667 research outputs found
On Representations of Conformal Field Theories and the Construction of Orbifolds
We consider representations of meromorphic bosonic chiral conformal field
theories, and demonstrate that such a representation is completely specified by
a state within the theory. The necessary and sufficient conditions upon this
state are derived, and, because of their form, we show that we may extend the
representation to a representation of a suitable larger conformal field theory.
In particular, we apply this procedure to the lattice (FKS) conformal field
theories, and deduce that Dong's proof of the uniqueness of the twisted
representation for the reflection-twisted projection of the Leech lattice
conformal field theory generalises to an arbitrary even (self-dual) lattice. As
a consequence, we see that the reflection-twisted lattice theories of Dolan et
al are truly self-dual, extending the analogies with the theories of lattices
and codes which were being pursued. Some comments are also made on the general
concept of the definition of an orbifold of a conformal field theory in
relation to this point of view.Comment: 11 pages, LaTeX. Updated references and added preprint n
The Emperor's Last Clothes?
We are in the middle of a remarkable paradigm shift in particle physics, a
shift of opinion that occurred so slowly that some even try to deny that they
changed their minds at all. It concerns a very basic question: can we expect to
derive the laws of particle physics from a fundamental theory? The Standard
Model of particle physics as well as the 1984 string theory revolution provided
ample food for thought about this. The reason this was ignored for so long can
be traced back to an old fallacy: a misguided idea about our own importance.Comment: 88 pages, Review intended for readers with an education in physics.
Preprint Nr. added, some statements corrected, some references added. A short
version (about 20 pages) was published in Rept. Prog. Phys. 71:072201,2008.
July 2010: Footnote added to correct a remark on nuclear bindin
Comments on the classification of orientifolds
The simple current construction of orientifolds based on rational conformal
field theories is reviewed. When applied to SO(16) level 1, one can describe
all ten-dimensional orientifolds in a unified framework.Comment: 9 pages, Contribution to proceedings of RTN-workshop in Leuven,
Belgium, September 200
Hydrogen peroxide in breath condensate during a common cold.
BACKGROUND: Hydrogen peroxide (H2O2) in exhaled air condensate is elevated in inflammatory disorders of the lower respiratory tract. It is unknown whether viral colds contribute to exhaled H2O2. AIM: To assess exhaled H2O2 during and after a common cold. METHODS: We examined H2O2 in the breath condensate of 20 normal subjects with acute symptoms of a common cold and after recovery 2 weeks later and, similarly, in 10 subjects without infection. H2O2 was measured with a fluorimetric assay. RESULTS: At the time of infection exhaled H2O2 (median, ranges) was 0.20 microM (0.03-1.2 microM), and this decreased to 0.09 microM (< 0.01-0.40 microM) after recovery (p = 0.006). There was no significant difference in lung function (forced vital capacity and forced expiratory volume in 1 sec) during and after colds. In the controls, exhaled H2O2 did not change over a 2-week period. CONCLUSIONS: H2O2 in exhaled air condensate is elevated during a common cold, and returns to normal within 2 weeks of recovery in healthy subjects. Hence, symptomatic upper respiratory tract infection may act as a confounder in studies of H2O2 as a marker of chronic lower airway inflammation
Theory for a Hanbury Brown Twiss experiment with a ballistically expanding cloud of cold atoms
We have studied one-body and two-body correlation functions in a
ballistically expanding, non-interacting atomic cloud in the presence of
gravity. We find that the correlation functions are equivalent to those at
thermal equilibrium in the trap with an appropriate rescaling of the
coordinates. We derive simple expressions for the correlation lengths and give
some physical interpretations. Finally a simple model to take into account
finite detector resolution is discussed
A new topological aspect of the arbitrary dimensional topological defects
We present a new generalized topological current in terms of the order
parameter field to describe the arbitrary dimensional topological
defects. By virtue of the -mapping method, we show that the topological
defects are generated from the zero points of the order parameter field , and the topological charges of these topological defects are topological
quantized in terms of the Hopf indices and Brouwer degrees of -mapping
under the condition that the Jacobian . When , it is shown that there exist the crucial case of branch process.
Based on the implicit function theorem and the Taylor expansion, we detail the
bifurcation of generalized topological current and find different directions of
the bifurcation. The arbitrary dimensional topological defects are found
splitting or merging at the degenerate point of field function but
the total charge of the topological defects is still unchanged.Comment: 24 pages, 10 figures, Revte
Time interval distributions of atoms in atomic beams
We report on the experimental investigation of two-particle correlations
between neutral atoms in a Hanbury Brown and Twiss experiment. Both an atom
laser beam and a pseudo-thermal atomic beam are extracted from a Bose-Einstein
condensate and the atom flux is measured with a single atom counter. We
determine the conditional and the unconditional detection probabilities for the
atoms in the beam and find good agreement with the theoretical predictions.Comment: 4 pages, 3 figure
Mindfulness-based cognitive therapy versus treatment as usual in adults with ADHD: A trial-based economic evaluation
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Higher Loop Spin Field Correlators in D=4 Superstring Theory
We develop calculational tools to determine higher loop superstring
correlators involving massless fermionic and spin fields in four space time
dimensions. These correlation functions are basic ingredients for the
calculation of loop amplitudes involving both bosons and fermions in D=4
heterotic and superstring theories. To obtain the full amplitudes in Lorentz
covariant form the loop correlators of fermionic and spin fields have to be
expressed in terms of SO(1,3) tensors. This is one of the main achievements in
this work.Comment: 59 pages, 1 figure; v2: final version published in JHE
Crossings, Motzkin paths and Moments
Kasraoui, Stanton and Zeng, and Kim, Stanton and Zeng introduced certain
-analogues of Laguerre and Charlier polynomials. The moments of these
orthogonal polynomials have combinatorial models in terms of crossings in
permutations and set partitions. The aim of this article is to prove simple
formulas for the moments of the -Laguerre and the -Charlier polynomials,
in the style of the Touchard-Riordan formula (which gives the moments of some
-Hermite polynomials, and also the distribution of crossings in matchings).
Our method mainly consists in the enumeration of weighted Motzkin paths, which
are naturally associated with the moments. Some steps are bijective, in
particular we describe a decomposition of paths which generalises a previous
construction of Penaud for the case of the Touchard-Riordan formula. There are
also some non-bijective steps using basic hypergeometric series, and continued
fractions or, alternatively, functional equations.Comment: 21 page
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