355 research outputs found
S-Duality and Cosmological Constant in String Theory
The S-duality invariance of the equations of motion of four dimensional
string effective action with cosmological constant, , is studied. It
is demonstrated that the S-duality symmetry of the field equations are broken
for nonzero . The ``naturalness'' hypothesis is invoked to argue that
should remain small since exact S-duality symmetry will force the
cosmological constant to vanish in the string effective action.Comment: 13 pages, RevTex , slightly extended version with more discussions
added ( To appear in Phys. Lett. B
Massless Black Holes as Black Diholes and Quadruholes
Massless black holes can be understood as bound states of a (positive mass)
extreme a=\sqrt{3} black hole and a singular object with opposite (i.e.
negative) mass with vanishing ADM (total) mass but non-vanishing gravitational
field. Supersymmetric balance of forces is crucial for the existence of this
kind of bound states and explains why the system does not move at the speed of
light. We also explain how supersymmetry allows for negative mass as long as it
is never isolated but in bound states of total non-negative mass.Comment: Version to be published in Physical Review Letters. Latex2e fil
Duality Versus Supersymmetry and Compactification
We study the interplay between T-duality, compactification and supersymmetry.
We prove that when the original configuration has unbroken space-time
supersymmetries, the dual configuration also does if a special condition is
met: the Killing spinors of the original configuration have to be independent
on the coordinate which corresponds to the isometry direction of the bosonic
fields used for duality. Examples of ``losers" (T-duals are not supersymmetric)
and ``winners" (T-duals are supersymmetric) are given.Comment: LaTeX file, 19 pages, U. of Groningen Report UG-8/94, Stanford U.
Report SU-ITP-94-19, QMW College Report QMW-PH-94-1
O(d,d)-invariance in inhomogeneous string cosmologies with perfect fluid
In the first part of the present paper, we show that O(d,d)-invariance
usually known in a homogeneous cosmological background written in terms of
proper time can be extended to backgrounds depending on one or several
coordinates (which may be any space-like or time-like coordinate(s)). In all
cases, the presence of a perfect fluid is taken into account and the equivalent
duality transformation in Einstein frame is explicitly given. In the second
part, we present several concrete applications to some four-dimensional
metrics, including inhomogeneous ones, which illustrate the different duality
transformations discussed in the first part. Note that most of the dual
solutions given here do not seem to be known in the literature.Comment: 25 pages, no figures, Latex. Accepted for publication in General
Relativity and Gravitatio
Classical Hair in String Theory II: Explicit Calculations
After emphasizing the importance of obtaining a space-time understanding of
black hole entropy, we further elaborate our program to identify the degrees of
freedom of black holes with classical space-time degrees of freedom. The
Cveti\v{c}-Youm dyonic black holes are discussed in some detail as an example.
In this example hair degrees of freedom transforming as an effective string can
be identified explicitly. We discuss issues concerning charge quantization,
identification of winding, and tension renormalization that arise in counting
the associated degrees of freedom. The possibility of other forms of hair in
this example, and the prospects for making contact with D-brane ideas, are
briefly considered.Comment: Latex, 40 pages, no figure
Black Hole Solutions in Heterotic String Theory on a Torus
We construct the general electrically charged, rotating black hole solution
in the heterotic string theory compactified on a six dimensional torus and
study its classical properties. This black hole is characterized by its mass,
angular momentum, and a 28 dimensional electric charge vector. We recover the
axion-dilaton black holes and Kaluza-Klein black holes for special values of
the charge vector. For a generic black hole of this kind, the 28 dimensional
magnetic dipole moment vector is not proportional to the electric charge
vector, and we need two different gyromagnetic ratios for specifying the
relation between these two vectors. We also give an algorithm for constructing
a 58 parameter rotating dyonic black hole solution in this theory,
characterized by its mass, angular momentum, a 28 dimensional electric charge
vector and a 28 dimensional magnetic charge vector. This is the most general
asymptotically flat black hole solution in this theory consistent with the
no-hair theorem.Comment: LaTeX, 20 pages, A paragraph added discussing the relatioship between
area of the stretched horizon and density of string states in the extremal
limi
D-brane Approach to Black Hole Quantum Mechanics
Strominger and Vafa have used D-brane technology to identify and precisely
count the degenerate quantum states responsible for the entropy of certain
extremal, BPS-saturated black holes. Here we give a Type-II D-brane description
of a class of extremal {\it and} non-extremal five-dimensional
Reissner-Nordstr\"om solutions and identify a corresponding set of degenerate
D-brane configurations. We use this information to do a string theory
calculation of the entropy, radiation rate and ``Hawking'' temperature. The
results agree perfectly with standard Hawking results for the corresponding
nearly extremal Reissner-Nordstr\"om black holes. Although these calculations
suffer from open-string strong coupling problems, we give some reasons to
believe that they are nonetheless qualitatively reliable. In this optimistic
scenario there would be no ``information loss'' in black hole quantum
evolution.Comment: 18 pages, uses harvmac and psfig. The new version of the paper
corrects various errors, omissions and obscurities of the original
submission. The major error was an underestimate of the severity of the
strong coupling problem in the D-brane description of black holes with a
macroscopic event horizon. The new version has a more sober, but still
optimistic assessment of what aspects of black hole quantum mechanics are be
brought under control by D-branes. We thank several correspondents for
helpful criticism and advic
A Unified Approach to Solvable Models of Dilaton Gravity in Two-Dimensions Based on Symmetry
A large class of solvable models of dilaton gravity in two space-time
dimensions, capable of describing black hole geometry, are analyzed in a
unified way as non-linear sigma models possessing a special symmetry. This
symmetry, which can be neatly formulated in the target-space-covariant manner,
allows one to decompose the non-linearly interacting dilaton-gravity system
into a free field and a field satisfying the Liouville equation with in general
non-vanishing cosmological term. In this formulation, all the existent models
are shown to fall into the category with vanishing cosmological constant.
General analysis of the space-time structureinduced by a matter shock wave is
performed and new models, with and without the cosmological term, are
discussed.Comment: 29 pages, LaTe
Kaluza-Klein Black Holes in String Theory
Exact solutions of heterotic string theory corresponding to four-dimensional
magnetic black holes in supergravity are described. The solutions
describe the black holes in the throat limit, and consist of a tensor product
of an WZW orbifold with the linear dilaton vacuum, supersymmetrized to
world sheet SUSY. One dimension of the model is interpreted as
a compactified fifth dimension, leading to a four dimensional solution with a
Kaluza-Klein gauge field having a magnetic monopole background; this
corresponds to a solution in supergravity, since that theory is obtained
by dimensional reduction of string theory.Comment: 13p. uses Harvma
Pure type I supergravity and DE(10)
We establish a dynamical equivalence between the bosonic part of pure type I
supergravity in D=10 and a D=1 non-linear sigma-model on the Kac-Moody coset
space DE(10)/K(DE(10)) if both theories are suitably truncated. To this end we
make use of a decomposition of DE(10) under its regular SO(9,9) subgroup. Our
analysis also deals partly with the fermionic fields of the supergravity theory
and we define corresponding representations of the generalized spatial Lorentz
group K(DE(10)).Comment: 28 page
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