Multiple colliding electromagnetic pulses: a way to lower the threshold of e+e−e^+e^- pair production from vacuum

The scheme of simultaneous multiple pulse focusing on one spot naturally arises from the structural features of projected new laser systems, such as ELI and HiPER. It is shown that the multiple pulse configuration is beneficial for observing $e^+e^-$ pair production from vacuum under the action of sufficiently strong electromagnetic fields. The field of the focused pulses is described using a realistic three-dimensional model based on an exact solution of the Maxwell equations. The $e^+e^-$ pair production threshold in terms of electromagnetic field energy can be substantially lowered if, instead of one or even two colliding pulses, multiple pulses focused on one spot are used. The multiple pulse interaction geometry gives rise to subwavelength field features in the focal region. These features result in the production of extremely short $e^+e^-$ bunches.Comment: 10 pages, 4 figure

Fermion Pair Production From an Electric Field Varying in Two Dimensions

The Hamiltonian describing fermion pair production from an arbitrarily time-varying electric field in two dimensions is studied using a group-theoretic approach. We show that this Hamiltonian can be encompassed by two, commuting SU(2) algebras, and that the two-dimensional problem can therefore be reduced to two one-dimensional problems. We compare the group structure for the two-dimensional problem with that previously derived for the one-dimensional problem, and verify that the Schwinger result is obtained under the appropriate conditions.Comment: Latex, 14 pages of text. Full postscript version available via the worldwide web at http://nucth.physics.wisc.edu/ or by anonymous ftp from ftp://nucth.physics.wisc.edu:/pub/preprints

Multidimensional Worldline Instantons

We extend the worldline instanton technique to compute the vacuum pair production rate for spatially inhomogeneous electric background fields, with the spatial inhomogeneity being genuinely two or three dimensional, both for the magnitude and direction of the electric field. Other techniques, such as WKB, have not been applied to such higher dimensional problems. Our method exploits the instanton dominance of the worldline path integral expression for the effective action.Comment: 22 pages, 13 figure

Electron-Positron Pair Production in Space- or Time-Dependent Electric Fields

Treating the production of electron and positron pairs by a strong electric field from the vacuum as a quantum tunneling process we derive, in semiclassical approximation, a general expression for the pair production rate in a $z$-dependent electric field $E(z)$ pointing in the $z$-direction. We also allow for a smoothly varying magnetic field parallel to $E(z)$. The result is applied to a confined field $E(z)\not=0$ for $|z|\lesssim \ell$, a semi-confined field $E(z)\not=0$ for $z\gtrsim 0$, and a linearly increasing field $E(z)\sim z$. The boundary effects of the confined fields on pair-production rates are exhibited. A simple variable change in all formulas leads to results for electric fields depending on time rather than space. In addition, we discuss tunneling processes in which empty atomic bound states are spontaneously filled by negative-energy electrons from the vacuum under positron emission. In particular, we calculate the rate at which the atomic levels of a bare nucleus of finite size $r_{\rm n}$ and large $Z\gg 1$ are filled by spontaneous pair creation.Comment: 33 pages and 9 figures. to appear in Phys. Rev.

Polarization of the electron and positron produced in combined Coulomb and strong laser fields

The process of $e^+e^-$ production in the superposition of a Coulomb and a strong laser field is considered. The pair production rate integrated over the momentum and summed over the spin projections of one of the particles is derived exactly in the parameters of the laser field and in the Born approximation with respect to the Coulomb field. The case of a monochromatic circularly polarized laser field is considered in detail. A very compact analytical expression of the pair production rate and its dependence on the polarization of one of the created particles is obtained in the quasiclassical approximation for the experimentally relevant case of an undercritical laser field. As a result, the polarization of the created electron (positron) is derived.Comment: 16 pages, no figure

Critical nucleus charge in a superstrong magnetic field: effect of screening

A superstrong magnetic field stimulates the spontaneous production of positrons by naked nuclei by diminishing the value of the critical charge Z_{cr} . The phenomenon of screening of the Coulomb potential by a superstrong magnetic field which has been discovered recently acts in the opposite direction and prevents the nuclei with Z52 for a nucleus to become critical stronger B are needed than without taking screening into account.Comment: 13 pages, 2 figures, version to be published in Physical Review