168 research outputs found
On the Geometry of Supersymmetric Quantum Mechanical Systems
We consider some simple examples of supersymmetric quantum mechanical systems
and explore their possible geometric interpretation with the help of geometric
aspects of real Clifford algebras. This leads to natural extensions of the
considered systems to higher dimensions and more complicated potentials.Comment: 18 page
The Dirac operator on generalized Taub-NUT spaces
We find sufficient conditions for the absence of harmonic spinors on
spin manifolds constructed as cone bundles over a compact K\"ahler base. These
conditions are fulfilled for certain perturbations of the Euclidean metric, and
also for the generalized Taub-NUT metrics of Iwai-Katayama, thus proving a
conjecture of Vi\csinescu and the second author.Comment: Final version, 16 page
Heat kernel coefficients for chiral bag boundary conditions
We study the asymptotic expansion of the smeared L2-trace of fexp(-tP^2)
where P is an operator of Dirac type, f is an auxiliary smooth smearing
function which is used to localize the problem, and chiral bag boundary
conditions are imposed. Special case calculations, functorial methods and the
theory of zeta and eta invariants are used to obtain the boundary part of the
heat-kernel coefficients a1 and a2.Comment: Published in J. Phys. A38, 2259-2276 (2005). Record without file
already exists on the SLAC recor
Killing spinors in supergravity with 4-fluxes
We study the spinorial Killing equation of supergravity involving a torsion
3-form \T as well as a flux 4-form \F. In dimension seven, we construct
explicit families of compact solutions out of 3-Sasakian geometries, nearly
parallel \G_2-geometries and on the homogeneous Aloff-Wallach space. The
constraint \F \cdot \Psi = 0 defines a non empty subfamily of solutions. We
investigate the constraint \T \cdot \Psi = 0, too, and show that it singles
out a very special choice of numerical parameters in the Killing equation,
which can also be justified geometrically
Effective Wess-Zumino-Witten Action for Edge States of Quantum Hall Systems on Bergman Ball
Using a group theory approach, we investigate the basic features of the
Landau problem on the Bergman ball {\bf B}^k. This can be done by considering a
system of particles living on {\bf B}^k in the presence of an uniform magnetic
field B and realizing the ball as the coset space SU(k,1)/U(k). In quantizing
the theory on {\bf{B}}^k, we define the wavefunctions as the Wigner
\cal{D}-functions satisfying a set of suitable constraints. The corresponding
Hamiltonian is mapped in terms of the right translation generators. In the
lowest Landau level, we obtain the wavefunctions as the SU(k,1) coherent
states. This are used to define the star product, density matrix and excitation
potential in higher dimensions. With these ingredients, we construct a
generalized effective Wess-Zumino-Witten action for the edge states and discuss
their nature.Comment: 19 pages, clarifications and some equations removed, version
published in NP
Twisted k-graph algebras associated to Bratteli diagrams
Given a system of coverings of k-graphs, we show that the cohomology of the
resulting (k+1)-graph is isomorphic to that of any one of the k-graphs in the
system. We then consider Bratteli diagrams of 2-graphs whose twisted
C*-algebras are matrix algebras over noncommutative tori. For such systems we
calculate the ordered K-theory and the gauge-invariant semifinite traces of the
resulting 3-graph C*-algebras. We deduce that every simple C*-algebra of this
form is Morita equivalent to the C*-algebra of a rank-2 Bratteli diagram in the
sense of Pask-Raeburn-R{\o}rdam-Sims.Comment: 28 pages, pictures prepared using tik
Supersymmetric Nonlinear O(3) Sigma Model on the Lattice
A supersymmetric extension of the nonlinear O(3) sigma model in two spacetime
dimensions is investigated by means of Monte Carlo simulations. We argue that
it is impossible to construct a lattice action that implements both the O(3)
symmetry as well as at least one supersymmetry exactly at finite lattice
spacing. It is shown by explicit calculations that previously proposed
discretizations fail to reproduce the exact symmetries of the target manifold
in the continuum limit. We provide an alternative lattice action with exact
O(3) symmetry and compare two approaches based on different derivative
operators. Using the nonlocal SLAC derivative for the quenched model on
moderately sized lattices we extract the value {\sigma}(2, u_0) = 1.2604(13)
for the step scaling function at u_0 = 1.0595, to be compared with the exact
value 1.261210. For the supersymmetric model with SLAC derivative the discrete
chiral symmetry is maintained but we encounter strong sign fluctuations,
rendering large lattice simulations ineffective. By applying the Wilson
prescription, supersymmetry and chiral symmetry are broken explicitly at finite
lattice spacing, though there is clear evidence that both are restored in the
continuum limit by fine tuning of a single mass parameter.Comment: 35 pages, 36 figures, 2 tables; updated version as accepted by JHE
Providing Alternative Declarative Descriptions for Entity Sets Using Parallel Concept Lattices
We propose an approach for modifying a declarative description of a set of entities (e.g., a SPARQL query) for the purpose of finding alternative declarative descriptions for the entities. Such a shift in representation can help to get new insights into the data, to discover related attributes, or to find a more concise description of the entities of interest. Allowing the alternative descriptions furthermore to be close approximations of the original entity set leads to more flexibility in finding such insights. Our approach is based on the construction of parallel formal concept lattices over different sets of attributes for the same entities. Between the formal concepts in the parallel lattices, we define mappings which constitute approximations of the extent of the concepts. In this paper, we formalise the idea of two types of mappings between parallel concept lattices, provide an implementation of these mappings and evaluate their ability to find alternative descriptions in a scenario of several real-world RDF data sets. In this scenario we use descriptions for entities based on RDF classes and seek for alternative representations based on properties associated with the entities
A Dual FluorescenceâSpin Label Probe for Visualization and Quantification of Target Molecules in Tissue by Multiplexed FLIMâEPR Spectroscopy
Simultaneous visualization and concentration quantification of molecules in biological tissue is an important though challenging goal. The advantages of fluorescence lifetime imaging microscopy (FLIM) for visualization, and electron paramagnetic resonance (EPR) spectroscopy for quantification are complementary. Their combination in a multiplexed approach promises a successful but ambitious strategy because of spin label-mediated fluorescence quenching. Here, we solved this problem and present the molecular design of a dual label (DL) compound comprising a highly fluorescent dye together with an EPR spin probe, which also renders the fluorescence lifetime to be concentration sensitive. The DL can easily be coupled to the biomolecule of choice, enabling inâ
vivo and inâ
vitro applications. This novel approach paves the way for elegant studies ranging from fundamental biological investigations to preclinical drug research, as shown in proof-of-principle penetration experiments in human skin exâ
vivo
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