Browsing by Author "Kar, Sayan"

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    R=O spacetimes and self-dual lorentzian wormholes
    (2001-04-02) Dadhich, Naresh; Kar, Sayan; Mukherjee, Sailajananda; et al.
    A two–parameter family of spherically symmetric, static Lorentzian wormholes is obtained as the general solution of the equation ρ = ρt = 0, where ρ = Tij ui uj , ρt = (Tij − 1 2T gij ) ui uj , and ui ui = −1. This equation characterizes a class of spacetimes which are “self dual” (in the sense of electrogravity duality). The class includes the Schwarzschild black hole, a family of naked singularities, and a disjoint family of Lorentzian wormholes, all of which have vanishing scalar curvature (R = 0). Properties of these spacetimes are discussed. Using isotropic coordinates we delineate clearly the domains of parameter space for which wormholes, nakedly singular spacetimes and the Schwarzschild black hole can be obtained. A model for the required “exotic” stress–energy is discussed, and the notion of traversability for the wormholes is also examined.
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    Traversable wormholes with arbitrarily small energy condition violations
    (2011-07-05) Matt, Visser; Kar, Sayan; Dadhich, Naresh
    Traversable 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”.