265 research outputs found
On the Topology of the Inflaton Field in Minimal Supergravity Models
We consider global issues in minimal supergravity models where a single field
inflaton potential emerges. In a particular case we reproduce the Starobinsky
model and its description dual to a certain formulation of R+R^2 supergravity.
For definiteness we confine our analysis to spaces at constant curvature,
either vanishing or negative. Five distinct models arise, two flat models with
respectively a quadratic and a quartic potential and three based on the
SU(1,1)/U(1) space where its distinct isometries, elliptic, hyperbolic and
parabolic are gauged. Fayet-Iliopoulos terms are introduced in a geometric way
and they turn out to be a crucial ingredient in order to describe the de Sitter
inflationary phase of the Starobinsky model.Comment: 31 pages, LaTex, 7 eps figures, 2 table
R-Symmetry and the Topological Twist of N=2 Effective Supergravities of Heterotic Strings
We discuss R-symmetries in locally supersymmetric N=2 gauge theories coupled
to hypermultiplets which can be thought of as effective theories of heterotic
superstring models. In this type of supergravities a suitable R-symmetry exists
and can be used to topologically twist the theory: the vector multiplet
containing the dilaton-axion field has different R-charge assignments with
respect to the other vector multiplets. Correspondingly a system of coupled
instanton equations emerges, mixing gravitational and Yang--Mills instantons
with triholomorphic hyperinstantons and axion-instantons. For the tree-level
classical special manifolds R-symmetry with the specified properties is a continuous symmetry, but
for the quantum corrected manifolds a discrete R--group of
electric--magnetic duality rotations is sufficient and we argue that it exists.Comment: 40 pages, plain LaTeX. Final version to appear on IJMP
Brane solutions and integrability: a status report
We review the status of the integrability and solvability of the geodesics
equations of motion on symmetric coset spaces that appear as sigma models of
supergravity theories when reduced over respectively the timelike and spacelike
direction. Such geodesic curves describe respectively timelike and spacelike
brane solutions. We emphasize the applications to black holes.Comment: 4 pages, Proceedings of ERE 2010, Granada, 6-10 september 201
Brane solutions and integrability: a status report
We review the status of the integrability and solvability of the geodesics
equations of motion on symmetric coset spaces that appear as sigma models of
supergravity theories when reduced over respectively the timelike and spacelike
direction. Such geodesic curves describe respectively timelike and spacelike
brane solutions. We emphasize the applications to black holes.Comment: 4 pages, Proceedings of ERE 2010, Granada, 6-10 september 201
The Great Green Forest is here and expanding all on its own: A call for action
Prosopis juliflora is recognized as one of the most invasive tree species worldwide. Following
widespread introductions throughout arid and semi-arid regions of Africa and throughout the
world, it has spread rapidly, threatening natural ecosystems and livelihoods. Control through
utilization as a resource is now accepted as the way forward in developing countries, but
efforts have so far been uncoordinated, with only isolated impacts. This paper reports on the
global state of knowledge and recent advances, but focuses on prosopis-related research and
innovations from IGAD member countries; the successes, failures, challenges and
opportunities. It underlines the need to build and apply scientific knowledge to scale up new,
resilient, drought-proof livelihood options in the Greater Horn of Africa and elsewhere where
introduced, from value-added prosopis wood and non wood products. The authors estimate
that there are at least five million hectares of prosopis forest across the region of the perhaps
ten million throughout Africa, and growing significantly in extent every year. Experiences
from the native range such as in Peru are well documented, where community associations
sustainably manage and make a living from fuel, fodder, food, honey and timber from their
prosopis forests. Efforts in Ethiopia, Djibouti and Kenya have had mixed results, but milling
the sweet protein-rich pods into animal feed is becoming increasingly popular with the
introduction of appropriate small scale technologies. Its use as a human food ingredient has
also been promoted, though with little uptake, but there is sharp rise in the use of prosopis
charcoal in the region, and the possibility of electricity generation using wood chips (bioenergy), with the transfer of experiences from India where there are at least 15 power stations
fueled entirely by prosopis. But much more can be done by applying scientific knowledge and
innovation to enhance the role of prosopis in improving food security, climate change
mitigation and adaptation, and building resilience for millions of the poorest rural and urban
people in the Greater Horn of Africa, with great potential for exchange and scaling up in other
arid areas in Africa, Asia and the Americas. This paper is a call to the African Union, national
governments, IGAD, IFAD, FAO, the Arab League and other international, regional and
bilateral donors, to come together and support a regional research and development
programme to push the frontiers on prosopis management and utilization and develop a
transnational strategy, as the impacts are potentially enormous and immediate. The initial
objectives are to take stock of existing knowledge and practices, assess prosopis forest areas
throughout the region, estimate wood and pod volumes and production rates, document
prosopis management and utilization experiences, enhance South-South knowledge sharing,
and rapidly and effectively scale up the successes
- …