5,999 research outputs found

    Formation of Black Holes in Topologically Massive Gravity

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    We present an exact solution in 3-dimensional topologically massive gravity with negative cosmological constant which dynamically interpolates between a past horizon and a chiral AdS pp-wave. Similarly, upon time reversal, one obtains an AdS pp-wave with a future event horizonComment: Improved presentation. Extended discussion of linear stability and regularity of the metric. Added reference

    On the Canonical Equivalence of Liouville and Free Fields

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    We obtain the parity invariant generating functional for the canonical transformation mapping the Liouville theory into a free scalar field and explain how it is related to the pseudoscalar transformationComment: 8 pages, Latex, Important earlier work by G.P. Jordadze acknowledge

    Non-Abelian Born-Infeld Action and Solitons for Critical Non-BPS Branes

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    The non-abelian flat directions in the tachyon potential of stable non-BPS branes recently found are shown to persist to all orders in alpha' at tree level in the string coupling. We also obtain the non-abelian Born-Infeld action including the tachyon potential for a stack of stable non-BPS branes on a critical orbifold. Finally we discuss stable soliton states on the non-BPS brane.Comment: 12+1 pages, Latex. Typos, a reference and the discussion of the monopole solution are correcte

    Brief Resume of Seiberg-Witten Theory

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    Talk presented by the second author at the Inaugural Coference of the Asia Pacific Center for Theoretical Physics, Seoul, June 1996. The purpose of this note is to give a resume of the Seiberg-Witten theory in the simplest possible mathematical terms.Comment: 10 pages, LaTe

    Fiscal Federalism and Optimum Currency Areas: Evidence for Europe From the United States

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    The main goal of this paper is to estimate to what extent the federal government of the United States insures member states against regional income shocks. We find that a one dollar reduction in a region's per capita personal income triggers a decrease in federal taxes of about 34 cents and an increase in federal transfers of about 6 cents. Hence, the final reduction in disposable per capita income is on the order of 60 cents. That is, between one third and one half of the initial shock is absorbed by the federal government. The much larger reaction of taxes than transfers to these regional imbalances reflects the fact that the main mechanism at work is the federal income tax system which in turn means that the stabilization process is automatic rather than specifically designed each time there is a cyclical movement in income. Some economists may want to argue that this regional insurance scheme provided by the federal government is an important reason why the system of fixed exchange rates that exists within the United States today has survived without major problems. Under this view, the creation of a European Central Bank that issues unified European currency without the simultaneous introduction (or expansion) of a fiscal federalist system could put the project at risk. Rough calculations of the impact of the existing European tax system on regional income suggests that a one dollar shock to regional GDP will reduce tax payments to the EEC government by half a cent!. Hence, the current European tax system has a long way to go before it reaches the 34 cents of the U.S. Federal Government.

    Adhesion and electronic structure of graphene on hexagonal boron nitride substrates

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    We investigate the adsorption of graphene sheets on h-BN substrates by means of first-principles calculations in the framework of adiabatic connection fluctuation-dissipation theory in the random phase approximation. We obtain adhesion energies for different crystallographic stacking configurations and show that the interlayer bonding is due to long-range van der Waals forces. The interplay of elastic and adhesion energies is shown to lead to stacking disorder and moir\'e structures. Band structure calculations reveal substrate induced mass terms in graphene which change their sign with the stacking configuration. The dispersion, absolute band gaps and the real space shape of the low energy electronic states in the moir\'e structures are discussed. We find that the absolute band gaps in the moir\'e structures are at least an order of magnitude smaller than the maximum local values of the mass term. Our results are in agreement with recent STM experiments.Comment: 8 pages, 8 figures, revised and extended version, to appear in Phys. Rev.
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