13,527 research outputs found
Multiple colliding electromagnetic pulses: a way to lower the threshold of 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 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 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
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
Manifestation of spin-orbit interaction in tunneling between 2D electron layers
An influence of spin-orbit interaction on the tunneling between two 2D
electron layers is considered. Particular attention is addressed to the
relation between the contribution of Rashba and Dresselhaus types. It is shown
that without scattering of the electrons, the tunneling conductance can either
exhibit resonances at certain voltage values or be substantially suppressed
over the whole voltage range. The dependence of the conductance on voltage
turns out to be very sensitive to the relation between Rashba and Dresselhaus
contributions even in the absence of magnetic field. The elastic scattering
broadens the resonances in the first case and restores the conductance to a
larger magnitude in the latter one. These effects open possibility to determine
the parameters of spin-orbit interaction and electrons scattering time in
tunneling experiments with no necessity of external magnetic field
Quantum effects with an X-ray free electron laser
A quantum kinetic equation coupled with Maxwell's equation is used to
estimate the laser power required at an XFEL facility to expose intrinsically
quantum effects in the process of QED vacuum decay via spontaneous pair
production. A 9 TW-peak XFEL laser with photon energy 8.3 keV could be
sufficient to initiate particle accumulation and the consequent formation of a
plasma of spontaneously produced pairs. The evolution of the particle number in
the plasma will exhibit non-Markovian aspects of the strong-field pair
production process and the plasma's internal currents will generate an electric
field whose interference with that of the laser leads to plasma oscillations.Comment: 4 pages, LaTeX2
Damping of electromagnetic waves due to electron-positron pair production
The problem of the backreaction during the process of electron-positron pair
production by a circularly polarized electromagnetic wave propagating in a
plasma is investigated. A model based on the relativistic Boltzmann-Vlasov
equation with a source term corresponding to the Schwinger formula for the pair
creation rate is used. The damping of the wave, the nonlinear up-shift of its
frequency due to the plasma density increase and the effect of the damping on
the wave polarization and on the background plasma acceleration are
investigated as a function of the wave amplitude.Comment: 11 pages, 5 figures; revtex
Schwinger Pair Production in dS_2 and AdS_2
We study Schwinger pair production in scalar QED from a uniform electric
field in dS_2 with scalar curvature R_{dS} = 2 H^2 and in AdS_2 with R_{AdS} =
- 2 K^2. With suitable boundary conditions, we find that the pair-production
rate is the same analytic function of the scalar curvature in both cases.Comment: RevTex 6 pages, no figure; replaced by the version published in PR
Virtual Processes and Superradiance in Spin-Boson Models
We consider spin-boson models composed by a single bosonic mode and an
ensemble of identical two-level atoms. The situation where the coupling
between the bosonic mode and the atoms generates real and virtual processes is
studied, where the whole system is in thermal equilibrium with a reservoir at
temperature . Phase transitions from ordinary fluorescence to
superradiant phase in three different models is investigated. First a model
where the coupling between the bosonic mode and the atom is via the
pseudo-spin operator is studied. Second, we investigate the
generalized Dicke model, introducing different coupling constants between the
single mode bosonic field and the environment, and for rotating
and counter-rotating terms, respectively. Finally it is considered a modified
version of the generalized Dicke model with intensity-dependent coupling in the
rotating terms. In the first model the zero mode contributes to render the
canonical entropy a negative quantity for low temperatures. The last two models
presents phase transitions, even when only Hamiltonian terms which generates
virtual processes are considered
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 -dependent electric field pointing in the -direction. We also
allow for a smoothly varying magnetic field parallel to . The result is
applied to a confined field for , a
semi-confined field for , and a linearly increasing
field . 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 and large
are filled by spontaneous pair creation.Comment: 33 pages and 9 figures. to appear in Phys. Rev.
Worldline Instantons II: The Fluctuation Prefactor
In a previous paper [1], it was shown that the worldline expression for the
nonperturbative imaginary part of the QED effective action can be approximated
by the contribution of a special closed classical path in Euclidean spacetime,
known as a worldline instanton. Here we extend this formalism to compute also
the prefactor arising from quantum fluctuations about this classical closed
path. We present a direct numerical approach for determining this prefactor,
and we find a simple explicit formula for the prefactor in the cases where the
inhomogeneous electric field is a function of just one spacetime coordinate. We
find excellent agreement between our semiclassical approximation, conventional
WKB, and recent numerical results using numerical worldline loops.Comment: 28 pages, 1 figure; v2 references added, version in PR
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