651 research outputs found
De Sitter solutions in N=4 matter coupled supergravity
We investigate the scalar potential of gauged N=4 supergravity with matter.
The extremum in the SU(1,1)/U(1) scalars is obtained for an arbitrary number of
matter multiplets. The constraints on the matter scalars are solved in terms of
an explicit parametrisation of an
SO(6,6+n) element. For the case of six matter multiplets we discuss both
compact and noncompact gauge groups.
In an example involving noncompact groups and four scalars we find a
potential with an absolute minimum and a positive cosmological constant.Comment: 14 page
Regulation of Water Supply in Germany
Wasserversorgung, Privatisierung, Regulierung, Deutschland, Water supply, Privatization, Regulation, Germany
Global-scale regionalization of hydrologic model parameters
Current state-of-the-art models typically applied at continental to global scales (hereafter called macroscale) tend to use a priori parameters, resulting in suboptimal streamflow (Q) simulation. For the first time, a scheme for regionalization of model parameters at the global scale was developed. We used data from a diverse set of 1787 small-to-medium sized catchments ( 10-10,000 km(2)) and the simple conceptual HBV model to set up and test the scheme. Each catchment was calibrated against observed daily Q, after which 674 catchments with high calibration and validation scores, and thus presumably good-quality observed Q and forcing data, were selected to serve as donor catchments. The calibrated parameter sets for the donors were subsequently transferred to 0.5 degrees grid cells with similar climatic and physiographic characteristics, resulting in parameter maps for HBV with global coverage. For each grid cell, we used the 10 most similar donor catchments, rather than the single most similar donor, and averaged the resulting simulated Q, which enhanced model performance. The 1113 catchments not used as donors were used to independently evaluate the scheme. The regionalized parameters outperformed spatially uniform (i.e., averaged calibrated) parameters for 79% of the evaluation catchments. Substantial improvements were evident for all major Koppen-Geiger climate types and even for evaluation catchments>5000 km distant from the donors. The median improvement was about half of the performance increase achieved through calibration. HBV with regionalized parameters outperformed nine state-of-the-art macroscale models, suggesting these might also benefit from the new regionalization scheme. The produced HBV parameter maps including ancillary data are available via
Potential and mass-matrix in gauged N=4 supergravity
We discuss the potential and mass-matrix of gauged N=4 matter coupled
supergravity for the case of six matter multiplets, extending previous work by
considering the dependence on all scalars. We consider all semi-simple gauge
groups and analyse the potential and its first and second derivatives in the
origin of the scalar manifold. Although we find in a number of cases an
extremum with a positive cosmological constant, these are not stable under
fluctuations of all scalar fields.Comment: 28 pages, LaTe
`Stringy' Newton-Cartan Gravity
We construct a "stringy" version of Newton-Cartan gravity in which the
concept of a Galilean observer plays a central role. We present both the
geodesic equations of motion for a fundamental string and the bulk equations of
motion in terms of a gravitational potential which is a symmetric tensor with
respect to the longitudinal directions of the string. The extension to include
a non-zero cosmological constant is given. We stress the symmetries and
(partial) gaugings underlying our construction. Our results provide a
convenient starting point to investigate applications of the AdS/CFT
correspondence based on the non-relativistic "stringy" Galilei algebra.Comment: 44 page
The R-map and the Coupling of N=2 Tensor Multiplets in 5 and 4 Dimensions
We study the dimensional reduction of five dimensional N=2
Yang-Mills-Einstein supergravity theories (YMESGT) coupled to tensor
multiplets. The resulting 4D theories involve first order interactions among
tensor and vector fields with mass terms. If the 5D gauge group, K, does not
mix the 5D tensor and vector fields, the 4D tensor fields can be integrated out
in favor of 4D vector fields and the resulting theory is dual to a standard 4D
YMESGT. The gauge group has a block diagonal symplectic embedding and is a
semi-direct product of the 5D gauge group K with a Heisenberg group of
dimension (2P+1), where 2P is the number of tensor fields in five dimensions.
There exists an infinite family of theories, thus obtained, whose gauge groups
are pp-wave contractions of the simple noncompact groups of type SO*(2M). If,
on the other hand, the 5D gauge group does mix the 5D tensor and vector fields,
the resulting 4D theory is dual to a 4D YMESGT whose gauge group does, in
general,NOT have a block diagonal symplectic embedding and involves additional
topological terms. The scalar potentials of the dimensionally reduced theories
naturally have some of the ingredients that were found necessary for stable de
Sitter ground states. We comment on the relation between the known 5D and 4D,
N=2 supergravities with stable de Sitter ground states.Comment: 42 pages;latex fil
Gauged N=4 supergravities
We present the gauged N=4 (half-maximal) supergravities in four and five
spacetime dimensions coupled to an arbitrary number of vector multiplets. The
gaugings are parameterized by a set of appropriately constrained constant
tensors, which transform covariantly under the global symmetry groups SL(2) x
SO(6,n) and SO(1,1) x SO(5,n), respectively. In terms of these tensors the
universal Lagrangian and the Killing Spinor equations are given. The known
gaugings, in particular those originating from flux compactifications, are
incorporated in the formulation, but also new classes of gaugings are found.
Finally, we present the embedding chain of the five dimensional into the four
dimensional into the three dimensional gaugings, thereby showing how the
deformation parameters organize under the respectively larger duality groups.Comment: 36 pages, v2: references added, comments added, v3: published
version, references added, typos corrected, v4: sign mistakes in footnote 4
and equation (2.13) correcte
Charting the landscape of N=4 flux compactifications
We analyse the vacuum structure of isotropic Z_2 x Z_2 flux
compactifications, allowing for a single set of sources. Combining algebraic
geometry with supergravity techniques, we are able to classify all vacua for
both type IIA and IIB backgrounds with arbitrary gauge and geometric fluxes.
Surprisingly, geometric IIA compactifications lead to a unique theory with four
different vacua. In this case we also perform the general analysis allowing for
sources compatible with minimal supersymmetry. Moreover, some relevant examples
of type IIB non-geometric compactifications are studied. The computation of the
full N=4 mass spectrum reveals the presence of a number of non-supersymmetric
and nevertheless stable AdS_4 vacua. In addition we find a novel dS_4 solution
based on a non-semisimple gauging.Comment: Minor corrections and references added. Version published in JHE
The minimal N=4 no-scale model from generalized dimensional reduction
We consider the generalized dimensional reduction of pure ungauged N=4, D=5
supergravity, where supersymmetry is spontaneously broken to N=2 or N=0 with
identically vanishing scalar potential. We explicitly construct the resulting
gauged D=4 theory coupled to a single vector multiplet, which provides the
minimal N=4 realization of a no-scale model. We discuss its relation with the
standard classification of N=4 gaugings, extensions to non-compact twists and
to higher dimensions, the N=2 theories obtained via consistent Z_2 orbifold
projections and prospects for further generalizations.Comment: 1+28 pages, no figures, JHEP3 LaTeX, published versio
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