482 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
Towards reduction of type II theories on SU(3) structure manifolds
We revisit the reduction of type II supergravity on SU(3) structure
manifolds, conjectured to lead to gauged N=2 supergravity in 4 dimensions. The
reduction proceeds by expanding the invariant 2- and 3-forms of the SU(3)
structure as well as the gauge potentials of the type II theory in the same set
of forms, the analogues of harmonic forms in the case of Calabi-Yau reductions.
By focussing on the metric sector, we arrive at a list of constraints these
expansion forms should satisfy to yield a base point independent reduction.
Identifying these constraints is a first step towards a first-principles
reduction of type II on SU(3) structure manifolds.Comment: 20 pages; v2: condition (2.13old) on expansion forms weakened,
replaced by (2.13new), (2.14new
Radiation-dominated area metric cosmology
We provide further crucial support for a refined, area metric structure of
spacetime. Based on the solution of conceptual issues, such as the consistent
coupling of fermions and the covariant identification of radiation fields on
area metric backgrounds, we show that the radiation-dominated epoch of area
metric cosmology is equivalent to that epoch in standard Einstein cosmology.
This ensures, in particular, successful nucleosynthesis. This surprising result
complements the previously derived prediction of a small late-time acceleration
of an area metric universe.Comment: 23 pages, no figures; references adde
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
Area metric gravity and accelerating cosmology
Area metric manifolds emerge as effective classical backgrounds in quantum
string theory and quantum gauge theory, and present a true generalization of
metric geometry. Here, we consider area metric manifolds in their own right,
and develop in detail the foundations of area metric differential geometry.
Based on the construction of an area metric curvature scalar, which reduces in
the metric-induced case to the Ricci scalar, we re-interpret the
Einstein-Hilbert action as dynamics for an area metric spacetime. In contrast
to modifications of general relativity based on metric geometry, no continuous
deformation scale needs to be introduced; the extension to area geometry is
purely structural and thus rigid. We present an intriguing prediction of area
metric gravity: without dark energy or fine-tuning, the late universe exhibits
a small acceleration.Comment: 52 pages, 1 figure, companion paper to hep-th/061213
Generalized structures of N=1 vacua
We characterize N=1 vacua of type II theories in terms of generalized complex
structure on the internal manifold M. The structure group of T(M) + T*(M) being
SU(3) x SU(3) implies the existence of two pure spinors Phi_1 and Phi_2. The
conditions for preserving N=1 supersymmetry turn out to be simple
generalizations of equations that have appeared in the context of N=2 and
topological strings. They are (d + H wedge) Phi_1=0 and (d + H wedge) Phi_2 =
F_RR. The equation for the first pure spinor implies that the internal space is
a twisted generalized Calabi-Yau manifold of a hybrid complex-symplectic type,
while the RR-fields serve as an integrability defect for the second.Comment: 21 pages. v2, v3: minor changes and correction
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
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
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