118 research outputs found
Significance of tension for gravitating masses in Kaluza-Klein models
In this letter, we consider the six-dimensional Kaluza-Klein models with
spherical compactification of the internal space. Here, we investigate the case
of bare gravitating compact objects with the dustlike equation of state in the external (our) space and an arbitrary equation of state in the internal space, where is
the energy density of the source. This gravitating mass is spherically
symmetric in the external space and uniformly smeared over the internal space.
In the weak field approximation, the conformal variations of the internal space
volume generate the admixture of the Yukawa potential to the usual Newton's
gravitational potential. For sufficiently large Yukawa masses, such admixture
is negligible and the metric coefficients of the external spacetime coincide
with the corresponding expressions of General Relativity. Then, these models
satisfy the classical gravitational tests. However, we show that gravitating
masses acquire effective relativistic pressure in the external space. Such
pressure contradicts the observations of compact astrophysical objects (e.g.,
the Sun). The equality (i.e. tension) is the only possibility to
preserve the dustlike equation of state in the external space. Therefore, in
spite of agreement with the gravitational experiments for an arbitrary value of
, tension () plays a crucial role for the considered
models.Comment: 8 pages, no figure
On the problem of inflation in nonlinear multidimensional cosmological models
We consider a multidimensional cosmological model with nonlinear quadratic
and quartic actions. As a matter source, we include a monopole form
field, D-dimensional bare cosmological constant and tensions of branes located
in fixed points. In the spirit of the Universal Extra Dimensions models, the
Standard Model fields are not localized on branes but can move in the bulk. We
define conditions which ensure the stable compactification of the internal
space in zero minimum of the effective potentials. Such effective potentials
may have rather complicated form with a number of local minima, maxima and
saddle points. Then, we investigate inflation in these models. It is shown that
and models can have up to 10 and 22 e-foldings, respectively. These
values are not sufficient to solve the homogeneity and isotropy problem but big
enough to explain the recent CMB data. Additionally, model can provide
conditions for eternal topological inflation. However, the main drawback of the
given inflationary models consists in a value of spectral index which is
less than observable now . For example, in the case of
model we find .Comment: 18 pages, RevTex4, References are correcte
Problematic aspects of Kaluza-Klein excitations in multidimensional models with Einstein internal spaces
We consider Kaluza-Klein (KK) models where internal spaces are compact
Einstein spaces. These spaces are stabilized by background matter (e.g.,
monopole form-fields). We perturb this background by a compact matter source
(e.g., the system of gravitating masses) with the zero pressure in the
external/our space and an arbitrary pressure in the internal space. We show
that the Einstein equations are compatible only if the matter source is smeared
over the internal space and perturbed metric components do not depend on
coordinates of extra dimensions. The latter means the absence of KK modes
corresponding to the metric fluctuations. Maybe, the absence of KK particles in
LHC experiments is explained by such mechanism.Comment: 10 pages, no figure
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