International Journal of Modern Physics D

Self-similar solutions of a collapsing perfect fluid and a massless scalar field with kinematic self-similarity of the second kind in (2 + 1) dimensions are obtained. The local and global properties of the solutions are studied. It is found that some of them represent gravitational collapse, in which black holes are always formed, and some may be interpreted as representing cosmological models.

The structure of strange dwarfs and that of hybrid stars with the same baryonic number is compared. There is a critical mass (M ≈ 0.24M_⊙) in the strange dwarf branch, below which configurations with the same baryonic number in the hybrid star branch are more stable. If a transition occurs between both branches, the collapse releases an energy of about of 3 × 10⁵⁰erg, mostly in the form of neutrinos resulting from the conversion of hadronic matter onto strange quark matter. Only a fraction (~ 4%) is required to expel the outer neutron-rich layers. These events may contribute significantly to the chemical yield of nuclides with A ≥ 80 in the Galaxy, if their frequency is of about one per 1,500 years.

In induced-matter theory, a 4D non-empty physical space–time is obtained from the 5D Ricci-flat one by setting the extra dimension coordinate equal to a constant. On the basis of this theory, we construct a 4D physical space–time by choosing a certain supersurface equation F(x^A) = 0 (A runs over 0 ~ 4). It is shown that, the 4D two-fluid FRW cosmological model can be obtained from 5D flat space–time by specifying F(x^A) = 0 as x⁴-x⁰ = 0.

A black string generalization of the Myers–Perry N-dimensional rotating black hole is considered in an (N + 1)-dimensional Randall–Sundrum brane world. The black string intercepts the (N - 1) brane in a N-dimensional rotating black hole. We examine the diverse cases arising for various non-zero rotation components and obtain the geodesic equations for these space–times. The causal structure and asymptotics of the resulting brane world geometries are analyzed.

We consider the evolution of a flat Friedmann–Roberstson–Walker Universe in a higher derivative theory, including αR² terms for the Einstein–Hilbert action in the presence of variable gravitational and cosmological constants. We study the evolution of the gravitational and cosmological constants in the radiation and matter domination era of the universe. We present new cosmological solutions which are physically interesting for model building.

We consider the phantom cosmology with a Lagrangian originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(X_c) at the critical point (X_c, 0) should be maximum and greater than zero. We study a specific potential with the form of via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ω_ϕ≃10^-12 at the equipartition epoch), and also avoid the future collapse of the universe.

We consider a class of five-dimensional cosmological solutions which contain two arbitrary function μ(t) and ν(t). We find that the arbitrary function μ(t) contained in the solutions can be rewritten in terms of the redshift z as a new arbitrary function f(z). We further show that this new arbitrary function f(z) can be solved for four known parameterized equations of state of dark energy. Then 5D models can be reconstructed and the evolution of the density and deceleration parameters of the universe can be determined.

We study the problem of all-sky search in reference to a continuous gravitational wave (CGW) whose wave-form is known in advance. We employ the concept of fitting factor and study the variation in the bank of search templates with different Earth azimuth at t = 0. We found that the number of search templates varies significantly. Hence, accordingly, the computational demand for the search may be reduced up to two orders by time shifting the data.

The coalescence rate of two neutron stars (NS) is revisited. To estimate the number of bound NS-NS and the probability of their coalescence in a time scale τ, the galactic star formation history, directly derived from observations, and the evolution of massive stars are considered. The newly established galactic merging rate is (1.7±1.0) × 10^-5yr^-1, while the local merging rate, including the contribution of elliptical galaxies, is about a factor of two higher, 3.4 × 10^-5yr^-1. Using the present data basis on galaxy distribution in the local universe and the expected sensitivity of the first generation of laser beam interferometers, we estimate that one event should occur every 125 years for LIGO and one event each 148 years for VIRGO. The situation is considerably improved for advanced-LIGO, since we predict that 6 events per year should be detected whereas for a recently proposed VIRGO new configuration, the event rate might increase up to 3 events every two years.

We analyze the dynamics of an apparent horizon in higher dimensional (HD) dust collapse. We have taken into consideration two different types of dust models. We propose the concept of a "trapped range" of initial data in different higher dimensional space–times. We show that "trapped range" of initial data increases with the increase in dimensions of the space–times.

We compile all the available optical B band data for the quasar 3C 273 from 1887 to 2001 from the literature, and obtain 1,890 data points. Using these data, we analyze the light curve properties by means of the Jurkevich method and the discrete correlation function (DCF) method. The analysis results of the two methods are self consistent; the cross-checked variability period is 13.51 years. The 13.51-year period variation in the optical band is in good agreement with the previous results in the optical and X-ray bands. However, the other claimed periods of the quasar 3C 273 are not confirmed in our work.

A recent review article by S. Samuel "On the Speed of Gravity and the Jupiter/Quasar Measurement" published as Int. J. Mod. Phys. D13, 1753 (2004), provides the reader with a misleading "theory" of the relativistic time delay in the general theory of relativity. Furthermore, it misquotes original publications by Kopeikin and Fomalont and Kopeikin related to the measurement of the speed of gravity by VLBI. We summarize the general relativistic principles of the Lorentz-invariant theory of the propagation of light in a time-dependent gravitational field, derive a Lorentz-invariant expression for the relativistic time delay, and finally explain why Samuel's "theory" is conceptually incorrect and confuses the speed of gravity with the speed of light.

The observation of Shapiro time delay of quasar light passing near Jupiter¹ generated considerable excitement, but also considerable controversy. The disagreements involve two distinct issues: (i) Is there a v_J/c term in the time delay that is large enough to detect? (ii) If so, is the factor of c in the delay the "speed of gravity" c_g or the "speed of light" c? I will comment briefly on each.