International Journal of Modern Physics D

The history of cosmic structure goes back to the time of Einstein's youth, although few scientists actually thought of the problem of galaxy and cluster formation. The data and ideas were collected slowly as astronomers slowly realized the nature of the problem of large-scale structure. This paper will review several of the key episodes in the history of the field. Starting with the discovery of dark matter in the 30s, the CMBR discovery in the 1960s to the idea of an early episode of inflation in the 1980s, the field has had an acceleration of discovery. In the 80s it was realized that the initial conditions of the universe were specified by the cold dark matter (CDM). Now initial conditions for the formation of structure could be specified for any type of dark matter. With the advent of computing resources, highly nonlinear phases of galaxy formation could be simulated and scientists could ask whether cold dark matter was the correct theory, even on the scale of dwarf spheroidal galaxies, or do the properties of the dwarfs require a different type of dark matter? In an idiosyncratic list, we review several of the key events of the history of cosmic structure, including the first measurements of ξ(r), then the remarkable success of Λ CDM explanations of the large-scale universe. We next turn to velocity fields, the large-scale flow problem, a field which was so promising 20 years ago, and to the baryon acoustic oscillations, a field of remarkable promise today. We review the problem of dwarf galaxies and Lyman-α absorption systems, asking whether the evidence is pointing toward a major switch in our understanding of the nature of dark matter. Finally, we discuss flux anomalies in multiply-lensed systems, which set constraints on the number of dwarf galaxies associated with the lensing galaxy, a topic that is now very interesting since simulations have indicated there should be hundreds of dwarfs orbiting the Milky Way, rather than the 10 that are known. It is quite remarkable that many of the today's results are dependent on techniques first used by Einstein.

Inspiralling and coalescing binary black holes are promising sources of gravitational radiation. The orbital motion and gravitational-wave emission of such system can be modeled using a variety of approximation schemes and numerical methods in general relativity: The post-Newtonian (PN) formalism, black hole perturbation theory (BHP), numerical relativity (NR) simulations and the effective one-body (EOB) model. We review recent work at the multiple interfaces of these analytical and numerical techniques, emphasizing the use of coordinate-invariant relationships to perform meaningful comparisons. Such comparisons provide independent checks of the validity of the various calculations, they inform the development of a universal, semi-analytical model of the binary dynamics and gravitational-wave emission and they help to delineate the respective domains of validity of each approximation method. For instance, several recent comparisons suggest that perturbation theory may find applications in a broader range of physical problems than previously thought, including the radiative inspiral of intermediate mass-ratio and comparable-mass black hole binaries.

In this paper, we study a warm intermediate inflationary model with a general form for the dissipative coefficient Γ(T, ϕ) = C_ϕT^m/ϕ^m-1 in the context of Loop Quantum Cosmology (LQC). We examine this model in the weak and strong dissipative regimes. In general, we discuss in great detail the characteristics of this model in the slow-roll approximation. Also, we assume that the modifications to perturbation equations result exclusively from Hubble rate. In this approach, we use recent astronomical observations from Planck and BICEP2 experiments to restrict the parameters in our model.

We investigate the interacting holographic dark energy (HDE) with Granda–Oliveros (GO) infrared (IR)-cutoff in the framework of Brans–Dicke (BD) cosmology. We obtain the equation of state (EoS) parameter of HDE, w_D, the effective EoS parameter w_eff, the deceleration parameter q and the squared of sound speed in a flat Friedmann–Robertson–Walker (FRW) universe. We show that at late-time the cosmic coincidence problem can be alleviated. Also we show that for noninteracting case, HDE can give a unified dark matter–dark energy (DM–DE) profile in BD cosmology, except that it cannot solve the coincidence problem in the future. By studying the EoS parameter, we see that the phantom divide may be crossed. Using the latest observational data, we calculate the best values of the parameters for interacting HDE in BD framework. Computing the deceleration parameter implies that the transition from deceleration to the acceleration phase occurred for redshift z ≥ 0.5. Finally, we investigate the sound stability of the model, and find that HDE with Granda–Oliveros (GO)-cutoff in the framework of BD cosmology can lead to a stable DE-dominated universe favored by observations, provided we take β = 0.44 and b² < 0.35. This is in contrast to HDE model in Einstein gravity which does not lead to a stable DE-dominated universe.

In this paper, we investigate the viscous modified Chaplygin gas cosmological model. Solutions for different values of the viscosity parameter are obtained using both analytical and numerical methods. We have calculated the deceleration and defined newly statefinder {r, s} pair in D dimensions. It is shown that when D = 4, the usual statefinder parameters are recovered. Furthermore, we apply the statefinder diagnostic to the MCG model with and without viscosity in D dimensions and explore these parameters graphically.

In this work, we examine the evolution of a sample of isolated pulsars connected to Galactic supernova remnants (SNRs) five of which have measured braking indices. For the pulsars in our sample without measured braking index values we have calculated the estimated braking indices adopting the supernova remnant ages as the real ages of pulsar-SNR pairs assuming short initial spin periods (10–30 ms). Some of these pulsars exhibit at least one order of magnitude differences between the characteristic pulsar ages and the ages of the SNRs they are physically connected to. We adopt an exponential B-decay model, which is the decrease in the surface dipole magnetic field component perpendicular to the spin axis, in order to explain the evolutions of such pulsars on the spin period versus the spin period change diagram. The decay can be either due to a decrease in the angle between the spin axis and the magnetic axis and/or due to a decay in the surface dipole magnetic field itself. Based on a previous work by Ankay et al. on the X-ray pulsar 1E1207-5209 we show that there are some other young isolated pulsars which experience B-decay as the predominant effect throughout their observational lifetimes. As compared to ordinary radio pulsars the magneto-dipole radiation torques are not so effective for such pulsars and the characteristic decay times are significantly shorter (about three orders of magnitude). Assuming simple exponential evolutionary tracks we give possible physical interpretations for this new class of neutron stars by examining the observational data of each pulsar-SNR pair.

In this paper, we investigate induced oscillations by the gravitational field of a fast stellar object, such as a neutron star or a black-hole in a near miss collision with another star. Nonadiabatic collision conditions may lead to large amplitude oscillations in the star. We show that for a solar-type star a resonant condition can be achieved by a fast moving stellar object with velocity in the range of 100 to 1000 km/s, passing at a distance of a few multiples of the star radius. Although such collisions are rare, they are more frequent than head-on collisions, and their effects could be observed through a visible change of the star luminosity occurring within a few hours.

This paper formulates the instability regions of a general charged spherically symmetric matter distribution with anisotropic pressure, shear viscosity, radiation density and radial heat flux. Matching conditions are found by taking Reissner–Nordström–Vaidya spacetime as an exterior geometry. The perturbed forms of Einstein–Maxwell field equations and conservation laws are constructed to formulate the collapse equation. The instability regions are identified under N and pN limits for the stability analysis. We conclude that the adiabatic index identifies the instability range which depends upon physical parameters like anisotropic pressure, energy density, shear viscosity and electromagnetic field and heat flux but radiation density has no role.