11,882 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
On the dynamics of capillaries and the existence of plasma flow in the pericapillary lymph space
Hydrodynamic analysis of dynamic blood plasma flow in capillaries and lymph annulu
Emergency braking for free piston energy converters
Free piston energy converters are a potential technology for future hybrid vehicles, as well as stationary power generation applications. A candidate 2-stroke system comprises of two opposing combustion chambers with a common piston rod, and integrated with a tubular permanent magnet electrical machine for the conversion of mechanical to electrical energy. A key issue for the ultimate adoption of such systems, however, is their robustness in the event of a fault to enable a safe shutdown, with minimal mechanical or electrical damage. The paper considers system braking issues and the importance of early fault detection. Results are presented to demonstrate the effectiveness of passive and active braking techniques for a range of dc-link supply voltage and operating output power
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
Performance of the Birmingham Solar-Oscillations Network (BiSON)
The Birmingham Solar-Oscillations Network (BiSON) has been operating with a
full complement of six stations since 1992. Over 20 years later, we look back
on the network history. The meta-data from the sites have been analysed to
assess performance in terms of site insolation, with a brief look at the
challenges that have been encountered over the years. We explain how the
international community can gain easy access to the ever-growing dataset
produced by the network, and finally look to the future of the network and the
potential impact of nearly 25 years of technology miniaturisation.Comment: 31 pages, 19 figures. Accepted by Solar Physics: 2015 October 20.
First online: 2015 December 7. Open Acces
AdS/SCFT in Superspace
A discussion of the AdS/CFT correspondence in IIB is given in a superspace
context. The main emphasis is on the properties of SCFT correlators on the
boundary which are studied using harmonic superspace techniques. These
techniques provide the easiest way of implementing the superconformal Ward
identities. The Ward identities, together with analyticity, can be used to give
a compelling argument in support of the non-renormalisation theorems for two-
and three-point functions, and to establish the triviality of extremal and
next-to-extremal correlation functions. The OPE in is also briefly discussed.Comment: 10 pages; talk given by PSH at 2nd Gursey Memorial Conference, June
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