International Journal of Modern Physics D

The data collected by ATIC, PPB-BETS, FERMI-LAT and HESS all indicate that there is an electron/positron excess in the cosmic ray energy spectrum above ~100 GeV, although different instrumental teams do not agree on the detailed spectral shape. PAMELA also reported clearly the excessive feature of the fraction of positron above several GeV, but with no excess in antiprotons. Here we review the observational status and theoretical models of this interesting observational feature. We pay special attention to various physical interpretations proposed in the literature, including modified supernova remnant models for the e^± background, new astrophysical sources, and new physics (the dark matter models). We suggest that although most models can make a case to interpret the data, with the current observational constraints the dark matter interpretations, especially those invoking annihilation, require much more exotic assumptions than some other astrophysical interpretations. Future observations may present some "smoking-gun" observational tests to differentiate different models and to identify the correct interpretation of the phenomenon.

Accretion flow on a horizon is supersonic, no matter what the flow angular momentum or the spin of the black hole is. This means that a black hole accretion can always be viewed as a flow in a flat space–time through one or more convergent–divergent ducts. In this paper, we study how the area of cross-sections must vary in order that the flow has the same properties in both systems. We show that the accretion flow experiencing a shock is equivalent to having two ducts connected back-to-back, both with a neck where the flow becomes supersonic. We study the pressure and Mach number variations for corotating, contrarotating flows and flows around a black hole with evolving spin.

In this work, we have considered a noncanonical complex scalar field named hessence to play the role of quintom in anisotropic universe (particularly in the Bianchi I model) as a new approach to look into the unknown mysterious world of dark energy. We have solved the field equations by considering the power-law form of scale factors and found the potential function in terms of ϕ with some restrictions. We also show here that hessence can avoid the Q-ball formation in anisotropic universe.

The purpose of this paper is to find and analyze plane symmetric, static (non-static) solutions in Hořava–Lifshitz gravity. We discussed two versions of Horava gravity. First we show that if the detailed balance principle is considered, there are both static and non-static solutions. We show that in the static case there are two families of solvable models, either one of them having a well-defined EoS, analogous to the perfect fluid solutions in GR. In the non-static case we find a family of solutions. Some physical properties of these solutions are discussed. Secondly we investigated the plane symmetric solutions for a new modified version of Hořava gravity, which has the new terms of action inserted into it.

It was recently suggested that the magnetic component of gravitational waves (GWs) is relevant in the evaluation of frequency response functions of gravitational interferometers. In this paper we extend the analysis to the magnetic component of the scalar mode of GWs which arises from scalar–tensor gravity theory. In the low frequency approximation, the response function of ground-based interferometers is calculated. The angular dependence of the electric and magnetic contributions on the response function is discussed. Finally, for an arbitrary frequency range, the proper distance between two test masses is calculated and its usefulness in the high frequency limit for space-based interferometers is briefly considered.

In the present study, we perform the numerical simulation of a relativistic thin accretion disk around the nonrotating and rapidly rotating black holes using the general relativistic hydrodynamic code with Kerr in Kerr–Schild coordinate that describes the central rotating black hole. Since the high energy X-rays are produced close to the event horizon resulting the black hole–disk interaction, this interaction should be modeled in the relativistic region.

We have set up two different initial conditions depending on the values of thermodynamical variables around the black hole. In the first setup, the computational domain is filled with constant parameters without injecting gas from the outer boundary. In the second, the computational domain is filled with the matter which is then injected from the outer boundary. The matter is assumed to be at rest far from the black hole. Both cases are modeled over a wide range of initial parameters such as the black hole angular momentum, adiabatic index, Mach number and asymptotic velocity of the fluid. It has been found that initial values and setups play an important role in determining the types of the shock cone and in designating the events on the accretion disk. The continuing injection from the outer boundary presents a tail shock to the steady state accretion disk. The opening angle of shock cone grows as long as the rotation parameter becomes larger. A more compressible fluid (bigger adiabatic index) also presents a bigger opening angle, a spherical shock around the rotating black hole, and less accumulated gas in the computational domain. While results from [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc.305 (1999) 920] indicate that the tail shock is warped around for the rotating hole, our study shows that it is the case not only for the warped tail shock but also for the spherical and elliptical shocks around the rotating black hole. The warping around the rotating black hole in our case is much smaller than the one by [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc.305 (1999) 920], due to the representation of results at the different coordinates. Contrary to the nonrotating black hole, the tail shock is slightly warped around the rotating black hole. The filled computational domain without any injection leads to an unstable accretion disk. However much of it reaches a steady state for a short period of time and presents quasi-periodic oscillation (QPO). Furthermore, the disk tends to loose mass during the whole dynamical evolution. The time-variability of these types of accretion flowing close to the black hole may clarify the light curves in Sgr A*.

Supernova matter consisting of protons, neutrons and electrons with proton fraction y_p = 0.3 are studied within finite temperature Brueckner–Goldstone approach with effective two-body Sussex interaction for various values of densities and at temperatures T = 5, 7 and 10 MeV. It is found that at a given density, temperature and proton fraction, the entropy production, internal energy per nucleon, free energy per nucleon and pressure generated by protons and electrons are not equal. Entropy produced in the supernova matter is larger than that of corresponding asymmetric nuclear matter. The rise in temperature with densities in this matter under adiabatic condition is relatively suppressed with respect to corresponding asymmetric nuclear matter. Contribution to internal energy and free energy due to electron components is more pronounced than those of nuclear components. But the contribution to entropy and pressure due to nuclear components is larger than those of electron components. It is observed that for the matter with proton fraction y_p = 0.1, the internal energy, free energy and pressure generated due to protons are density-independent whereas, for supernova matter, these quantities are density-dependent. Distribution function, fraction of particles and mean field are the key factors to explain the characteristic properties of the constituent particles of supernova matter.