Accretion flow in a contracting magnetized interstellar cloud was studied using magnetohydrodynamical simulations and a nested grid technique. First, the interstellar magnetized cloud experiences a “runaway collapse” phase, in which the central density increases drastically within a finite time scale. Finally, it enters an accretion phase, in which inflowing matter accretes onto a central high-...

A covariant scalar-tensor-vector gravity theory is developed which allows the gravitational constant G, a vector field coupling ω and the vector field mass μ to vary with space and time. The equations of motion for a test particle lead to a modified gravitational acceleration law that can fit galaxy rotation curves and cluster data without non-baryonic dark matter. The theory is consistent with...

In this paper, the effect of a positive cosmological constant on spherically symmetric collapse with perfect fluid has been investigated. The matching conditions between static exterior and non-static interior spacetimes are given in the presence of a cosmological constant. We also study the apparent horizons and their physical significance. It is concluded that the cosmological constant slows ...

Dynamical vacuum energy or quintessence, a slowly varying and spatially inhomogeneous component of the energy density with negative pressure, is currently consistent with the observational data. One potential difficulty with the idea of quintessence is that couplings to ordinary matter should be strongly suppressed so as not to lead to observable time variations of the constants of nature. We f...

We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (i) the three independent time-delays and flux-ratios from Very Large Array (VLA) observations, (ii) the radio-image positions from Very Large Baseline Array (VLBA) observations, (iii) the shape of the deconvolved Einstein Ring from optical and infrared Hubb...

ADSTRACT We describe field theories for which the action is completely independent of the metric and connection of the space-time manifold. The metric in our approach is no more a fundamental field than a hadron field is a fundamental field in &CD. The fundamental fields in the action are O(5) gauge fields and combinations of these fields are interpreted as the metric and connection so that con...

Measurement of the Gravitational Constant G 8 Measurement of the Gravitational Constant G F. Nolting, J. Schurr, E. Holzschuh, and W. K undig The most precise published results for the gravitational constant G have claimed uncertainties of about 100 ppm. Such measurements are usually done by some variant of the Cavendish torsion balance [1], but other methods have also been tried. During the l...

We study S-duality transformations that mix the graviton with various forms of matter. In the case of matter in the form of a 3-form field, the dual of an (A)dS space time – with arbitrary curvature – is seen to be flat Minkowski space time, if the 3-form field has vanishing field strength before the duality transformation. Then we show that the Schwarzschild metric can be obtained as a suitabl...

In this paper, we study the effect of a positive cosmological constant on spherically symmetric dust collapse. We take the FRW metric in the interior region whereas Schwarzschild-de Sitter in the exterior region. The matching conditions between exterior and interior spacetimes are given in the presence of a cosmological constant. We also discuss the apparent horizons and their physical signific...

One of the main objectives of the Cosmic Lens All-Sky Survey (CLASS) collaboration has been to find gravitational lens (GL) systems at radio wavelengths that are suitable for the determination of time delays between image pairs. The survey is now near completion and at least 18 GL systems have been found. Here, I will discuss our efforts to measure time delays from several of these systems with...