39 research outputs found
Intra--Galactic thin shell wormhole and its stability
In this paper, we construct an intra-galactic thin shell wormhole joining two
copies of identical galactic space times described by the Mannheim-Kazanas de
Sitter solution in conformal gravity and study its stability under spherical
perturbations. We assume the thin shell material as a Chaplygin gas and discuss
in detail the values of the relevant parameters under which the wormhole is
stable. We study the stability following the method by Eiroa and we also
qualitatively analyze the dynamics through the method of Weierstrass. We find
that the wormhole is generally unstable but there is a small interval in radius
for which the wormhole is stable
Simplicial Approach to Fractal Structures
A fractal lattice is defined by iterative maps on a simplex. In particular, Sierpinski gasket and von Koch flake are explicitly obtained by simplex transformations
An Application of Saint Venant's Theory to Volterra's Distortions
This paper deals with the analysis of the sixth elementary Volterra's distortion for a circular hollow, homogeneous, elastic, isotropic cylinder. More precisely, the specific load connected to the sixth distortion is proved to be equivalent (in Saint Venant's theory) to a right combined compressive and bending stress and to a right combined tensile and bending stress. Our results have been applied to a material made up of steel to compare the obtained numerical results with Volterra's predictions: the values calculated through Saint Venant's theory are more strictly related to those calculated by Volterra when the cylinder thickness tends to zero
Correct light deflection in Weyl conformal gravity
The conformal gravity fit to observed galactic rotation curves requires
{\gamma}>0. On the other hand, conventional method for light deflection by
galaxies gives a negative contribution to Schwarzschild value for {\gamma}>0,
which is contrary to observation. Thus, it is very important that the
contribution to bending should in principle be positive, no matter how small
its magnitude is. Here we show that the Rindler-Ishak method gives a positive
contribution to Schwarzschild deflection for {\gamma}>0, as desired. We also
obtain the exact local coupling term derived earlier by Sereno. These results
indicate that conformal gravity can potentially test well against all
astrophysical observations to date.Comment: 6 page
Generalized potential for apparent forces: the Coriolis effect
It is well known, from Newtonian physics, that apparent forces appear when
the motion of masses is described by using a non-inertial frame of reference.
The generalized potential of such forces is rigorously analyzed focusing on
their mathematical aspects.Comment: 8 pages, accepted for publication in Eur. J. Phy
The Vacuole Model: New Terms in the Second Order Deflection of Light
The present paper is an extension of a recent work (Bhattacharya et al. 2010)
to the Einstein-Strauss vacuole model with a cosmological constant, where we
work out the light deflection by considering perturbations up to order M^3 and
confirm the light bending obtained previously in their vacuole model by Ishak
et al. (2008). We also obtain another local coupling term
-((5{\pi}M^2{\Lambda})/8) related to {\Lambda}, in addition to the one obtained
by Sereno (2008, 2009). We argue that the vacuole method for light deflection
is exclusively suited to cases where the cosmological constant {\Lambda}
disappears from the path equation. However, the original Rindler-Ishak method
(2007) still applies even if a certain parameter {\gamma} of Weyl gravity does
not disappear. Here, using an alternative prescription, we obtain the known
term -(({\gamma}R)/2), as well as another new local term ((3{\pi}{\gamma}M)/2)
between M and {\gamma}. Physical implications are compared, where we argue that
the repulsive term -(({\gamma}R)/2) can be masked by the Schwarzschild term
((2M)/R) in the halo regime supporting attractive property of the dark matter.Comment: 15 page
A Nonsingular Brans Wormhole: An Analogue to Naked Black Holes
In a recent paper, we showed the Jordan frame vacuum Brans Class I solution
provided a wormhole analogue to Horowitz-Ross naked black hole in the wormhole
range -3/2<{\omega}<-4/3. Thereafter, the solution has been criticized by some
authors that, because of the presence of singularity in that solution within
this range, a wormhole interpretation of it is untenable. While the criticism
is correct, we show here that (i) a singularity-free wormhole can actually be
obtained from Class I solution by performing a kind of Wick rotation on it,
resulting into what Brans listed as his independent Class II solution (ii) the
Class II solution has all the necessary properties of a regular wormhole in a
revised range -2<{\omega}<-3/2 and finally, (iii) naked black holes, as
described by Horowitz and Ross, are spacetimes where the tidal forces attain
their maxima above the black hole horizon. We show that in the non-singular
Class II spacetime this maxima is attained above the throat and thus can be
treated as a wormhole analogue. Some related issues are also addressed.Comment: 20 pages, 4 figure