1,071 research outputs found
Deformations of generalized calibrations and compact non-Kahler manifolds with vanishing first Chern class
We investigate the deformation theory of a class of generalized calibrations
in Riemannian manifolds for which the tangent bundle has reduced structure
group U(n), SU(n), G_2 and Spin(7). For this we use the property of the
associated calibration form to be parallel with respect to a metric connection
which may have non-vanishing torsion. In all these cases, we find that if there
is a moduli space, then it is finite dimensional.
We present various examples of generalized calibrations that include almost
hermitian manifolds with structure group U(n) or SU(n), nearly parallel G_2
manifolds and group manifolds. We find that some Hopf fibrations are
deformation families of generalized calibrations. In addition, we give
sufficient conditions for a hermitian manifold (M,g,J) to admit Chern and
Bismut connections with holonomy contained in SU(n). In particular we show that
any connected sum of copies of admits a hermitian
structure for which the restricted holonomy of a Bismut connection is contained
in SU(3).Comment: 43 pages, Latex, typos corrected, reference added in section
Geometry and supersymmetry of heterotic warped flux AdS backgrounds
We classify the geometries of the most general warped, flux AdS backgrounds
of heterotic supergravity up to two loop order in sigma model perturbation
theory. We show under some mild assumptions that there are no
backgrounds with . Moreover the warp factor of AdS backgrounds is
constant, the geometry is a product and such solutions
preserve, 2, 4, 6 and 8 supersymmetries. The geometry of has been
specified in all cases. For 2 supersymmetries, it has been found that
admits a suitably restricted structure. For 4 supersymmetries, has
an structure and can be described locally as a circle fibration over a
6-dimensional KT manifold. For 6 and 8 supersymmetries, has an
structure and can be described locally as a fibration over a
4-dimensional manifold which either has an anti-self dual Weyl tensor or a
hyper-K\"ahler structure, respectively. We also demonstrate a new Lichnerowicz
type theorem in the presence of corrections.Comment: 34 pages. Reference adde
All Killing Superalgebras for Warped AdS Backgrounds
We present all the symmetry superalgebras of all warped
AdS, , flux backgrounds in dimensions
preserving any number of supersymmetries. First we give the conditions for
to decompose into a direct sum of the isometry algebra of
AdS and that of the internal space . Assuming this decomposition,
we identify all symmetry superalgebras of AdS backgrounds by showing that
the isometry groups of internal spaces act transitively on spheres. We
demonstrate that in type II and theories the AdS symmetry
superalgebras may not be simple and also present all symmetry superalgebras of
heterotic AdS backgrounds. Furthermore, we explicitly give the symmetry
superalgebras of AdS, , backgrounds and prove that they are all
classical.Comment: 41 pages, late
HKT Geometry and Fake Five Dimensional Supergravity
Recent results on the relation between hyper-Kahler geometry with torsion and
solutions admitting Killing spinors in minimal de sitter supergravity are
extended to more general supergravity models with vector multiplets.Comment: 14 pages, latex. Minor typos corrected, references adde
Vanishing Preons in the Fifth Dimension
We examine supersymmetric solutions of N=2, D=5 gauged supergravity coupled
to an arbitrary number of abelian vector multiplets using the spinorial
geometry method. By making use of methods developed in hep-th/0606049 to
analyse preons in type IIB supergravity, we show that there are no solutions
preserving exactly 3/4 of the supersymmetry.Comment: 19 pages, latex. Reference added, and further modification to the
introductio
Maximally Minimal Preons in Four Dimensions
Killing spinors of N=2, D=4 supergravity are examined using the spinorial
geometry method, in which spinors are written as differential forms. By making
use of methods developed in hep-th/0606049 to analyze preons in type IIB
supergravity, we show that there are no simply connected solutions preserving
exactly 3/4 of the supersymmetry.Comment: 18 pages. References added, comments added discussing the possibility
of discrete quotients of AdS(4) preserving 3/4 supersymmetry
Calibrated Entanglement Entropy
The Ryu-Takayanagi prescription reduces the problem of calculating
entanglement entropy in CFTs to the determination of minimal surfaces in a dual
anti-de Sitter geometry. For 3D gravity theories and BTZ black holes, we
identify the minimal surfaces as special Lagrangian cycles calibrated by the
real part of the holomorphic one-form of a spacelike hypersurface. We show that
(generalised) calibrations provide a unified way to determine holographic
entanglement entropy from minimal surfaces, which is applicable to warped
AdS geometries. We briefly discuss generalisations to higher dimensions.Comment: v1 22 pages, 1 figure; v2 appendix improved and moved into the body
to show the application of calibrations to find minimal surfaces in warped
AdS, matches published versio
Do supersymmetric anti-de Sitter black rings exist?
We determine the most general near-horizon geometry of a supersymmetric,
asymptotically anti-de Sitter, black hole solution of five-dimensional minimal
gauged supergravity that admits two rotational symmetries. The near-horizon
geometry is that of the supersymmetric, topologically spherical, black hole
solution of Chong et al. This proves that regular supersymmetric anti-de Sitter
black rings with two rotational symmetries do not exist in minimal
supergravity. However, we do find a solution corresponding to the near-horizon
geometry of a supersymmetric black ring held in equilibrium by a conical
singularity, which suggests that nonsupersymmetric anti-de Sitter black rings
may exist but cannot be "balanced" in the supersymmetric limit.Comment: Latex, 18 pages, 1 figure. v2: minor change
Mapping the G-structures and supersymmetric vacua of five-dimensional N=4 supergravity
We classify the supersymmetric vacua of N=4, d=5 supergravity in terms of
G-structures. We identify three classes of solutions: with R^3, SU(2) and
generic SO(4) structure. Using the Killing spinor equations, we fully
characterize the first two classes and partially solve the latter. With the N=4
graviton multiplet decomposed in terms of N=2 multiplets: the graviton, vector
and gravitino multiplets, we obtain new supersymmetric solutions corresponding
to turning on fields in the gravitino multiplet. These vacua are described in
terms of an SO(5) vector sigma-model coupled with gravity, in three or four
dimensions. A new feature of these N=4 vacua, which is not seen from an N=2
point of view, is the possibility for preserving more exotic fractions of
supersymmetry. We give a few concrete examples of these new supersymmetric
(albeit singular) solutions. Additionally, we show how by truncating the N=4,
d=5 set of fields to minimal supergravity coupled with one vector multiplet we
recover the known two-charge solutions.Comment: 31 pages, late
All null supersymmetric backgrounds of N=2, D=4 gauged supergravity coupled to abelian vector multiplets
The lightlike supersymmetric solutions of N=2, D=4 gauged supergravity
coupled to an arbitrary number of abelian vector multiplets are classified
using spinorial geometry techniques. The solutions fall into two classes,
depending on whether the Killing spinor is constant or not. In both cases, we
give explicit examples of supersymmetric backgrounds. Among these BPS
solutions, which preserve one quarter of the supersymmetry, there are
gravitational waves propagating on domain walls or on bubbles of nothing that
asymptote to AdS_4. Furthermore, we obtain the additional constraints obeyed by
half-supersymmetric vacua. These are divided into four categories, that include
bubbles of nothing which are asymptotically AdS_4, pp-waves on domain walls,
AdS_3 x R, and spacetimes conformal to AdS_3 times an interval.Comment: 55 pages, uses JHEP3.cls. v2: Minor errors corrected, small changes
in introductio
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