8,118 research outputs found

### On Quantization of Time-Dependent Systems with Constraints

The Dirac method of canonical quantization of theories with second class
constraints has to be modified if the constraints depend on time explicitly. A
solution of the problem was given by Gitman and Tyutin. In the present work we
propose an independent way to derive the rules of quantization for these
systems, starting from physical equivalent theory with trivial
non-stationarity.Comment: 4 page

### The relation between isotopic composition of argon and carbon in natural gases

The methods and results of determination of the argon and carbon isotope compositions of hydrocarbon gases of Mezozoic complexes of Western Siberia are presented. Based on the Ar-36, Ar-40, C-12, C-13 content of the various deposits and on the presumed mechanisms of entry of these isotopes into the deposits, it is concluded that formation of natural gas in some deposits included vertical migration from a lower complex

### 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

### Coherent and semiclassical states in magnetic field in the presence of the Aharonov-Bohm solenoid

A new approach to constructing coherent states (CS) and semiclassical states
(SS) in magnetic-solenoid field is proposed. The main idea is based on the fact
that the AB solenoid breaks the translational symmetry in the xy-plane, this
has a topological effect such that there appear two types of trajectories which
embrace and do not embrace the solenoid. Due to this fact, one has to construct
two different kinds of CS/SS, which correspond to such trajectories in the
semiclassical limit. Following this idea, we construct CS in two steps, first
the instantaneous CS (ICS) and the time dependent CS/SS as an evolution of the
ICS. The construction is realized for nonrelativistic and relativistic spinning
particles both in (2+1)- and (3+1)- dimensions and gives a non-trivial example
of SS/CS for systems with a nonquadratic Hamiltonian. It is stressed that CS
depending on their parameters (quantum numbers) describe both pure quantum and
semiclassical states. An analysis is represented that classifies parameters of
the CS in such respect. Such a classification is used for the semiclassical
decompositions of various physical quantities.Comment: 35 pages, 2 figures. Some typos in (77), (101), and (135) corrected
with respect to the published version. Results unchange

### On "Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field"

Recently the paper "Schwinger Mechanism for Gluon Pair Production in the
Presence of Arbitrary Time Dependent Chromo-Electric Field" by G. C. Nayak was
published [Eur. Phys. J. C 59, 715 (2009); arXiv:0708.2430]. Its aim is to
obtain an exact expression for the probability of non-perturbative gluon pair
production per unit time per unit volume and per unit transverse momentum in an
arbitrary time-dependent chromo-electric background field. We believe that the
obtained expression is open to question. We demonstrate its inconsistency on
some well-known examples. We think that this is a consequence of using the
so-called "shift theorem" [arXiv:hep-th/0609192] in deriving the expression for
the probability. We make some critical comments on the theorem and its
applicability to the problem in question.Comment: 4 page

### Quantum scalar field in FRW Universe with constant electromagnetic background

We discuss massive scalar field with conformal coupling in
Friedmann-Robertson-Walker (FRW) Universe of special type with constant
electromagnetic field. Treating an external gravitational-electromagnetic
background exactly, at first time the proper-time representations for out-in,
in-in, and out-out scalar Green functions are explicitly constructed as
proper-time integrals over the corresponding (complex) contours. The
vacuum-to-vacuum transition amplitudes and number of created particles are
found and vacuum instability is discussed. The mean values of the current and
energy-momentum tensor are evaluated, and different approximations for them are
investigated. The back reaction of the particles created to the electromagnetic
field is estimated in different regimes. The connection between proper-time
method and effective action is outlined. The effective action in scalar QED in
weakly-curved FRW Universe (De Sitter space) with weak constant electromagnetic
field is found as derivative expansion over curvature and electromagnetic field
strength. Possible further applications of the results are briefly mentioned.Comment: 38 pages, LaTe

### 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 $M = R \times M_{1}
\times M_{2}$ describing the evolution of 2 Einsteinian factor spaces, $M_1$
and $M_2$, 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 $M_1,M_2$
and the 2-component perfect fluid source.Comment: LaTeX file, no figure

### Quantization of Point-Like Particles and Consistent Relativistic Quantum Mechanics

We revise the problem of the quantization of relativistic particle models
(spinless and spinning), presenting a modified consistent canonical scheme. One
of the main point of the modification is related to a principally new
realization of the Hilbert space. It allows one not only to include arbitrary
backgrounds in the consideration but to get in course of the quantization a
consistent relativistic quantum mechanics, which reproduces literally the
behavior of the one-particle sector of the corresponding quantum field. In
particular, in a physical sector of the Hilbert space a complete positive
spectrum of energies of relativistic particles and antiparticles is reproduced,
and all state vectors have only positive norms.Comment: 57 pages, LaTex fil

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