We construct an effective action for gravity in which all homogeneous solutions are nonsingular1). In particular, there is neither a big bang nor a big crunch. The action is a higher derivative modification of Einstein’s theory constructed in analogy to how the action for point particle motion of particles in special relativity is obtained from Newtonian mechanics. ⋆ Invited talk at Internation...

We consider string theory in a time dependent orbifold with a null singularity. The singularity separates a contracting universe from an expanding universe, thus constituting a big crunch followed by a big bang. We quantize the theory both in light-cone gauge and covariantly. We also compute some tree and one loop amplitudes which exhibit interesting behavior near the singularity. Our results a...

We investigate topology change in 3D. Using Morse theory and handle decomposition we find the set of elementary cobordisms for 3-manifolds. These are: (i) Ø ↔ S 2 ; (ii) Σ g ↔ Σ g+1 ; (iii) Σ g 1 ⊔ Σ g 2 ↔ Σ g 1 +g 2 , and they have appealing physical interpretations, e.g. Big Bang/Big Crunch, wormhole creation/annihilation and Einstein-Rosen bridge cre-ation/annihilation, respectively. This de...

The supersymmetric (AdS3×S)/ZN orbifold constructed by the authors in hep-th/0106171 is shown to describe AdS fragmentation, where fivebranes are emerging from the F1-NS5 background. The twisted sector moduli of the orbifold are the collective coordinates of groups of n5/N fivebranes. We discuss the relation between the descriptions of this background as a perturbative string orbifold and as a ...

We show that the dynamics of a spatially closed Friedmann Robertson Walker Universe conformally coupled to a real, free, massive scalar field, is chaotic, for large enough field amplitudes. We do so by proving that this system is integrable under the adiabatic approximation, but that the corresponding KAM tori break up when non adiabatic terms are considered. This finding is confirmed by numeri...

We compute correlation functions of closed strings in Misner space, a big crunch big bang universe. We develop a general method for correlators with twist fields, which are relevant for the investigation on the condensation of winding tachyon. We propose to compute the correlation functions by performing an analytic continuation of the results in C/ZN Euclidean orbifold. In particular, we obtai...

To gain insight in the quantum nature of the big bang, we study the dual field theory description of asymptotically anti-de Sitter solutions of supergravity that have cosmological singularities. The dual theories do not appear to have a stable ground state. One regularization of the theory causes the cosmological singularities in the bulk to turn into giant black holes with scalar hair. We inte...

A coupling is a mechanism that transmits operative power between two shafts are revolving at different speeds. connects their ends and can slip or fail depending on the torque limit. It an essential component of any transmission system may survive for very long time if properly designed maintained. This study's current research, newly developed optimization algorithms used to minimize volume co...