2,317 research outputs found
Associations between selected immune-mediated diseases and tuberculosis: record-linkage studies
PMCID: PMC3616814This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited
Froggatt-Nielsen models from E8 in F-theory GUTs
This paper studies F-theory SU(5) GUT models where the three generations of
the standard model come from three different curves. All the matter is taken to
come from curves intersecting at a point of enhanced E8 gauge symmetry. Giving
a vev to some of the GUT singlets naturally implements a Froggatt-Nielsen
approach to flavour structure. A scan is performed over all possible models and
the results are filtered using phenomenological constraints. We find a unique
model that fits observations of quark and lepton masses and mixing well. This
model suffers from two drawbacks: R-parity must be imposed by hand and there is
a doublet-triplet splitting problem.Comment: 42 pages; v2:journal version; v3:corrected typo in neutrino masse
Preliminary analysis of space mission applications for electromagnetic launchers
The technical and economic feasibility of using electromagnetically launched EML payloads propelled from the Earth's surface to LEO, GEO, lunar orbit, or to interplanetary space was assessed. Analyses of the designs of rail accelerators and coaxial magnetic accelerators show that each is capable of launching to space payloads of 800 KG or more. A hybrid launcher in which EML is used for the first 2 KM/sec followed by chemical rocket stages was also tested. A cost estimates study shows that one to two EML launches per day are needed to break even, compared to a four-stage rocket. Development models are discussed for: (1) Earth orbital missions; (2) lunar base supply mission; (3) solar system escape mission; (4) Earth escape missions; (5) suborbital missions; (6) electromagnetic boost missions; and (7) space-based missions. Safety factors, environmental impacts, and EML systems analysis are discussed. Alternate systems examined include electrothermal thrustors, an EML rocket gun; an EML theta gun, and Soviet electromagnetic accelerators
LARGE Volume String Compactifications at Finite Temperature
We present a detailed study of the finite-temperature behaviour of the LARGE
Volume type IIB flux compactifications. We show that certain moduli can
thermalise at high temperatures. Despite that, their contribution to the
finite-temperature effective potential is always negligible and the latter has
a runaway behaviour. We compute the maximal temperature , above which
the internal space decompactifies, as well as the temperature , that is
reached after the decay of the heaviest moduli. The natural constraint
implies a lower bound on the allowed values of the internal
volume . We find that this restriction rules out a significant
range of values corresponding to smaller volumes of the order , which lead to standard GUT theories. Instead, the bound favours
values of the order , which lead to TeV scale
SUSY desirable for solving the hierarchy problem. Moreover, our result favours
low-energy inflationary scenarios with density perturbations generated by a
field, which is not the inflaton. In such a scenario, one could achieve both
inflation and TeV-scale SUSY, although gravity waves would not be observable.
Finally, we pose a two-fold challenge for the solution of the cosmological
moduli problem. First, we show that the heavy moduli decay before they can
begin to dominate the energy density of the Universe. Hence they are not able
to dilute any unwanted relics. And second, we argue that, in order to obtain
thermal inflation in the closed string moduli sector, one needs to go beyond
the present EFT description.Comment: 54 pages + appendix, 5 figures; v2: minor corrections, references and
footnotes added, version published on JCA
Moduli Redefinitions and Moduli Stabilisation
Field redefinitions occur in string compactifications at the one loop level.
We review arguments for why such redefinitions occur and study their effect on
moduli stabilisation and supersymmetry breaking in the LARGE volume scenario.
For small moduli, although the effect of such redefinitions can be larger than
that of the corrections in both the K\"ahler and scalar potentials,
they do not alter the structure of the scalar potential. For the less well
motivated case of large moduli, the redefinitions can dominate all other terms
in the scalar potential. We also study the effect of redefinitions on the
structure of supersymmetry breaking and soft terms.Comment: 21 pages, 3 figures; v2. references adde
Metastable SUSY Breaking, de Sitter Moduli Stabilisation and K\"ahler Moduli Inflation
We study the influence of anomalous U(1) symmetries and their associated
D-terms on the vacuum structure of global field theories once they are coupled
to N=1 supergravity and in the context of string compactifications with moduli
stabilisation. In particular, we focus on a IIB string motivated construction
of the ISS scenario and examine the influence of one additional U(1) symmetry
on the vacuum structure. We point out that in the simplest one-Kahler modulus
compactification, the original ISS vacuum gets generically destabilised by a
runaway behaviour of the potential in the modulus direction. In more general
compactifications with several Kahler moduli, we find a novel realisation of
the LARGE volume scenario with D-term uplifting to de Sitter space and both
D-term and F-term supersymmetry breaking. The structure of soft supersymmetry
breaking terms is determined in the preferred scenario where the standard model
cycle is not stabilised non-perturbatively and found to be flavour universal.
Our scenario also provides a purely supersymmetric realisation of Kahler moduli
(blow-up and fibre) inflation, with similar observational properties as the
original proposals but without the need to include an extra (non-SUSY)
uplifting term.Comment: 38 pages, 8 figures. v2: references added, minor correction
Gauge Threshold Corrections for Local String Models
We study gauge threshold corrections for local brane models embedded in a
large compact space. A large bulk volume gives important contributions to the
Konishi and super-Weyl anomalies and the effective field theory analysis
implies the unification scale should be enhanced in a model-independent way
from M_s to R M_s. For local D3/D3 models this result is supported by the
explicit string computations. In this case the scale R M_s comes from the
necessity of global cancellation of RR tadpoles sourced by the local model. We
also study D3/D7 models and discuss discrepancies with the effective field
theory analysis. We comment on phenomenological implications for gauge coupling
unification and for the GUT scale.Comment: 30 pages; v2: references added, minor typos correcte
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.
Slight changes in the tex
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
On hypercharge flux and exotics in F-theory GUTs
We study SU(5) Grand Unified Theories within a local framework in F-theory
with multiple extra U(1) symmetries arising from a small monodromy group. The
use of hypercharge flux for doublet-triplet splitting implies massless exotics
in the spectrum that are protected from obtaining a mass by the U(1)
symmetries. We find that lifting the exotics by giving vacuum expectation
values to some GUT singlets spontaneously breaks all the U(1) symmetries which
implies that proton decay operators are induced. If we impose an additional
R-parity symmetry by hand we find all the exotics can be lifted while proton
decay operators are still forbidden. These models can retain the gauge coupling
unification accuracy of the MSSM at 1-loop. For models where the generations
are distributed across multiple curves we also present a motivation for the
quark-lepton mass splittings at the GUT scale based on a Froggatt-Nielsen
approach to flavour.Comment: 38 pages; v2: emphasised possibility of avoiding exotics in models
without a global E8 structure, added ref, journal versio
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