27,943 research outputs found
Nonsingular 4d-flat branes in six-dimensional supergravities
We show that six-dimensional supergravity models admit nonsingular solutions
in the presence of flat three-brane sources with positive tensions. The models
studied in this paper are nonlinear sigma models with the target spaces of the
scalar fields being noncompact manifolds. For the particular solutions of the
scalar field equations which we consider, only two brane sources are possible
which are positioned at those points where the scalar field densities diverge,
without creating a divergence in the Ricci scalar or the total energy. These
solutions are locally invariant under 1/2 of D=6 supersymmetries, which,
however, do not integrate to global Killing spinors. Other branes can be
introduced by hand by allowing for local deficit angles in the transverse space
without generating any kind of curvature singularities.Comment: 13 pages. The discussion of modular invariance is amended and a
reference has been adde
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The P3 platform: an approach and software system for developing diagrammatic model-based methods in design research
Many issues in design and design management have been explored by building models which capture the relationships between different aspects of the problem at hand. These models require computer support to construct and analyse. However, appropriate modelling tools can be time-consuming to develop in a research environment. Reflecting upon five design research projects, this paper proposes that such projects can be facilitated by recognising the iterative and tightly-coupled nature of research and tool development, and by attempting to minimise the effort of solution prototyping within this process. Our approach is enabled by a software platform which can be rapidly configured to implement many conceivable modelling approaches. This configurability is complemented by an emerging library of modelling and analysis approaches tailored to explore design process systems. The platform-based approach enables any mix of modelling concepts to be easily created. We propose it could thus help researchers to explore a wide range of questions without being constrained to existing conventions for modelling – or for model integration
Solitons in a six-dimensional super Yang-Mills-tensor system and noncritical strings
In this letter we study a coupled system of six-dimensional N=1 tensor and
super Yang-Mills multiplets. We identify some of the solitonic states of this
system which exhibit stringy behaviour in six dimensions. A discussion of the
supercharges and energy for the tensor multiplet as well as zero modes is also
given. We speculate about the possible relationship between our solution and
what is known as tensionless strings.Comment: Plain TeX, 10 page
Magnetic Field and Curvature Effects on Pair Production I: Scalars and Spinors
The pair production rates for spin-zero and spin- particles are
calculated on spaces of the form with
corresponding to (flat), (flat, compactified),
(positive curvature) and (negative curvature), with and without a
background magnetic field on . The motivation is to elucidate the effects of
curvature and background magnetic field. Contrasting effects for positive and
negative curvature on the two cases of spin are obtained. For positive
curvature, we find enhancement for spin-zero and suppression for
spin-, with the opposite effect for negative curvature.Comment: 28 pages, 10 figure
Magnetic Field and Curvature Effects on Pair Production II: Vectors and Implications for Chromodynamics
We calculate the pair production rates for spin- or vector particles on
spaces of the form with corresponding to
(flat), (positive curvature) and (negative
curvature), with and without a background (chromo)magnetic field on . Beyond
highlighting the effects of curvature and background magnetic field, this is
particularly interesting since vector particles are known to suffer from the
Nielsen-Olesen instability, which can dramatically increase pair production
rates. The form of this instability for and is obtained. We also
give a brief discussion of how our results relate to ideas about confinement in
nonabelian theories.Comment: 24 pages, 9 figure
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