560 research outputs found
Brane-World Black Hole Solutions via a Confining Potential
Using a confining potential, we consider spherically symmetric vacuum (static
black hole) solutions in a brane-world scenario. Working with a constant
curvature bulk, two interesting cases/solutions are studied. A Schwarzschild-de
Sitter black hole solution similar to the standard solution in the presence of
a cosmological constant is obtained which confirms the idea that an extra term
in the field equations on the brane can play the role of a positive
cosmological constant and may be used to account for the accelerated expansion
of the universe. The other solution is one in which we can have a proper
potential to explain the galaxy rotation curves without assuming the existence
of dark matter and without working with new modified theories (modified
Newtonian dynamics).Comment: 12 pages, to appear in PR
Unimodular cosmology and the weight of energy
Some models are presented in which the strength of the gravitational coupling
of the potential energy relative to the same coupling for the kinetic energy
is, in a precise sense, adjustable. The gauge symmetry of these models consists
of those coordinate changes with unit jacobian.Comment: LaTeX, 23 pages, conclusions expanded. Two paragraphs and a new
reference adde
Gauss-Bonnet brane gravity with a confining potential
A brane scenario is envisaged in which the -dimensional bulk is endowed
with a Gauss-Bonnet term and localization of matter on the brane is achieved by
means of a confining potential. The resulting Friedmann equations on the brane
are modified by various extra terms that may be interpreted as the X-matter,
providing a possible phenomenological explanation for the accelerated expansion
of the universe. The age of the universe in this scenario is studied and shown
to be consistent with the present observational data.Comment: 14 pages, 4 figures, to appear in PR
Chaplygin gas dominated anisotropic brane world cosmological models
We present exact solutions of the gravitational field equations in the
generalized Randall-Sundrum model for an anisotropic brane with Bianchi type I
geometry, with a generalized Chaplygin gas as matter source. The generalized
Chaplygin gas, which interpolates between a high density relativistic era and a
non-relativistic matter phase, is a popular dark energy candidate. For a
Bianchi type I space-time brane filled with a cosmological fluid obeying the
generalized Chaplygin equation of state the general solution of the
gravitational field equations can be expressed in an exact parametric form,
with the comoving volume taken as parameter. In the limiting cases of a stiff
cosmological fluid, with pressure equal to the energy density, and for a
pressureless fluid, the solution of the field equations can be expressed in an
exact analytical form. The evolution of the scalar field associated to the
Chaplygin fluid is also considered and the corresponding potential is obtained.
The behavior of the observationally important parameters like shear, anisotropy
and deceleration parameter is considered in detail.Comment: 13 pages, 6 figures, accepted for publication in PR
Geometric Properties of Static EMdL Horizons
We study non-degenerate and degenerate (extremal) Killing horizons of
arbitrary geometry and topology within the Einstein-Maxwell-dilaton model with
a Liouville potential (the EMdL model) in d-dimensional (d>=4) static
space-times. Using Israel's description of a static space-time, we construct
the EMdL equations and the space-time curvature invariants: the Ricci scalar,
the square of the Ricci tensor, and the Kretschmann scalar. Assuming that
space-time metric functions and the model fields are real analytic functions in
the vicinity of a space-time horizon, we study behavior of the space-time
metric and the fields near the horizon and derive relations between the
space-time curvature invariants calculated on the horizon and geometric
invariants of the horizon surface. The derived relations generalize the similar
relations known for horizons of static four and 5-dimensional vacuum and
4-dimensional electrovacuum space-times. Our analysis shows that all the
extremal horizon surfaces are Einstein spaces. We present necessary conditions
for existence of static extremal horizons within the EMdL model.Comment: 10 page
On extra forces from large extra dimensions
The motion of a classical test particle moving on a 4-dimensional brane
embedded in an -dimensional bulk is studied in which the brane is allowed to
fluctuate along the extra dimensions. It is shown that these fluctuations
produce three different forces acting on the particle, all stemming from the
effects of extra dimensions. Interpretations are then offered to describe the
origin of these forces and a relationship between the 4 and -dimensional
mass of the particle is obtained by introducing charges associated with large
extra dimensions.Comment: 9 pages, no figuer
Invariant classification of orthogonally separable Hamiltonian systems in Euclidean space
The problem of the invariant classification of the orthogonal coordinate webs
defined in Euclidean space is solved within the framework of Felix Klein's
Erlangen Program. The results are applied to the problem of integrability of
the Calogero-Moser model
Stress condensation in crushed elastic manifolds
We discuss an M-dimensional phantom elastic manifold of linear size L crushed
into a small sphere of radius R << L in N-dimensional space. We investigate the
low elastic energy states of 2-sheets (M=2) and 3-sheets (M=3) using analytic
methods and lattice simulations. When N \geq 2M the curvature energy is
uniformly distributed in the sheet and the strain energy is negligible. But
when N=M+1 and M>1, both energies appear to be condensed into a network of
narrow M-1 dimensional ridges. The ridges appear straight over distances
comparable to the confining radius R.Comment: 4 pages, RevTeX + epsf, 4 figures, Submitted to Phys. Rev. Let
A Comprehensive Mechanism Reproducing the Mass and Mixing Parameters of Quarks and Leptons
It is shown that if, from the starting point of a universal rank-one mass
matrix long favoured by phenomenologists, one adds the assumption that it
rotates (changes its orientation in generation space) with changing scale, one
can reproduce, in terms of only 6 real parameters, all the 16 mass ratios and
mixing parameters of quarks and leptons. Of these 16 quantities so reproduced,
10 for which data exist for direct comparison (i.e. the CKM elements including
the CP-violating phase, the angles in
-oscillation, and the masses ) agree well with
experiment, mostly to within experimental errors; 4 others (), the experimental values for which can only be inferred, agree
reasonably well; while 2 others ( for leptons), not yet
measured experimentally, remain as predictions. In addition, one gets as
bonuses, estimates for (i) the right-handed neutrino mass and (ii)
the strong CP angle inherent in QCD. One notes in particular that the
output value for from the fit agrees very well with
recent experiments. By inputting the current experimental value with its error,
one obtains further from the fit 2 new testable constraints: (i) that
must depart from its "maximal" value: , (ii) that the CP-violating (Dirac) phase in the PMNS would be
smaller than in the CKM matrix: of order only if
not vanishing altogether.Comment: 37 pages, 1 figur
Autonomous three dimensional Newtonian systems which admit Lie and Noether point symmetries
We determine the autonomous three dimensional Newtonian systems which admit
Lie point symmetries and the three dimensional autonomous Newtonian Hamiltonian
systems, which admit Noether point symmetries. We apply the results in order to
determine the two dimensional Hamiltonian dynamical systems which move in a
space of constant non-vanishing curvature and are integrable via Noether point
symmetries. The derivation of the results is geometric and can be extended
naturally to higher dimensions.Comment: Accepted for publication in Journal of Physics A: Math. and Theor.,13
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