187 research outputs found
Weak-field limit of Kaluza-Klein models with spherical compactification: experimental constraints
We investigate the classical gravitational tests for the six-dimensional
Kaluza-Klein model with spherical (of a radius ) compactification of the
internal space. The model contains also a bare multidimensional cosmological
constant . The matter, which corresponds to this ansatz, can be
simulated by a perfect fluid with the vacuum equation of state in the external
space and an arbitrary equation of state with the parameter in the
internal space. For example, and correspond to the
monopole two-forms and the Casimir effect, respectively. In the particular case
, the parameter is also absent: . In the
weak-field approximation, we perturb the background ansatz by a point-like
mass. We demonstrate that in the case the perturbed metric
coefficients have the Yukawa type corrections with respect to the usual
Newtonian gravitational potential. The inverse square law experiments restrict
the parameters of the model: $a/\sqrt{\omega_1}\lesssim 6\times10^{-3}\
{{cm}}\gamma\omega_1>0\omega_1=0\gamma=1/3$,
which strongly contradicts the observations.Comment: 8 pages, no figures, revised version, equations and references added,
accepted for publication in Phys. Rev. D. arXiv admin note: significant text
overlap with arXiv:1107.338
Asymptotic latent solitons, black strings and black branes in f(R)-gravity
We investigate nonlinear f(R) theories in the Kaluza-Klein models with
toroidal compactification of extra dimensions. A point-like matter source has
the dust-like equation of state in our three dimensions and nonzero equations
of state in the extra dimensions. We obtain solutions of linearized Einstein
equations with this matter source taking into account effects of nonlinearity
of the model. There are two asymptotic regions where solutions satisfy the
gravitational tests at the same level of accuracy as General Relativity.
According to these asymptotic regions, there are two classes of solutions. We
call these solutions asymptotic latent solitons. The asymptotic latent solitons
from the first class generalize the known result of the linear theory. The
asymptotic black strings and black branes are particular cases of these
asymptotic solutions. The second class of asymptotic solitons exists only in
multidimensional nonlinear models. The main feature for both of these classes
of solutions is that the matter sources have tension in the extra dimensions.Comment: RevTex4 5 pages, no figure
Kaluza-Klein models: can we construct a viable example?
In Kaluza-Klein models, we investigate soliton solutions of Einstein
equation. We obtain the formulas for perihelion shift, deflection of light,
time delay of radar echoes and PPN parameters. We find that the solitonic
parameter k should be very big: |k|\geq 2.3\times10^4. We define a soliton
solution which corresponds to a point-like mass source. In this case the
soliton parameter k=2, which is clearly contrary to this restriction. Similar
problem with the observations takes place for static spherically symmetric
perfect fluid with the dust-like equation of state in all dimensions. The
common for both of these models is the same equations of state in our three
dimensions and in the extra dimensions. All dimensions are treated at equal
footing. To be in agreement with observations, it is necessary to break the
symmetry between the external/our and internal spaces. It takes place for black
strings which are particular examples of solitons with k\to \infty. For such k,
black strings are in concordance with the observations. Moreover, we show that
they are the only solitons which are at the same level of agreement with the
observations as in general relativity. Black strings can be treated as perfect
fluid with dust-like equation of state p_0=0 in the external/our space and very
specific equation of state p_1=-(1/2)\epsilon in the internal space. The latter
equation is due to negative tension in the extra dimension. We also demonstrate
that dimension 3 for the external space is a special one. Only in this case we
get the latter equation of state. We show that the black string equations of
state satisfy the necessary condition of the internal space stabilization.
Therefore, black strings are good candidates for a viable model of
astrophysical objects (e.g., Sun) if we can provide a satisfactory explanation
of negative tension for particles constituting these objects.Comment: 11 pages, Revtex4, no figures, appendix and references adde
Bouncing inflation in nonlinear gravitational model
We study a gravitational model with curvature-squared and
curvature-quartic nonlinearities. The effective scalar degree of freedom
(scalaron) has a multi-valued potential consisting of a number
of branches. These branches are fitted with each other in the branching and
monotonic points. In the case of four-dimensional space-time, we show that the
monotonic points are penetrable for scalaron while in the vicinity of the
branching points scalaron has the bouncing behavior and cannot cross these
points. Moreover, there are branching points where scalaron bounces an infinite
number of times with decreasing amplitude and the Universe asymptotically
approaches the de Sitter stage. Such accelerating behavior we call bouncing
inflation. For this accelerating expansion there is no need for original
potential to have a minimum or to check the slow-roll conditions. A
necessary condition for such inflation is the existence of the branching
points. This is a new type of inflation. We show that bouncing inflation takes
place both in the Einstein and Brans-Dicke frames.Comment: RevTex 13 pages, 13 figures, a few comments and references adde
Weak-field limit of f(R)-gravity in three and more spatial dimensions
We investigate a point-like massive source in non-linear f(R) theories in the
case of arbitrary number of spatial dimensions D\geq 3. If D>3 then extra
dimensions undergo toroidal compactification. We consider a weak-field
approximation with Minkowski and de Sitter background solutions. In both these
cases point-like massive sources demonstrate good agreement with experimental
data only in the case of ordinary three-dimensional (D=3) space. We generalize
this result to the case of perfect fluid with dust-like equations of state in
the external and internal spaces. This perfect fluid is uniformly smeared over
all extra dimensions and enclosed in a three-dimensional sphere. In ordinary
three dimensional (D=3) space, our formulas are useful for experimental
constraints on parameters of f(R) models.Comment: 8 pages, Revtex4, no figure
Restrictions on dilatonic brane-world models
We consider dilatonic brane-world models with a non-minimal coupling between
a dilaton and usual matter on a brane. We demonstrate that variation of the
fundamental constants on the brane due to such interaction leads to strong
restrictions on parameters of models. In particular, the experimental bounds on
variation of the fine structure constant rule out non-minimal dilatonic models
with a Liouville-type coupling potential f(varphi) = exp (b varphi) where b is
order of 1.Comment: MiKTeX2-LaTeX2e, 10 pages, minor changes, improved references, to
appear in IJMP
Multidimensional cosmological models: cosmological and astrophysical implications and constraints
We investigate four-dimensional effective theories which are obtained by
dimensional reduction of multidimensional cosmological models with factorizable
geometry and consider the interaction between conformal excitations of the
internal space (geometrical moduli excitations) and Abelian gauge fields. It is
assumed that the internal space background can be stabilized by minima of an
effective potential. The conformal excitations over such a background have the
form of massive scalar fields (gravitational excitons) propagating in the
external spacetime. We discuss cosmological and astrophysical implications of
the interaction between gravexcitons and four-dimensional photons as well as
constraints arising on multidimensional models of the type considered in our
paper. In particular, we show that due to the experimental bounds on the
variation of the fine structure constant, gravexcitons should decay before
nucleosynthesis starts. For a successful nucleosynthesis the masses of the
decaying gravexcitons should be m>10^4 GeV. Furthermore, we discuss the
possible contribution of gravexcitons to UHECR. It is shown that, at energies
of about 10^{20}eV, the decay length of gravexcitons with masses m>10^4 GeV is
very small, but that for m <10^2 GeV it becomes much larger than the
Greisen-Zatsepin-Kuzmin cut-off distance. Finally, we investigate the
possibility for gravexciton-photon oscillations in strong magnetic fields of
astrophysical objects. The corresponding estimates indicate that even the high
magnetic field strengths of magnetars are not sufficient for an efficient and
copious production of gravexcitons.Comment: 16 pages, LaTeX2e, minor changes, improved references, to appear in
PR
ОСУЧАСНЕННЯ ТА МОДЕРНІЗАЦІЯ СИСТЕМИ ЕЛЕКТРОННИХ ПЛАТЕЖІВ НАЦІОНАЛЬНОГО БАНКУ УКРАЇНИ ЗА ЄВРОПЕЙСЬКИМ ДОСВІДОМ У КОНТЕКСТІ ГЛОБАЛІЗАЦІЙНИХ ПРОЦЕСІВ
Today for the System of Electronic Payments of the National Bank of Ukraine is actual modernization and updating according to the real needs of payment system participants in the current economic situation in Ukraine. For improvement forms of interbank payments important is a restructuring of the national payment system in accordance with international and EU standards.
The article analyzes the functioning of the payment system TARGET2, discloses its advantages and principles of organization. The authors conducted a comparative analysis of payment systems TARGET2 and The System of Electronic Payments of the National Bank of Ukraine, as well as provided recommendations for improving the domestic payment system based on the experience of the European Union
The NBU’s Electronic Payment System is quite modern and efficient, but the existence of a certain time in the payment process, insufficient level of regulatory and information support of the electronic payment system participants and its control lead to the possibility of opaque financial transactions in the system itself. The lack of organizational and financial mechanisms today is also a serious drawback in his work.
In Ukraine, the technological level of the NBU system of calculations does not quite allow to use qualitatively most of the means of supporting intraday liquidity. This is a significant disadvantage of EPS compared to its foreign counterpart TARGET2.
An analysis of the functioning of TARGET2 and SEP enabled us to examine in more detail the positives and negatives of both payment systems.
A significant advantage of TARGET2 is its liquidity management system, which, under certain conditions, is an effective tool in the planning of settlement operations. This allows system members to prevent problems during the calculations and to solve them effectively. Optimization of liquidity management in the SEP is negligible.
The National Bank of Ukraine, unlike the European Central Bank, does not provide full information on EPS, which indicates the closedness of the payment system and the NBU’s unwillingness to provide the most transparent settlement mechanism.
Today, the TARGET2 settlement system is more modern and open compared to the NBU’s Electronic Payment System.На сьогодні для Системи електронних платежів Національного банку України актуальною є модернізація та осучаснення відповідно до реальних потреб учасників платіжної системи в умовах сучасної економічної ситуації в Україні. Для вдосконалення форм міжбанківських розрахунків важливою є перебудова національної платіжної системи відповідно до міжнародних стандартів і стандартів ЄС.
Проведено аналіз функціонування платіжної системи ТАРГЕТ2, розкрито її переваги і принципи організації. Проведено порівняльний аналіз платіжних систем ТАРГЕТ2 та системи електронних платежів Національного банку, а також надано рекомендації щодо вдосконалення вітчизняної платіжної системи на основі досвіду Європейського Союзу.
Система електронних платежів НБУ є досить сучасною та ефективною, але існування певного часу у проходженні платежу, недостатньо високий рівень нормативного та інформаційного забезпечення учасників системи електронних платежів та її контролю призводять до можливості непрозорих фінансових операцій у самій системі.
В Україні технологічний рівень розрахункової системи НБУ не зовсім дозволяє якісно використовувати більшість із засобів підтримки внутрішньоденної ліквідності, що є значним недоліком СЕП у порівнянні з її зарубіжним аналогом — ТАРГЕТ2.
Аналіз функціонування ТАРГЕТ2 та СЕП надав змогу більш детально розглянути позитивні і негативні моменти обох платіжних систем.
Значною перевагою ТАРГЕТ2 є система управління ліквідністю, що за певних умов є дієвим інструментом при плануванні розрахункових операцій. Це дозволяє учасникам системи попереджувати виникнення проблем під час розрахунків та ефективно розв’язувати їх. Оптимізація управління ліквідністю у СЕП є незначною.
Національний банк України, на відміну від Європейського центрального банку, надає інформацію стосовно СЕП не в повному обсязі, що свідчить про закритість платіжної системи та неготовність НБУ забезпечувати максимально прозорий механізм розрахунків.
На сьогодні система розрахунків ТАРГЕТ2 є більш сучасною та відкритою у порівнянні із Cистемою електронних платежів НБУ
Slow-roll inflation in (R+R*4) gravity
We reconsider the toy-model of topological inflation, based on the
R*4-modified gravity. By using its equivalence to the certain scalar-tensor
gravity model in four space-time dimensions, we compute the inflaton scalar
potential and investigate a possibility of inflation. We confirm the existence
of the slow-roll inflation with an exit. However, the model suffers from the
eta-problem that gives rise to the unacceptable value of the spectral index n_s
of scalar perturbations.Comment: 12 pages, 3 figures, LaTeX, misprints corrected and references
update
Anisotropic Inflation and the Origin of Four Large Dimensions
In the context of (4+d)-dimensional general relativity, we propose an
inflationary scenario wherein 3 spatial dimensions grow large, while d extra
dimensions remain small. Our model requires that a self-interacting d-form
acquire a vacuum expectation value along the extra dimensions. This causes 3
spatial dimensions to inflate, whilst keeping the size of the extra dimensions
nearly constant. We do not require an additional stabilization mechanism for
the radion, as stable solutions exist for flat, and for negatively curved
compact extra dimensions. From a four-dimensional perspective, the radion does
not couple to the inflaton; and, the small amplitude of the CMB temperature
anisotropies arises from an exponential suppression of fluctuations, due to the
higher-dimensional origin of the inflaton. The mechanism triggering the end of
inflation is responsible, both, for heating the universe, and for avoiding
violations of the equivalence principle due to coupling between the radion and
matter.Comment: 24 pages, 2 figures; uses RevTeX4. v2: Minor changes and added
references. v3: Improved discussion of slow-rol
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