1-form and 0-form symmetries arising in 5d \mathcal{N}=1𝒩=1 non-abelian gauge theories and its relation to the 2-groupS.

Long-range parity-nonconserving electron-nucleon interaction

As known, electron vacuum polarization by nuclear Coulomb field produces Uehling potential with the range $\hbar/2m_e c$. Similarly, neutrino vacuum polarization by $Z$ boson field produces long range potential $\sim G^2/r^5$ with the large range $\hbar/2m_{\nu}c$. Attempts to measure parity-conserving part of this potential produced only limits on this potential which are several orders of magnitude higher than the standard model predictions. We show that parity non-conserving (PNC) part of the neutrino exchange potential $W_L(r)$ gives a significant fraction of the observed PNC effects. Mixed $Z-\gamma$ electron vacuum polarization produces PNC potential with range $\hbar/2m_e c$, which exceeds the range of the weak interaction by five orders of magnitude. We calculate contribution of the long-range PNC potentials to the nuclear spin independent and nuclear spin dependent PNC effects. The cases of the single-isotope PNC effects and the ratio of PNC effects in different isotopes are considered for Ca, Cs, Ba, Sm, Dy, Yb, Hg, Tl, Pb, Bi, Fr, Ra atoms and ions. Contributions of the long-range PNC potentials ($\sim$1\%) significantly exceed experimental error (0.35\%) for PNC effect in Cs.

Nonequilibrium phenomena in driven and active Coulomb field theories

The classical Coulomb gas model has served as one of the most versatile frameworks in statistical physics, connecting a vast range of phenomena across many different areas. Nonequilibrium generalisations of this model have so far been studied much more scarcely. With the abundance of contemporary research into active and driven systems, one would naturally expect that such generalisations of systems with long-ranged Coulomb-like interactions will form a fertile playground for interesting developments. Here, we present two examples of novel macroscopic behaviour that arise from nonequilibrium fluctuations in long-range interacting systems, namely (1) unscreened long-ranged correlations in strong electrolytes driven by an external electric field and the associated fluctuation-induced forces in the confined Casimir geometry, and (2) out-of-equilibrium critical behaviour in self-chemotactic models that incorporate the particle polarity in the chemotactic response of the cells. Both of these systems have nonlocal Coulomb-like interactions among their constituent particles, namely, the electrostatic interactions in the case of the driven electrolyte, and the chemotactic forces mediated by fast-diffusing signals in the case of self-chemotactic systems. The results presented here hint to the rich phenomenology of nonequilibrium effects that can arise from strong fluctuations in Coulomb interacting systems, and a rich variety of potential future directions, which are discussed.

Non-perturbative effects in the QED-vacuum energy exposed to the supercritical Coulomb field

Non-perturbative effects of the QED-vacuum reconstruction exposed to the supercritical Coulomb field are considered with emphasis on the behavior of the vacuum energy [Formula: see text]. It is shown that in the supercritical region [Formula: see text] turns out to be a decreasing function of the Coulomb source, resulting in decay into the negative range as [Formula: see text], and that it is indeed the decline of [Formula: see text], which provides the required energy for (presumably possible) positron emission. The properties of the resonance decay, found this way, are in agreement with those achieved by other methods. The additional problems of spontaneous emission, caused by lepton number conservation, are also discussed.

Bose-Einstein condensation in finite drops of α particles

Ground-state properties of finite drops of $\ensuremath{\alpha}$ particles (Q-balls) are studied within a field-theoretical approach in the mean-field approximation. The strong interaction of $\ensuremath{\alpha}$'s is described by the scalar field with a sextic Skyrme-like potential. The radial profiles of scalar and Coulomb fields are found by solving the coupled system of Klein-Gordon and Poisson equations. The formation of shell-like nuclei, with vanishing density around the center, is predicted at high enough attractive strength of Skyrme potential. The equilibrium values of energy and baryon number of Q-balls and Q-shells are calculated for different sets of interaction parameters. Empirical binding energies of $\ensuremath{\alpha}$-conjugate nuclei are reproduced only if the gradient term in the Lagrangian is strongly enhanced. It is demonstrated that this enhancement can be explained by a finite size of $\ensuremath{\alpha}$ particles.