Browsing by Author "Surya, Sumati"

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    Global anomalies in canonical gravity
    (2015-03-11) Surya, Sumati; Vaidya, Sachindeo
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    Localized branes and black holes
    (2015-03-11) Surya, Sumati; Marolf , Donald
    We address the delocalization of low dimensional D-branes and NS-branes when they are a part of a higher dimensional BPS black brane, and the homogeneity of the resulting horizon. We show that the effective delocalization of such branes is a classical effect that occurs when localized branes are brought together. Thus, the fact that the ~ew known solutions with inhomogeneous horizons are highly singular need not indicate a singularity of generic D- and NS-brane states. Rather, these singular solutions are likely to be unphysical as they cannot be constructed from localized branes which are brought together from a finite separation.
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    Topology change and causal continuity
    (2015-03-11) Dowker, Fay; Surya, Sumati
    The result that, for a scalar quantum field propagating on a "trousers" topology in 1 + 1 dimensions, the crotch singularity is a source for an infinite burst of energy has been used to argue against the occurrence of topology change in quantum gravity. We draw attention to a conjecture due to Sorkin that it may be the particular type of topology change involved in the trousers transition that is problematic and that other topology changes may not cause the same difficulties. The conjecture links the singular behaviour to the existence of "causal discontinuities" in the spacetime and relies on a classification of topology changes using Morse theory. We investigate various topology changing transitions, including the pair production of black holes and of topological geons, in the light of these ideas.