10,368 research outputs found
Half-maximal supergravity in three dimensions: supergeometry, differential forms and algebraic structure
The half-maximal supergravity theories in three dimensions, which have local
SO(8)\xz SO(n) and rigid SO(8,n) symmetries, are discussed in a superspace
setting starting from the superconformal theory. The on-shell theory is
obtained by imposing further constraints; it is essentially a non-linear sigma
model that induces a Poincar\'e supergeometry. The deformations of the geometry
due to gauging are briefly discussed. The possible -form field strengths are
studied using supersymmetry and SO(8,n) symmetry. The set of such forms obeying
consistent Bianchi identities constitutes a Lie super co-algebra while the
demand that these identities admit solutions places a further constraint on the
possible representations of SO(8,n) that the forms transform under which can be
easily understood using superspace cohomology. The dual Lie superalgebra can
then be identified as the positive sector of a Borcherds superalgebra that
extends the Lie algebra of the duality group. In addition to the known
forms, which we construct explicitly, there are five-forms that can
be non-zero in supergravity, while all forms with vanish. It is shown
that some six-forms can have non-trivial contributions at order \a'.Comment: 30 pages. References added. Some clarification of the tex
The supermembrane revisited
The M2-brane is studied from the perspective of superembeddings. We review
the derivation of the M2-brane dynamics and the supergravity constraints from
the standard superembedding constraint and we discuss explicitly the induced
d=3, N=8 superconformal geometry on the worldvolume. We show that the gauged
supermembrane, for a target space with a U(1) isometry, is the standard
D2-brane in a type IIA supergravity background. In particular, the D2-brane
action, complete with the Dirac-Born-Infeld term, arises from the gauged
Wess-Zumino worldvolume 4-form via the brane action principle. The discussion
is extended to the massive D2-brane considered as a gauged supermembrane in a
massive D=11 superspace background. Type IIA supergeometry is derived using
Kaluza-Klein techniques in superspace.Comment: Latex, 46 pages, clarifying remarks and references adde
L-branes
The superembedding approach to -branes is used to study a class of
-branes which have linear multiplets on the worldvolume. We refer to these
branes as L-branes. Although linear multiplets are related to scalar multiplets
(with 4 or 8 supersymmetries) by dualising one of the scalars of the latter to
a -form field strength, in many geometrical situations it is the linear
multiplet version which arises naturally. Furthermore, in the case of 8
supersymmetries, the linear multiplet is off-shell in contrast to the scalar
multiplet. The dynamics of the L-branes are obtained by using a systematic
procedure for constructing the Green-Schwarz action from the superembedding
formalism. This action has a Dirac-Born-Infeld type structure for the -form.
In addition, a set of equations of motion is postulated directly in superspace,
and is shown to agree with the Green-Schwarz equations of motion.Comment: revised version, minor changes, references added, 22 pages, no
figures, LaTe
Codimension zero superembeddings
Superembeddings which have bosonic codimension zero are studied in 3,4 and 6
dimensions. The worldvolume multiplets of these branes are off-shell vector
multiplets in these dimensions, and their self-interactions include a
Born-Infeld term. It is shown how they can be written in terms of standard
vector multiplets in flat superspace by working in the static gauge. The action
formula is used to determine both Green-Schwarz type actions and superfield
actions.Comment: Improved spelling, one reference adde
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Integer polyhedra for program analysis
Polyhedra are widely used in model checking and abstract interpretation. Polyhedral analysis is effective when the relationships between variables are linear, but suffers from imprecision when it is necessary to take into account the integrality of the represented space. Imprecision also arises when non-linear constraints occur. Moreover, in terms of tractability, even a space defined by linear constraints can become unmanageable owing to the excessive number of inequalities. Thus it is useful to identify those inequalities whose omission has least impact on the represented space. This paper shows how these issues can be addressed in a novel way by growing the integer hull of the space and approximating the number of integral points within a bounded polyhedron
Believing Does Not Equal Remembering: The Effects of Social Feedback and Objective False Evidence on Belief in Occurrence, Belief in Accuracy, and Recollection
We examined the impact of social feedback and objective false evidence on belief in occurrence, belief in accuracy, and recollection of an autobiographical experience. Participants viewed six virtual scenes (e.g., park) and were tested on their belief/recollection. After 1-week, participants were randomly assigned to four groups. One group received social feedback that one scene was not experienced. A second group received objective false evidence that one of the scenes was not shown. A third group received both social feedback and objective false evidence and the control group did not receive any manipulation. Belief in occurrence dropped considerably in the social feedback group and in the combined group. Also, nonbelieved memories were most likely to occur in participants receiving both social feedback and objective false evidence. We show that social feedback and objective false evidence undermine belief in occurrence, but that they leave belief in accuracy and recollection unaffected
Temporal fluctuations in the differential rotation of cool active stars
This paper reports positive detections of surface differential rotation on
two rapidly rotating cool stars at several epochs, by using stellar surface
features (both cool spots and magnetic regions) as tracers of the large scale
latitudinal shear that distorts the convective envelope in this type of stars.
We also report definite evidence that this differential rotation is different
when estimated from cool spots or magnetic regions, and that it undergoes
temporal fluctuations of potentially large amplitude on a time scale of a few
years. We consider these results as further evidence that the dynamo processes
operating in these stars are distributed throughout the convective zone rather
than being confined at its base as in the Sun. By comparing our observations
with two very simple models of the differential rotation within the convective
zone, we obtain evidence that the internal rotation velocity field of the stars
we investigated is not like that of the Sun, and may resemble that we expect
for rapid rotators. We speculate that the changes in differential rotation
result from the dynamo processes (and from the underlying magnetic cycle) that
periodically converts magnetic energy into kinetic energy and vice versa. We
emphasise that the technique outlined in this paper corresponds to the first
practical method for investigating the large scale rotation velocity field
within convective zones of cool active stars, and offers several advantages
over asteroseismology for this particular purpose and this specific stellar
class.Comment: 14 pages, 4 figure
Volume-reflecting dielectric heat shield
White, volume-reflecting dielectric material absorbs essentially none of the incident radiant energy, and continues to reflect even though in severe environment its surface is melted and is being vaporized. Process of overall reflectance in dielectric material, involving internal refractions and reflections, is similar to process of reflection in paints
BPS Solitons in M5-Brane Worldvolume Theory with Constant Three-Form Field
We study BPS solutions for a self-dual string and a neutral string in
M5-brane worldvolume theory with constant three-form field. We further
generalize such solitons to superpose with a calibrated surface. We also study
a traveling wave on a calibrated surface in the constant three-form field
background.Comment: 12 pages, LaTeX, minor correction, added referenc
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