267 research outputs found

### (Super-) String in Two Dimensional Black Hole and Target Space Dualities

We review the recently proposed string theory in two dimensional black hole
background. Especially, the structure of the duality in the target space is
discussed. The duality is analogous to \lq\lq $R \rightarrow 1/R$" symmetry of
a compactified boson. We consider the duality in more general target space
manifolds which have Killing symmetries and we give an explicit formula which
connects two different manifolds which are dual to each other. Superstring
theory in two dimensional black hole background is also discussed based on
supersymmetric $SU(1,1)/U(1)$ gauged Wess-Zumino-Witten model.Comment: 19pp (Talk at YITP workshop, ``Developments in Strings and Field
Theories'', Kyoto, JAPAN

### Group Theoretical Structure of $N=1$ and $N=2$ Two-Form Supegravity

We clarifies the group theoretical structure of $N=1$ and $N=2$ two-form
supergravity, which is classically equivalent to the Einstein supergravity.
$N=1$ and $N=2$ two-form supergravity theories can be formulated as gauge
theories. By introducing two Grassmann variables $\theta^A$ ($A=1,2$), we
construct the explicit representations of the generators $Q^i$ of the gauge
group, which makes to express any product of the generators as a linear
combination of the generators $Q^iQ^j=\sum_k f^{ij}_k Q^k$. By using the
expression and the tensor product representation, we explain how to construct
finite-dimensional representations of the gauge groups. Based on these
representations, we construct the Lagrangeans of $N=1$ and $N=2$ two-form
supergravity theories.Comment: Latex file, 15

### Inverse problem - reconstruction of dark energy models

We review how we can construct the gravity models which reproduces the
arbitrary development of the universe. We consider the reconstruction in the
Einstein gravity coupled with generalized perfect fluid, scalar-Einstein
gravity, scalar-Einstein-Gauss-Bonnet gravity, Einstein-$F(G)$-gravity, and
$F(R)$-gravity. Very explicit formulas are given to reconstruct the models,
which could be used when we find the detailed data of the development of the
universe by future observations. Especially we find the formulas using
e-foldings, which has a direct relation with observed redshift. As long as we
observe the time development of the Hubble rate $H$, there exists a variety of
models describing the arbitrary development of universe.Comment: LaTeX 11 pages, references are added, to appear in Proceedings of
International Workshop on Dark Matter, Dark Energy and Matter-Antimatter
Asymmetry, National Tsing Hua University, Hsinchu, Taiwan, November 20-21,
200

### Exact Four Dimensional Exploding Universe Solution in String Theory

We obtain a four dimensional exploding universe solution in string theory.
The solution is obtained from the string theory in the flat background by using
non-abelian $T$-duality and the analytic continuation. In the solution, the
radius of the universe is finite for fixed time and the universe is surrounded
with the boundary which is composed of the singularity. The boundary runs away
with the speed of light and the flat space-time is left behind.Comment: Latex file, 6 pages, misprints in Eqs.(14), (16), (19) and (26) are
correcte

### Wormholes in Two Dimensional Dilaton Gravity

It is shown that the general solution of classical equations of motion in two
dimensional dilaton gravity proposed by Callan, Giddings, Harvey and Strominger
(CGHS) includes a Lorentzian wormhole solution in addition to a black hole
solution. We also show that matter perturbation of the wormhole by a shock wave
leads to the formation of a black hole where the curvature singularity is
cloaked by the global event horizon. It is also argued that the classical
wormhole would be stable against quantum corrections.Comment: INS-Rep.-1012, NDA-FP-13/93, OCHA-PP-37, LATEX file, 9p

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