Related papers: Four Dimensional Black Holes and Duality in Supers…
The nature of duality symmetries is explored in closed bosonic string theory, particularly in the case of a four-dimensional target space admitting a one-parameter isometry. It appears that the S-duality of string theory behaves analogously…
In six spacetime dimensions, the heterotic string is dual to a Type $IIA$ string. On further toroidal compactification to four spacetime dimensions, the heterotic string acquires an $SL(2,\BbbZ)_S$ strong/weak coupling duality and an…
We present the explicit form for all the four dimensional, static, spherically symmetric solutions in $(4+n)$-d Abelian Kaluza-Klein theory by performing a subset of $SO(2,n)$ transformations corresponding to four $SO(1,1)$ boosts on the…
We find all the classical solutions (minimal surfaces) of open or closed strings in {\it any} two dimensional curved spacetime. As examples we consider the SL(2,R)/R two dimensional black hole, and any 4D black hole in the Schwarzschild…
In this talk I review recent developments in superstring theory. In the first half of the talk I discuss some of the earlier developments in this subject. This includes a review of the status of string theory as a unified theory of gravity…
We examine non-abelian duality transformations in the open string case. After gauging the isometries of the target space and developing the general formalism, we study in details the duals oftarget spaces with SO(N) isometries which, for…
We investigate spherically symmetric solutions in string theory. Such solutions depend on three parameters, one of which corresponds to the asymptotic mass while the other two are the dilaton and two-form field amplitudes, respectively. If…
Special solutions of string theory in supercritical dimensions can interpolate in time between theories with different numbers of spacetime dimensions (via dimension quenching) and different amounts of worldsheet supersymmetry (via…
Using the entropy function formalism we compute the entropy of extremal supersymmetric and non-supersymmetric black holes in N=2 supergravity theories in four dimensions with higher derivative corrections. For supersymmetric black holes our…
We use solution-generating techniques to construct interpolating geometries between general asymptotically flat, charged, rotating, non-extremal black holes in four and five dimensions and their subtracted geometries. In the…
We study gravitational collapse of the axion/dilaton field in classical low energy string theory, at the threshold for black hole formation. A new critical solution is derived that is spherically symmetric and continuously self-similar. The…
We construct an effective four dimensional string-corrected black hole (4D SCBH) by rescaling the string coupling parameter in a $D$-dimensional Callan-Myers-Perry black hole. From the theoretical point of view, the most interesting…
In (super)gravity theories, T-duality relates solutions with an exact isometry which can have wildly different asymptotic behaviors: a well-known example is the duality between BTZ black holes and (non-extremal) three-dimensional black…
We report two surprising results on $\alpha'$ corrections in string theory restricted to massless fields. First, for critical dimension Bianchi type I cosmologies with $q$ scale factors only $q-1$ of them have non-trivial $\alpha'$…
We perform the spherical symmetric dimensional reduction $4d\to2d$ of heterotic string theory. We find a class of two-dimensional (2d) dilaton gravity models that gives a general description of the near-horizon, near-extremal behavior of…
We discuss the relationship between target space modular invariance and discrete gauge symmetries in four-dimensional orbifold-like strings. First we derive the modular transformation properties of various string vertex operators of the…
We report on some general results on the physics of extremal BPS black holes in four and five dimensions. The duality-invariant entropy-formula for all $N>2$ extended supergravities is derived. Its relation with the fixed-scalar condition…
This thesis investigates two main topics concerning black holes in extensions of general relativity inspired by string theory. First, the structure of the equations of motion underlying black hole solutions is considered, in theories of…
We present a generalization of the $U(1)^{2}$ charged dilaton black holes family whose main feature is that both $U(1)$ fields have electric and magnetic charges, the axion field still being trivial. We show the supersymmetry of these…
By taking large mass and charge limit of a black hole in string theory we can create arbitrarily large regions where the space-time is approximately flat, but the moduli fields take values different from their asymptotic values. In this…