International Journal of Modern Physics D

In this paper we consider the Extrasolar Planetary Systems recently discovered in our Galaxy as potential sources of gravitational waves. We estimate the frequency and characteristic amplitude of the radiation they emit due to the orbital motion, using the quadrupole formalism. In addition, we check whether the conditions needed for the resonant excitation of the f- and g-modes of the central star can be fulfilled. By a Roche-lobe analysis, we show that there could exist systems in which the low-order g-modes could be excited, although this does not happen in the systems discovered up to now.

An attempt is made to go beyond the semiclassical approximation for gravity in the Born–Oppenheimer decomposition of the wave-function in minisuperspace. New terms are included which correspond to quantum gravitational fluctuations on the background metric. They induce a back-reaction on the semiclassical background and can lead to the avoidance of the singularities the classical theory predicts in cosmology and in the gravitational collapse of compact objects.

A link between the possibility of extending a geodesically incomplete kinked spacetime to a spacetime which is geodesically complete and the energy conditions is discussed for the case of a cylindrically-symmetric spacetime kink. It is concluded that neither the strong nor the weak energy condition can be satisfied in the four-dimensional example, though the latter condition may survive on the transversal sections of such a spacetime. It is also shown that the matter which propagates quantum-mechanically in a kinked spacetime can always be trapped by closed timelike curves, but signaling connections between that matter and any possible observer can only be made of totally incoherent radiation, so preventing observation of causality violation.

In this paper, we have considered generalized scalar–tensor theory for four-dimensional Bianchi-I model and also for a five-dimensional cosmological model. We have studied both exponential and power law solutions, considering a bulk viscous fluid. To solve the complicated coupled field equations, we have made assumptions among the physical parameters and solutions have been discussed.

It is shown that the event horizon of 4D black hole or ds²=0 surfaces of multidimensional wormhole-like solutions reduce the amount of information necessary for determining the whole spacetime and hence satisfy the Holography principle. This leads to the fact that by matching two metrics on a ds²=0 surface (an event horizon for 4D black holes) we can match only the metric components but not their derivatives. For example, this allows us to obtain a composite wormhole inserting a 5D wormhole-like flux tube between two Reissner–Nordström black holes and matching them on the event horizon. Using the Holography principle, the entropy of a black hole from the algorithm theory is obtained.

A statistical quantity suitable for distinguishing simply-connected Robertson–Walker (RW) universes is introduced, and its explicit expressions for the three possible classes of simply-connected RW universes with an uniform distribution of matter are determined. Graphs of the distinguishing mark for each class of RW universes are presented and analyzed. There sprout from our results an improvement on the procedure to extract the topological signature of multiply-connected RW universes, and a refined understanding of that topological signature of these universes studied in previous works.

While the pressureless dust assumption has been widely adopted in the standard model of cosmology, a quantitative estimate of the actual contribution of thermal pressure of the baryonic matter and the hot/cold dark matter to the dynamical evolution of the Universe has not yet been made in literature. In this paper we provide a simple scenario of how the solution, e.g. the age of the Universe, is affected by the inclusion of the thermal pressure of the baryon and dark matter particles.

With the ulterior motivation in mind to investigate the contribution of quantum processes on the dynamics of the expansion of the universe, we investigate dissipative cosmological solutions which preserve the isotropy and the homogeneity. For performing such an investigation, we derive a method which enables us to describe a 2D dynamical system by a Hamiltonian formulation. As formal example, an admissible form for the bulk (viscous) pressure is derived.

Various astronomical observations have been consistently making a strong case for the existence of a component of dark energy with negative pressure in the universe. It is now necessary to take the dark energy component(s) into account in gravitational lensing statistics and other cosmological tests. By using the comoving distance we derive analytic but simple expressions for the optical depth of multiple image, the expected value of image separation and the probability distribution of image separation caused by an assemble of singular isothermal spheres in general FRW cosmological models with dark energy component(s). We also present the kinematical and dynamical properties of these kinds of cosmological models and calculate the age of the universe and the distance measures, which are often used in classical cosmological tests. In some cases we are able to give formulae that are simpler than those found elsewhere in the literature, which could make the cosmological tests for dark energy component(s) more convenient.

We study boson star configurations with generic, but not nontopological, self-interaction terms. When compared with the usual λ|ψ|⁴ potential, similar results for masses and number of particles appear. However, changes are noticed in the order of a few percent of the star mass. We explore, using catastrophe theory, the stability properties of the configurations and look for possible observational outputs that may differentiate one model from the other: gravitational redshifts, rotation curves of accreted particles, and lensing phenomena are computed for our new cases.

We present a detailed analysis of the motion of test particles around a charged dilatonic black hole, using the Hamilton–Jacobi (HJ) formalism. We have considered test particles with various masses, electric charges and dilatonic charges and examine its behavior both in static and nonstatic cases.

A detailed analysis of the motion of test particles have been done around changed black hole. The study of the trajectories of the test particles have been done using the Hamilton–Jacobi formalism. We have considered test particles with various masses and electric charges and examine its behaviour both in static and nonstatic cares.