5,295 research outputs found
Cosmic String Wakes in Scalar-Tensor Gravities
The formation and evolution of cosmic string wakes in the framework of a
scalar-tensor gravity are investigated in this work. We consider a simple model
in which cold dark matter flows past an ordinary string and we treat this
motion in the Zel'dovich approximation. We make a comaprison between our
results and previous results obtained in the context of General Relativity. We
propose a mechanism in which the contribution of the scalar field to the
evolution of the wakes may lead to a cosmological observation.Comment: Replaced version to be published in the Classical and Quantum Gravit
Quantum Effects in the Spacetime of a Magnetic Flux Cosmic String
In this work we compute the vacuum expectation values of the energy-momentum
tensor and the average value of a massive, charged scalar field in the presence
of a magnetic flux cosmic string for both zero- and finite-temperature cases.Comment: To appear in the Int. Journal of Modern Phys. A (special issue).
Proceedings of the Second International Londrina Winter School on
Mathematical Methods in Physics, Londrina, Brazil, August 200
Local cosmic string in generalised scalar tensor theory
A recent investigation shows that a local gauge string with a
phenomenological energy momentum tensor, as prescribed by Vilenkin, is
inconsistent in Brans-Dicke theory. In this work it has been shown that such a
string is consistent in a more general scalar tensor theory where is
function of the scalar field.A set of solutions of full nonlinear Einstein's
equations for interior region of such a string are presented.Comment: 7 pages, latex format, minor changes according to referee's
suggestions, revised version submitted in Phys.Rev.
Contributions from Dilatonic Strings to the Flat Behaviour of the Rotational Curves in Galaxies
We analyse the flat behaviour of the rotational curves in some galaxies in
the framework of a dilatonic, current-carrying string. We determine the
expression of the tangential velocity of test objects following a stable
circular equatorial orbit in this spacetime.Comment: This version to be published in the Int. Journal of Modern Phys.
Cosmic String in Scalar-Tensor Gravity
The gravitational properties of a local cosmic string in the framework of
scalar-tensor gravity are examined. We find the metric in the weak-field
approximation and we show that, contrary to the General Relativity case, the
cosmic string in scalar-tensor gravitation exerces a force on non-relativistic,
neutral test particle. This force is proportional to the derivative of the
conformal factor and it is always attractive. Moreover, this
force could have played an important role at the Early Universe, although
nowadays it can be neglegible. It is also shown that the angular separation
remains unaltered for scalar-tensor cosmic strings.Comment: 15 pages, LATEX, no figure
The effect of pre-maturation culture using phosphodiesterase type 3 inhibitor and insulin, transferrin and selenium on nuclear and cytoplasmic maturation of bovine oocytes.
This study aims to evaluate if a pre-maturation culture (PMC) using cilostamide as a meiotic inhibitor in combination with insulin, transferrin and selenium (ITS) for 8 or 24 h increases in vitro embryo production. To evaluate the effects of PMC on embryo development, cleavage rate, blastocyst rate, embryo size and total cell number were determined. When cilostamide (20 M) was used in PMC for 8 or 24 h, 98% of oocytes were maintained in germinal vesicles. Although the majority of oocytes resumed meiosis after meiotic arrest, the cleavage and blastocyst rates were lower than the control (P 0.05) to the control. The deleterious effect of 20 M cilostamide treatment for 24 h on a PMC was confirmed by lower cumulus cell viability, determined by trypan blue staining, in that group compared with the other groups. A lower concentration (10 M) and shorter exposure time (8 h) minimized that effect but did not improve embryo production. More studies should be performed to determine th
Massive scalar field near a cosmic string
The function of a massive scalar field near a cosmic string is
computed and then employed to find the vacuum fluctuation of the field. The
vacuum expectation value of the energy-momentum tensor is also computed using a
point-splitting approach. The obtained results could be useful also for the
case of self-interacting scalar fields and for the finite-temperature Rindler
space theory.Comment: 15 pages, standard LaTeX, no figures. Reference [14] correcte
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