342 research outputs found
Methodologies for the design of LCC voltage-output resonant converters
Abstract: The paper presents five structured design methodologies for third-order LCC voltage output resonant converters. The underlying principle of each technique is based on an adaptation of a FMA equivalent circuit that accommodates the nonlinear behaviour of the converter. In contrast to previously published methods, the proposed methodologies explicitly incorporate the effects of the transformer magnetising inductance. Furthermore, a number of the methodologies allow the resonant-tank components to be specified at the design phase, thereby facilitating the use
of standard off-the-shelf components. A procedure for sizing the filter capacitor is derived, and the use of error mapping, to identify parameter boundaries and provide the designer with a qualitative
feel for the accuracy of a proposed converter design, is explored
Holonomy groups and W-symmetries
Irreducible sigma models, i.e. those for which the partition function does
not factorise, are defined on Riemannian spaces with irreducible holonomy
groups. These special geometries are characterised by the existence of
covariantly constant forms which in turn give rise to symmetries of the
supersymmetric sigma model actions. The Poisson bracket algebra of the
corresponding currents is a W-algebra. Extended supersymmetries arise as
special cases.Comment: pages 2
Non-Abelian Gravity and Antisymmetric Tensor Gauge Theory
A non-abelian generalisation of a theory of gravity coupled to a 2-form gauge
field and a dilaton is found, in which the metric and 3-form field strength are
Lie algebra-valued. In the abelian limit, the curvature with torsion is
self-dual in four dimensions, or has SU(n) holonomy in dimensions. The
coupling to self-dual Yang-Mills fields in 4 dimensions, or their higher
dimensional generalisation, is discussed. The abelian theory is the effective
action for (2,1) strings, and the non-abelian generalisation is relevant to the
study of coincident branes in the (2,1) string approach to M-theory. The theory
is local when expressed in terms of a vector pre-potential.Comment: 14 pages, phyzzx macro. Minor correction
Potentials for (p,0) and (1,1) supersymmetric sigma models with torsion
Using (1,0) superfield methods, we determine the general scalar potential
consistent with off-shell (p,0) supersymmetry and (1,1) supersymmetry in
two-dimensional non-linear sigma models with torsion. We also present an
extended superfield formulation of the (p,0) models and show how the (1,1)
models can be obtained from the (1,1)-superspace formulation of the gauged, but
massless, (1,1) sigma model.Comment: 11 page
Actions For (2,1) Sigma-Models and Strings
Effective actions are derived for (2,0) and (2,1) superstrings by studying
the corresponding sigma-models. The geometry is a generalisation of Kahler
geometry involving torsion and the field equations imply that the curvature
with torsion is self-dual in four dimensions, or has SU(n,m) holonomy in other
dimensions. The Yang-Mills fields are self-dual in four dimensions and satisfy
a form of the Uhlenbeck-Yau equation in higher dimensions. In four dimensions
with Euclidean signature, there is a hyperkahler structure and the sigma-model
has (4,1) supersymmetry, while for signature (2,2) there is a hypersymplectic
structure consisting of a complex structure squaring to -1 and two real
structures squaring to 1. The theory is invariant under a twisted form of the
(4,1) superconformal algebra which includes an SL(2,R) Kac-Moody algebra
instead of an SU(2) Kac-Moody algebra. Kahler and related geometries are
generalised to ones involving real structures.Comment: 32 pages, phyzzx macr
On the symmetries of special holonomy sigma models
In addition to superconformal symmetry, (1,1) supersymmetric two-dimensional
sigma models on special holonomy manifolds have extra symmetries that are in
one-to-one correspondence with the covariantly constant forms on these
manifolds. The superconformal algebras extended by these symmetries close as
W-algebras, i.e. they have field-dependent structure functions. It is shown
that it is not possible to write down cohomological equations for potential
quantum anomalies when the structure functions are field-dependent. In order to
do this it is necessary to linearise the algebras by treating composite
currents as generators of additional symmetries. It is shown that all cases can
be linearised in a finite number of steps, except for G_2 and SU(3). Additional
problems in the quantisation procedure are briefly discussed.Comment: 16 pages. Abstract improved and a few typographical errors correcte
Massive IIA supergravities
We perform a systematic search for all possible massive deformations of IIA
supergravity in ten dimensions. We show that there exist exactly two
possibilities: Romans supergravity and Howe-Lambert-West supergravity. Along
the way we give the full details of the ten-dimensional superspace formulation
of the latter. The scalar superfield at canonical mass dimension zero (whose
lowest component is the dilaton), present in both Romans and massless IIA
supergravities, is not introduced from the outset but its existence follows
from a certain integrability condition implied by the Bianchi identities. This
fact leads to the possibility for a certain topological modification of
massless IIA, reflecting an analogous situation in eleven dimensions.Comment: 35 pages; v2: typos corrected, added eq. (A4
Decoupling Limits in M-Theory
Limits of a system of N Dn-branes in which the bulk and string degrees of
freedom decouple to leave a `matter' theory are investigated and, for n>4,
either give a free theory or require taking . The decoupled
matter theory is described at low energies by the limit of n+1
dimensional \sym, and at high energies by a free type II string theory in a
curved space-time. Metastable bound states of D6-branes with mass and
D0-branes with mass are shown to have an energy proportional to
and decouple, whereas in matrix theory they only decouple in
the large N limit.Comment: 23 Pages, Tex, Phyzzx Macro. Minor correction
Intrinsic Geometry of D-Branes
We obtain forms of Born-Infeld and D-brane actions that are quadratic in
derivatives of and linear in by introducing an auxiliary
`metric' which has both symmetric and anti-symmetric parts, generalising the
simplification of the Nambu-Goto action for -branes using a symmetric
metric. The abelian gauge field appears as a Lagrange multiplier, and solving
the constraint gives the dual form of the dimensional action with an
form gauge field instead of a vector gauge field. We construct the dual action
explicitly, including cases which could not be covered previously. The
generalisation to supersymmetric D-brane actions with local fermionic symmetry
is also discussed.Comment: 10 pages, LaTeX, no figures. Minor correction; version to appear in
Physics Letters
Geometric Actions for D-Branes and M-Branes
New forms of Born-Infeld, D-brane and M theory five-brane actions are found
which are quadratic in the abelian field strength. The gauge fields couple both
to a background or induced metric and a new auxiliary metric, whose elimination
reproduces the non-polynomial Born-Infeld action. This is similar to the
introduction of an auxiliary metric to simplify the Nambu-Goto string action.
This simplifies the quantisation and dualisation of the gauge fields.Comment: LaTeX, 9 pages, no figures. Minor corrections; version to appear in
Physics Letters
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