5,730 research outputs found
Vacua Analysis in Extended Supersymmetry Compactifications
We analyse geometric type IIA flux compactifications leading to N=4 gauged
supergravities in four dimensions. The complete landscape of isotropic vacua is
presented, which turns out to belong to a unique theory. The solutions admit an
uplift to maximal supergravity due to the vanishing of the flux-induced
tadpoles for all the supersymmetry-breaking branes. Such an uplift is sketched
out and the full N=8 mass spectra are discussed. We find the interesting
presence of a non-supersymmetric and nevertheless stable minimum.Comment: 7 pages, contribution to the proceedings of the XVII European
Workshop on String Theory, Padua 201
Supergravities without an Action: Gauging the Trombone
We present a systematic account of supergravity theories in which the global
scaling symmetry is gauged. This generalizes the standard gaugings of
non-abelian off-shell symmetries. A particular feature of these theories is an
additional positive contribution to the effective cosmological constant.
As the scaling symmetry is an on-shell symmetry, the resulting gaugings do no
longer possess an action. We develop the algebraic framework for the maximal
theories in various dimensions and construct explicit solutions to the
algebraic consistency constraints - related to `pure-spinor-like' structures
for the exceptional groups. As an example, we explicitly work out the modified
supersymmetry transformation rules and equations of motion in three dimensions.
Finally, we speculate about the role of these theories from the perspective of
very extended Kac-Moody algebras.Comment: 40 pages; v2: refs added, minor corrections, version to be published
in NP
Towards micro-arcsecond spatial resolution with Air Cherenkov Telescope arrays as optical intensity interferometers
In this poster contribution we highlight the equivalence between an Imaging
Air Cherenkov Telescope (IACT) array and an Intensity Interferometer for a
range of technical requirements. We touch on the differences between a
Michelson and an Intensity Interferometer and give a brief overview of the
current IACT arrays, their upgrades and next generation concepts (CTA, AGIS,
completion 2015). The latter are foreseen to include 30-90 telescopes that will
provide 400-4000 different baselines that range in length between 50m and a
kilometre. Intensity interferometry with such arrays of telescopes attains 50
micro-arcseconds resolution for a limiting V magnitude of ~8.5. This technique
opens the possibility of a wide range of studies, amongst others, probing the
stellar surface activity and the dynamic AU scale circumstellar environment of
stars in various crucial evolutionary stages. Here we discuss possibilities for
using IACT arrays as optical Intensity Interferometers.Comment: Appeared in the proceedings of "The Universe under the Microscope -
Astrophysics at High Angular Resolution", Journal of Physics:Conference
Series (IOP; http://www.iop.org/EJ/toc/1742-6596/131/1
Recovering coefficients of the complex Ginzburg-Landau equation from experimental spatio-temporal data: two examples from hydrodynamics
International audienceThere are many examples where the description of the complexity of flows can only be achieved by the use of simple models. These models, obtained usually from phenomenological arguments, need in general the knowledge of some parameters. The challenge is then to determine the values of these parameters from experiments. We will give two examples where we have been able to evaluate the coefficients of the complex Ginzburg-Landau equation (CGLE) from space-time chaotic data applied to first a row of coupled cylinder wakes and then to wave propagation in the Ekman layer of a rotating disk. In the first case, our analysis is based on a proper decomposition of experimental chaotic flow fields, followed by a projection of the CGLE onto the proper directions. We show that our method is able to recover the parameters of the model which permits to reconstruct the spatio-temporal chaos observed in the experiment. The second physical system under consideration is the flow above a rotating disk and its cross-flow instability. Our aim is to study the properties of the wavefield through a Volterra series equation. The kernels of the Volterra expansion, which contain relevant physical information about the system, are estimated by fitting two-point measurements via a nonlinear parametric model. We then consider describing the wavefield with the CGLE, and derive analytical relations which express the coefficients of the Ginzburg-Landau equation in terms of the kernels of the Volterra expansion
Minimal Stability in Maximal Supergravity
Recently, it has been shown that maximal supergravity allows for
non-supersymmetric AdS critical points that are perturbatively stable. We
investigate this phenomenon of stability without supersymmetry from the
sGoldstino point of view. In particular, we calculate the projection of the
mass matrix onto the sGoldstino directions, and derive the necessary conditions
for stability. Indeed we find a narrow window allowing for stable SUSY breaking
points. As a by-product of our analysis, we find that it seems impossible to
perturb supersymmetric critical points into non-supersymmetric ones: there is a
minimal amount of SUSY breaking in maximal supergravity.Comment: 27 pages, 1 figure. v2: two typos corrected, published versio
Critical points of maximal D=8 gauged supergravities
We study the general deformations of maximal eight-dimensional supergravity
by using the embedding tensor approach. The scalar potential induced by these
gaugings is determined. Subsequently, by combining duality covariance arguments
and algebraic geometry techniques, we find the complete set of critical points
of the scalar potential. Remarkably, up to SO(2) X SO(3) rotations there turns
out to be a unique theory admitting extrema. The gauge group of the theory is
CSO(2,0,1).Comment: 14 pages. v2: minor changes - published versio
Duality orbits of non-geometric fluxes
Compactifications in duality covariant constructions such as generalised
geometry and double field theory have proven to be suitable frameworks to
reproduce gauged supergravities containing non-geometric fluxes. However, it is
a priori unclear whether these approaches only provide a reformulation of old
results, or also contain new physics. To address this question, we classify the
T- and U-duality orbits of gaugings of (half-)maximal supergravities in
dimensions seven and higher. It turns out that all orbits have a geometric
supergravity origin in the maximal case, while there are non-geometric orbits
in the half-maximal case. We show how the latter are obtained from
compactifications of double field theory.Comment: 39 pages, 1 figure, 6 tables; v2: refs added, published versio
Lectures on Gauged Supergravity and Flux Compactifications
The low-energy effective theories describing string compactifications in the
presence of fluxes are so-called gauged supergravities: deformations of the
standard abelian supergravity theories. The deformation parameters can be
identified with the various possible (geometric and non-geometric) flux
components. In these lecture notes we review the construction of gauged
supergravities in a manifestly duality covariant way and illustrate the
construction in several examples.Comment: 48 pages, lectures given at the RTN Winter School on Strings,
Supergravity and Gauge Theories, CERN, January 200
A many-body singlet prepared by a central spin qubit
Controllable quantum many-body systems are platforms for fundamental
investigations into the nature of entanglement and promise to deliver
computational speed-up for a broad class of algorithms and simulations. In
particular, engineering entanglement within a dense spin ensemble can turn it
into a robust quantum memory or a computational platform. Recent experimental
progress in dense central spin systems motivates the design of algorithms that
use a central-spin qubit as a convenient proxy for the ensemble. Here we
propose a protocol that uses a central spin to initialize two dense spin
ensembles into a pure anti-polarized state and from there creates a many-body
entangled state -- a singlet -- from the combined ensemble. We quantify the
protocol performance for multiple material platforms and show that it can be
implemented even in the presence of realistic levels of decoherence. Our
protocol introduces an algorithmic approach to preparation of a known many-body
state and to entanglement engineering in a dense spin ensemble, which can be
extended towards a broad class of collective quantum states.Comment: 11 pages, 6 figures, and supplementary material
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