International Journal of Modern Physics D

I review the theory of angular momentum acquisition of galaxies by tidal torquing, the resulting angular momentum distribution and the angular momentum correlation function, and discuss the implications of angular momentum alignments for weak lensing measurements. Starting from linear models for tidal torquing, I summarize perturbative approaches and the results from n-body simulations of cosmic structure formation. Then I discuss the validity of decompositions of the tidal shear and inertia fields, the effects of angular momentum biasing, the applicability of parametrized angular momentum correlation models and the consequences of angular momentum correlations for shape alignments. I compile the results of observations of shape alignments in recent galaxy surveys as well as in n-body simulations. Finally, I review the contamination of weak lensing surveys by spin-induced shape alignments and methods for suppressing this contamination.

The aim of this paper is to determine how the gravitational field inside a massive star affects the propagation of photons, and to investigate the consequences for the radiation field. The chosen approach consists in modeling the curved metric by an effective refractive medium: from this very simple perspective, the energy transport problem is investigated and the new form of the radiative transfer is derived. Then, the main effects of curvature on the energy balance are discussed and, in particular, it is shown that these effects influence the radiative flux emitted by the star.

We study a charged particle in a medium with different continuous distributions of topological defects in the approach of the geometric theory of defects. Those distributions allow us to evaluate the self-energy for a single charge in both the internal and external regions of each distribution.

In four-dimensional general relativity the space–time outside of an isolated spherical star is described by a unique line element, which is the Schwarzschild metric. As a consequence, the "gravitational" mass and the "inertial" mass of a star are equal to each other. However, theories that envision our world as being embedded in a larger universe, with more than four dimensions, permit a number of possible non-Schwarzschild 4D exteriors, which typically lead to different masses, violating the weak equivalence principle of ordinary general relativity. Therefore, the question arises as to whether the violation of this principle, i.e. the equality of gravitational and inertial mass, is a necessary consequence of the existence of extra dimensions. In this paper, in the context of Kaluza–Klein gravity in 5D, we show that the answer to this question is negative. We find a one-parameter family of asymptotically flat non-Schwarzschild static exteriors for which the inertial and gravitational masses are equal to each other, and equal to the Deser–Soldate mass. This family is consistent with the Newtonian weak field limit as well as with the general-relativistic Schwarzschild limit. Thus, we conclude that the existence of an extra dimension, and the corresponding non-Schwarzschild exterior, does not necessarily require different masses. However, to an observer in 4D, it does affect the motion of test particles in 4D, which is a consequence of the departure from the usual (4D) law of geodesic motion.

In this paper, we study anisotropic spheres built from known static spherical solutions. In particular, we are interested in the physical consequences of a "small" departure from a physically sensible configuration. The obtained solutions smoothly depend on free parameters. By setting these parameters to zero, the starting seed solution is regained. We apply our procedure in detail by taking as seed solutions the Florides metrics, and the Tolman IV solution. We show that the chosen Tolman IV solution, and also the Heint IIa and Durg IV,V perfect fluid solutions, can be used to generate a class of parametric solutions where the anisotropic factor has features recalling boson stars. This is an indication that boson stars could emerge by "perturbing" appropriately a perfect fluid solution (at least for the seed metrics considered). Finally, starting with the Tolman IV, Heint IIa and Durg IV,V solutions, we build anisotropic gravastar-like sources with the appropriate boundary conditions.

We investigate the cosmological effects of an alternative theory of gravity on the four-dimensional Randall–Sundrum braneworld of type II with a higher-order string curvature term added to the action. We discuss the possibility of a varying speed of light, which has recently attracted considerable attention, in the presence a Maxwell field and of a dynamically evolving bulk scalar field nonminimally coupled to scalar curvature in a quadratic form, together with a dark matter–dark energy interaction term. After deriving the modified Friedmann equation on the brane, as well as the scalar field equations, we then analyze the dynamical equations obtained so far. Special attention is paid to scaling solutions which could be important building blocks in constructing the models of dark energy. The constructed model exhibits several features of cosmological and astrophysical interest for both the early and the late universe, consistent with recent observations, in particular the ones concerned with celerity of light, four and five gravitational constants, black hole masses and entropies.

It has recently been debated whether a class of generalized uncertainty principles that include gravitational sources of error is compatible with the holographic principle in models with extra spatial dimensions. We had in fact shown elsewhere that the holographic scaling is lost when more than four space–time dimensions are present. However, we shall show here that the validity of the holographic counting can be maintained also in models with extra spatial dimensions, but at than intriguing price — the equivalence principle for a pointlike source is violated and the inertial mass differs from the gravitational mass in a specific, nontrivial way.

In this paper, the RS-II model of brane gravity is considered for the phantom universe using a nonlinear equation of state. Phantom fluid is known to violate the weak energy condition. It is found that this characteristic of phantom energy is affected drastically by the negative brane tension λ of the RS-II model. It is interesting to see that up to a certain value of energy density ρ satisfying ρ/λ < 1, the weak energy condition is violated and the universe superaccelerates. But, as ρ increases more, only the strong energy condition is violated and the universe accelerates. When 1 < ρ/λ < 2, even the strong energy condition is not violated and the universe decelerates. Expansion of the universe stops when ρ = 2 λ. This is contrary to earlier results of the phantom universe exhibiting acceleration only.