87 research outputs found
The identification of conformal hypercomplex and quaternionic manifolds
We review the map between hypercomplex manifolds that admit a closed
homothetic Killing vector (i.e. `conformal hypercomplex' manifolds) and
quaternionic manifolds of 1 dimension less. This map is related to a method for
constructing supergravity theories using superconformal techniques. An explicit
relation between the structure of these manifolds is presented, including
curvatures and symmetries. An important role is played by `\xi
transformations', relating connections on quaternionic manifolds, and a new
type `\hat\xi transformations' relating complex structures on conformal
hypercomplex manifolds. In this map, the subclass of conformal hyper-Kaehler
manifolds is mapped to quaternionic-Kaehler manifolds.Comment: 22 pages, 2 figures, Contribution to the proceedings volume for the
Conference "Symmetry in Geometry and Physics" in honour of Dmitri
Alekseevsky, September 200
D-instantons and twistors: some exact results
We present some results on instanton corrections to the hypermultiplet moduli
space in Calabi-Yau compactifications of Type II string theories. Previously,
using twistor methods, only a class of D-instantons (D2-instantons wrapping
A-cycles) was incorporated exactly and the rest was treated only linearly. We
go beyond the linear approximation and give a set of holomorphic functions
which, through a known procedure, capture the effect of D-instantons at all
orders. Moreover, we show that for a sector where all instanton charges have
vanishing symplectic invariant scalar product, the hypermultiplet metric can be
computed explicitly.Comment: 32 pages, 3 figures, uses JHEP3.cls; some changes in section 3.3.3;
corrected formula for the contact potentia
Theory of Ultracold Superstrings
The combination of a vortex line in a one-dimensional optical lattice with
fermions bound to the vortex core makes up an ultracold superstring. We give a
detailed derivation of the way to make this supersymmetric string in the
laboratory. In particular, we discuss the presence of a fermionic bound state
in the vortex core and the tuning of the laser beams needed to achieve
supersymmetry. Moreover, we discuss experimental consequences of supersymmetry
and identify the precise supersymmetry in the problem. Finally, we make the
mathematical connection with string theory.Comment: 16 pages, 9 figures, important factor 2 corrected, accepted for
publication in PR
Regularisation, the BV method, and the antibracket cohomology
We review the Lagrangian Batalin--Vilkovisky method for gauge theories. This
includes gauge fixing, quantisation and regularisation. We emphasize the role
of cohomology of the antibracket operation. Our main example is gravity,
for which we also discuss the solutions for the cohomology in the space of
local integrals. This leads to the most general form for the action, for
anomalies and for background charges.Comment: 12 pages, LaTeX, Preprint-KUL-TF-94/2
Hypermultiplets and hypercomplex geometry from 6 to 3 dimensions
The formulation of hypermultiplets that has been developed for 5-dimensional
matter multiplets is by dimensional reductions translated into the appropriate
spinor language for 6 and 4 dimensions. We also treat the theories without
actions that have the geometrical structure of hypercomplex geometry. The
latter is the generalization of hyper-Kaehler geometry that does not require a
Hermitian metric and hence corresponds to field equations without action. The
translation tables of this paper allow the direct application of superconformal
tensor calculus for the hypermultiplets using the available Weyl multiplets in
6 and 4 dimensions. Furthermore, the hypermultiplets in 3 dimensions that
result from reduction of vector multiplets in 4 dimensions are considered,
leading to a superconformal formulation of the c-map and an expression for the
main geometric quantities of the hyper-Kaehler manifolds in the image of this
map.Comment: 18 pages; v2: several clarifications in text and formulae, version to
appear in Class.Quantum Gravit
Einstein-Maxwell gravitational instantons and five dimensional solitonic strings
We study various aspects of four dimensional Einstein-Maxwell multicentred
gravitational instantons. These are half-BPS Riemannian backgrounds of minimal
N=2 supergravity, asymptotic to R^4, R^3 x S^1 or AdS_2 x S^2. Unlike for the
Gibbons-Hawking solutions, the topology is not restricted by boundary
conditions. We discuss the classical metric on the instanton moduli space. One
class of these solutions may be lifted to causal and regular multi `solitonic
strings', without horizons, of 4+1 dimensional N=2 supergravity, carrying null
momentum.Comment: 1+30 page
Generalized instantons in N = 4 super Yang-Mills theory and spinorial geometry
Using spinorial geometry techniques, we classify the supersymmetric solutions
of euclidean super Yang-Mills theory. These backgrounds represent
generalizations of instantons with nontrivial scalar fields turned on, and
satisfy some constraints that bear a similarity with the Hitchin equations, and
contain the Donaldson equations as a special subcase. It turns out that these
constraints can be obtained by dimensional reduction of the octonionic
instanton equations, and may be rephrased in terms of a selfduality-like
condition for a complex connection. We also show that the supersymmetry
conditions imply the equations of motion only partially.Comment: 29 pages, 3 tables. v2: references added. v3: conclusion extended,
version published in JHE
Supergravity description of spacetime instantons
We present and discuss BPS instanton solutions that appear in type II string
theory compactifications on Calabi-Yau threefolds. From an effective action
point of view these arise as finite action solutions of the Euclidean equations
of motion in four-dimensional N=2 supergravity coupled to tensor multiplets. As
a solution generating technique we make use of the c-map, which produces
instanton solutions from either Euclidean black holes or from Taub-NUT like
geometries.Comment: 35 pages, some clarifications adde
The CubeSpec space mission: Asteroseismology of massive stars from time-series optical spectroscopy
The ESA/KU Leuven CubeSpec mission is specifically designed to provide
low-cost space-based high-resolution optical spectroscopy. Here we highlight
the science requirements and capabilities of CubeSpec. The primary science goal
is to perform pulsation mode identification from spectroscopic line profile
variability and empower asteroseismology of massive stars.Comment: Authors' submitted version of poster proceedings paper for IAU
Symposium 361: Massive Stars Near and Far, held in Ballyconnell, Ireland,
9-13 May 202
Black holes and black branes in Lifshitz spacetimes
We construct analytic solutions describing black holes and black branes in
asymptotically Lifshitz spacetimes with arbitrary dynamical exponent z and for
arbitrary number of dimensions. The model considered consists of Einstein
gravity with negative cosmological constant, a scalar, and N U(1) gauge fields
with dilatonic-like couplings. We study the phase diagrams and thermodynamic
instabilities of the solution, and find qualitative differences between the
cases with 12.Comment: 27 pages, 10 figures; v2 references added, minor comments adde
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