2003 (IPP)
Permanent URI for this collectionhttp://localhost:4000/handle/11007/626
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Item Traversable wormholes with arbitrarily small energy condition violations(2011-07-05) Matt, Visser; Kar, Sayan; Dadhich, NareshTraversable wormholes necessarily require violations of the averaged null energy condition; this being the definition of “exotic matter”. However, the theorems which guarantee the energy condi- tion violation are remarkably silent when it comes to making quantitative statements regarding the “total amount” of energy condition violating matter in the spacetime. We develop a suitable mea- sure for quantifying this notion, and demonstrate the existence of spacetime geometries containing traversable wormholes that are supported by arbitrarily small quantities of “exotic matter”.Item Steep inflation followed by born-infeld reheating(2011-07-05) Sami, M.; Dadhich, NareshWe discuss a model in which high energy brane corrections allow a single scalar field to describe inflation at early epochs and quintessence at late times. The reheating mechanism in the model originates from Born-Infeld matter whose energy density mimics cosmological constant at very early times and manifests itself as radiation subsequently. For most of the inflationary evolution the Born- Infeld matter remains subdominant to the the scalar field. Shortly before the end of inflation driven by the scalar field, the energy density of Born-Infeld matter starts scaling as radiation and drops by several orders of magnitudes at the epoch inflation ends. The problem of over production of gravity wave background in scenarios based upon reheating through gravitational particle production is successfully resolved by suitably fixing the initial value of radiation energy density at the end of inflation. No additional fine tuning of the parameters is required for a viable evolution.Item Cosmological Dynamics of Phantom Field(2011-07-05) Singh, Parampreet; Sami, M.; Dadhich, NareshWe study the general features of the dynamics of the phantom field in the cosmological context. In the case of inverse coshyperbolic potential, we demonstrate that the phantom field can successfully drive the observed current accelerated expansion of the universe with the equation of state parameter wφ < −1. The de-Sitter universe turns out to be the late time attractor of the model. The main features of the dynamics are independent of the initial conditions and the parameters of the model. The model fits the supernova data very well, allowing for −2.4 < wφ < −1 at 95 % confidence levelItem Brane corresponding to the nariai bulk(2011-07-05) Dadhich, Naresh; Shtanov, YuriWe consider the five-dimensional bulk spacetime with negative Λ described by the Nariai metric (which is not conformally flat) and match it with a vacuum brane satisfying the proper boundary conditions. It is shown that the brane metric corresponds to a cloud of string dust of constant energy density.