7,621 research outputs found
Energy-momentum tensor in thermal strong-field QED with unstable vacuum
The mean value of the one-loop energy-momentum tensor in thermal QED with
electric-like background that creates particles from vacuum is calculated. The
problem differes essentially from calculations of effective actions (similar to
that of Heisenberg--Euler) in backgrounds that do not violate the stability of
vacuum. The role of a constant electric background in the violation of both the
stability of vacuum and the thermal character of particle distribution is
investigated. Restrictions on the electric field and its duration under which
one can neglect the back-reaction of created particles are established.Comment: 7 pages, Talk presented at Workshop "Quantum Field Theory under the
Influence of External Conditions", Leipzig, September 17-21, 2007;
introduction extended, version accepted for publication in J.Phys.
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
Integration of D-dimensional 2-factor spaces cosmological models by reducing to the generalized Emden-Fowler equation
The D-dimensional cosmological model on the manifold describing the evolution of 2 Einsteinian factor spaces,
and , in the presence of multicomponent perfect fluid source is
considered. The barotropic equation of state for mass-energy densities and the
pressures of the components is assumed in each space. When the number of the
non Ricci-flat factor spaces and the number of the perfect fluid components are
both equal to 2, the Einstein equations for the model are reduced to the
generalized Emden-Fowler (second-order ordinary differential) equation, which
has been recently investigated by Zaitsev and Polyanin within discrete-group
analysis. Using the integrable classes of this equation one generates the
integrable cosmological models. The corresponding metrics are presented. The
method is demonstrated for the special model with Ricci-flat spaces
and the 2-component perfect fluid source.Comment: LaTeX file, no figure
The MRO-accompanied modes of Re-implantation into SiO2-host matrix: XPS and DFT based scenarios
The following scenarios of Re-embedding into SiO2-host by pulsed
Re-implantation were derived and discussed after XPS-and-DFT electronic
structure qualification: (i) low Re-impurity concentration mode -> the
formation of combined substitutional and interstitial impurities with
Re2O7-like atomic and electronic structures in the vicinity of oxygen
vacancies; (ii) high Re-impurity concentration mode -> the fabrication of
interstitial Re-metal clusters with the accompanied formation of ReO2-like
atomic structures and (iii) an intermediate transient mode with Re-impurity
concentration increase, when the precursors of interstitial defect clusters are
appeared and growing in the host-matrix structure occur. An amplification
regime of Re-metal contribution majority to the final Valence Band structure
was found as one of the sequences of intermediate transient mode. It was shown
that most of the qualified and discussed modes were accompanied by the MRO
(middle range ordering) distortions in the initial oxygen subnetwork of the
a-SiO2 host-matrix because of the appeared mixed defect configurations.Comment: 19 pages, 7 figures, accepted to J. Alloys and Compound
Toda chains with type A_m Lie algebra for multidimensional m-component perfect fluid cosmology
We consider a D-dimensional cosmological model describing an evolution of
Ricci-flat factor spaces, M_1,...M_n (n > 2), in the presence of an m-component
perfect fluid source (n > m > 1). We find characteristic vectors, related to
the matter constants in the barotropic equations of state for fluid components
of all factor spaces.
We show that, in the case where we can interpret these vectors as the root
vectors of a Lie algebra of Cartan type A_m=sl(m+1,C), the model reduces to the
classical open m-body Toda chain.
Using an elegant technique by Anderson (J. Math. Phys. 37 (1996) 1349) for
solving this system, we integrate the Einstein equations for the model and
present the metric in a Kasner-like form.Comment: LaTeX, 2 ps figure
Dirac Hamiltonian with superstrong Coulomb field
We consider the quantum-mechanical problem of a relativistic Dirac particle
moving in the Coulomb field of a point charge . In the literature, it is
often declared that a quantum-mechanical description of such a system does not
exist for charge values exceeding the so-called critical charge with based on the fact that the standard expression for the
lower bound state energy yields complex values at overcritical charges. We show
that from the mathematical standpoint, there is no problem in defining a
self-adjoint Hamiltonian for any value of charge. What is more, the transition
through the critical charge does not lead to any qualitative changes in the
mathematical description of the system. A specific feature of overcritical
charges is a non uniqueness of the self-adjoint Hamiltonian, but this non
uniqueness is also characteristic for charge values less than the critical one
(and larger than the subcritical charge with ). We present the spectra and (generalized) eigenfunctions for all
self-adjoint Hamiltonians. The methods used are the methods of the theory of
self-adjoint extensions of symmetric operators and the Krein method of guiding
functionals. The relation of the constructed one-particle quantum mechanics to
the real physics of electrons in superstrong Coulomb fields where multiparticle
effects may be of crucial importance is an open question.Comment: 44 pages, LaTex file, to be published in Teor.Mat.Fiz.
(Theor.Math.Phys.
Quantization of (2+1)-spinning particles and bifermionic constraint problem
This work is a natural continuation of our recent study in quantizing
relativistic particles. There it was demonstrated that, by applying a
consistent quantization scheme to a classical model of a spinless relativistic
particle as well as to the Berezin-Marinov model of 3+1 Dirac particle, it is
possible to obtain a consistent relativistic quantum mechanics of such
particles. In the present article we apply a similar approach to the problem of
quantizing the massive 2+1 Dirac particle. However, we stress that such a
problem differs in a nontrivial way from the one in 3+1 dimensions. The point
is that in 2+1 dimensions each spin polarization describes different fermion
species. Technically this fact manifests itself through the presence of a
bifermionic constant and of a bifermionic first-class constraint. In
particular, this constraint does not admit a conjugate gauge condition at the
classical level. The quantization problem in 2+1 dimensions is also interesting
from the physical viewpoint (e.g. anyons). In order to quantize the model, we
first derive a classical formulation in an effective phase space, restricted by
constraints and gauges. Then the condition of preservation of the classical
symmetries allows us to realize the operator algebra in an unambiguous way and
construct an appropriate Hilbert space. The physical sector of the constructed
quantum mechanics contains spin-1/2 particles and antiparticles without an
infinite number of negative-energy levels, and exactly reproduces the
one-particle sector of the 2+1 quantum theory of a spinor field.Comment: LaTex, 24 pages, no figure
Vacuum instability in external fields
We study particles creation in arbitrary space-time dimensions by external
electric fields, in particular, by fields, which are acting for a finite time.
The time and dimensional analysis of the vacuum instability is presented. It is
shown that the distributions of particles created by quasiconstant electric
fields can be written in a form which has a thermal character and seems to be
universal. Its application, for example, to the particles creation in external
constant gravitational field reproduces the Hawking temperature exactly.Comment: 36 pages, LaTe
Field on Poincare group and quantum description of orientable objects
We propose an approach to the quantum-mechanical description of relativistic
orientable objects. It generalizes Wigner's ideas concerning the treatment of
nonrelativistic orientable objects (in particular, a nonrelativistic rotator)
with the help of two reference frames (space-fixed and body-fixed). A technical
realization of this generalization (for instance, in 3+1 dimensions) amounts to
introducing wave functions that depend on elements of the Poincare group . A
complete set of transformations that test the symmetries of an orientable
object and of the embedding space belongs to the group . All
such transformations can be studied by considering a generalized regular
representation of in the space of scalar functions on the group, ,
that depend on the Minkowski space points as well as on the
orientation variables given by the elements of a matrix .
In particular, the field is a generating function of usual spin-tensor
multicomponent fields. In the theory under consideration, there are four
different types of spinors, and an orientable object is characterized by ten
quantum numbers. We study the corresponding relativistic wave equations and
their symmetry properties.Comment: 46 page
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