7,549 research outputs found
Flux Compactifications of M-Theory on Twisted Tori
We find the bosonic sector of the gauged supergravities that are obtained
from 11-dimensional supergravity by Scherk-Schwarz dimensional reduction with
flux to any dimension D. We show that, if certain obstructions are absent, the
Scherk-Schwarz ansatz for a finite set of D-dimensional fields can be extended
to a full compactification of M-theory, including an infinite tower of
Kaluza-Klein fields. The internal space is obtained from a group manifold
(which may be non-compact) by a discrete identification. We discuss the
symmetry algebra and the symmetry breaking patterns and illustrate these with
particular examples. We discuss the action of U-duality on these theories in
terms of symmetries of the D-dimensional supergravity, and argue that in
general it will take geometric flux compactifications to M-theory on
non-geometric backgrounds, such as U-folds with U-duality transition functions.Comment: Latex, 47 page
Generalised Geometry for M-Theory
Generalised geometry studies structures on a d-dimensional manifold with a
metric and 2-form gauge field on which there is a natural action of the group
SO(d,d). This is generalised to d-dimensional manifolds with a metric and
3-form gauge field on which there is a natural action of the group .
This provides a framework for the discussion of M-theory solutions with flux. A
different generalisation is to d-dimensional manifolds with a metric, 2-form
gauge field and a set of p-forms for either odd or even on which there is a
natural action of the group . This is useful for type IIA or IIB
string solutions with flux. Further generalisations give extended tangent
bundles and extended spin bundles relevant for non-geometric backgrounds.
Special structures that arise for supersymmetric backgrounds are discussed.Comment: 31 page
A Cosmic Microwave Background Radiation Polarimeter Using Superconducting Bearings
Measurements of the polarization of the cosmic microwave background (CMB)
radiation are expected to significantly increase our understanding of the early
universe. We present a design for a CMB polarimeter in which a cryogenically
cooled half wave plate rotates by means of a high-temperature superconducting
(HTS) bearing. The design is optimized for implementation in MAXIPOL, a
balloon-borne CMB polarimeter. A prototype bearing, consisting of commercially
available ring-shaped permanent magnet and an array of YBCO bulk HTS material,
has been constructed. We measured the coefficient of friction as a function of
several parameters including temperature between 15 and 80 K, rotation
frequency between 0.3 and 3.5 Hz, levitation distance between 6 and 10 mm, and
ambient pressure between 10^{-7} and 1 torr. The low rotational drag of the HTS
bearing allows rotations for long periods of time with minimal input power and
negligible wear and tear thus making this technology suitable for a future
satellite mission.Comment: 6 pages, IEEE-Transactions of Applied Superconductivity, 2003, Vol.
13, in pres
Conformal topological Yang-Mills theory and de Sitter holography
A new topological conformal field theory in four Euclidean dimensions is
constructed from N=4 super Yang-Mills theory by twisting the whole of the
conformal group with the whole of the R-symmetry group, resulting in a theory
that is conformally invariant and has two conformally invariant BRST operators.
A curved space generalisation is found on any Riemannian 4-fold. This
formulation has local Weyl invariance and two Weyl-invariant BRST symmetries,
with an action and energy-momentum tensor that are BRST-exact. This theory is
expected to have a holographic dual in 5-dimensional de Sitter space.Comment: 34 pages, AMSTex, Reference adde
Thermodynamics of Exotic Black Holes in Lovelock Gravity
We examine the thermodynamics of a new class of asymptotically AdS black
holes with non-constant curvature event horizons in Gauss-Bonnet Lovelock
gravity, with the cosmological constant acting as thermodynamic pressure. We
find that non-trivial curvature on the horizon can significantly affect their
thermodynamic behaviour. We observe novel triple points in 6 dimensions between
large and small uncharged black holes and thermal AdS. For charged black holes
we find a continuous set of triple points whose range depends on the parameters
in the horizon geometry. We also find new generalizations of massless and
negative mass solutions previously observed in Einstein gravity.Comment: 28 pages, 15 figure
Anaplasmosis in a Hereford Cow
Anaplasmosis is a condition recognized more frequently in the bovine in recent years. However, even more important is the fact that it is becoming more prevalent in areas outside the epizootic areas. The organism was first observed by workers studying Texas cattle fever, therefore it is plausible these men were often seeing cattle with two conditions
Dielectric branes in non-trivial backgrounds
We present a procedure to evaluate the action for dielectric branes in
non-trivial backgrounds. These backgrounds must be capable to be taken into a
Kaluza-Klein form, with some non-zero wrapping factor. We derive the way this
wrapping factor is gauged away. Examples of this are AdS_5xS^5 and
AdS_3xS^3xT^4, where we perform the construction of different stable systems,
which stability relies in its dielectric character.Comment: 14 pages, published versio
Rigid N=2 superconformal hypermultiplets
We discuss superconformally invariant systems of hypermultiplets coupled to
gauge fields associated with target-space isometries.Comment: Invited talk given at the International Seminar "Supersymmetries and
Quantum Symmetries", July 1997, Dubna. Latex, 9 p
Dynamic stability of crack fronts: Out-of-plane corrugations
The dynamics and stability of brittle cracks are not yet fully understood.
Here we use the Willis-Movchan 3D linear perturbation formalism [J. Mech. Phys.
Solids {\bf 45}, 591 (1997)] to study the out-of-plane stability of planar
crack fronts in the framework of linear elastic fracture mechanics. We discuss
a minimal scenario in which linearly unstable crack front corrugations might
emerge above a critical front propagation speed. We calculate this speed as a
function of Poisson's ratio and show that corrugations propagate along the
crack front at nearly the Rayleigh wave-speed. Finally, we hypothesize about a
possible relation between such corrugations and the long-standing problem of
crack branching.Comment: 5 pages, 2 figures + supplementary informatio
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