3,923 research outputs found
String Landscape and the Standard Model of Particle Physics
In this paper we describe ideas about the string landscape, and how to relate
it to the physics of the Standard Model of particle physics. First, we give a
short status report about heterotic string compactifications. Then we focus on
the statistics of D-brane models, on the problem of moduli stabilization, and
finally on some attempts to derive a probability wave function in moduli space,
which goes beyond the purely statistical count of string vacua.Comment: Contribution to the 11th. Marcel Grossmann Meeting on General
Relativity in Berlin, July 2006}, new refs. added, typos correcte
Supertranslations and Holography near the Horizon of Schwarzschild Black Holes
In this paper we review and discuss several aspects of supertranslations and
their associated algebras at the horizon of a Schwarzschild black hole. We will
compare two different approaches on horizon supertranslations, which were
recently considered in separate publications. Furthermore we describe a
possible holographic description of a Schwarzschild black hole in terms of a
large N boundary theory, which accommodates the Goldstone bosons of the horizon
supertranslations.Comment: 21 pages, replaced version contains some new references and corrected
typo
Ornstein-Uhlenbeck semi-groups on stratified groups
We consider, in the setting of stratified groups G, two analogues of the
Ornstein-Uhlenbeck semi-group, namely Markovian diffusion semi-groups acting on
, whose invariant density is a heat kernel at time 1 on G
Gaugino Condensation in the Chiral and Linear Representation of the Dilaton
String effective theories with N=1 supersymmetry in four dimensions are
subject of the discussion. Gaugino condensation in the chiral representation of
the dilaton is reviewed in the truncated formalism in the
-superspace. Using the supersymmetric duality of the dilaton the same
investigation is made in the linear representation of the dilaton. We show that
for the simple case of one gaugino condensate the results concerning
supersymmtry breaking are independent of the representation of the dilaton.Comment: 16 pagex, latex, no figure
Branes, Waves and AdS Orbifolds
The embedding of a Taub-NUT space in the directions transverse to the world
volume of branes describes branes at (spherical) orbifold singularities.
Similarly, the embedding of a pp-wave in the brane world volume yields an AdS
orbifold. In case of the D1-D5--brane system, the AdS3 orbifolds yields a BTZ
black hole; as we will show, the same holds for D3-branes corresponding to
AdS5. In addition we will show that the AdS orbifolds and the spherical
orbifolds are U-dual to each other. However in contrast to spherical orbifolds
the AdS orbifolds lead to a running coupling, which is in the IR inverse to the
coupling of the spherical orbifold. A discussion of the general pp-wave
solution in AdS space is added.Comment: 13 pages, replaced version: more refs. adde
Classification of maximally supersymmetric backgrounds in supergravity theories
We study maximally supersymmetric solutions of all gauged or deformed
supergravity theories in space-time dimensions. For vanishing
background fluxes the space-time background has to be either Minkowski or
anti-de Sitter. We derive a simple criterion for the existence of solutions
with non-trivial fluxes and determine all supergravities that satisfy it. We
show that their solutions coincide with those of the corresponding ungauged
theories and conclude that the known list of maximally supersymmetric solutions
is exhaustive.Comment: 25 pages; improved discussion of the gauged R-symmetry, references
added, version to be published in JHE
Consistent Compactification of Double Field Theory on Non-geometric Flux Backgrounds
In this paper, we construct non-trivial solutions to the -dimensional
field equations of Double Field Theory (DFT) by using a consistent
Scherk-Schwarz ansatz. The ansatz identifies internal directions with
a twist which is directly connected to the covariant fluxes
. It exhibits linear independent generalized
Killing vectors and gives rise to a gauged supergravity in
dimensions. We analyze the covariant fluxes and the corresponding gauged
supergravity with a Minkowski vacuum. We calculate fluctuations around such
vacua and show how they gives rise to massive scalars field and vectors field
with a non-abelian gauge algebra. Because DFT is a background independent
theory, these fields should directly correspond the string excitations in the
corresponding background. For we perform a complete scan of all
allowed covariant fluxes and find two different kinds of backgrounds: the
single and the double elliptic case. The later is not T-dual to a geometric
background and cannot be transformed to a geometric setting by a field
redefinition either. While this background fulfills the strong constraint, it
is still consistent with the Killing vectors depending on the coordinates and
the winding coordinates, thereby giving a non-geometric patching. This
background can therefore not be described in Supergravity or Generalized
Geometry.Comment: 44 pages, 3 tables, references added, typos correcte
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