Electron-Positron Vacuum Instability in Strong Electric Fields. Relativistic Semiclassical Approach

The instability of electron-positron vacuum in strong electric fields is studied. First, falling to the Coulomb center is discussed at Z>137/2 for a spinless boson and at Z>137 for electron. Subsequently, focus is concentrated on description of deep electron levels and spontaneous positron production in the field of a finite-size nucleus with the charge Z>Zcr≃170. Next, these effects are studied in application to the low-energy heavy-ion collisions. Subsequently, we consider phenomenon of “electron condensation” on levels of upper continuum crossed the boundary of the lower continuum ϵ=−m in the field of a supercharged nucleus with Z≫Zcr. Finally, attention is focused on many-particle problems of polarization of the quantum electrodynamics (QED) vacuum and electron condensation at ultra-short distances from a source of charge. We argue for a principal difference of cases, when the size of the source is larger than the pole size rpole, at which the dielectric permittivity of the vacuum reaches zero and smaller rpole. Some arguments are presented in favor of the logical consistency of QED. All of the problems are considered within the same relativistic semiclassical approach.

Estimating the radiative part of QED effects in systems with supercritical charge

The effective interaction of the electron magnetic moment anomaly with the Coulomb fileld of superheavy nuclei is investigated by taking into account its dynamical screening at small distances. The shift of the electronic levels, caused by this interaction, is considered for H-like atoms and for compact nuclear quasi-molecules, non-perturbatively both in Zα and (partially) in α/π. It is shown that the levels shift reveals a non-monotonic behavior in the region Zα 1 and near the threshold of the lower continuum decreases both with the increasing the charge and with enlarging the size of the system of Coulomb sources. The last result is generalized to the total self-energy contribution to the levels shift and so to the possible behavior of radiative QED effects with virtual photon exchange near the lower continuum in the supercritical region.

Critical nucleus charge in a superstrong magnetic field

Due to strong enhancement of loop effects in a superstrong magnetic field (B ≫ m2=e3) the Coulomb potential becomes screened. This phenomenon dramatically changes the dependence of the electron energy levels on magnetic field. In particular, the freezing of energy levels occurs so the ground energy level of light ions can never reach the lower continuum (become critical), no matter how strong the field is. Therefore, the magnetic field affects the critical nucleus charge Zcr in two ways: i. it makes the electron movement essentially one-dimensional diminishing the value of Zcr; ii. it makes the potential weaker increasing the value of critical charge. The phenomenon of critical charge itself is also discussed.

Enhancement of Laser-Induced Breakdown Spectroscopic Signals in a Liquid Jet with Glow Discharge

In this work, emission signals of laser-induced breakdown (LIBS) plasma of a flowing liquid jet in the absence and presence of an air-supported glow discharge have been investigated. In combination with a needle-to-needle glow discharge, a Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) laser (1064 nm, 5 ns) with power density ∼1010 W/cm2 was used to generate a plasma from a liquid jet. Emission lines of Mg, Ca, Al, Li, Na, and K all showed significant enhancements in the presence of the glow discharge. Lower continuum background was also observed. Mechanisms of the line emission enhancement and continuum radiation reduction were discussed.

Perturbativity vs nonperturbativity in QED-effects for H-like atoms with Zα > 1

The behavior of levels near the threshold of the lower continuum in superheavy H-like atoms with [Formula: see text], caused by the interaction [Formula: see text] of the electron’s magnetic anomaly (AMM) dynamically screened at small distances [Formula: see text], with the Coulomb field of atomic nucleus is considered by taking into account the complete dependence of electron’s wave function (WF) on [Formula: see text]. It is shown that the calculation of the contribution caused by [Formula: see text] via both the quark structure and the whole nucleus, considered as a uniformly charged extended Coulomb source, leads to results, which coincide within the accepted precision of calculations. It is also shown that there appears some difference in results between perturbative and nonperturbative methods of accounting for the contribution from [Formula: see text] within the corresponding Dirac equation (DE) in favor of the latter. Moreover, the growth rate of the contribution from [Formula: see text] reaches its maximum at [Formula: see text], while by further increase of [Formula: see text] into the supercritical region [Formula: see text], the shift of levels caused by [Formula: see text] near the lower continuum decreases monotonically to zero. The last result is generalized to the whole self-energy contribution to the shift of levels and so to the possible behavior of radiative QED-effects with virtual photon exchange near the lower continuum.