255 research outputs found
A Study of Accelerating Cosmologies from Superstring/M theories
We study aspects of the accelerating cosmologies obtained from the
compactification of vacuum solution and S2-branes of superstring/M theories.
Parameter dependence of the resulting expansion of our universe and internal
space is examined for all cases. We find that accelerating expansions are
obtained also from spherical internal spaces, albeit the solution enters into
contracting phase eventually. The relation between the models of SM2- and
SD2-branes are also discussed, and a potential problem with SD2-brane model is
noted.Comment: 20 pages, 17 figures, a typo corrected, to be published in Prog.
Theor. Phy
Introduction to branes and M-theory for relativists and cosmologists
We review the recent developments in superstrings. We start with a brief
summary of various consistent superstring theories and discuss T-duality which
necessarily leads to the presence of D-branes. The properties of D-branes are
summarized and we discuss how these suggest the existence of 11-dimensional
quantum theory, M-theory, which is believed to give rise to various
superstrings as perturbative expansions around particular backgrounds in the
theory. We also discuss the interpretation of brane solutions as black holes in
string theories and statistical explanation of Bekenstein-Hawking entropy. The
idea behind this interpretation is that there is a fundamental duality between
closed (gravity) and open (gauge theory) string degrees of freedom, one of
whose manifestation is what is kown as AdS/CFT correspondence. The idea is used
to discuss the greybody factors for BTZ black holes. Finally the entropy of
various balck holes are discussed in connection with Cardy-Verlinde formula.Comment: 28 pages, 7 figures, Latex. Lectures at the international workshop
``Brane world'' at YITP, 15--18 January 2002, to be published in Prog. Theor.
Phys. Suppl. ptp style files included. v2: minor corrections, v3: minor
corrections and refs. added, v4: eq.(7.14) correcte
Null-Brane Solutions in Supergravities
We find a new class of time-dependent brane solutions in supergravities in
arbitrary dimensions . These are general intersecting light-like branes
(null-branes), and their superposition and intersection rules are obtained.
This is achieved by directly solving bosonic field equations for supergravity
coupled to a dilaton and antisymmetric tensor fields. We discuss their possible
significance.Comment: 12 pages, v2: minor corrections, refs. added, v3: expressions of the
solutions modifie
Black Holes in the Dilatonic Einstein-Gauss-Bonnet Theory in Various Dimensions III -- Asymptotically AdS Black Holes with --
We study black hole solutions in the Einstein-Gauss-Bonnet gravity with the
dilaton and a negative ``cosmological constant''. We derive the field equations
for the static spherically symmetric () and hyperbolically symmetric
() spacetime in general dimensions. The system has some scaling
symmetries which are used in our analysis of the solutions. We find exact
solutions, i.e., regular AdS solution for and a massless black hole
solution for . Nontrivial asymptotically AdS solutions are obtained
numerically in D=4 -- 6 and 10 dimensional spacetimes. For spherically
symmetric solutions, there is the minimum horizon radius below which no
solution exists in D=4 -- 6. However in D=10, there is not such lower bound but
the solution continues to exist to zero horizon size. For hyperbolically
symmetric solution, there is the minimum horizon radius in all dimensions. Our
solution can be used for investigations of the boundary theory through AdS/CFT
correspondence.Comment: 25 pages, 16 figure
Interactions of Discrete States with Nonzero Ghost Number \\ in Gravity
We study the interactions of the discrete states with nonzero ghost number in
two-dimensional () quantum gravity. By using the vertex operator
representations, it is shown that their interactions are given by the structure
constants of the group of the area preserving diffeomorphism similar to those
of vanishing ghost number. The effective action for these states is also worked
out. The result suggests the whole system has a BRST-like symmetry.Comment: 10 pages, OS-GE 25-9
Global Structure of Black Holes in String Theory with Gauss-Bonnet Correction in Various Dimensions
We study global structures of black hole solutions in Einstein gravity with
Gauss-Bonnet term coupled to dilaton in various dimensions. In particular we
focus on the problem whether the singularity is weakened due to the
Gauss-Bonnet term and dilaton. We find that there appears the non-central
singularity between horizon and the center in many cases, where the metric does
not diverge but the Kretschmann invariant does diverge. Hence this is a
singularity, but we find the singularity is much milder than the Schwarzschild
solution and the non-dilatonic one. We discuss the origin of this "fat"
singularity. In other cases, we encounter singularity at the center which is
much stronger than the usual one. We find that our black hole solutions have
three different types of the global structures; the Schwarzschild,
Schwarzschild-AdS and "regular AdS black hole" types.Comment: 22 pages, 6 figure
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