45 research outputs found
Ghost Systems: A Vertex Algebra Point of View
Fermionic and bosonic ghost systems are defined each in terms of a single
vertex algebra which admits a one-parameter family of conformal structures. The
observation that these structures are related to each other provides a simple
way to obtain character formulae for a general twisted module of a ghost
system. The U(1) symmetry and its subgroups that underly the twisted modules
also define an infinite set of invariant vertex subalgebras. Their structure is
studied in detail from a W-algebra point of view with particular emphasis on
Z_N-invariant subalgebras of the fermionic ghost system.Comment: 20 pages, plain Te
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
Lectures on conformal field theory and Kac-Moody algebras
This is an introduction to the basic ideas and to a few further selected
topics in conformal quantum field theory and in the theory of Kac-Moody
algebras.Comment: 59 pages, LaTeX2e, extended version of lectures given at the Graduate
Course on Conformal Field Theory and Integrable Models (Budapest, August
1996), to appear in Springer Lecture Notes in Physic
An Introduction to Conformal Field Theory
A comprehensive introduction to two-dimensional conformal field theory is
given.Comment: 69 pages, LaTeX; references adde
No rapid audiovisual recalibration in adults on the autism spectrum
Autism spectrum disorders (ASD) are characterized by difficulties in social cognition, but are also associated with atypicalities in sensory and perceptual processing. Several groups have reported that autistic individuals show reduced integration of socially relevant audiovisual signals, which may contribute to the higher-order social and cognitive difficulties observed in autism. Here we use a newly devised technique to study instantaneous adaptation to audiovisual asynchrony in autism. Autistic and typical participants were presented with sequences of brief visual and auditory stimuli, varying in asynchrony over a wide range, from 512âms auditory-lead to 512âms auditory-lag, and judged whether they seemed to be synchronous. Typical adults showed strong adaptation effects, with trials proceeded by an auditory-lead needing more auditory-lead to seem simultaneous, and vice versa. However, autistic observers showed little or no adaptation, although their simultaneity curves were as narrow as the typical adults. This result supports recent Bayesian models that predict reduced adaptation effects in autism. As rapid audiovisual recalibration may be fundamental for the optimisation of speech comprehension, recalibration problems could render language processing more difficult in autistic individuals, hindering social communication
Lectures on Branes in Curved Backgrounds
These lectures provide an introduction to the microscopic description of
branes in curved backgrounds. After a brief reminder of the flat space theory,
the basic principles and techniques of (rational) boundary conformal field
theory are presented in the second lecture. The general formalism is then
illustrated through a detailed discussion of branes on compact group manifolds.
In the final lecture, many more recent developments are reviewed, including
some results for non-compact target spaces.Comment: 109 pages, 11 figures, Lectures presented at the third RTN school on
`The Quantum Structure of Spacetime and the Geometric Nature of Fundamental
Interactions', Utrecht, January 200
The Fine-Tuning of the Universe for Intelligent Life
The fine-tuning of the universe for intelligent life has received a great
deal of attention in recent years, both in the philosophical and scientific
literature. The claim is that in the space of possible physical laws,
parameters and initial conditions, the set that permits the evolution of
intelligent life is very small. I present here a review of the scientific
literature, outlining cases of fine-tuning in the classic works of Carter, Carr
and Rees, and Barrow and Tipler, as well as more recent work. To sharpen the
discussion, the role of the antagonist will be played by Victor Stenger's
recent book The Fallacy of Fine-Tuning: Why the Universe is Not Designed for
Us. Stenger claims that all known fine-tuning cases can be explained without
the need for a multiverse. Many of Stenger's claims will be found to be highly
problematic. We will touch on such issues as the logical necessity of the laws
of nature; objectivity, invariance and symmetry; theoretical physics and
possible universes; entropy in cosmology; cosmic inflation and initial
conditions; galaxy formation; the cosmological constant; stars and their
formation; the properties of elementary particles and their effect on chemistry
and the macroscopic world; the origin of mass; grand unified theories; and the
dimensionality of space and time. I also provide an assessment of the
multiverse, noting the significant challenges that it must face. I do not
attempt to defend any conclusion based on the fine-tuning of the universe for
intelligent life. This paper can be viewed as a critique of Stenger's book, or
read independently.Comment: 77 pages, 9 figures. A condensed version of this paper has been
accepted to appear in Publications of the Astronomical Society of Australia.
Some small changes to match published versio