1,435 research outputs found
AdS spacetimes from wrapped M5 branes
We derive a complete geometrical characterisation of a large class of
, and supersymmetric spacetimes in eleven-dimensional
supergravity using G-structures. These are obtained as special cases of a class
of supersymmetric , and
geometries, naturally associated to M5-branes wrapping calibrated cycles in
manifolds with , SU(3) or SU(2) holonomy. Specifically, the latter class
is defined by requiring that the Killing spinors satisfy the same set of
projection conditions as for wrapped probe branes, and that there is no
electric flux. We show how the R-symmetries of the dual field theories appear
as isometries of the general AdS geometries. We also show how known solutions
previously constructed in gauged supergravity satisfy our more general
G-structure conditions, demonstrate that our conditions for half-BPS
geometries are precisely those of Lin, Lunin and Maldacena, and construct some
new singular solutions.Comment: 1+56 pages, LaTeX; v2, references added; v3, minor corrections, final
version to appear in JHE
Consistent supersymmetric Kaluza--Klein truncations with massive modes
We construct consistent Kaluza--Klein reductions of D=11 supergravity to four
dimensions using an arbitrary seven-dimensional Sasaki--Einstein manifold. At
the level of bosonic fields, we extend the known reduction, which leads to
minimal N=2 gauged supergravity, to also include a multiplet of massive fields,
containing the breathing mode of the Sasaki--Einstein space, and still
consistent with N=2 supersymmetry. In the context of flux compactifications,
the Sasaki--Einstein reductions are generalizations of type IIA SU(3)-structure
reductions which include both metric and form-field flux and lead to a massive
universal tensor multiplet. We carry out a similar analysis for an arbitrary
weak G_2 manifold leading to an N=1 supergravity with massive fields. The
straightforward extension of our results to the case of the seven-sphere would
imply that there is a four-dimensional Lagrangian with N=8 supersymmetry
containing both massless and massive spin two fields. We use our results to
construct solutions of M-theory with non-relativistic conformal symmetry.Comment: 33 pages. v2: Added section on skew-whiffed solutions and some brief
comments on holographic superconductors. v3: typos corrected, version to be
published in JHE
Marginal Deformations of Field Theories with AdS_4 Duals
We generate new AdS_4 solutions of D=11 supergravity starting from AdS_4 x
X_7 solutions where X_7 has U(1)^3 isometry. We consider examples where X_7 is
weak G_2, Sasaki-Einstein or tri-Sasakian, corresponding to d=3 SCFTs with
N=1,2 or 3 supersymmetry, respectively, and where the deformed solutions
preserve N=1,2 or 1 supersymmetry, respectively. For the special cases when X_7
is M(3,2), Q(1,1,1) or N(1,1)_I we identify the exactly marginal deformation in
the dual field theory. We also show that the volume of supersymmetric 5-cycles
of N(1,1)_I agrees with the conformal dimension predicted by the baryons of the
dual field theory.Comment: 28 pages, 2 figures; v2. typos correcte
Approaches to dealing with highâsized polynuclear systems with ab initio methods
This contribution sununarizes sorne of the theoretical strategies developed in the recent past to study systems with an increasing size and complexity by means of accurate extended CI calculations. Sorne examples ofthe capabilities of these strategies are also given, conceming the evaluation of magnetic exchange constants, as well as many other effective interaction parameters, such as hopping integrals, on-site Coulomb repulsion, four-body exchange term, ... on 2D and spin-ladder cuprates, polyoxovanadates, as well as polynuclear molecular compound
Friedel oscillations in one-dimensional metals: from Luttinger's theorem to the Luttinger liquid
Charge density and magnetization density profiles of one-dimensional metals
are investigated by two complementary many-body methods: numerically exact
(Lanczos) diagonalization, and the Bethe-Ansatz local-density approximation
with and without a simple self-interaction correction. Depending on the
magnetization of the system, local approximations reproduce different Fourier
components of the exact Friedel oscillations.Comment: 3 pages, 3 figures, Manuscript accepted by Journal of Magnetism and
Magnetic Materials, special issue for LAWMMM 2007 conferenc
Supersymmetric AdS_3, AdS_2 and Bubble Solutions
We present new supersymmetric AdS_3 solutions of type IIB supergravity and
AdS_2 solutions of D=11 supergravity. The former are dual to conformal field
theories in two dimensions with N=(0,2) supersymmetry while the latter are dual
to conformal quantum mechanics with two supercharges. Our construction also
includes AdS_2 solutions of D=11 supergravity that have non-compact internal
spaces which are dual to three-dimensional N=2 superconformal field theories
coupled to point-like defects. We also present some new bubble-type solutions,
corresponding to BPS states in conformal theories, that preserve four
supersymmetries.Comment: v2: 33 pages, published version in JHE
Twitter, Google, iPhone/iPad, and Facebook (TGIF) and Smart Technology Environments: How Well Do Educators Communicate with Students via TGIF?
This article is a summary of a 2011 Association for Information Systems Americas Conference on Information Systems (AMCIS) panel discussion regarding current issues and future directions in the use of mobile technologies and social networks in education. The invited panelists are four faculty members from the United States specializing in Information Systems. The covered topics included evolution and history of e-learning, use of smartphones and tablets in education, development of social network services, and the use of social media (i.e., teaching with blogs and wikis) in the classroom. We discuss future directions in Twitter, Google, iPhone/iPad, and Facebook technology environments. Several resources for social media for college instructors are provided in the Appendix
Distributed Fault Detection Using Relative Information in Linear Multi-Agent Networks
This paper addresses the problem of fault detection in the context of a collection of agents performing a shared task and exchanging relative information over a communication network. We resort to techniques in the literature to construct a meaningful observable system and overcome the issue that the system of systems is not observable. A solution involving Set-Valued Observers (SVOs) is proposed to estimate the state in a distributed fashion and a proof of convergence of the estimates is given under mild assumptions. The performance of the proposed algorithm is assessed through simulations
Finite-time average consensus in a Byzantine environment using Set-Valued Observers
This paper addresses the problem of consensus in the presence of Byzantine faults, modeled by an attacker injecting a perturbation in the state of the nodes of a network. It is firstly shown that Set-Valued Observers (SVOs) attain finite-time consensus, even in the case where the state estimates are not shared between nodes, at the expenses of requiring large horizons, thus rendering the computation problem intractable in the general case. A novel algorithm is therefore proposed that achieves finite-time consensus, even if the aforementioned requirement is dropped, by intersecting the set-valued state estimates of neighboring nodes, making it suitable for practical applications and enabling nodes to determine a stopping time. This is in contrast with the standard iterative solutions found in the literature, for which the algorithms typically converge asymptotically and without any guarantees regarding the maximum error of the final consensus value, under faulty environments. The algorithm suggested is evaluated in simulation, illustrating, in particular, the finite-time consensus property
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