453 research outputs found
Canonical differential geometry of string backgrounds
String backgrounds and D-branes do not possess the structure of Lorentzian
manifolds, but that of manifolds with area metric. Area metric geometry is a
true generalization of metric geometry, which in particular may accommodate a
B-field. While an area metric does not determine a connection, we identify the
appropriate differential geometric structure which is of relevance for the
minimal surface equation in such a generalized geometry. In particular the
notion of a derivative action of areas on areas emerges naturally. Area metric
geometry provides new tools in differential geometry, which promise to play a
role in the description of gravitational dynamics on D-branes.Comment: 20 pages, no figures, improved journal versio
Heterotic compactifications and nearly-Kahler manifolds
We propose that under certain conditions heterotic string compactifications
on half-flat and nearly-Kahler manifolds are equivalent. Based on this
correspondence we argue that the moduli space of the nearly-Kahler manifolds
under discussion consists only of the Kahler deformations moduli space and
there is no correspondent for the complex structure deformations.Comment: 5 pages, references added, typos correcte
Conifolds and Geometric Transitions
Conifold geometries have recieved a lot of attention in string theory and
string-inspired cosmology recently, in particular the Klebanov-Strassler
background that is known as the "warped throat". It is our intention in this
article to give a pedagogical explanation for the singularity resolution in
this geometry and emphasise its connection to geometric transitions. The first
part focuses on the gauge theory dual to the Klebanov-Strassler background,
which we also explain from a T-dual intersecting branes scenario. We then make
the connection to the Gopakumar-Vafa conjecture for open/closed string duality
and summarise a series of papers verifying this model on the supergravity
level.
An appendix provides extensive background material about conifold geometries.
We pay special attention to their complex structures and re-evaluate the
supersymmetry conditions on the background flux in constructions with
fractional D3-branes on the singular (Klebanov-Tseytlin) and resolved (Pando
Zayas-Tseytlin) conifolds. We agree with earlier results that only the singular
solution allows a supersymmetric flux, but point out the importance of using
the correct complex structure to reach this conclusion.Comment: 37 pages, v3: accepted for publication in Reviews of Modern Physic
Supersymmetric completion of M-theory 4D-gauge algebra from twisted tori and fluxes
We present the supersymmetric completion of the M-theory free differential
algebra resulting from a compactification to four dimensions on a twisted
seven-torus with 4-form and 7-form fluxes turned on. The super--curvatures are
given and the local supersymmetry transformations derived. Dual formulations of
the theory are discussed in connection with classes of gaugings corresponding
to diverse choices of vacua. This also includes seven dimensional
compactifications on more general spaces not described by group manifolds.Comment: 19 pages, LaTeX, typos corrected, references adde
Heterotic-type IIA duality with fluxes
In this paper we study a possible non-perturbative dual of the heterotic
string compactified on K3 x T^2 in the presence of background fluxes. We show
that type IIA string theory compactified on manifolds with SU(3) structure can
account for a subset of the possible heterotic fluxes. This extends our
previous analysis to a case of a non-perturbative duality with fluxes.Comment: 26 pages, minor corrections; version to appear in JHE
Non-Kaehler attracting manifolds
We observe that the new attractor mechanism describing IIB flux vacua for
Calabi-Yau compactifications has a possible extension to the landscape of
non-Kaehler vacua that emerge in heterotic compactifications with fluxes. We
focus on the effective theories coming from compactifications on generalized
half-flat manifolds, showing that the Minkowski "attractor points'' for 3-form
fluxes are special-hermitian manifolds.Comment: 18 pages. v2: Minor polishing, reference added. v3: More cleanup,
final version for JHE
Towards Minkowski Vacua in Type II String Compactifications
We study the vacuum structure of compactifications of type II string theories
on orientifolds with SU(3)xSU(3) structure. We argue that generalised geometry
enables us to treat these non-geometric compactifications using a supergravity
analysis in a way very similar to geometric compactifications. We find
supersymmetric Minkowski vacua with all the moduli stabilised at weak string
coupling and all the tadpole conditions satisfied. Generically the value of the
moduli fields in the vacuum is parametrically controlled and can be taken to
arbitrarily large values.Comment: 33 pages; v2 minor corrections, references added, version to appear
in JHE
Scales and hierarchies in warped compactifications and brane worlds
Warped compactifications with branes provide a new approach to the hierarchy
problem and generate a diversity of four-dimensional thresholds. We investigate
the relationships between these scales, which fall into two classes.
Geometrical scales, such as thresholds for Kaluza-Klein, excited string, and
black hole production, are generically determined soley by the spacetime
geometry. Dynamical scales, notably the scale of supersymmetry breaking and
moduli masses, depend on other details of the model. We illustrate these
relationships in a class of solutions of type IIB string theory with imaginary
self-dual fluxes. After identifying the geometrical scales and the resulting
hierarchy, we determine the gravitino and moduli masses through explicit
dimensional reduction, and estimate their value to be near the four-dimensional
Planck scale. In the process we obtain expressions for the superpotential and
Kahler potential, including the effects of warping. We identify matter living
on certain branes to be effectively sequestered from the supersymmetry breaking
fluxes: specifically, such "visible sector" fields receive no tree-level masses
from the supersymmetry breaking. However, loop corrections are expected to
generate masses, at the phenomenologically viable TeV scale.Comment: 33 pages, LaTeX. v2: reference added v3: reference added, typos
correcte
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