150 research outputs found
New extended superconformal sigma models and Quaternion Kahler manifolds
Quaternion Kahler manifolds are known to be the target spaces for matter
hypermultiplets coupled to N=2 supergravity. It is also known that there is a
one-to-one correspondence between 4n-dimensional quaternion Kahler manifolds
and those 4(n+1)-dimensional hyperkahler spaces which are the target spaces for
rigid superconformal hypermultiplets (such spaces are called hyperkahler
cones). In this paper we present a projective-superspace construction to
generate a hyperkahler cone M^{4(n+1)}_H of dimension 4(n+1) from a
2n-dimensional real analytic Kahler-Hodge manifold M^{2n}_K. The latter emerges
as a maximal Kahler submanifold of the 4n-dimensional quaternion Kahler space
M^{4n}_Q such that its Swann bundle coincides with M^{4(n+1)}_H. Our approach
should be useful for the explicit construction of new quaternion Kahler
metrics. The results obtained are also of interest, e.g., in the context of
supergravity reduction N=2 --> N=1, or alternatively from the point of view of
embedding N=1 matter-coupled supergravity into an N=2 theory.Comment: 30 page
Domain walls between gauge theories
Noncommutative U(N) gauge theories at different N may be often thought of as
different sectors of a single theory: the U(1) theory possesses a sequence of
vacua labeled by an integer parameter N, and the theory in the vicinity of the
N-th vacuum coincides with the U(N) noncommutative gauge theory. We construct
noncommutative domain walls on fuzzy cylinder, separating vacua with different
gauge theories. These domain walls are solutions of BPS equations in gauge
theory with an extra term stabilizing the radius of the cylinder. We study
properties of the domain walls using adjoint scalar and fundamental fermion
fields as probes. We show that the regions on different sides of the wall are
not disjoint even in the low energy regime -- there are modes penetrating from
one region to the other. We find that the wall supports a chiral fermion zero
mode. Also, we study non-BPS solution representing a wall and an antiwall, and
show that this solution is unstable. We suggest that the domain walls emerge as
solutions of matrix model in large class of pp-wave backgrounds with
inhomogeneous field strength. In the M-theory language, the domain walls have
an interpretation of a stack of branes of fingerstall shape inserted into a
stack of cylindrical branes.Comment: Final version; minor corrections; to appear in Nucl.Phys.
The R-map and the Coupling of N=2 Tensor Multiplets in 5 and 4 Dimensions
We study the dimensional reduction of five dimensional N=2
Yang-Mills-Einstein supergravity theories (YMESGT) coupled to tensor
multiplets. The resulting 4D theories involve first order interactions among
tensor and vector fields with mass terms. If the 5D gauge group, K, does not
mix the 5D tensor and vector fields, the 4D tensor fields can be integrated out
in favor of 4D vector fields and the resulting theory is dual to a standard 4D
YMESGT. The gauge group has a block diagonal symplectic embedding and is a
semi-direct product of the 5D gauge group K with a Heisenberg group of
dimension (2P+1), where 2P is the number of tensor fields in five dimensions.
There exists an infinite family of theories, thus obtained, whose gauge groups
are pp-wave contractions of the simple noncompact groups of type SO*(2M). If,
on the other hand, the 5D gauge group does mix the 5D tensor and vector fields,
the resulting 4D theory is dual to a 4D YMESGT whose gauge group does, in
general,NOT have a block diagonal symplectic embedding and involves additional
topological terms. The scalar potentials of the dimensionally reduced theories
naturally have some of the ingredients that were found necessary for stable de
Sitter ground states. We comment on the relation between the known 5D and 4D,
N=2 supergravities with stable de Sitter ground states.Comment: 42 pages;latex fil
3D FEA modelling of laminated composites in bending and their failure mechanisms
keywords: 3D keywords: 3D keywords: 3D keywords: 3D keywords: 3DAbstract This paper developed three-dimensional (3D) Finite Element Analysis (FEA) to investigate the effect of fibre lay-up on the initiation of failure of laminated composites in bending. Tsai-Hill failure criterion was applied to identify the critical areas of failure in composite laminates. In accordance with the 3D FEA, unidirectional ([0]16), cross-ply ([0/90]4s) and angle-ply ([±45]4s) laminates made up of pre-preg Carbon Fibre Reinforced Plastics (CFRP) composites were manufactured and tested under three-point bending. The basic principles of Classical Laminate Theory (CLT) were extended to three-dimension, and the analytical solution was critically compared with the FEA results. The 3D FEA results revealed significant transverse normal stresses in the cross-ply laminate and in-plane shear stress in the angle-ply laminate near free edge regions which are overlooked by conventional laminate model. The microscopic images showed that these free edge effects were the main reason for stiffness reduction observed in the bending tests. The study illustrated the significant effects of fibre lay-up on the flexural failure mechanisms in composite laminates which lead to some suggestions to improve the design of composite laminates
Properties of hyperkahler manifolds and their twistor spaces
We describe the relation between supersymmetric sigma-models on hyperkahler
manifolds, projective superspace, and twistor space. We review the essential
aspects and present a coherent picture with a number of new results.Comment: 26 pages. v2: Sign mistakes corrected; Kahler potential explicitly
calculated in example; references added. v3: Published version--several small
clarifications per referee's reques
Area metric gravity and accelerating cosmology
Area metric manifolds emerge as effective classical backgrounds in quantum
string theory and quantum gauge theory, and present a true generalization of
metric geometry. Here, we consider area metric manifolds in their own right,
and develop in detail the foundations of area metric differential geometry.
Based on the construction of an area metric curvature scalar, which reduces in
the metric-induced case to the Ricci scalar, we re-interpret the
Einstein-Hilbert action as dynamics for an area metric spacetime. In contrast
to modifications of general relativity based on metric geometry, no continuous
deformation scale needs to be introduced; the extension to area geometry is
purely structural and thus rigid. We present an intriguing prediction of area
metric gravity: without dark energy or fine-tuning, the late universe exhibits
a small acceleration.Comment: 52 pages, 1 figure, companion paper to hep-th/061213
Measurement of the Cross Sections and Analyzing Powers for Transitions in 58-Ni Using 200 MeV Proton Scattering
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Relating the Cosmological Constant and Supersymmetry Breaking in Warped Compactifications of IIB String Theory
It has been suggested that the observed value of the cosmological constant is
related to the supersymmetry breaking scale M_{susy} through the formula Lambda
\sim M_p^4 (M_{susy}/M_p)^8. We point out that a similar relation naturally
arises in the codimension two solutions of warped space-time varying
compactifications of string theory in which non-isotropic stringy moduli induce
a small but positive cosmological constant.Comment: 7 pages, LaTeX, references added and minor changes made, (v3) map
between deSitter and global cosmic brane solutions clarified, supersymmetry
breaking discussion improved and references adde
General Axisymmetric Solutions and Self-Tuning in 6D Chiral Gauged Supergravity
We re-examine the properties of the axially-symmetric solutions to chiral
gauged 6D supergravity, recently found in refs. hep-th/0307238 and
hep-th/0308064. Ref. hep-th/0307238 finds the most general solutions having two
singularities which are maximally-symmetric in the large 4 dimensions and which
are axially-symmetric in the internal dimensions. We show that not all of these
solutions have purely conical singularities at the brane positions, and that
not all singularities can be interpreted as being the bulk geometry sourced by
neutral 3-branes. The subset of solutions for which the metric singularities
are conical precisely agree with the solutions of ref. hep-th/0308064.
Establishing this connection between the solutions of these two references
resolves a minor conflict concerning whether or not the tensions of the
resulting branes must be negative. The tensions can be both negative and
positive depending on the choice of parameters. We discuss the physical
interpretation of the non-conical solutions, including their significance for
the proposal for using 6-dimensional self-tuning to understand the small size
of the observed vacuum energy. In passing we briefly comment on a recent paper
by Garriga and Porrati which criticizes the realization of self-tuning in 6D
supergravity.Comment: 27 pages, 1 figure; JHEP3 style; Some references added, and
discussion of tension constraints and unwarped solutions made more explici
De Sitter Holography and the Cosmic Microwave Background
We interpret cosmological evolution holographically as a renormalisation
group flow in a dual Euclidean field theory, as suggested by the conjectured
dS/CFT correspondence. Inflation is described by perturbing around the
infra-red fixed point of the dual field theory. The spectrum of the cosmic
microwave background radiation is determined in terms of scaling violations in
the field theory. The dark energy allows similar, albeit less predictive,
considerations. We discuss the cosmological fine-tuning problems from the
holographic perspective.Comment: 17 pages, 2 figures, uses JHEP style files; corrected and added
reference
- …