508 research outputs found
On supersymmetric Minkowski vacua in IIB orientifolds
Supersymmetric Minkowski vacua in IIB orientifold compactifications based on
orbifolds with background fluxes and non-perturbative superpotentials are
investigated. Especially, microscopic requirements and difficulties to obtain
such vacua are discussed. We show that orbifold models with one and two complex
structure moduli and supersymmetric 2-form flux can be successfully stabilized
to such vacua. By taking additional gaugino condensation on fixed space-time
filling D3-branes into account also models without complex structure can be
consistently stabilized to Minkowski vacua.Comment: 17 pages, 2 figures; More detailed proof for absence of complex flat
directions in susy AdS vacua given; Footnotes and reference adde
Exploring segregation and sharing in a divided city: A PGIS approach
This article presents a novel exploratory investigation into the location and characteristics of spaces that are segregated and shared between Protestant and Catholic communities in Belfast, Northern Ireland (UK). Focusing on a particularly segregated part of the city, this study uses state-of-the-art participatory geographic information systems (PGIS) and visualization techniques to create qualitative, bottom-up maps of segregation and sharing within the city, as experienced by the people who live there. In doing so, it identifies important and previously unreported patterns in segregation and sharing between sectarian communities, challenging normative approaches to PGIS, illustrating how alternative methods might provide deeper insights into complex social geographies such as those of segregation. Finally, the findings of this work are formulated into a set of hypotheses that can contribute to a future research agenda into segregation and sharing, both in Belfast and in other divided cities
An Effect of Corrections on Racetrack Inflation
We study the effects of corrections to the K\"ahler potential on
volume stabilisation and racetrack inflation. In a region where classical
supergravity analysis is justified, stringy corrections can nevertheless be
relevant for correctly analyzing moduli stabilisation and the onset of
inflation.Comment: 13 pages, 4 figures. Typos corrected, references added, this version
to appear in JHE
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The Ultraviolet Behavior of N
We describe the construction of the complete four-loop four-particle amplitude of N = 8 supergravity. The amplitude is ultraviolet finite, not only in four dimensions, but in five dimensions as well. The observed extra cancellations provide additional non-trivial evidence that N = 8 supergravity in four dimensions may be ultraviolet finite to all orders of perturbation theory
Cosmological String Gas on Orbifolds
It has long been known that strings wound around incontractible cycles can
play a vital role in cosmology. In particular, in a spacetime with toroidal
spatial hypersurfaces, the dynamics of the winding modes may help yield three
large spatial dimensions. However, toroidal compactifications are
phenomenologically unrealistic. In this paper we therefore take a first step
toward extending these cosmological considerations to -dimensional toroidal
orbifolds. We use numerical simulation to study the timescales over which
"pseudo-wound" strings unwind on these orbifolds with trivial fundamental
group. We show that pseudo-wound strings can persist for many ``Hubble times''
in some of these spaces, suggesting that they may affect the dynamics in the
same way as genuinely wound strings. We also outline some possible extensions
that include higher-dimensional wrapped branes.Comment: 14 pages, 8 eps fig
Observation of two relaxation mechanisms in transport between spin split edge states at high imbalance
Using a quasi-Corbino geometry to directly study electron transport between
spin-split edge states, we find a pronounced hysteresis in the I-V curves,
originating from slow relaxation processes. We attribute this long-time
relaxation to the formation of a dynamic nuclear polarization near the sample
edge. The determined characteristic relaxation times are 25 s and 200 s which
points to the presence of two different relaxation mechanisms. The two time
constants are ascribed to the formation of a local nuclear polarization due to
flip-flop processes and the diffusion of nuclear spins.Comment: Submitted to PR
Gauging and symplectic blowing up in nonlinear sigma-models: I. point singularities
In this paper a two dimensional non-linear sigma model with a general
symplectic manifold with isometry as target space is used to study symplectic
blowing up of a point singularity on the zero level set of the moment map
associated with a quasi-free Hamiltonian action. We discuss in general the
relation between symplectic reduction and gauging of the symplectic isometries
of the sigma model action. In the case of singular reduction, gauging has the
same effect as blowing up the singular point by a small amount. Using the
exponential mapping of the underlying metric, we are able to construct
symplectic diffeomorphisms needed to glue the blow-up to the global reduced
space which is regular, thus providing a transition from one symplectic sigma
model to another one free of singularities.Comment: 32 pages, LaTex, THEP 93/24 (corrected and expanded(about 5 pages)
version
Inflation on an Open Racetrack
We present a variant of warped D-brane inflation by incorporating multiple
sets of holomorphically-embedded D7-branes involved in moduli stabilization
with extent into a warped throat. The resultant D3-brane motion depends on the
D7-brane configuration and the relative position of the D3-brane in these
backgrounds. The non-perturbative moduli stabilization superpotential takes the
racetrack form, but the additional D3-brane open string moduli dependence
provides more flexibilities in model building. For concreteness, we consider
D3-brane motion in the warped deformed conifold with the presence of multiple
D7-branes, and derive the scalar potential valid for the entire throat. By
explicit tuning of the microphysical parameters, we obtain inflationary
trajectories near an inflection point for various D7-brane configurations.
Moreover, the open racetrack potential admits approximate Minkowski vacua
before uplifting. We demonstrate with a concrete D-brane inflation model where
the Hubble scale during inflation can exceed the gravitino mass. Finally, the
multiple sets of D7-branes present in this open racetrack setup also provides a
mechanism to stabilize the D3-brane to metastable vacua in the intermediate
region of the warped throat.Comment: 29 pages, 15 figures, pre-print number and references adde
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