5,862 research outputs found
Wave-like Solutions for Bianchi type-I cosmologies in 5D
We derive exact solutions to the vacuum Einstein field equations in 5D, under
the assumption that (i) the line element in 5D possesses self-similar symmetry,
in the classical understanding of Sedov, Taub and Zeldovich, and that (ii) the
metric tensor is diagonal and independent of the coordinates for ordinary 3D
space. These assumptions lead to three different types of self-similarity in
5D: homothetic, conformal and "wave-like". In this work we present the most
general wave-like solutions to the 5D field equations. Using the standard
technique based on Campbell's theorem, they generate a large number of
anisotropic cosmological models of Bianchi type-I, which can be applied to our
universe after the big-bang, when anisotropies could have played an important
role. We present a complete review of all possible cases of self-similar
anisotropic cosmologies in 5D. Our analysis extends a number of previous
studies on wave-like solutions in 5D with spatial spherical symmetry
Brane world solutions of perfect fluid in the background of a bulk containing dust or cosmological constant
The paper presents some solutions to the five dimensional Einstein equations
due to a perfect fluid on the brane with pure dust filling the entire bulk in
one case and a cosmological constant (or vacuum) in the bulk for the second
case. In the first case, there is a linear relationship between isotropic
pressure, energy density and the brane tension, while in the second case, the
perfect fluid is assumed to be in the form of chaplygin gas. Cosmological
solutions are found both for brane and bulk scenarios and some interesting
features are obtained for the chaplygin gas on the brane which are distinctly
different from the standard cosmology in four dimensions.Comment: 10 Latex pages, 5 figure
An exact self-similar solution for an expanding ball of radiation
We give an exact solution of the Einstein equations which in 4D can be
interpreted as a spherically symmetric dissipative distribution of matter, with
heat flux, whose effective density and pressure are nonstatic, nonuniform, and
satisfy the equation of state of radiation. The matter satisfies the usual
energy and thermodynamic conditions. The energy density and temperature are
related by the Stefan-Boltzmann law. The solution admits a homothetic Killing
vector in , which induces the existence of self-similar symmetry in 4D,
where the line element as well as the dimensionless matter quantities are
invariant under a simple "scaling" group.Comment: New version expanded and improved. To appear in Int. J. Mod. Phys.
Late time cosmic acceleration from vacuum Brans-Dicke theory in 5D
We show that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to
Brans-Dicke theory in 4D with a self interacting potential and an effective
matter field. The cosmological implication, in the context of FRW models, is
that the observed accelerated expansion of the universe comes naturally from
the condition that the scalar field is not a ghost, i.e., . We
find an effective matter-dominated 4D universe which shows accelerated
expansion if . We study the question of whether
accelerated expansion can be made compatible with large values of ,
within the framework of a 5D scalar-vacuum Brans-Dicke theory with variable,
instead of constant, parameter . In this framework, and based on a
general class of solutions of the field equations, we demonstrate that
accelerated expansion is incompatible with large values of .Comment: In V2 the summary section is expanded. To be published in Classical
and Quantum Gravity
The principle of least action for test particles in a four-dimensional spacetime embedded in 5D
It is well known that, in the five-dimensional scenario of braneworld and
space-time-mass theories, geodesic motion in 5D is observed to be non-geodesic
in 4D. Usually, the discussion is purely geometric and based on the dimensional
reduction of the geodesic equation in 5D, without any reference to the test
particle whatsoever. In this work we obtain the equation of motion in 4D
directly from the principle of least action. So our main thrust is not the
geometry but the particle observed in 4D. A clear physical picture emerges from
our work. Specifically, that the deviation from the geodesic motion in 4D is
due to the variation of the rest mass of a particle, which is induced by the
scalar field in the 5D metric and the explicit dependence of the spacetime
metric on the extra coordinate. Thus, the principle of least action not only
leads to the correct equations of motion, but also provides a concrete physical
meaning for a number of algebraic quantities appearing in the geometrical
reduction of the geodesic equation
The Big Bang as a Phase Transition
We study a five-dimensional cosmological model, which suggests that the
universe bagan as a discontinuity in a (Higgs-type) scalar field, or
alternatively as a conventional four-dimensional phase transition.Comment: 10 pages, 2 figures; typo corrected in equation (18); 1 reference
added; version to appear in International Journal of Modern Physics
The internal structure and formation of early-type galaxies: the gravitational--lens system MG2016+112 at z=1.004
[Abridged] We combine our measurements of the velocity dispersion and the
surface brightness profile of the lens galaxy D in the system MG2016+112
(z=1.004) with constraints from gravitational lensing to study its internal
mass distribution. We find that: (i) dark matter accounts for >50% of the total
mass within the Einstein radius (99% CL), excluding at the 8-sigma level that
mass follows light inside the Einstein radius with a constant mass-to-light
ratio (M/L). (ii) the total mass distribution inside the Einstein radius is
well-described by a density profile ~r^-gamma' with an effective slope
gamma'=2.0+-0.1+-0.1, including random and systematic uncertainties. (iii) The
offset of galaxy D from the local Fundamental Plane independently constrains
the stellar M/L, and matches the range derived from our models, leading to a
more stringent lower limit of >60% on the fraction of dark matter within the
Einstein radius (99%CL).
Under the assumption of adiabatic contraction, the inner slope of the dark
matter halo before the baryons collapsed is gamma_i<1.4 (68 CL), marginally
consistent with the highest-resolution cold dark matter simulations that
indicate gamma_i~1.5. This might indicate that either adiabatic contraction is
a poor description of E/S0 formation or that additional processes play a role
as well. Indeed, the apparently isothermal density distribution inside the
Einstein radius, is not a natural outcome of adiabatic contraction models,
where it appears to be a mere coincidence. By contrast, we argue that
isothermality might be the result of a stronger coupling between luminous and
dark-matter, possibly the result of (incomplete) violent relaxation processes.
Hence, we conclude that galaxy D appears already relaxed 8 Gyr ago.Comment: 8 pages, 4 figures, ApJ, in press, minor change
Distribution of Manganese in a Bio-Topo Sequence of Southeastern Iowa Soils
Manganese extractable by sodium hydrosulfite was determined for 9 soil profiles of a bio-topo (vegetation and drainage) sequence in southeastern Iowa. The distribution of manganese in the soils studied is influenced by vegetation, drainage, and pH. Under prairie vegetation the manganese is evenly distributed with depth in the well-drained soil, but with increasing wetness of the soil profile, manganese is apparently lost from the A1 horizon and accumulates in the lower part of the B horizon. Manganese accumulates in the A1 and A2 horizons of the well-drained soils developed under forest vegetation, but in profiles of increasing wetness the amount of manganese in the A1 and A2 horizons decreases and the amount of manganese in the lower B horizon increases. The distribution of manganese in the transition prairie forest soils was intermediate between soils developed under prairie vegetation and those developed under forest vegetation
Effective spacetime from multi-dimensional gravity
We study the effective spacetimes in lower dimensions that can be extracted
from a multidimensional generalization of the Schwarzschild-Tangherlini
spacetimes derived by Fadeev, Ivashchuk and Melnikov ({\it Phys. Lett,} {\bf A
161} (1991) 98). The higher-dimensional spacetime has
dimensions, where and are the number of "internal" and "external" extra
dimensions, respectively. We analyze the effective spacetime obtained
after dimensional reduction of the external dimensions. We find that when
the extra dimensions are compact (i) the physics in lower dimensions is
independent of and the character of the singularities in higher dimensions,
and (ii) the total gravitational mass of the effective matter distribution
is less than the Schwarzshild mass. In contrast, when the extra dimensions
are large this is not so; the physics in does explicitly depend on
, as well as on the nature of the singularities in high dimensions, and the
mass of the effective matter distribution (with the exception of wormhole-like
distributions) is bigger than the Schwarzshild mass. These results may be
relevant to observations for an experimental/observational test of the theory.Comment: A typo in Eq. (24) is fixe
Active gravitational mass and the invariant characterization of Reissner-Nordstrom spacetime
We analyse the concept of active gravitational mass for Reissner-Nordstrom
spacetime in terms of scalar polynomial invariants and the Karlhede
classification. We show that while the Kretschmann scalar does not produce the
expected expression for the active gravitational mass, both scalar polynomial
invariants formed from the Weyl tensor, and the Cartan scalars, do.Comment: 6 pages Latex, to appear in General Relativity and Gravitatio
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