165 research outputs found
Computing Yukawa Couplings from Magnetized Extra Dimensions
We compute Yukawa couplings involving chiral matter fields in toroidal
compactifications of higher dimensional super-Yang-Mills theory with magnetic
fluxes. Specifically we focus on toroidal compactifications of D=10
super-Yang-Mills theory, which may be obtained as the low-energy limit of Type
I, Type II or Heterotic strings. Chirality is obtained by turning on constant
magnetic fluxes in each of the 2-tori. Our results are general and may as well
be applied to lower D=6,8 dimensional field theories. We solve Dirac and
Laplace equations to find out the explicit form of wavefunctions in extra
dimensions. The Yukawa couplings are computed as overlap integrals of two Weyl
fermions and one complex scalar over the compact dimensions. In the case of
Type IIB (or Type I) string theories, the models are T-dual to (orientifolded)
Type IIA with D6-branes intersecting at angles. These theories may have
phenomenological relevance since particular models with SM group and three
quark-lepton generations have been recently constructed. We find that the
Yukawa couplings so obtained are described by Riemann theta-functions, which
depend on the complex structure and Wilson line backgrounds. Different patterns
of Yukawa textures are possible depending on the values of these backgrounds.
We discuss the matching of these results with the analogous computation in
models with intersecting D6-branes. Whereas in the latter case a string
computation is required, in our case only field theory is needed.Comment: 73 pages, 9 figures. Using JHEP3.cls. Typos and other minor
corrections fixed. References adde
Stringy Instantons and Cascading Quivers
D-brane instantons can perturb the quantum field theories on space-time
filling D-branes by interesting operators. In some cases, these D-brane
instantons are novel "stringy" effects (not interpretable directly as instanton
effects in the low-energy quantum field theory), while in others the D-brane
instantons can be directly interpreted as field theory effects. In this note,
we describe a situation where both perspectives are available, by studying
stringy instantons in quivers which arise at simple Calabi-Yau singularities.
We show that a stringy instanton which wraps an unoccupied node of the quiver,
and gives rise to a non-perturbative mass in the space-time field theory, can
be reinterpreted as a conventional gauge theory effect by going up in an
appropriate renormalization group cascade. Interestingly, in the cascade, the
contribution of the stringy instanton does not come from gauge theory
instantons but from strong coupling dynamics.Comment: 17 pages, 6 figures, harvma
Bounds on Four-Fermion Contact Interactions Induced by String Resonances
Based on tree-level open-string scattering amplitudes in the low string-scale
scenario, we derive the massless fermion scattering amplitudes. The amplitudes
are required to reproduce those of the Standard Model at tree level in the low
energy limit. We then obtain four-fermion contact interactions by expanding in
inverse powers of the string scale and explore the constraints on the string
scale from low energy data. The Chan-Paton factors and the string scale are
treated as free parameters. We find that data from the neutral and charged
current processes at HERA, Drell-Yan process at the Tevatron, and from LEP-II
put lower bounds on the string scale M_S >= 0.9-1.3 TeV for typical values of
the Chan-Paton factors, which are comparable to Tevatron bounds on Z' and W'
masses.Comment: 13 pages, 1 ps figure, version to appear in PR
D-Matter
We study the properties and phenomenology of particle-like states originating
from D-branes whose spatial dimensions are all compactified. They are
non-perturbative states in string theory and we refer to them as D-matter. In
contrast to other non-perturbative objects such as 't Hooft-Polyakov monopoles,
D-matter states could have perturbative couplings among themselves and with
ordinary matter. The lightest D-particle (LDP) could be stable because it is
the lightest state carrying certain (integer or discrete) quantum numbers.
Depending on the string scale, they could be cold dark matter candidates with
properties similar to that of wimps or wimpzillas. The spectrum of excited
states of D-matter exhibits an interesting pattern which could be distinguished
from that of Kaluza-Klein modes, winding states, and string resonances. We
speculate about possible signatures of D-matter from ultra-high energy cosmic
rays and colliders.Comment: 25 pages, 5 figures, references adde
On Deformations of n-Lie algebras
The aim of this paper is to review the deformation theory of -Lie
algebras. We summarize the 1-parameter formal deformation theory and provide a
generalized approach using any unital commutative associative algebra as a
deformation base. Moreover, we discuss degenerations and quantization of
-Lie algebras.Comment: Proceeding of the conference Dakar's Workshop in honor of Pr Amin
Kaidi. arXiv admin note: text overlap with arXiv:hep-th/9602016 by other
author
Effects of SO(10)-inspired scalar non-universality on the MSSM parameter space at large tan beta
We analyze the parameter space of the (mu > 0, A_0 = 0) CMSSM at large tan
beta with a small degree of non-universality originating from D-terms and
Higgs-sfermion splitting inspired by SO(10) GUT models. The effects of such
non-universalities on the sparticle spectrum and observables such as (g-2)_mu,
B(b -> X_s gamma), the SUSY threshold corrections to the bottom mass and
Omega_CDM h^2 are examined in detail and the consequences for the allowed
parameter space of the model are investigated. We find that even small
deviations to universality can result in large qualitative differences compared
to the universal case; for certain values of the parameters, we find, even at
low m_16, that radiative electroweak symmetry breaking fails as a consequence
of either |mu|^2 < 0 or m_(A^0)^2 < 0. We find particularly large departures
from the mSugra case for the neutralino relic density, which is sensitive to
significant changes in the position and shape of the A^0 resonance and a
substantial increase in the Higgsino component of the LSP. However, we find
that the corrections to the bottom mass are not sufficient to allow for Yukawa
unification.Comment: 53 pages, 14 figures, elsart format, some minor corrections,
references adde
Complementarity of the CERN Large Hadron Collider and the International Linear Collider
The next-generation high-energy facilities, the CERN Large Hadron Collider
(LHC) and the prospective International Linear Collider (ILC), are
expected to unravel new structures of matter and forces from the electroweak
scale to the TeV scale. In this report we review the complementary role of LHC
and ILC in drawing a comprehensive and high-precision picture of the mechanism
breaking the electroweak symmetries and generating mass, and the unification of
forces in the frame of supersymmetry.Comment: 14 pages, 17 figures, to be published in "Supersymmetry on the Eve of
the LHC", a special volume of European Physical Journal C, Particles and
Fields (EPJC) in memory of Julius Wes
Rare Variants in 48 Genes Account for 42% of Cases of Epilepsy With or Without Neurodevelopmental Delay in 246 Pediatric Patients
In order to characterize the genetic architecture of epilepsy in a pediatric population from the Iberian Peninsula (including the Canary Islands), we conducted targeted exome sequencing of 246 patients with infantile-onset seizures with or without neurodevelopmental delay. We detected 107 variants in 48 different genes, which were implicated in neuronal excitability, neurodevelopment, synaptic transmission, and metabolic pathways. In 104 cases (42%) we detected variant(s) that we classified as pathogenic or likely pathogenic. Of the 48 mutated genes, 32 were dominant, 8 recessive and 8 X-linked. Of the patients for whom family studies could be performed and in whom pathogenic variants were identified in dominant or X-linked genes, 82% carried de novo mutations. The involvement of small copy number variations (CNVs) is 9%. The use of progressively updated custom panels with high mean vertical coverage enabled establishment of a definitive diagnosis in a large proportion of cases (42%) and detection of CNVs (even duplications) with high fidelity. In 10.5% of patients we detected associations that are pending confirmation via functional and/or familial studies. Our findings had important consequences for the clinical management of the probands, since a large proportion of the cohort had been clinically misdiagnosed, and their families were subsequently able to avail of genetic counseling. In some cases, a more appropriate treatment was selected for the patient in question, or an inappropriate treatment discontinued. Our findings suggest the existence of modifier genes that may explain the incomplete penetrance of some epilepsy-related genes. We discuss possible reasons for non-diagnosis and future research directions. Further studies will be required to uncover the roles of structural variants, epimutations, and oligogenic inheritance in epilepsy, thereby providing a more complete molecular picture of this disease. In summary, given the broad phenotypic spectrum of most epilepsy-related genes, efficient genomic tools like the targeted exome sequencing panel described here are essential for early diagnosis and treatment, and should be implemented as first-tier diagnostic tools for children with epilepsy without a clear etiologic basis
Serum magnesium and calcium levels in relation to ischemic stroke : Mendelian randomization study
ObjectiveTo determine whether serum magnesium and calcium concentrations are causally associated with ischemic stroke or any of its subtypes using the mendelian randomization approach.MethodsAnalyses were conducted using summary statistics data for 13 single-nucleotide polymorphisms robustly associated with serum magnesium (n = 6) or serum calcium (n = 7) concentrations. The corresponding data for ischemic stroke were obtained from the MEGASTROKE consortium (34,217 cases and 404,630 noncases).ResultsIn standard mendelian randomization analysis, the odds ratios for each 0.1 mmol/L (about 1 SD) increase in genetically predicted serum magnesium concentrations were 0.78 (95% confidence interval [CI] 0.69-0.89; p = 1.3
7 10-4) for all ischemic stroke, 0.63 (95% CI 0.50-0.80; p = 1.6
7 10-4) for cardioembolic stroke, and 0.60 (95% CI 0.44-0.82; p = 0.001) for large artery stroke; there was no association with small vessel stroke (odds ratio 0.90, 95% CI 0.67-1.20; p = 0.46). Only the association with cardioembolic stroke was robust in sensitivity analyses. There was no association of genetically predicted serum calcium concentrations with all ischemic stroke (per 0.5 mg/dL [about 1 SD] increase in serum calcium: odds ratio 1.03, 95% CI 0.88-1.21) or with any subtype.ConclusionsThis study found that genetically higher serum magnesium concentrations are associated with a reduced risk of cardioembolic stroke but found no significant association of genetically higher serum calcium concentrations with any ischemic stroke subtype
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele
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