Using the energy-momentum complexes of Einstein, Bergmann-Thomson, LandauLifshitz (LL), Møller and Papapetrou we have tried to solve energy-momentum and colliding plane wave problems for Bertotti-Robinson (BR) space-time (it has been also a subject of an extensive study in the context of the so-called colliding plane wave problem in General relativity) in General Relativity (GR). Moreover Einst...

Classes of exact static solutions in four-dimensional Einstein-MaxwellDilaton gravity are found. Besides of the well-known solutions previously found in the literature, new solutions are presented.It’s shown that spherically symmetric solutions, except the case of charged dilaton black hole, represent globally naked strong curvature singularities. The scalar field is believed to play an importa...

The Original Cosmological Constant As we have seen, in 1917 Einstein boldly launched modern cosmology by applying general relativity to the entire universe. He disposed of the Newtonian problem at infinity by invoking a closed geometry.[2] For his model to be consistent with contemporary astronomical data that suggested a static universe, Einstein reluctantly introduced an extra term that oppos...

We argue that “effective” superluminal travel, potentially caused by the tipping over of light cones in Einstein gravity, is always associated with violations of the null energy condition (NEC). This is most easily seen by working perturbatively around Minkowski spacetime, where we use linearized Einstein gravity to show that the NEC forces the light cones to contract (narrow). Given the NEC, t...

We show that if one takes into account Penrose’s conformal technique in the Einstein-Cartan gravity, it is possible to obtain a relation between Hubble’s expansion and Birch’s rotation of the Universe at spacelike infinity. This relation also leads to the final reduction of the gravitational coupling to a dimensionless quantity of order unity at spacelike infinity. Initial-value equations at sp...

We present new classes of exact solutions with noncommutative symmetries constructed in vacuum Einstein gravity (in general, with nonzero cosmological constant), five dimensional (5D) gravity and (anti) de Sitter gauge gravity. Such solutions are generated by anholonomic frame transforms and parametrized by generic off–diagonal metrics. For certain particular cases, the new classes of metrics h...

Lovelock theory is a natural extension of Einstein theory of gravity to higher dimensions, and it is of great interest in theoretical physics as it describes a wide class of models. In particular, it describes string theory inspired ultraviolet corrections to Einstein-Hilbert action, while admits the Einstein general relativiy and the so called Chern-Simons theories of gravity as particular cas...

Starting from the weak field limit, we discuss astrophysical applications of Extended Theories of Gravity where higher order curvature invariants and scalar fields are considered by generalizing the Hilbert-Einstein action linear in the Ricci curvature scalar R. Results are compared to General Relativity in the hypothesis that Dark Matter contributions to the dynamics can be neglected thanks to...

Abstract. We present solutions for the late time evolution of cosmological tensor and scalar perturbations in a single-Randall-Sundrum brane world model. Assuming that the bulk is anti-de Sitter spacetime, the solutions for cosmological perturbations are derived by summing mode functions in Poincaré coordinate. The junction conditions imposed at the moving brane are solved numerically. The reco...