Electron-positron pair generation by a neutrino in a magnetic field

The probability of generation of an e⁺ e^– pair by a neutrino moving in a magnetic field is calculated in the low energy approximation of the Weinberg-Salam model with consideration of electron and positron spin states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 30–34, August, 1983.The authors thank A. A. Sokolov forhis kind evaluation of the study.     

Coulomb distortion effects in electron positron pair production near threshold

The cross section for electron positron pair production in non relativistic collisions of protons with heavy nuclei has been calculated. Extending previous calculations, the Coulomb distortion of electron, positron, and projectile wave functions in the target field has been taken into account. Former discrepancies between calculation and experimental results have been removed.     

Electron-positron pair production in a strong asymmetric laser electric field

By solving the quantum Vlasov equation, electron positron pair production in a strong electric field with asymmetric laser pulses has been investigated. We consider three different situations of subcycle, cycle and supercycle laser pulses. It is found that in asymmetric laser pulse field, i.e.. when the pulse length of one rising or falling side is fixed while the pulse length of the other side is changed, the pair production rate and mnnber density can be significantly modified comparable to symmetric situation. For each ca,se of these three different cycle pulses, when one side pulse length is constant and the other side pulse length becomes shorter, i.e., the whole pulse is compressed, the more pairs can be produced than that in tile vice versa case, i.e., the whole pulse is elongated. In compressed pulse case there exists an optimum pulse length ratio of asylnmetric pulse lengths which makes the pair number density maximunn. Moreover, the created maximum pair number density by subcycle pulse is larger than that by cycle or/and supercycle pulse. In elongated pulse case, however, only for supercycle laser pulse the created pairs is enhanced and there exists also an optimum asymmetric pulse length ratio that maximizes the pair number density. On the other hand. surprisingly, in both cases of subcycle and cycle elongated laser pulses, the pair number density is monotonically decreasing as the asymmetry of pulse increases.     

Electron-positron pair production by electromagnetic pulses

Electron-positron pair production in vacuum by a single focused laser pulse and by two counter-propagating colliding focused pulses is analyzed. A focused laser pulse is described using a realistic three-dimensional model based on an exact solution of Maxwell’s equations. In particular, this model reproduces an important property of focused beams, namely, the existence of two types of waves with a transverse electric or magnetic vector (e-or h-polarized wave, respectively). The dependence of the number of produced pairs on the radiation intensity and focusing parameter is studied. It has been shown that the number of pairs produced in the field of a single e-polarized pulse is many orders of magnitude larger than that for an h-polarized pulse. The pulse-intensity dependence of the number of pairs produced by a single pulse is so sharp that the total energy of pairs produced by the e-polarized pulse with intensity near the intensity I _S = 4.65 × 10²⁹ W/cm² characteristic of QED is comparable with the energy of the pulse itself. This circumstance imposes a natural physical bound on the maximum attainable intensity of a laser pulse. For the case of two colliding circularly polarized pulses, it is shown that pair production becomes experimentally observable when the intensity of each beam is I ～ 10²⁶ W/cm², which is one to two orders of magnitude lower than that for a single pulse.     

Electron-positron pair creation by a strong tightly focused laser field

The analytical calculation of the electron-positron pair creation yield by an extremely strong focused laser pulse in the vacuum is presented. In particular, dependence of the total yield of the pair production on the focusing parameter and the polarization properties of the laser pulse are analyzed. Comparison with the previous consideration of N.B. Narozhny, V.S. Popov, V.D. Mur, and S.S. Bulanov is given and discussed. As a result, we confirm their conclusion that the electron-positron pair production can be observed in principle at the level of intensity of 10²⁷ W/cm².     

超强场下的正负电子对产生

随着现代强激光技术的迅速发展,激光场强已经进入到了强相对论区域,并正在向产生正负电子对的施温格临界场强逼近。文章着重介绍了超强场下真空失稳产生正负电子对的问题,从历史及其发展的脉络中梳理出有重要价值的研究方法和有趣的研究成果,对目前的研究现状做了综述,并对未来的研究进行展望。     

Electron-positron pair production in the low-density approximation

Electron–positron pair creation is studied in the low-density approximation by solving the quantum Vlasov equation exactly and the mapping equation approximately. The simpler mapping equation is an approximate treatment of the quantum Vlasov equation in which the continuous external field is regarded as a series of delta kicks. Our study indicates that this new treatment is appropriate because the results of the two methods are in good agreement with each other. However, as the period number increases, interference and a complicated structure in the momentum distribution are observed. Furthermore, we also obtain the square power law relation of the number density to the applied electric field strength.     

Top-quark pair production near threshold at LHC

The next-to-leading order analysis for the cross section for hadroproduction of top-quark pairs close to threshold is presented. Within the framework of non-relativistic QCD a significant enhancement compared to fixed-order perturbation theory is observed which originates from the characteristic remnant of the 1S peak below production threshold of top-quark pairs. The analysis includes all color-singlet and color-octet configurations of top-quark pairs in S-wave states and, for the dominant configurations, it employs all-order soft-gluon resummation for the hard parton cross section. Numerical results for the Large Hadron Collider at TeV and TeV and also for the Tevatron are presented. The possibility of a top-quark mass measurement from the invariant-mass distribution of top-quark pairs is discussed.     

Monopole pair production in a magnetic field

The rate of monopole pair production in a weak external magnetic field is computed by a semiclassical method. The result is analogous to that for electron-positron pair production in an electric field.     

Electron-positron pair production by photons in nonuniform strong fields

A probability of electron-positron pair production by photons in strong nonuniform fields is derived by applying a model trajectory method in the frame of a semiclassical approach. In addition to the well known invariant field parameter chi, a new invariant parameter nu is introduced to characterize the nonuniformity of the field. For nu>1, the obtained expression is reduced to the uniform-field approximation while it approaches the Bethe-Heitler formula for nu<1. The pair production is predicted for relatively weak external fields where the uniform-field approximation gives no effect. The theory agrees well with the experimental results of crystal-assisted pair production.     

Ultrasoft contribution to heavy-quark pair production near threshold

We compute the third-order correction to the heavy-quark current correlation function due to the emission and absorption of an ultrasoft gluon. Our result supplies a missing contribution to top-quark pair production near threshold and the determination of the bottom quark mass from QCD sum rules.     

Electron-positron pair formation by two identical photons in the nuclear field

The effect of electron-positron pair formation by two identical photons in the Coulomb field of an atomic nucleus is considered in the Born approximation of perturbation theory.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 20–23, February, 1977.     

Electron-positron pair production by collisions of non-relativistic charged particles

The cross-section for (e ⁺,e ^?)-pair production in collisions of non-relativistic charged particles has been calculated to lowest order in the fine structure constant and leading power of the relative velocity of the colliding particles. Thus the deflection of colliding particles is included in one-photon-exchange approximation, while the Coulomb distortion of the (e ⁺,e ^?)-pair is omitted. We have laid particular emphasis on current conservation. The previously neglected contribution of the spatial part of the current turns out to be dominant.     

Electron-positron pair formation in the field of a bichromatic plane electromagnetic wave

On the basis of the accurate solution of the Dirac equation for an electron in the field of a bichromatic plane wave consisting of two monochromatic waves propagating in the same direction, the probability of formation of an e⁺e^– pair by a quantum in the wave field is calculated. The cases of small and large intensities of the wave components are considered, together with the transition in the limit to a constant field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 46–53, February, 1977.The authors thank A. A. Sokolov for his constant interest in the work and discussion of the results.     

Supersymmetric correction to top quark pair production near threshold

We studied the leading supersymmetric contribution to top–antitop threshold production using the NRQCD framework. The one-loop matching to the potential and the Wilson coefficient of the leading ³S₁ production current were considered. We point out that the leading correction to the potential is zero due to SU(3)_c gauge invariance. This is true in general for any new physics that enters above the electroweak scale. The shape of the top quark pair production cross section is therefore almost unaffected near threshold, allowing a precise determination of the top quark mass based on the Standard Model calculations. The supersymmetric correction to the Wilson coefficient c₁ of the production current decouples for heavy super particles. Its contribution is smaller than the Standard Model next-to-next-leading-log results.     

Photon damping caused by electron-positron pair production in a strong magnetic field

Damping of an electromagnetic wave in a strong magnetic field is analyzed in the kinematic region near the threshold of electron-positron pair production. Damping of the electromagnetic field is shown to be noticeably nonexponential in this region. The resulting width of the photon γ→e ⁺ e ^? decay is considerably smaller than previously known results.     

Production of a pair of heavy particles by a polarized electron in a magnetic field

The probability that an electron in a constant uniform magnetic field will generate a pair of heavy particles is calculated, neglecting the effect of the field on their motion. It is shown that the emission of pairs leads to a preferential orientation of the electron spins in the opposite direction to the magnetic field, as in the case of synchrotron radiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 101–105, May, 1982.     

Pair production in a slowly varying electromagnetic field and the pair production process

The numerical analysis of pair production (PP) by γ-quanta intersecting the crystal axis with a small angle is given on the basis of the formulae describing the PP in a slightly inhomogeneous electric field.