426 research outputs found
The Coincidence Limit of the Graviton Propagator in de Donder Gauge on de Sitter Background
We explicitly work out the de Sitter breaking contributions to the recent
solution for the de Donder gauge graviton propagator on de Sitter. We also
provide explicit power series expansions for the two structure functions, which
are suitable for implementing dimensional regularization. And we evaluate the
coincidence limit of the propagator.Comment: 41 pages, uses LaTeX 2e, version 2 has some typoes correcte
De Sitter Breaking through Infrared Divergences
Just because the propagator of some field obeys a de Sitter invariant
equation does not mean it possesses a de Sitter invariant solution. The classic
example is the propagator of a massless, minimally coupled scalar. We show that
the same thing happens for massive scalars with , and for massive
transverse vectors with , where is the dimension
of spacetime and is the Hubble parameter. Although all masses in these
ranges give infrared divergent mode sums, using dimensional regularization (or
any other analytic continuation technique) to define the mode sums leads to the
incorrect conclusion that de Sitter invariant solutions exist except at
discrete values of the masses.Comment: 27 pages, no figures, uses LaTeX 2epsilo
Transforming to Lorentz Gauge on de Sitter
We demonstrate that certain gauge fixing functionals cannot be added to the
action on backgrounds such as de Sitter in which a linearization instability is
present. We also construct the field dependent gauge transformation which
carries the electromagnetic vector potential from a convenient, non-de Sitter
invariant gauge to the de Sitter invariant, Lorentz gauge. The transformed
propagator agrees with the de Sitter invariant result previously found by
solving the propagator equation in Lorentz gauge. This shows that the gauge
transformation technique will eliminate unphysical breaking of de Sitter
invariance introduced by a gauge condition. It is suggested that the same
technique can be used to finally resolve the issue of whether or not free
gravitons are de Sitter invariant.Comment: 45 page
Investigation of flat spectrum radio sources by the interplanetary scintillation method at 111 MHz
Interplanetary scintillation observations of 48 of the 55 Augusto et al.
(1998) flat spectrum radio sources were carried out at 111 MHz using the
interplanetary scintillation method on the Large Phased Array (LPA) in Russia.
Due to the large size of the LPA beam (1\degr \times 0.5\degr) a careful
inspection of all possible confusion sources was made using extant large radio
surveys: 37 of the 48 sources are not confused. We were able to estimate the
scintillating flux densities of 13 sources, getting upper limits for the
remaining 35. Gathering more or improving extant VLBI data on these sources
might significantly improve our results. This proof-of-concept project tells us
that compact () flat spectrum radio sources show strong enough
scintillations at 111 MHz to establish/constrain their spectra (low-frequency
end).Comment: 14 pages, 3 figure
Theory of gravitation theories: a no-progress report
Already in the 1970s there where attempts to present a set of ground rules,
sometimes referred to as a theory of gravitation theories, which theories of
gravity should satisfy in order to be considered viable in principle and,
therefore, interesting enough to deserve further investigation. From this
perspective, an alternative title of the present paper could be ``why are we
still unable to write a guide on how to propose viable alternatives to general
relativity?''. Attempting to answer this question, it is argued here that
earlier efforts to turn qualitative statements, such as the Einstein
Equivalence Principle, into quantitative ones, such as the metric postulates,
stand on rather shaky grounds -- probably contrary to popular belief -- as they
appear to depend strongly on particular representations of the theory. This
includes ambiguities in the identification of matter and gravitational fields,
dependence of frequently used definitions, such as those of the stress-energy
tensor or classical vacuum, on the choice of variables, etc. Various examples
are discussed and possible approaches to this problem are pointed out. In the
course of this study, several common misconceptions related to the various
forms of the Equivalence Principle, the use of conformal frames and equivalence
between theories are clarified.Comment: Invited paper in the Gravity Research Foundation 2007 special issue
to be published by Int. J. Mod. Phys.
Conformally invariant wave-equations and massless fields in de Sitter spacetime
Conformally invariant wave equations in de Sitter space, for scalar and
vector fields, are introduced in the present paper. Solutions of their wave
equations and the related two-point functions, in the ambient space notation,
have been calculated. The ``Hilbert'' space structure and the field operator,
in terms of coordinate independent de Sitter plane waves, have been defined.
The construction of the paper is based on the analyticity in the complexified
pseudo-Riemanian manifold, presented first by Bros et al.. Minkowskian limits
of these functions are analyzed. The relation between the ambient space
notation and the intrinsic coordinates is then studied in the final stage.Comment: 21 pages, LaTeX, some details adde
МЕТОД РАСЧЕТА ПЕРЕХОДНЫХ РЕЖИМОВ ГРЕБНЫХ ЭЛЕКТРОЭНЕРГЕТИЧЕСКИХ УСТАНОВОК ЭЛЕКТРОХОДОВ
The purpose of the work is to develop the method for calculating the transient modes of electric ships’ propelling electric plants during maneuver. This will allow us to evaluate and improve the maneuverability of vessels with electric motion. Methodology. The solution to the problems is proposed to be carried out on the basis of mathematical modeling of maneuvering modes. The duration of transient modes in an electric power plant at electric ships’ maneuvers is commensurable with the transient operation modes of the vessel itself. Therefore, the analysis of the electric power plants’ maneuvering modes should be made in unity with all the components of the ship’s propulsion complex. Results. A specified mathematical model of transient regimes of electric ship’s propulsion complex, including thermal motors, synchronous generators, electric power converters, propulsion motors, propellers, rudder, ship’s hull is developed. The model is universal. It covers the vast majority of modern and promising electric ships with a traditional type of propulsors. It allows calculating the current values of the basic mode indicators and assessing the quality indicators of maneuvering. The model is made in relative units. Dimensionless parameters of the complex are obtained. These parameters influence the main indicators of the quality of maneuvering. The adequacy of the suggested specified mathematical model and the developed computation method based on it were confirmed. To do this, the results of mathematical modeling for a real electric ship were compared with the data obtained in the course of field experiments conducted by other researchers. Originality. The mathematical description of a generator unit, as an integral part of an indivisible ship’s propulsion complex, makes it possible to calculate the dynamic operation modes of electric power sources during electric vessels’ maneuvering. There is an opportunity to design the electric ships’ propulsion power plant according to the final result – according to the indicators characterizing the vessel and its maneuvering properties. The use of a system of dimensionless units provides a generality to the results obtained. Electric ships with equal values of dimensionless parameters will have correspondingly the same values (in relative units) of maneuvering quality indicators. Practical value. The developed mathematical model and the research method constructed on its basis allow calculating the current values of the basic regime parameters of all the components of the ship’s propulsion complex. A mathematical apparatus for estimating the main indicators of the quality of electric ships’ maneuvering is proposed. There is an opportunity to improve the electric ships’ maneuvering characteristics by optimizing the operation of propulsion motors.Целью работы является разработка метода расчета переходных режимов гребных электроэнергетических установок в составе судовых пропульсивных комплексов. Методика. На маневрах продолжительности переходных режимов в электроэнергетической установке соизмеримы с переходными режимами работы судна. Поэтому анализ маневренных режимов ее работы следует проводить в единстве со всеми составными частями судового пропульсивного комплекса. Результаты. Разработаны уточненная математическая модель и метод расчета переходных режимов всех составных частей пропульсивного комплекса электрохода на маневрах. Найдены безразмерные параметры комплекса. Они определяют основные показатели качества маневрирования. Адекватность модели и метода расчета подтверждены сравнением результатов математического моделирования с натурными экспериментами. Научная новизна. Метод расчета позволяет рассчитывать динамические режимы работы всех составных частей комплекса. Появляется возможность проектирования гребных электроэнергетических установок по конечному результату – по показателям качества маневрирования судна. Практическое значение. Метод расчета позволяет проводить исследования поведения пропульсивных комплексов на маневрах и отыскивать пути повышения маневренности электроходов
"Massless" vector field in de Sitter Universe
In the present work the massless vector field in the de Sitter (dS) space has
been quantized. "Massless" is used here by reference to conformal invariance
and propagation on the dS light-cone whereas "massive" refers to those dS
fields which contract at zero curvature unambiguously to massive fields in
Minkowski space. Due to the gauge invariance of the massless vector field, its
covariant quantization requires an indecomposable representation of the de
Sitter group and an indefinite metric quantization. We will work with a
specific gauge fixing which leads to the simplest one among all possible
related Gupta-Bleuler structures. The field operator will be defined with the
help of coordinate independent de Sitter waves (the modes) which are simple to
manipulate and most adapted to group theoretical matters. The physical states
characterized by the divergencelessness condition will for instance be easy to
identify. The whole construction is based on analyticity requirements in the
complexified pseudo-Riemanian manifold for the modes and the two-point
function.Comment: 33 pages, 3 figure
Two loop stress-energy tensor for inflationary scalar electrodynamics
We calculate the expectation value of the coincident product of two field
strength tensors at two loop order in scalar electrodynamics on de Sitter
background. The result agrees with the stochastic formulation which we have
developed in a companion paper [2] for the nonperturbative resummation of
leading logarithms of the scale factor. When combined with a previous
computation of scalar bilinears [1], our current result also gives the two loop
stress-energy tensor for inflationary scalar electrodynamics. This shows a
secular decrease in the vacuum energy which derives from the vacuum
polarization induced by the inflationary production of charged scalars.Comment: 62 pages, 1 eps figur
The restricted two-body problem in constant curvature spaces
We perform the bifurcation analysis of the Kepler problem on and .
An analogue of the Delaunay variables is introduced. We investigate the motion
of a point mass in the field of the Newtonian center moving along a geodesic on
and (the restricted two-body problem). When the curvature is small,
the pericenter shift is computed using the perturbation theory. We also present
the results of the numerical analysis based on the analogy with the motion of
rigid body.Comment: 29 pages, 7 figure
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