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We present a static solution for $d = 2$ critical string theory including the tachyon $T$ but not its potential $V(T)$. This solution thus incorporates tachyon back reaction and, when $T = 0$, reduces to the black hole solution. When $T…
We describe a static solution for $d = 2$ critical string theory including the tachyon $T$ but with its potential $V (T)$ set to zero. This solution thus incorporates tachyon back reaction and, when $T = 0$, reduces to the black hole…
Static black holes in two-dimensional string theory can carry tachyon hair. Configurations which are non-singular at the event horizon have non-vanishing asymptotic energy density. Such solutions can be smoothly extended through the event…
We analyze the fate of excitations in regions of closed string tachyon condensate, a question crucial for understanding unitarity in a class of black holes in string theory. First we introduce a simple new example of {\it quasilocal}…
We study solutions of the tree level string effective action in the presence of the tachyon mode.We find that the 2-dim. static black hole is stable against tachyonic perturbations.For a particular ansatz for the tachyon field we find an…
We study the geometry of the two dimensional string theoretic black hole under tachyonic perturbations. These perturbations are restricted to affect only the metric and the dilaton, while other string theoretic excitations (like the axion)…
The classical black hole background of two-dimensional string theory is examined after including the effect of the tachyon field. Keeping all terms upto $O(T^2)$, and making no other approximations, the only consistent classical solution to…
We further study the nonperturbative formulation of two-dimensional black holes. We find a nonlinear differential equation satisfied by the tachyon in the black hole background. We show that singularities in the tachyon field configurations…
In the light of recent blackhole solutions inspired by string theory, we review some old statements on field theoretic hair on blackholes. We also discuss some stability issues. In particular we argue that the two dimensional string…
The two-dimensional model which emerges from low-energy considerations of string theory is written down. Solutions of this classical model are noted, including some examples which have nontrivial tachyon field. One such represents the…
We examine the two-dimensional spacetimes that emerge from string theory. We find all the solutions with no tachyons, and show that the only non-trivial solution is the black hole spacetime. We examine the role of duality in this picture.…
(Lecture at the workshop "Basic Problems in String Theory", Yukawa Institute for Theoretical Physics, Kyoto, October 19-21) In this talk, we first review the possibility of matrix models toward a nonperturbative (critical) string theory. We…
In this work we find static black hole solutions in the context of the two-dimensional dilaton gravity, which is modified by the addition of an $R^2$ term. This term arises from the one-loop effective action of a massive scalar field in its…
We solve the equations of motion of the tachyon and the discrete states in the background of Witten's semiclassical black hole and in the exact 2D dilaton-graviton background of Dijkgraaf et al. We find the exact solutions for weak fields,…
We discuss time-dependent perturbations (induced by matter fields) of a black-hole background in tree-level two-dimensional string theory. We analyse the linearized case and show the possibility of having black-hole solutions with…
We consider the perturbation of tachyon about the extremal ground state of a two-dimensional (2D) electrically charged black hole. It is found that the presenting potential to on-coming tachyonic wave takes a double-humped barrier well.…
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…
Starting with the two-derivative limit of $D=2$ string theory, we explore the space of T-duality invariant $\alpha'$ corrections, a space that contains a point representing the fully $\alpha'$-corrected classical string theory. Using a…
The sequence of intertwined T-S-T duality transformations acting on the 4D static uncharged black hole leads to a new black hole background with horizon and singularity exchanged. It is shown that this space-time is extendible too. In…
We identify a quantity in the $c=1$ matrix model which describes the wavefunction for physical scattering of a tachyon from a black hole of the two dimensional critical string theory. At the semiclassical level this quantity corresponds to…