530 research outputs found
Toda Fields on Riemann Surfaces: remarks on the Miura transformation
We point out that the Miura transformation is related to a holomorphic
foliation in a relative flag manifold over a Riemann Surface. Certain
differential operators corresponding to a free field description of
--algebras are thus interpreted as partial connections associated to the
foliation.Comment: AmsLatex 1.1, 10 page
A heterotic sigma model with novel target geometry
We construct a (1,2) heterotic sigma model whose target space geometry
consists of a transitive Lie algebroid with complex structure on a Kaehler
manifold. We show that, under certain geometrical and topological conditions,
there are two distinguished topological half--twists of the heterotic sigma
model leading to A and B type half--topological models. Each of these models is
characterized by the usual topological BRST operator, stemming from the
heterotic (0,2) supersymmetry, and a second BRST operator anticommuting with
the former, originating from the (1,0) supersymmetry. These BRST operators
combined in a certain way provide each half--topological model with two
inequivalent BRST structures and, correspondingly, two distinct perturbative
chiral algebras and chiral rings. The latter are studied in detail and
characterized geometrically in terms of Lie algebroid cohomology in the
quasiclassical limit.Comment: 83 pages, no figures, 2 references adde
Topological twisted sigma model with H-flux revisited
In this paper we revisit the topological twisted sigma model with H-flux. We
explicitly expand and then twist the worldsheet Lagrangian for bi-Hermitian
geometry. we show that the resulting action consists of a BRST exact term and
pullback terms, which only depend on one of the two generalized complex
structures and the B-field. We then discuss the topological feature of the
model.Comment: 16 pages. Appendix adde
Gauging the Poisson sigma model
We show how to carry out the gauging of the Poisson sigma model in an AKSZ
inspired formulation by coupling it to the a generalization of the Weil model
worked out in ref. arXiv:0706.1289 [hep-th]. We call the resulting gauged field
theory, Poisson--Weil sigma model. We study the BV cohomology of the model and
show its relation to Hamiltonian basic and equivariant Poisson cohomology. As
an application, we carry out the gauge fixing of the pure Weil model and of the
Poisson--Weil model. In the first case, we obtain the 2--dimensional version of
Donaldson--Witten topological gauge theory, describing the moduli space of flat
connections on a closed surface. In the second case, we recover the gauged A
topological sigma model worked out by Baptista describing the moduli space of
solutions of the so--called vortex equations.Comment: 49 pages, no figures. Typos corrected. Presentation improve
The biHermitian topological sigma model
BiHermitian geometry, discovered long ago by Gates, Hull and Roceck, is the
most general sigma model target space geometry allowing for (2,2) world sheet
supersymmetry. By using the twisting procedure proposed by Kapustin and Li, we
work out the type A and B topological sigma models for a general biHermtian
target space, we write down the explicit expression of the sigma model's action
and BRST transformations and present a computation of the topological gauge
fermion and the topological action.Comment: 40 pages, Latex. Analysis of sect. 6 improved; references adde
Supersymmetric Oscillator: Novel Symmetries
We discuss various continuous and discrete symmetries of the supersymmetric
simple harmonic oscillator (SHO) in one (0 + 1)-dimension of spacetime and show
their relevance in the context of mathematics of differential geometry. We show
the existence of a novel set of discrete symmetries in the theory which has,
hitherto, not been discussed in the literature on theoretical aspects of SHO.
We also point out the physical relevance of our present investigation.Comment: REVTeX file, 5 pages, minor changes in title, text and abstract,
references expanded, version to appear in EP
Deformation Theory of Holomorphic Vector Bundles, Extended Conformal Symmetry and Extensions of 2D Gravity
Developing on the ideas of R. Stora and coworkers, a formulation of two
dimensional field theory endowed with extended conformal symmetry is given,
which is based on deformation theory of holomorphic and Hermitian spaces. The
geometric background consists of a vector bundle over a closed surface
endowed with a holomorphic structure and a Hermitian structure
subordinated to it. The symmetry group is the semidirect product of the
automorphism group of and the extended Weyl group of and acts on the holomorphic and Hermitian structures. The
extended Weyl anomaly can be shifted into an automorphism chirally split
anomaly by adding to the action a local counterterm, as in ordinary conformal
field theory. The dependence on the scale of the metric on the fiber of is
encoded in the Donaldson action, a vector bundle generalization of the
Liouville action. The Weyl and automorphism anomaly split into two
contributions corresponding respectively to the determinant and
projectivization of . The determinant part induces an effective ordinary
Weyl or diffeomorphism anomaly and the induced central charge can be computed.Comment: 49 pages, plain TeX. A number of misprints have been correcte
Generalized structures of N=1 vacua
We characterize N=1 vacua of type II theories in terms of generalized complex
structure on the internal manifold M. The structure group of T(M) + T*(M) being
SU(3) x SU(3) implies the existence of two pure spinors Phi_1 and Phi_2. The
conditions for preserving N=1 supersymmetry turn out to be simple
generalizations of equations that have appeared in the context of N=2 and
topological strings. They are (d + H wedge) Phi_1=0 and (d + H wedge) Phi_2 =
F_RR. The equation for the first pure spinor implies that the internal space is
a twisted generalized Calabi-Yau manifold of a hybrid complex-symplectic type,
while the RR-fields serve as an integrability defect for the second.Comment: 21 pages. v2, v3: minor changes and correction
Poisson sigma model on the sphere
We evaluate the path integral of the Poisson sigma model on sphere and study
the correlators of quantum observables. We argue that for the path integral to
be well-defined the corresponding
Poisson structure should be unimodular. The construction of the finite
dimensional BV theory is presented and we argue that it is responsible for the
leading semiclassical contribution. For a (twisted) generalized Kahler manifold
we discuss the gauge fixed action for the Poisson sigma model. Using the
localization we prove that for the holomorphic Poisson structure the
semiclassical result for the correlators is indeed the full quantum result.Comment: 38 page
A dataset of future daily weather data for crop modelling over Europe derived from climate change scenarios
Coupled atmosphere-ocean general circulation models (AOGCMs, or just GCMs for
short) simulate different realizations of possible future climates at global scale under
contrasting scenarios of greenhouse gases emissions. While these datasets provide
several meteorological variables as output, but two of the most important ones are air
temperature at the Earth's surface and daily precipitation. GCMs outputs are spatially
downscaled using different methodologies, but it is accepted that such data require
further processing to be used in impact models, and particularly for crop simulation
models. Daily values of solar radiation, wind, air humidity, and, at times, rainfall may
have values which are not realistic, and/or the daily record of data may contain values
of meteorological variables which are totally uncorrelated. Crop models are
deterministic, but they are typicallyrun in a stochastic fashion by using a sample of
possible weather time series that can be generated using stochastic weather
generators. With their random variability, these multiple years of weather data can
represent the time horizon of interest. GCMs estimate climate dynamics, hence
providing unique time series for a given emission scenario; the multiplicity of years to
evaluate a given time horizon is consequently not available from such outputs.
Furthermore, if the time horizons of interest are very close (e.g. 2020 and 2030),
averaging only the non-overlapping years of the GCM weather variables time series
may not adequately represent the time horizon; this may lead to apparent inversions
of trends, creating artefacts also in the impact model simulations. This paper presents
a database of consolidated and coherent future daily weather data covering Europe
with a 25 km grid, which is adequate for crop modelling in the near-future. Climate data
are derived from the ENSEMBLES downscaling of the HadCM3, ECHAM5, and ETHZ
realizations of the IPCC A1B emission scenario, using for HadCM3 two different
regional models for downscaling. Solar radiation, wind and relative air humidity
weather variables where either estimated or collected from historical series, and
derived variables reference evapotranspiration and vapour pressure deficit were
estimated from other variables, ensuring consistency within daily records. Synthetic
time series data were also generated using the weather generator ClimGen. All data
are made available upon request to the European Commission Joint Research
Centre's MARS unit.JRC.H.7-Climate Risk Managemen
- …