56 research outputs found
Creation of Dirac Particles in the Presence of a Constant Electric Field in an Anisotropic Bianchi I Universe
In this article we compute the density of Dirac particles created by a
cosmological anisotropic Bianchi I universe in the presence of a constant
electric field. We show that the particle distribution becomes thermal when one
neglects the electric interaction.Comment: 9 page
Two-dimensional metric and tetrad gravities as constrained second order systems
Using the Gitman-Lyakhovich-Tyutin generalization of the Ostrogradsky method
for analyzing singular systems, we consider the Hamiltonian formulation of
metric and tetrad gravities in two-dimensional Riemannian spacetime treating
them as constrained higher-derivative theories. The algebraic structure of the
Poisson brackets of the constraints and the corresponding gauge transformations
are investigated in both cases.Comment: replaced with revised version published in
Mod.Phys.Lett.A22:17-28,200
One-loop energy-momentum tensor in QED with electric-like background
We have obtained nonperturbative one-loop expressions for the mean
energy-momentum tensor and current density of Dirac's field on a constant
electric-like background. One of the goals of this calculation is to give a
consistent description of back-reaction in such a theory. Two cases of initial
states are considered: the vacuum state and the thermal equilibrium state.
First, we perform calculations for the vacuum initial state. In the obtained
expressions, we separate the contributions due to particle creation and vacuum
polarization. The latter contributions are related to the Heisenberg-Euler
Lagrangian. Then, we study the case of the thermal initial state. Here, we
separate the contributions due to particle creation, vacuum polarization, and
the contributions due to the work of the external field on the particles at the
initial state. All these contributions are studied in detail, in different
regimes of weak and strong fields and low and high temperatures. The obtained
results allow us to establish restrictions on the electric field and its
duration under which QED with a strong constant electric field is consistent.
Under such restrictions, one can neglect the back-reaction of particles created
by the electric field. Some of the obtained results generalize the calculations
of Heisenberg-Euler for energy density to the case of arbitrary strong electric
fields.Comment: 35 pages; misprints in the sign in definitions (40)-(43), and (68)
corrected, results unchange
Spinors in Weyl Geometry
We consider the wave equation for spinors in -dimensional Weyl
geometry. By appropriately coupling the Weyl vector as well as
the spin connection to the spinor field, conformal
invariance can be maintained. The one loop effective action generated by the
coupling of the spinor field to an external gravitational field is computed in
two dimensions. It is found to be identical to the effective action for the
case of a scalar field propagating in two dimensions.Comment: 13 pages, REVTEX, no figure
Effect of electromagnetic fields on the creation of scalar particles in a flat Robertson-Walker space-time
The influence of electromagnetic fields on the creation of scalar particles
from vacuum in a flat Robertson-Walker space-time is studied. The Klein Gordon
equation with varying electric field and constant magnetic one is solved. The
Bogoliubov transformation method is applied to calculate the pair creation
probability and the number density of created particles. It is shown that the
electric field amplifies the creation of scalar particles while the magnetic
field minimizes it.Comment: Important modifications, 20 pages, To appear in Eurpean Physical
Journal C. arXiv admin note: text overlap with arXiv:1108.033
Finite temperature nonlocal effective action for quantum fields in curved space
Massless and massive scalar fields and massless spinor fields are considered
at arbitrary temperatures in four dimensional ultrastatic curved spacetime.
Scalar models under consideration can be either conformal or nonconformal and
include selfinteraction. The one-loop nonlocal effective action at finite
temperature and free energy for these quantum fields are found up to the second
order in background field strengths using the covariant perturbation theory.
The resulting expressions are free of infrared divergences. Spectral
representations for nonlocal terms of high temperature expansions are obtained.Comment: 32 pages, LaTe
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