The attempt to understand if AdS/CFT correspondence may be realized as the one between some AdS-like cosmological space and CFT living on the boundary is made. In order to obtain such cosmology we exchange the time and radial coordinates in d5 Schwarzschild-anti de Sitter (S-AdS) BH (with corresponding signature change). The test on proportionality of free energies from such d5 cosmological spa...

We show that with the help of a suitable coupling between dark energy and cold dark matter it is possible to reproduce any scaling solution ρX ∝ ρMa , where ρX and ρM are the densities of dark energy and dark matter, respectively. We demonstrate how the case ξ = 1 alleviates the coincidence problem. Future observations of supernovae at high redshift as well as quasar pairs which are planned to ...

A new cosmological model provides solutions for the flatness, smoothness, monopole, and classical singularity problems, with no adjustment of parameters. The prediction of a scale factor R (t) which is proportional to t (rather than t) yields a comfortably large age for the universe, and also implies that the deceleration parameter q0 is exactly zero.

We comment on two issues in quantum cosmology, in the context of the Wheeler–De Witt equation and wave function of the Universe: (i) arrow of time and interpretation of the wave function in the classically allowed regions; (ii) stability of an approximation of the Born–Oppenheimer type in classically forbidden regions of the scale factor.

“Old’ String Theory is a theory of one-dimensional extended objects, whose vibrations correspond to excitations of various target-space field modes including gravity. It is for this reason that strings present the first, up to now, mathematically consistent framework where quantum gravity is unified with the rest of the fundamental interactions in nature. In these lectures I will give an introd...

We explore nonlocally modified models of gravity, inspired by quantum loop corrections, as a mechanism for explaining current cosmic acceleration. These theories enjoy two major advantages: they allow a delayed response to cosmic events, here the transition from radiation to matter dominance, and they avoid the usual level of fine-tuning; instead, emulating Dirac's dictum, the required large nu...

If the cosmological evolution is followed back in time, we come to the initial singularity where the classical equations of general relativity break down. This led many people to believe that in order to understand what actually happened at the origin of the universe, we should treat the universe quantum-mechanically and describe it by a wave function rather than by a classical spacetime. This ...

We develop a fully covariant, well-posed 5D effective action for the 6D cascading gravity brane-world model, and use this to study cosmological solutions. We obtain this effective action through the 6D decoupling limit, in which an additional scalar degree mode, π , called the brane-bending mode, determines the bulk-brane gravitational interaction. The 5D action obtained this way inherits from ...

The problems encountered in trying to quantize the various cosmological models, are brought forward by means of a concrete example. The Automorphism groups are revealed as the key element through which G.C.T.’s can be used for a general treatment of these problems. At the classical level, the time dependent automorphisms lead to significant simplifications of the line element for the generic sp...