207 research outputs found
Gauge Independence of IR singularities in Non-Commutative QFT - and Interpolating Gauges
IR divergences of a non-commutative U(1) Maxwell theory are discussed at the
one-loop level using an interpolating gauge to show that quadratic IR
divergences are independent not only from a covariant gauge fixing but also
independent from an axial gauge fixing.Comment: 11 pages, 2 figures, v1 minor correction
Superstrings from Hamiltonian Reduction
In any string theory there is a hidden, twisted superconformal symmetry
algebra, part of which is made up by the BRST current and the anti-ghost. We
investigate how this algebra can be systematically constructed for strings with
supersymmetries, via quantum Hamiltonian reduction of the Lie
superalgebras . The motivation is to understand how one could
systematically construct generalized string theories from superalgebras. We
also briefly discuss the BRST algebra of the topological string, which is a
doubly twisted superconformal algebra.Comment: 32p, LaTeX, CERN-TH.7379/9
A Generalization of Slavnov-Extended Non-Commutative Gauge Theories
We consider a non-commutative U(1) gauge theory in 4 dimensions with a
modified Slavnov term which looks similar to the 3-dimensional BF model. In
choosing a space-like axial gauge fixing we find a new vector supersymmetry
which is used to show that the model is free of UV/IR mixing problems, just as
in the previously discussed model in arXiv:hep-th/0604154. Finally, we present
generalizations of our proposed model to higher dimensions.Comment: 25 pages, no figures; v2 minor correction
Strings from Gauged Wess-Zumino-Witten Models
We present an algebraic approach to string theory. An embedding of
in a super Lie algebra together with a grading on the Lie algebra determines a
nilpotent subalgebra of the super Lie algebra. Chirally gauging this subalgebra
in the corresponding Wess-Zumino-Witten model, breaks the affine symmetry of
the Wess-Zumino-Witten model to some extension of the superconformal
algebra. The extension is completely determined by the embedding. The
realization of the superconformal algebra is determined by the grading. For a
particular choice of grading, one obtains in this way, after twisting, the BRST
structure of a string theory. We classify all embeddings of into Lie
super algebras and give a detailed account of the branching of the adjoint
representation. This provides an exhaustive classification and characterization
of both all extended superconformal algebras and all string theories
which can be obtained in this way.Comment: 50 pages, LaTe
A Vector Supersymmetry in Noncommutative U(1) Gauge Theory with the Slavnov Term
We consider noncommutative U(1) gauge theory with the additional term,
involving a scalar field lambda, introduced by Slavnov in order to cure the
infrared problem. we show that this theory, with an appropriate space-like
axial gauge-fixing, wxhibits a linear vector supersymmetry similar to the one
present in the 2-dimensional BF model. This vector supersymmetry implies that
all loop corrections are independent of the -vertex and thereby
explains why Slavnov found a finite model for the same gauge-fixing.Comment: 18 pages, 3 figures; v2 Acknowledgments adde
On the Lagrangian Realization of Non-Critical -Strings
A large class of non-critical string theories with extended worldsheet gauge
symmetry are described by two coupled, gauged Wess-Zumino-Witten Models. We
give a detailed analysis of the gauge invariant action and in particular the
gauge fixing procedure and the resulting BRST symmetries. The results are
applied to the example of strings.Comment: 19 pages, LaTeX (REVTEX macro's
On the symmetries of BF models and their relation with gravity
The perturbative finiteness of various topological models (e.g. BF models)
has its origin in an extra symmetry of the gauge-fixed action, the so-called
vector supersymmetry. Since an invariance of this type also exists for gravity
and since gravity is closely related to certain BF models, vector supersymmetry
should also be useful for tackling various aspects of quantum gravity. With
this motivation and goal in mind, we first extend vector supersymmetry of BF
models to generic manifolds by incorporating it into the BRST symmetry within
the Batalin-Vilkovisky framework. Thereafter, we address the relationship
between gravity and BF models, in particular for three-dimensional space-time.Comment: 29 page
Addressing Grand Challenges in Earth Observation Science: The Earth Observation Data Centre for Water Resources Monitoring
Earth observation is entering a new era where the increasing availability of free and open global satellite data sets combined with the computing power offered by modern information technologies opens up the possibility to process high-resolution data sets at global scale and short repeat intervals in a fully automatic fashion. This will not only boost the availability of higher level earth observation data in purely quantitative terms, but can also be expected to trigger a step change in the quality and usability of earth observation data. However, the technical, scientific, and organisational challenges that need to be overcome to arrive at this point are significant. First of all, Petabyte-scale data centres are needed for storing and processing complete satellite data records. Second, innovative processing chains that allow fully automatic processing of the satellite data from the raw sensor records to higher-level geophysical products need to be developed. Last but not least, new models of cooperation between public and private actors need to be found in order to live up to the first two challenges. This paper offers a discussion of how the Earth Observation Data Centre for Water Resources Monitoring (EODC) â a catalyser for an open and international cooperation of public and private organisations â will address these three grand challenges with the aim to foster the use of earth observation for monitoring of global water resources
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
Structural Anisotropy in Polar Fluids Subjected to Periodic Boundary Conditions
A heuristic model based on dielectric continuum theory for the long-range solvation free energy of a dipolar system possessing periodic boundary conditions (PBCs) is presented. The predictions of the model are compared to simulation results for Stockmayer fluids simulated using three different cell geometries. The boundary effects induced by the PBCs are shown to lead to anisotropies in the apparent dielectric constant and the long-range solvation free energy of as much as 50%. However, the sum of all of the anisotropic energy contributions yields a value that is very close to the isotropic one derived from dielectric continuum theory, leading to a total system energy close to the dielectric value. It is finally shown that the leading-order contribution to the energetic and structural anisotropy is significantly smaller in the noncubic simulation cell geometries compared to when using a cubic simulation cell
- âŠ