209 research outputs found
Reduction of open membrane moduli
We perform a general reduction of the open membrane metric in a worldvolume
direction of the M5-brane. Using reduction rules analogous to the bulk, we show
that the open membrane metric leads to the standard open string metric and open
string coupling constant on the D4-brane only for an ``electric'' reduction in
which case the open membrane metric has no off-diagonal components and the
Born-Infeld curvature tensor is a matrix of rank 2. Instead, if we perform a
general reduction, with nonzero off-diagonal components of the open membrane
metric, we obtain a rank 4 Born-Infeld tensor corresponding to a bound state of
an open string with an open D2--brane. Next, we identify and reduce a 3-form
open membrane ``noncommutativity'' tensor on the M5-brane. This open membrane
parameter only reduces to the open string noncommutativity tensor on the
D4-brane provided we constrain ourselves to an ``electric'' or a ``magnetic''
reduction.Comment: 15 pages, LaTeX, uses JHEP.cls and JHEP.bst style file
Open membranes, ribbons and deformed Schild strings
We analyze open membranes immersed in a magnetic three-form field-strength
. While cylindrical membranes in the absence of behave like tensionless
strings, when the flux is present the strings polarize into thin membrane
ribbons, locally orthogonal to the momentum density, thus providing the strings
with an effective tension. The effective dynamics of the ribbons can be
described by a simple deformation of the Schild action for null strings.
Interactions become non-local due to the polarization, and lead to a
deformation of the string field theory, whereby string vertices receive a phase
factor proportional to the volume swept out by the ribbons. In a particular
limit, this reduces to the non-commutative loop space found previously.Comment: revte
An M-theory solution generating technique and SL(2,R)
In this paper we generalize the O(p+1,p+1) solution generating technique
(this is a method used to deform Dp-branes by turning on a NS-NS B-field) to
M-theory, in order to be able to deform M5-brane supergravity solutions
directly in eleven dimensions, by turning on a non zero three form A. We find
that deforming the M5-brane, in some cases, corresponds to performing certain
SL(2,R) transformations of the Kahler structure parameter for the three-torus,
on which the M5-brane has been compactified. We show that this new M-theory
solution generating technique can be reduced to the O(p+1,p+1) solution
generating technique with p=4. Further, we find that it implies that the open
membrane metric and generalized noncommutativity parameter are manifestly
deformation independent for electric and light-like deformations. We also
generalize the O(p+1,p+1) method to the type IIA/B NS5-brane in order to be
able to deform NS5-branes with RR three and two forms, respectively. In the
type IIA case we use the newly obtained solution generating technique and
deformation independence to derive a covariant expression for an open D2-brane
coupling, relevant for OD2-theory.Comment: 24 pages, Latex. v2:Sections 3.2 and 3.3 improved. v3:Some
clarifications added. Version published in JHE
Light-like noncommutativity and duality from open strings/branes
In this paper we perform some non-trivial tests for the recently obtained
open membrane/D-brane metrics and `generalized' noncommutativity parameters
using Dp/NS5/M5-branes which have been deformed by light-like fields. The
results obtained give further evidence that these open membrane/D-brane metrics
and `generalized' noncommutativity parameters are correct. Further, we use the
open brane data and supergravity duals to obtain more information about
non-gravitational theories with light-like noncommutativity, or `generalized'
light-like noncommutativity. In particular, we investigate various duality
relations (strong coupling limits). In the light-like case we also comment on
the relation between open membrane data (open membrane metric etc.) in six
dimensions and open string data in five dimensions. Finally, we investigate the
strong coupling limit (high energy limit) of five dimensional NCYM with
\Theta^{12}=\Theta^{34}. In particular, we find that this NCYM theory can be UV
completed by a DLCQ compactification of M-theory.Comment: 24 pages, Latex. v2:Comments and references added. v3:Version
published in JHE
Pure type I supergravity and DE(10)
We establish a dynamical equivalence between the bosonic part of pure type I
supergravity in D=10 and a D=1 non-linear sigma-model on the Kac-Moody coset
space DE(10)/K(DE(10)) if both theories are suitably truncated. To this end we
make use of a decomposition of DE(10) under its regular SO(9,9) subgroup. Our
analysis also deals partly with the fermionic fields of the supergravity theory
and we define corresponding representations of the generalized spatial Lorentz
group K(DE(10)).Comment: 28 page
Mapping Vesta: First Results from Dawn’s Survey Orbit
The geologic objectives of the Dawn Mission [1] are
to derive Vesta’s shape, map the surface geology,
understand the geological context and contribute to
the determination of the asteroids’ origin and
evolution.Geomorphology and distribution of surface features
will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral
measurements of the surface will provide evidence of
the compositional characteristics of geological units.
Age information, as derived from crater sizefrequency
distributions, provides the stratigraphic
context for the structural and compositional mapping
results, thus revealing the geologic history of Vesta.
We present here the first results of the Dawn mission
from data collected during the approach to Vesta, and
its first discrete orbit phase – the Survey Orbit, which
lasts 21 days after the spacecraft had established a
circular polar orbit at a radius of ~3000 km with a
beta angle of 10°-15°
Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models
Both community ecology and conservation biology seek further understanding of
factors governing the advance of an invasive species. We model biological
invasion as an individual-based, stochastic process on a two-dimensional
landscape. An ecologically superior invader and a resident species compete for
space preemptively. Our general model includes the basic contact process and a
variant of the Eden model as special cases. We employ the concept of a
"roughened" front to quantify effects of discreteness and stochasticity on
invasion; we emphasize the probability distribution of the front-runner's
relative position. That is, we analyze the location of the most advanced
invader as the extreme deviation about the front's mean position. We find that
a class of models with different assumptions about neighborhood interactions
exhibit universal characteristics. That is, key features of the invasion
dynamics span a class of models, independently of locally detailed demographic
rules. Our results integrate theories of invasive spatial growth and generate
novel hypotheses linking habitat or landscape size (length of the invading
front) to invasion velocity, and to the relative position of the most advanced
invader.Comment: The original publication is available at
www.springerlink.com/content/8528v8563r7u2742
Scale Vs. Conformal Invariance in the AdS/CFT Correspondence
We present two examples of non-trivial field theories which are scale
invariant, but not conformally invariant. This is done by placing certain field
theories, which are conformally invariant in flat space, onto curved
backgrounds of a specific type. We define this using the AdS/CFT
correspondence, which relates the physics of gravity in asymptotically Anti-de
Sitter (AdS) spacetimes to that of a conformal field theory (CFT) in one
dimension fewer. The AdS rotating (Kerr) black holes in five and seven
dimensions provide us with the examples, since by the correspondence we are
able to define and compute the action and stress tensor of four and six
dimensional field theories residing on rotating Einstein universes, using the
``boundary counterterm'' method. The rotation breaks conformal but not scale
invariance. The AdS/CFT framework is therefore a natural arena for generating
such examples of non-trivial scale invariant theories which are not conformally
invariant.Comment: 4 pages, RevTeX (v3: references added
O-folds. Orientifolds and orbifolds in exceptional field theory
We describe conventional orientifold and orbifold quotients of string and M-theory in a unified approach based on exceptional field theory (ExFT). Using an extended spacetime, ExFT combines all the maximal ten and eleven dimensional supergravities into a single theory manifesting a global symmetry corresponding to the exceptional series of Lie groups. Here we will see how this extends to half-maximal theories by showing how a single \emph{generalised orbifold} (or O-fold), of ExFT gives rise to M-theory on an interval, type II with orientifold planes and the heterotic theories in an elegant fashion. We study in more detail such orbifold and orientifold actions preserving half-maximal supersymmetry, and show how the half-maximal structure of \EFT{} permits the inclusion of localised non-Abelian vector multiplets located at the orbifold fixed points. This allows us to reproduce for the example the expected modifications to the gauge transformations, Bianchi identities and actions of the theories obtained from the single ExFT starting point. We comment on the prospects of studying anomaly cancellation and more complicated, non-perturbative O-folds in the ExFT framework
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