Electron-positron Pair Research Articles

Effective quantum electrodynamics: One-dimensional model of the relativistic hydrogen-like atom.

We consider a one-dimensional effective quantum electrodynamics (QED) model of the relativistic hydrogen-like atom using delta-potential interactions. We discuss the general exact theory and the Hartree-Fock approximation. The present one-dimensional effective QED model shares the essential physical feature of the three-dimensional theory: the nuclear charge polarizes the vacuum state (creation of electron-positron pairs), which results in a QED Lamb-type shift of the bound-state energy. Yet, this 1D effective QED model eliminates some of the most serious technical difficulties of the three-dimensional theory coming from renormalization. We show how to calculate the vacuum-polarization density at zeroth order in the two-particle interaction and the QED Lamb-type shift of the bound-state energy at first order in the two-particle interaction. The present work may be considered a step toward the development of a quantum-chemistry effective QED theory of atoms and molecules.

The Radiative Corrections to the Maxwell Equations

The one-loop radiative correction to the photon propagator can be graphically represented by the Feynman diagram of the second order. The physical meaning of this diagram is the process Y-> (e- + e+) -> Y , where Y is denotation for photon, and e-, e+ is the electron-positron pair. It means that photon can exist in the intermediate state with the electron and positron as virtual particles. The photon propagation function based on such process with electron-positron pair e-, e+ is derived. The modified Lagrangian of electromagnetic field is derived supposing the modified Green function of photon. The Schwinger source methods of quantum field theory was applied. Then, the modified Maxwell equations are derived from the new Lagrangian.

Probing strong-field QED in beam-plasma collisions

Ongoing progress in laser and accelerator technology opens new possibilities in high-field science, notably to investigate the largely unexplored strong-field quantum electrodynamics (SFQED) regime where electron-positron pairs can be created directly from light-matter or even light-vacuum interactions. Laserless strategies such as beam-beam collisions have also been proposed to access the nonperturbative limit of SFQED. Here we report on a concept to probe SFQED by harnessing the interaction between a high-charge, ultrarelativistic electron beam and a solid conducting target. When impinging onto the target surface, the beam self fields are reflected, partly or fully, depending on the beam shape; in the rest frame of the beam electrons, these fields can exceed the Schwinger field, thus triggering SFQED effects such as quantum nonlinear inverse Compton scattering and nonlinear Breit-Wheeler electron-positron pair creation. Through reduced modeling and kinetic numerical simulations, we show that this single-beam setup can achieve interaction conditions similar to those envisioned in beam-beam collisions, but in a simpler and more controllable way owing to the automatic overlap of the beam and driving fields. This scheme thus eases the way to precision studies of SFQED and is also a promising milestone towards laserless studies of nonperturbative SFQED.

Spontaneous vacuum decay in low-energy collisions of heavy nuclei beyond the monopole approximation

The problem of spontaneous vacuum decay in low-energy collisions of heavy nuclei is considered beyond the scope of the monopole approximation. The time-dependent Dirac equation is solved in a rotating coordinate system with $z$-axis directed along the internuclear line and the origin placed at the center of mass. The probabilities of electron-positron pair creation and the positron energy spectra are calculated in the approximation neglecting the rotational coupling. The two-center potential is expanded over spherical harmonics and the convergence with respect to the number of terms in this expansion is studied. The results show that taking into account the two-center potential instead of its spherically symmetric part preserves all the signatures of the transition to the supercritical regime that have been found in the framework of the monopole approximation and even enhances some of them.

Three-dimensional structure and stability of discontinuities between unmagnetized pair plasma and magnetized electron-proton plasma

We study with a 3D particle-in-cell simulation discontinuities between an electron–positron pair plasma and magnetized electrons and protons. A pair plasma is injected at one simulation boundary with a speed 0.6c along its normal. It expands into an electron-proton plasma and a magnetic field that points orthogonally to the injection direction. Diamagnetic currents expel the magnetic field from within the pair plasma and pile it up in front of it. It pushes electrons, which induces an electric field pulse ahead of the magnetic one. This initial electromagnetic pulse (EMP) confines the pair plasma magnetically and accelerates protons electrically. The fast flow of the injected pair plasma across the protons behind the initial EMP triggers the filamentation instability. Some electrons and positrons cross the injection boundary and build up a second EMP. Electron-cyclotron drift instabilities perturb the plasma ahead of both EMPs seeding a Rayleigh–Taylor (RT)-type instability. Despite equally strong perturbations ahead of both EMPs, the second EMP is much more stable than the initial one. We attribute the rapid collapse of the initial EMP to the filamentation instability, which perturbed the plasma behind it. The RT-type instability transforms the planar EMPs into transition layers, in which magnetic flux ropes and electrostatic forces due to uneven numbers of electrons and positrons slow down and compress the pair plasma and accelerate protons. In our simulation, the expansion speed of the pair cloud decreased by about an order of magnitude and its density increased by the same factor. Its small thickness implies that it is capable of separating a relativistic pair outflow from an electron-proton plasma, which is essential for collimating relativistic jets of pair plasma in collisionless astrophysical plasma.

Vortex Structures and Momentum Sharing in Dynamic Sauter-Schwinger Process

Vortex pattern formation in electron-positron pair creation from vacuum by a time-dependent electric field of linear polarization is analyzed. It is demonstrated that in such scenario the momentum distributions of created particles exhibit vortex-antivortex pairs. Their sensitivity to the laser field parameters such as the field frequency and intensity is also studied. Specifically, it is shown that with increasing field frequency accross the one-photon threshold additional vortex-antivortex pairs appear. Their location in the momentum space is consistent with a general threshold behavior of probability distributions of created electrons (positrons). Namely, while for small field frequencies the particles tend to be created along the field polarization direction, for large enough frequencies they are predominantly generated in the perpendicular direction. Such change in longitudinal and transverse momentum sharing of created particles occurs accross the one-photon threshold.

Seeking dark matter with γ -ray attenuation

The flux of high-energy astrophysical $\ensuremath{\gamma}$ rays is attenuated by the production of electron-positron pairs from scattering off of extragalactic background light (EBL). We use the most up-to-date information on galaxy populations to compute their contributions to the pair-production optical depth. We find that the optical depth inferred from $\ensuremath{\gamma}$-ray measurements exceeds that expected from galaxies at the $\ensuremath{\sim}2\ensuremath{\sigma}$ level. If the excess is modeled as a frequency-independent re-scaling of the standard contribution to the EBL from galaxies, then an excess (an overall 14--30% increase of the EBL) is favored over the null hypothesis of no excess at the $2.7\ensuremath{\sigma}$ level. If the frequency dependence of the excess is instead modeled as a two-photon decay of a dark-matter axion, then the excess is favored over the null hypothesis at the $2.1\ensuremath{\sigma}$ confidence level. While we find no evidence for a dark-matter signal, the analysis sets the strongest current bounds on the photon-axion coupling over the 8--25 eV mass range. This work highlights the sensitivity of $\ensuremath{\gamma}$-ray optical depth measurements to ALPs, which is expected to improve with new observatories and better EBL determinations from future observations.

Creation mechanism of electron–positron pair on equally spaced multiple localized fields

We investigate the electron–positron creation process from multiple equally spaced distributed oscillating electric fields. The computational quantum field theory (CQFT) is applied to analyze the effect of the number of local fields, the distance between them, and their potential height on the created particle number. It is found that whether adjacent electric fields overlap plays an important role. The creation rate exhibits a direct linear relationship with the number of fields when they do not overlap, but exceeds the sum of the rate when the fields alone. They exhibit a distinctly nonlinear relationship when they overlap, and in particular exhibit a quadratic relationship when the fields completely overlap. These phenomena corroborate that the particle pair creation in the interaction region is non-uniform and influenced by the strength of the central strongest electric field.

Electron-positron-pair creation in the superposition of two oscillating electric-field pulses with largely different frequency, duration, and relative positioning

Production of electron-positron pairs in two oscillating strong electric field pulses with largely different frequencies and durations is considered. In a first scenario, the influence of a low-frequency background field on pair production by a short main pulse of high frequency is analyzed. The background field is shown to cause characteristic modifications of the momentum spectra of created particles, which, in turn, may be used for imaging of the background pulse. In a second scenario, an ultrashort, relatively weak assisting pulse is superimposed onto a strong main pulse. By studying the dependence of the pair production on the field parameters it is shown that duration and relative position of the ultrashort pulse modify the momentum spectra of produced particles in a distinctive way. Both scenarios enable one, moreover, to extract partial information about the time periods when pairs with certain momenta are produced predominantly.

Locally monochromatic two-step nonlinear trident process in a plane wave

In many-cycle plane waves at intermediate intensities, the nonlinear trident process can be well-approximated by the two sequential steps of nonlinear Compton scattering of a polarised real photon followed by its transformation into an electron-positron pair via nonlinear Breit-Wheeler pair creation. We investigate this two-step process in the intermediate intensity regime by employing the locally monochromatic approximation for each step and numerically evaluating resulting expressions. When photon polarisation is included, it is found to produce an order 10% decrease in the trident rate: the importance of polarisation increases at lower intensities, and decreases at higher intensities. Its importance persists at higher intensities in a linearly-polarised background, but disappears at high intensities in a circularly-polarised background. If the two steps are made to take place in two linearly-polarised plane wave pulses with perpendicular polarisations, the pair yield can be increased by approximately 30% compared to two plane waves with the same polarisation. It is also shown that harmonic structures in the Compton step can be passed to the pair step if the Compton edge is at an energy of the order of the threshold for linear Breit-Wheeler.

Arthur E. Haas, from the Atom to the Cosmos—Struggles for a Scientific Career in the Early 20th Century

Arthur E. Haas, from the Atom to the Cosmos—Struggles for a Scientific Career in the Early 20th Century

Weakly interacting massive particle cross section limits from LOFAR observations of dwarf spheroidal galaxies

Context. Weakly interacting massive particles (WIMPs) can self-annihilate, thus providing us with a way to indirectly detect dark matter (DM). Dwarf spheroidal (dSph) galaxies are excellent places to search for annihilation signals because they are rich in DM and background emission is low. If O(0.1–10 μG) magnetic fields in dSph galaxies exist, the particles produced in DM annihilation emit synchrotron radiation in the radio band. Aims. We used the non-detection of 150 MHz radio continuum emission from dSph galaxies with the LOw Frequency ARray (LOFAR) to derive constraints on the annihilation cross section of WIMPs in electron–positron pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, which necessitates the existence of magnetic fields. Methods. We used observations of six dSph galaxies in the LOFAR Two-metre Sky Survey (LoTSS). The data were reimaged, and a radial profile was generated for each galaxy. We also used stacking to increase the sensitivity. In order to derive upper limits on the WIMP cross section, we injected fake Gaussian sources into the data, which were then detected with 2σ significance in the radial profile. These sources represent the lowest emission we would have been able to detect. Results. We present limits from the observations of individual galaxies as well as from stacking. We explored the uncertainty due to the choice of diffusion and magnetic field parameters by constructing three different model scenarios: optimistic (OPT), intermediate (INT), and pessimistic (PES). Assuming monochromatic annihilation into electron–positron pairs, the limits from the INT scenario exclude thermal WIMPs (⟨σv⟩≈2.2 × 10−26 cm3 s−1) below 20 GeV, and the limits from the OPT scenario even exclude thermal WIMPs below 70 GeV. The INT limits can compete with limits set by Fermi-LAT using γ-ray observations of multiple dwarf galaxies, and they are especially strong for low WIMP masses.

No Need for an Extreme Jet Energy in the Black Hole X-Ray Binary MAXI J1348–630

We model interaction with the surrounding medium of the main discrete jet ejection in the accreting black hole binary MAXI J1348–630. The kinetic energy in the ejection of that jet was estimated before to be >1046 erg. That energy requires that the jet power was about 2 orders of magnitude above the limit corresponding to a magnetically arrested accretion onto a maximally rotating black hole. That large estimate was obtained by considering the initial ballistic jet propagation in a surrounding cavity followed by a sudden deceleration in interstellar medium under the assumption of its standard density of ∼1 cm−3. Such densities are likely in the surrounding of this source given its location in the Galactic plane. Here, we show that the estimate of the kinetic energy can be reduced to realistic values of ∼1044 erg by considering the presence of a transition layer with an exponential density growth separating the cavity and the interstellar medium. In that case, the jet is found to decelerate mostly in the transition layer, in regions with densities ≪1 cm−3, which strongly reduces the energy requirement. Still, the required jet masses are large, ruling out the presence of a significant number of electron–positron pairs.

New upper limits on low-frequency radio emission from isolated neutron stars with LOFAR

Neutron stars that show X-ray and γ-ray pulsed emission must generate electron-positron pairs somewhere in the magnetosphere. Pairs like this are also required for radio emission, which poses the question why a number of these sources appear to be radio quiet. We carried out a deep radio search toward four such neutron stars that are isolated X-ray or γ-ray pulsars, but for which no radio pulsations have been detected so far. These sources are 1RXS J141256.0+792204 (Calvera), PSR J1958+2846, PSR J1932+1916, and SGR J1907+0919. A search at lower radio frequencies, where the radio beam is thought to be wider, increases the chances of detecting these sources compared to the earlier higher-frequency searches. We thus carried out a search for periodic and single-pulse radio emission with the LOFAR radio telescope at 150 MHz. We used the known periods and searched a wide range of dispersion measures because the distances are only poorly constrained. We did not detect pulsed emission from any of the four sources. However, we place highly constraining upper limits on the radio flux density at 150 MHz, of ≲1.4 mJy.

Pair production as a probe for the dynamics of nuclear fission and α decay

Electron-positron pairs can be produced via the Schwinger mechanism in the presence of strong electric fields. In particular, the fields involved in $\alpha$ decay and nuclear fission are strong enough to produce them. The energy of the $e^+e^-$ pair is related to the relative distance and velocity of the daughter nuclei. Thus, the energy distribution of the produced pairs can give information about the dynamics of the fission and $\alpha$ decay processes. A neck model of nuclear fission is used to illustrate how the pairs can be used as a probe of the dynamics.

Lorentz and CPT breaking in gamma-ray burst neutrinos from string theory

Previous studies on high-energy gamma-ray burst neutrinos from IceCube suggest a neutrino speed variation at the Lorentz violation (LV) scale of ~6.4 × 1017 GeV, with opposite velocity variances between neutrinos and antineutrinos. Within a spacetime foam model, inspired by string theory, we develop an approach to describe the suggested neutrino/antineutrino propagation properties with both Lorentz invariance and CPT symmetry breaking. A threshold analysis on the bremsstrahlung of electron-positron pair (ν → νee+) for the superluminal (anti)neutrino is performed. We find that, due to the energy violation caused by the quantum foam, such reaction may be restricted to occur at sufficient high energies and could even be kinematically forbidden. Constraints on neutrino LV from vacuum ee+ pair emission are naturally avoided. Future experiments are appealed to test further the CPT violation of cosmic neutrinos and/or neutrino superluminality.

Worldline instantons for the momentum spectrum of Schwinger pair production in spacetime dependent fields

We show how to use the worldline-instanton formalism to calculate the momentum spectrum of the electron-positron pairs produced by an electric field that depends on both space and time. Using the Lehmann-Symanzik-Zimmermann (LSZ) reduction formula with a worldline representation for the propagator in a spacetime field, we make use of the saddle-point method to obtain a semiclassical approximation of the pair-production spectrum. To check the final result, we integrate the spectrum and compare with the results obtained using a previous instanton method for the imaginary part of the effective action.

THE RADIATIVE CORRECTIONS TO THE COULOMB LAW

Photon can exist in the intermediate state with electron and positron as virtual particles. The photon propagation function based on such process with electron-positron pair is determined from the effective emission and absorption sources. The Schwinger source methods of quantum field theory is applied. Then, the Coulomb potential and Bohr energy with radiative corrections is determined.

Spontaneous Lorentz symmetry breaking effects on GRBs jets arising from neutrino pair annihilation process near a black hole

The study of neutrino pair annihilation into electron-positron pairs (nu {bar{nu }}rightarrow e^-e^+) is astrophysically well-motivated because it is a possible powering mechanism for the gamma-ray bursts (GRBs). In this paper, we estimate the gamma-ray energy deposition rate (EDR) arising from the annihilation of the neutrino pairs in the equatorial plane of a slowly rotating black hole geometry modified by the broken Lorentz symmetry (induced by a background bumblebee vector field). More specifically, owing to the presence of a dimensionless Lorentz symmetry breaking (LSB) parameter l arising from nonminimal coupling between the bumblebee field with nonzero vacuum expectation value and gravity, the metric solution in question differs from the standard slowly rotating Kerr black hole. By idealizing the thin accretion disk temperature profile in the two forms of isothermal and gradient around the bumblebee gravity-based slow rotating black hole, we investigate the influence of spontaneous LSB on the nu {bar{nu }}-annihilation efficiency. For both profiles, we find that positive values of LSB parameter l>0 induce an enhancement of the EDR associated with the neutrino-antineutrino annihilation. Therefore, the process of powering the GRBs jets around bumblebee gravity modified slowly rotating geometry is more efficient in comparison with standard metric. Using the observed gamma-ray luminosity associated with different GRBs types (short, long, and ultra-long), we find, through the analysis of the EDR in the parameter space l-a (a^2ll 1), some allowed ranges for the LSB parameter l.

Comparison of Different Detection Paradigm for WMIPs

Based on astrophysics observation, dark matter accounts for approximately 84% of all matter in the universe, with the remaining 16% being ordinary matter. According to the prevailing scientific model, dark matter particles are supersymmetric particles with a mass of 100 GeV (about the mass of 100 protons) with the density about 5000 particles m-3. Yet such a dominant substance dominates the universe, but one has not detected yet. Among various candidate, WIMPs are one of the most appealing one that plenty of facilities aim to detect. In this essay, the detection principles and some recent results of two representatives of the state-of-art mainstream detection methods were presented, i.e., the ‘Wukong’ astronomical satellite (DAMPE) and the Jinping Mountains of Sichuan Province, China (CJPL). It was shown that ‘Wukong’ has successfully detected an electron-positron pairs at an energy of 0.9 Tev. In Jinping, experiments are proposed to detect liquid argon dark matter. In this review, the two methods of detecting dark matter will be compared and the advantages, disadvantages will be analyzed. These results shed light on guiding further exploration of dark matter.