International Journal of Modern Physics D

Microquasars are X-ray binaries with relativistic jets. These jets are powerful energy carriers — thought to be fed by accretion — which produce nonthermal emission at different energy bands. The processes behind the bulk of the nonthermal emission in microquasars may be of leptonic (synchrotron and inverse Compton) and hadronic (proton–proton interactions, photomeson production, and photodisintegration) nature. When leptonic, the fast particle cooling would allow one to obtain relevant information about the properties close to the accelerator, like the radiation and the magnetic field energy densities, and the acceleration efficiency. When hadronic, the extreme conditions required in the emitter would have strong implications for the physics of jets and their surroundings. The very-high-energy part of the spectrum, i.e. > 100 GeV, is a good energy range to explore the physics behind the nonthermal radiation in these compact variable sources. In addition, this energy range, when taken together with lower energy bands, is a key piece for constructing a comprehensive picture of the processes occurring in the emitter. Until recently, the very-high-energy range was hard to probe due to the lack of sensitivity and spatial and spectral resolution of previous instrumentation. Nowadays, however, powerful gamma-ray instruments are operating and the quality of their observations is allowing one, for the first time, to start to understand the production of high-energy emission in microquasars.

To date, several galactic sources showing extended radio emission — among them at least one confirmed microquasar, Cygnus X-1 — have shown a TeV signal. All of them show complex patterns of spectral and temporal behavior. In this work, we discuss the physics behind the very-high-energy emission in Cygnus X-1, and also in the other two TeV binaries with detected extended outflows, LS 5039 and LS I +61 303, pointing out relevant aspects of the complex phenomena occurring in them. We conclude that the TeV emission is likely of leptonic origin, although hadrons cannot be discarded. In addition, efficient electromagnetic cascades can hardly develop since even relatively low magnetic fields suppress them. Also, the modeling of the radiation from some of the detected sources points to them as extremely efficient accelerators and/or having the TeV emitter at a distance from the compact object of about ~ 10¹² cm. Finally, we point out that the role of a massive and hot stellar companion, due to its strong photon field and wind, cannot be neglected when trying to understand the behavior of microquasars at high and very high energies. The complexity of microquasars precludes straightforward generalizations to a whole population, and are better studied presently on a source-by-source basis. The new and future gamma-ray instrumentation will imply a big step further in our understanding of the processes in microquasars and gamma-ray-emitting binaries.

Einstein field equations under spherically symmetric space–times are considered here in connection with dark energy investigation. A set of solutions is obtained for a kinematic Λ model, viz. , without assuming any a priori value for the curvature constant and the equation-of-state parameter ω. Some interesting results, such as the nature of cosmic density Ω and deceleration parameter q, have been obtained with the consideration of two-fluid structure instead of the usual unifluid cosmological model.

Though popular presentations give the Schwarzschild singularity as a point, it is known that it is spacelike and not timelike. Thus, it has a "length" and is not a "point." In fact, its length is necessarily infinite. It has been proven that the proper length of the Qadir–Wheeler suture model goes to infinity,¹ while its proper volume shrinks to zero, and the asymptotic behavior of the length and volume has been calculated. That model consists of two Friedmann sections connected by a Schwarzschild "suture." The question arises whether a similar analysis could provide the asymptotic behavior of the Schwarzschild black hole near the singularity. It is proven here that, unlike the behavior for the suture model, for the Schwarzschild essential singularity Δs ~ K^1/3ln K and V ~ K^-1ln K, where K is the mean extrinsic curvature, or the York time.

We apply the counterterm subtraction technique to calculate the action and other quantities of the Kerr-AdS black hole in five dimensions using two boundary metrics: the Einstein universe and the rotating Einstein universe with an arbitrary angular velocity. In both cases, the resulting thermodynamic quantities satisfy the first law of thermodynamics. We point out that the reason for the violation of the first law in previous calculations was that the rotating Einstein universe, used as a boundary metric, was rotating with an angular velocity that depended on the black hole rotation parameter. Using a new coordinate system with a boundary metric that has an arbitrary angular velocity, one can show that the resulting physical quantities satisfy the first law.

This paper, presents a model inspired by extra dimensions that is built on the DGP brane-world scenario. The dark energy component on the brane is then taken to be a Chaplygin gas. After that, a holographic model of the Chaplygin gas in the framework of DGP cosmology is considered. It is shown that the holographic Chaplygin gas can mimic a phantom fluid and cross the phantom divide in a DGP brane-world setup.

A new formulation of Carter's constant for geodesic motion in Kerr black holes is given. It is shown that Carter's constant corresponds to the total angular momentum plus a precisely defined part which is quadratic in the linear momenta. The characterization is exact in the weak field limit obtained by letting the gravitational constant go to zero. It is suggested that the new form can be useful in current studies of the dynamics of extreme mass ratio inspiral (EMRI) systems emitting gravitational radiation.

Neutrino (ν) oscillations during the core collapse and bounce of a supernova (SN) are shown to generate the most powerful detectable gravitational wave (GW) bursts. The SN neutronization phase produces mainly electron (ν_e) neutrinos, the oscillations of which must take place within a few mean-free paths of their resonance surface located near their neutrinosphere. Here we characterize the GW signals produced by spin-flip oscillations inside the fast-rotating protoneutron star in the SN core. In this novel mechanism, the release of both the oscillation-produced ν_μ's, ν_τ's and the spin-flip-driven GW pulse provides a unique emission offset for measuring the ν travel time to Earth. As massive ν's get noticeably delayed on its journey to Earth with respect to the GW, they generate over the oscillation transient, the accurate measurement of this time-of-flight delay by SNEWS + LIGO, VIRGO, BBO, DECIGO, etc. can assess the absolute ν mass spectrum straightforwardly.

In this paper it is shown that a simple functional form of ω(ϕ) in a generalized scalar–tensor theory can drive the present cosmic acceleration without any quintessence field or the cosmological constant Λ. Furthermore, it ensures a smooth transition from a decelerated to an accelerated phase of expansion in the matter-dominated regime.

In order to investigate the dependence of LRG luminosity on the environment, we compare the luminosity distribution of member galaxies of LRG groups with that of isolated LRGs. It turns out that luminous LRGs exist preferentially in the densest regions of the universe (e.g. in groups), but faint LRGs are located preferentially in low density regions. The level of significance is above 2σ. This further confirms the dependence of galaxy luminosity on the environment.

Modified Chaplygin gas (MCG) is a strong candidate for the unified model of dark matter and dark energy. The equation of state of this modified model is valid from the radiation era to the ΛCDM model. In the early epoch (when ρ was large), dark matter had the dominant role, while at later stages (when ρ is small), the MCG model behaves as dark energy. In this work, we have found an exact solution to static, spherically symmetric Einstein equations describing a wormhole for an inhomogeneous distribution of MCG. For the existence of a wormhole solution, there are some restrictions concerning the parameters in the equation of state for MCG and the throat radius of the wormhole. Physical properties and characteristics of such modified Chaplygin wormholes are analyzed in detail.

N-body simulations of dark matter halos show that the density profiles of the halos behave as ρ(r) ∝ r^-α(r), where the density logarithmic slope α ≃ 1–1.5 in the center and α ≃ 3–4 in the outer parts of the halos. However, some observations are not in agreement with simulations in the very central region of the halos. The simulations also show that the velocity dispersion anisotropy parameter β ≈ 0 in the inner part of the halo and the so-called pseudo–phase-space density ρ/σ³ behaves as a power law in radius r. With these results in mind, we study the distribution function and the pseudo–phase-space density ρ/σ³ of the center of dark matter halos and find that they are closely related.

The Maxwell and Maxwell–de Rham equations can be solved exactly to first order in an external gravitational field. The gravitational background induces phases in the wave functions of spin-1 particles. These phases yield the optics of the particles without requiring any thin lens approximation.

The cosmic defect (CD) theory is reviewed and used to fit the data for the accelerated expansion of the universe, obtained from the apparent luminosity of 192 SnIa's. The fit from the CD theory is compared with the one obtained by means of ΛCDM. The results from the two theories are in good agreement and the fits are satisfactory. The correspondence between the two approaches is discussed and interpreted.