We discuss construction and applications of instanton-like objects which we call fractional space-like branes. These objects are localised at a fixed point of a time-like (or more generally space-time) orbifold which is a string theoretical toy model of a cosmological singularity. We formulate them in boundary state, adsorption, and fermionisation approaches. 1 Fractional space-like branes in a...

We consider scalar perturbations in the time-dependent Hor̆avaWitten Model in order to probe its stability. We show that during the non-singular epoque the model evolves without instabilities until it encounters the curvature singularity where a big crunch is supposed to occur. We compute the frequencies of the scalar field oscillation during the stable period and show how the oscillations can b...

We show that globally and regularly hyperbolic future geodesically incomplete isotropic universes, except for the standard all-encompassing ‘big crunch’, can accommodate singularities of only one kind, namely, those having a non-integrable Hubble parameter, H. We analyze several examples from recent literature which illustrate this result and show that such behaviour may arise in a number of di...

K-means algorithm is a well-known clustering algorithm. In spite of its advantages such as high speed and ease of employment, this algorithm suffers from the problem of local optima. In order to overcome this problem, a lot of works have been carried out on clustering. This paper presents a hybrid extended cuckoo optimization algorithm (ECOA) and K-means (K) algorithm called ECOA-K. The COA alg...

We present an explicit exact solution of Einstein’s equations for an inhomogeneous dust universe with cylindrical symmetry. The spacetime is extremely simple but nonetheless it has new surprising features. The universe is “closed” in the sense that the dust expands from a big-bang singularity but recollapses to a big-crunch singularity. In fact, both singularities are connected so that the whol...

Dynamic behaviour of a WMN imposes stringent constraints on the routing policy of the network. In the shortest path based routing the shortest paths needs to be evaluated within a given time frame allowed by the WMN dynamics. The exact reasoning based shortest path evaluation methods usually fail to meet this rigid requirement. Thus, requiring some soft computing based approaches which can repl...

In this thesis we study the dynamics of higher-dimensional gravity in a universe emerging from a brane collision. We develop a set of powerful analytic methods which, we believe, render braneworld cosmological perturbation theory solvable. Our particular concern is to determine the extent to which the four-dimensional effective theory accurately captures the higher-dimensional dynamics about th...

We study the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon of bosonic closed string theory. We establish that whenever the tachyon induces the rolling process, the string metric remains fixed while the dilaton rolls to strong coupling. For negative definite potentials we show that this results in an Einstein metric that crunches the un...