997 research outputs found
On the Topology and Flux of T-Dual Manifolds
We present a general formula for the topology and H-flux of the T-dual of a
type two compactification. Our results apply to T-dualities with respect to any
free circle action. In particular we find that the manifolds on each side of
the duality are circle bundles whose curvatures are given by the integral of
the dual H-flux over the dual circle. As a corollary we conjecture an
obstruction to multiple T-dualities, generalizing an obstruction known to exist
on the twisted torus. Examples include SU(2) WZW models, Lens spaces and the
supersymmetric string theory on the non-spin AdS^5xCP^2xS^1 compactification.Comment: 4 Pages, No Figure
Global Aspects of T-Duality, Gauged Sigma Models and T-Folds
The gauged sigma-model argument that string backgrounds related by T-dual
give equivalent quantum theories is revisited, taking careful account of global
considerations. The topological obstructions to gauging sigma-models give rise
to obstructions to T-duality, but these are milder than those for gauging: it
is possible to T-dualise a large class of sigma-models that cannot be gauged.
For backgrounds that are torus fibrations, it is expected that T-duality can be
applied fibrewise in the general case in which there are no globally-defined
Killing vector fields, so that there is no isometry symmetry that can be
gauged; the derivation of T-duality is extended to this case. The T-duality
transformations are presented in terms of globally-defined quantities. The
generalisation to non-geometric string backgrounds is discussed, the conditions
for the T-dual background to be geometric found and the topology of T-folds
analysed.Comment: Minor corrections and addition
Random matrix theory within superstatistics
We propose a generalization of the random matrix theory following the basic
prescription of the recently suggested concept of superstatistics. Spectral
characteristics of systems with mixed regular-chaotic dynamics are expressed as
weighted averages of the corresponding quantities in the standard theory
assuming that the mean level spacing itself is a stochastic variable. We
illustrate the method by calculating the level density, the
nearest-neighbor-spacing distributions and the two-level correlation functions
for system in transition from order to chaos. The calculated spacing
distribution fits the resonance statistics of random binary networks obtained
in a recent numerical experiment.Comment: 20 pages, 6 figure
A Rigorous Path Integral for Supersymmetric Quantum Mechanics and the Heat Kernel
In a rigorous construction of the path integral for supersymmetric quantum
mechanics on a Riemann manifold, based on B\"ar and Pf\"affle's use of
piecewise geodesic paths, the kernel of the time evolution operator is the heat
kernel for the Laplacian on forms. The path integral is approximated by the
integral of a form on the space of piecewise geodesic paths which is the
pullback by a natural section of Mathai and Quillen's Thom form of a bundle
over this space.
In the case of closed paths, the bundle is the tangent space to the space of
geodesic paths, and the integral of this form passes in the limit to the
supertrace of the heat kernel.Comment: 14 pages, LaTeX, no fig
Homology and K--Theory Methods for Classes of Branes Wrapping Nontrivial Cycles
We apply some methods of homology and K-theory to special classes of branes
wrapping homologically nontrivial cycles. We treat the classification of
four-geometries in terms of compact stabilizers (by analogy with Thurston's
classification of three-geometries) and derive the K-amenability of Lie groups
associated with locally symmetric spaces listed in this case. More complicated
examples of T-duality and topology change from fluxes are also considered. We
analyse D-branes and fluxes in type II string theory on with torsion flux and demonstrate in details
the conjectured T-duality to with no flux. In the
simple case of , T-dualizing the circles reduces to
duality between with
flux and with no flux.Comment: 27 pages, tex file, no figure
Duality symmetry and the form fields of M-theory
In previous work we derived the topological terms in the M-theory action in
terms of certain characters that we defined. In this paper, we propose the
extention of these characters to include the dual fields. The unified treatment
of the M-theory four-form field strength and its dual leads to several
observations. In particular we elaborate on the possibility of a twisted
cohomology theory with a twist given by degrees greater than three.Comment: 12 pages, modified material on the differentia
Type I D-branes in an H-flux and twisted KO-theory
Witten has argued that charges of Type I D-branes in the presence of an
H-flux, take values in twisted KO-theory. We begin with the study of real
bundle gerbes and their holonomy. We then introduce the notion of real bundle
gerbe KO-theory which we establish is a geometric realization of twisted
KO-theory. We examine the relation with twisted K-theory, the Chern character
and provide some examples. We conclude with some open problems.Comment: 23 pages, Latex2e, 2 new references adde
Twisted topological structures related to M-branes
Studying the M-branes leads us naturally to new structures that we call
Membrane-, Membrane^c-, String^K(Z,3)- and Fivebrane^K(Z,4)-structures, which
we show can also have twisted counterparts. We study some of their basic
properties, highlight analogies with structures associated with lower levels of
the Whitehead tower of the orthogonal group, and demonstrate the relations to
M-branes.Comment: 17 pages, title changed on referee's request, minor changes to
improve presentation, typos correcte
M-theory and Characteristic Classes
In this note we show that the Chern-Simons and the one-loop terms in the
M-theory action can be written in terms of new characters involving the
M-theory four-form and the string classes. This sheds a new light on the
topological structure behind M-theory and suggests the construction of a theory
of `higher' characteristic classes.Comment: 8 pages. Error in gravitational term fixed; minor corrections;
reference and acknowledgement adde
Educating healthcare workers to optimal hand hygiene practices: addressing the need
The education of healthcare workers is essential to improve practices and is an integral part of hand hygiene promotional strategies. According to the evidence reviewed here, healthcare worker education has a positive impact on improving hand hygiene and reducing healthcare-associated infection. Detailed practical guidance on steps for the organization of education programmes in healthcare facilities and teaching-learning strategies are provided using the World Health Organization (WHO) Guidelines for Hand Hygiene in Health Care as the basis for recommendations. Several key elements for a successful educational programme are also identified. A particular emphasis is placed on concepts included in the tools developed by WHO for education, monitoring and performance feedbac
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