2,003 research outputs found
Scanning the Landscape of Flux Compactifications: Vacuum Structure and Soft Supersymmetry Breaking
We scan the landscape of flux compactifications for the Calabi-Yau manifold
with two K\" ahler moduli by varying the value of
the flux superpotential over a large range of values. We do not include
uplift terms. We find a rich phase structure of AdS and dS vacua. Starting with
we reproduce the exponentially large volume scenario, but as
is reduced new classes of minima appear. One of them corresponds to the
supersymmetric KKLT vacuum while the other is a new, deeper non-supersymmetric
minimum. We study how the bare cosmological constant and the soft supersymmetry
breaking parameters for matter on D7 branes depend on , for these classes
of minima. We discuss potential applications of our results.Comment: draft format remove
Systematics of String Loop Corrections in Type IIB Calabi-Yau Flux Compactifications
We study the behaviour of the string loop corrections to the N=1 4D
supergravity Kaehler potential that occur in flux compactifications of IIB
string theory on general Calabi-Yau three-folds. We give a low energy
interpretation for the conjecture of Berg, Haack and Pajer for the form of the
loop corrections to the Kaehler potential. We check the consistency of this
interpretation in several examples. We show that for arbitrary Calabi-Yaus, the
leading contribution of these corrections to the scalar potential is always
vanishing, giving an "extended no-scale structure". This result holds as long
as the corrections are homogeneous functions of degree -2 in the 2-cycle
volumes. We use the Coleman-Weinberg potential to motivate this cancellation
from the viewpoint of low-energy field theory. Finally we give a simple formula
for the 1-loop correction to the scalar potential in terms of the tree-level
Kaehler metric and the correction to the Kaehler potential. We illustrate our
ideas with several examples. A companion paper will use these results in the
study of Kaehler moduli stabilisation.Comment: 34 pages and 3 figures; typos corrected and references adde
Implementation of the Chicago Public Schools Service Learning Initiative: The Role of Teacher Coaches
The growth of service leaming during the past two decades is testimony to this method by which young people learn and develop through active participation in service experiences. Legislative initiatives have supported schools in their efforts to involve youth with their local communities through service linked to academic study. In 1984, 9 percent of all high schools offered some form of service learning. By 1999, 46 percent of public high schools alone were using service learning activities (Kleiner and Chapman 1999). At the same time, service learning studies are complicated by the subject\u27s broad-based goals, the varying contexts and age groups employed, and outcomes often difficult to measure
Forward: Symposium on State Sales Tax
One of the most remarkable developments in state finance is the rapidity with which the retail sales tax has become the most important fixture in the revenue system. Practically unknown a quarter century ago, by five years later in 1935 the tax yielded 2.6 billion, or about 23 per cent of state tax collections. For the future the prospect is that sooner or later all but a few, if indeed not all the states, will be in this tax field.
A symposium on the subject is most timely, and the editors of the Vanderbilt Law Review and its contributors are to be congratulated on this undertaking. It is true that considerable progress has been made toward solving many of the problems found in the early days of the sales tax-- the taxation of sales involving interstate elements, the extent of the obligation of sellers to collect use taxes, and the tax status of sales on federal areas, to name but a few. Administrative methods have improved considerably and with few exceptions the tax has gradually won acceptance in the states where it is imposed. Nevertheless, there are a number of points where the statutes, inter-governmental relations and administrative methods may be substantially improved, and a review and reappraisal of the type that follows might well encourage an effort to achieve desirable improvements and refinements
"Big" Divisor D3/D7 Swiss Cheese Phenomenology
We review progress made over the past couple of years in the field of Swiss
Cheese Phenomenology involving a mobile space-time filling D3-brane and
stack(s) of fluxed D7-branes wrapping the "big" (as opposed to the "small")
divisor in (the orientifold of a) Swiss-Cheese Calabi-Yau. The topics reviewed
include reconciliation of large volume cosmology and phenomenology, evaluation
of soft supersymmetry breaking parameters, one-loop RG-flow equations'
solutions for scalar masses, obtaining fermionic (possibly first two
generations' quarks/leptons) mass scales in the O(MeV-GeV)-regime as well as
(first two generations') neutrino masses (and their one-loop RG flow) of around
an eV. The heavy sparticles and the light fermions indicate the possibility of
"split SUSY" large volume scenario.Comment: Invited review for MPLA, 14 pages, LaTe
Towards Realistic String Vacua From Branes At Singularities
We report on progress towards constructing string models incorporating both
realistic D-brane matter content and moduli stabilisation with dynamical
low-scale supersymmetry breaking. The general framework is that of local
D-brane models embedded into the LARGE volume approach to moduli stabilisation.
We review quiver theories on del Pezzo () singularities including
both D3 and D7 branes. We provide supersymmetric examples with three
quark/lepton families and the gauge symmetries of the Standard, Left-Right
Symmetric, Pati-Salam and Trinification models, without unwanted chiral
exotics. We describe how the singularity structure leads to family symmetries
governing the Yukawa couplings which may give mass hierarchies among the
different generations. We outline how these models can be embedded into compact
Calabi-Yau compactifications with LARGE volume moduli stabilisation, and state
the minimal conditions for this to be possible. We study the general structure
of soft supersymmetry breaking. At the singularity all leading order
contributions to the soft terms (both gravity- and anomaly-mediation) vanish.
We enumerate subleading contributions and estimate their magnitude. We also
describe model-independent physical implications of this scenario. These
include the masses of anomalous and non-anomalous U(1)'s and the generic
existence of a new hyperweak force under which leptons and/or quarks could be
charged. We propose that such a gauge boson could be responsible for the ghost
muon anomaly recently found at the Tevatron's CDF detector.Comment: 40 pages, 10 figure
Henrike Donner (Ed.). Being Middle Class in India: A Way of Life. New York: Routledge, 2011
Book review
Sparticle Spectra and LHC Signatures for Large Volume String Compactifications
We study the supersymmetric particle spectra and LHC collider observables for
the large-volume string models with a fundamental scale of 10^{11} GeV that
arise in moduli-fixed string compactifications with branes and fluxes. The
presence of magnetic fluxes on the brane world volume, required for chirality,
perturb the soft terms away from those previously computed in the dilute-flux
limit. We use the difference in high-scale gauge couplings to estimate the
magnitude of this perturbation and study the potential effects of the magnetic
fluxes by generating many random spectra with the soft terms perturbed around
the dilute flux limit. Even with a 40% variation in the high-scale soft terms
the low-energy spectra take a clear and predictive form. The resulting spectra
are broadly similar to those arising on the SPS1a slope, but more degenerate.
In their minimal version the models predict the ratios of gaugino masses to be
M_1 : M_2 : M_3=(1.5 - 2) : 2 : 6, different to both mSUGRA and mirage
mediation. Among the scalars, the squarks tend to be lighter and the sleptons
heavier than for comparable mSUGRA models. We generate 10 fb^{-1} of sample LHC
data for the random spectra in order to study the range of collider
phenomenology that can occur. We perform a detailed mass reconstruction on one
example large-volume string model spectrum. 100 fb^{-1} of integrated
luminosity is sufficient to discriminate the model from mSUGRA and aspects of
the sparticle spectrum can be accurately reconstructed.Comment: 42 pages, 21 figures. Added references and discussion for section 3.
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