International Journal of Modern Physics D

We investigate numerically the process of the passage of a radiation pulse through a wormhole and the subsequent evolution of the wormhole that is caused by the gravitational action of this pulse. The initial static wormhole is modeled by a spherically symmetrical solution with zero mass. The radiation pulses are modeled by spherically symmetrical shells of self-gravitating massless scalar fields. We demonstrate that the compact signal propagates through the wormhole and investigate the dynamics of the fields in this process for both cases: collapse of the wormhole into the black hole and for the expanding wormhole.

We compute the effects of thermal Comptonization of soft photons emitted from a Keplerian disk around a black hole by the postshock region of a sub-Keplerian flow, known as the CENtrifugal-pressure-dominated BOundary Layer (CENBOL). We show that the spectral state transitions of black hole candidates could be explained either by varying the outer boundary of the CENBOL, which also happens to be the inner edge of the Keplerian disk, or by changing the central density of the CENBOL, which is governed by the rate of the sub-Keplerian flow. We confirm the conclusions of the previous theoretical studies that the interplay between the intensity of the soft photons emitted by the Keplerian flow, the optical depth and electron temperature of the Comptonizing cloud is responsible for the state transitions in a black hole.

An analysis is made for relations between the tunneling rate and the unified first law of thermodynamics at the trapping horizons of two kinds of spherically symmetric dynamical black holes. The first kind is the Vaidya–Bardeen black hole; the tunneling rate Γ ~ e^△S can be obtained naturally from the unified first law at the apparent horizon, which holds the form dE_H = TdS + WdV. The second kind is the McVittie solution; the action of the radial null geodesic of the outgoing particles does not always have a pole at the apparent horizon, while the ingoing mode always has one. The solution of the ingoing mode of the radiation can be mathematically reduced to the case in the FRW universe smoothly. However, as a black hole, the physical meaning is unclear and even puzzling.

In the previous work we introduced a new static cylindrically symmetric vacuum solution in Weyl coordinates in the context of the metric f(R) theories of gravity.¹ Now we obtain a two-parameter family of exact solutions which contains a cosmological constant and a new parameter as β. This solution corresponds to a constant Ricci scalar. We proved that in f(R) gravity the constant curvature solution in cylindrically symmetric cases is only one member of the most generalized Tian family in GR. We show that our constant curvature exact solution is applicable to the exterior of a string. The sensibility of stability under initial conditions is discussed.

For a class of viable cosmological models in f(R) gravity in which deviation from the Einstein gravity decreases as an inverse power law of the Ricci scalar R for large R, an analytic solution for density perturbations in the matter component during the matter-dominated stage is obtained in terms of hypergeometric functions. An analytical expression for the matter transfer function at scales much smaller than the present Hubble scale is also obtained.

A new diagnostic method, Om, is applied to the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy. On the basis of the recently observed data — the Union supernovae, the observational Hubble data, the SDSS baryon acoustic peak and the five-year WMAP shift parameter — we show the discriminations between the GCG model and the ΛCDM model. Furthermore, it is calculated that the current equation of state of dark energy w_0de = -0.964, according to the GCG model.

We propose holographic quintessence and tachyon models of dark energy. The correspondence between the quintessence and tachyon energy densities with the holographic density allows the reconstruction of the potentials and the dynamics for the quintessence and tachyon fields, in the flat FRW background. The proposed infrared cutoff for the holographic energy density works for two cases of the constant α: for α < 1 we reconstruct the holographic quintessence model in the region before the ω = -1 crossing for the EoS parameter. The cosmological dynamics for α > 1 is also reconstructed for the holographic quintessence and tachyon models.

A new exact solution to the cylindrically symmetric Einstein–Maxwell equations is presented. The solution is singular on the axis of symmetry and at the radial infinity, where sources should be placed. The accepted source at the origin can be interpreted as a charged domain wall shell.

We derive a new analytic solution of (n + 1)-dimensional (n ≥ 4) Brans–Dicke–Maxwell theory in the presence of a potential for the scalar field, by applying a conformal transformation to the dilaton gravity theory. Such solutions describe topological charged black holes with unusual asymptotics. We obtain the conserved and thermodynamic quantities through the use of the Euclidean action method. We also study the thermodynamics of the solutions and verify that the conserved and thermodynamic quantities of the solutions satisfy the first law of black hole thermodynamics.

The cosmological model of the modified Chaplygin gas (MCG) interacting with cold dark matter is studied. Our attention is focused on the final state of the universe in the model. It turns out that there exists a stable scaling solution, which provides the possibility of alleviating the coincidence problem. In addition, we investigate the effect of the coupling constants c₁ and c₂ on the dynamical evolution of this model from the statefinder viewpoint. It is found that the coupling constants play a significant role during the dynamical evolution of the interacting MCG model. Furthermore, we can distinguish this interacting model from other dark energy models in the s–r plane.