8,201 research outputs found
Non-universal gauge boson and the spin correlation of top quark pair production at colliders
In the off-diagonal basis, we discuss the contributions of the non-universal
gauge boson predicted by the topcolor-assisted technicolor () model
to the spin configurations and the spin correlation observable of the top quark
pair production via the process . Our numerical results
show that the production cross sections for the like-spin states, which vanish
in the standard model, can be significantly large as .
With reasonable values of the mass and the coupling parameter
,
exchange can generate large corrections to the spin correlation
observable.Comment: 16 pages, 5 figure
Radiative corrections to the semileptonic and hadronic Higgs-boson decays H -> W W/Z Z -> 4 fermions
The radiative corrections of the strong and electroweak interactions are
calculated for the Higgs-boson decays H -> WW/ZZ -> 4f with semileptonic or
hadronic four-fermion final states in next-to-leading order. This calculation
is improved by higher-order corrections originating from heavy-Higgs-boson
effects and photonic final-state radiation off charged leptons. The W- and
Z-boson resonances are treated within the complex-mass scheme, i.e. without any
resonance expansion or on-shell approximation. The calculation essentially
follows our previous study of purely leptonic final states. The electroweak
corrections are similar for all four-fermion final states; for integrated
quantities they amount to some per cent and increase with growing Higgs-boson
mass M_H, reaching 7-8% at M_H \sim 500 GeV. For distributions, the corrections
are somewhat larger and, in general, distort the shapes. Among the QCD
corrections, which include corrections to interference contributions of the
Born diagrams, only the corrections to the squared Born diagrams turn out to be
relevant. These contributions can be attributed to the gauge-boson decays, i.e.
they approximately amount to \alpha_s/\pi for semileptonic final states and
2\alpha_s/\pi for hadronic final states. The discussed corrections have been
implemented in the Monte Carlo event generator PROPHECY4F.Comment: 29 pages, LaTeX, 30 postscript figure
Ceramic identity contributes to mechanical properties and osteoblast behavior on macroporous composite scaffolds.
Implants formed of metals, bioceramics, or polymers may provide an alternative to autografts for treating large bone defects. However, limitations to each material motivate the examination of composites to capitalize on the beneficial aspects of individual components and to address the need for conferring bioactive behavior to the polymer matrix. We hypothesized that the inclusion of different bioceramics in a ceramic-polymer composite would alter the physical properties of the implant and the cellular osteogenic response. To test this, composite scaffolds formed from poly(lactide-co-glycolide) (PLG) and either hydroxyapatite (HA), β-tricalcium phosphate (TCP), or bioactive glass (Bioglass 45S®, BG) were fabricated, and the physical properties of each scaffold were examined. We quantified cell proliferation by DNA content, osteogenic response of human osteoblasts (NHOsts) to composite scaffolds by alkaline phosphatase (ALP) activity, and changes in gene expression by qPCR. Compared to BG-PLG scaffolds, HA-PLG and TCP-PLG composite scaffolds possessed greater compressive moduli. NHOsts on BG-PLG substrates exhibited higher ALP activity than those on control, HA-, or TCP-PLG scaffolds after 21 days, and cells on composites exhibited a 3-fold increase in ALP activity between 7 and 21 days versus a minimal increase on control scaffolds. Compared to cells on PLG controls, RUNX2 expression in NHOsts on composite scaffolds was lower at both 7 and 21 days, while expression of genes encoding for bone matrix proteins (COL1A1 and SPARC) was higher on BG-PLG scaffolds at both time points. These data demonstrate the importance of selecting a ceramic when fabricating composites applied for bone healing
Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited
We re-examine the implications of allowing fermion fields to propagate in the
five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We
find that mixing between the Standard Model top quark and its Kaluza Klein
excitations generates large contributions to the rho parameter and consequently
restricts the fundamental RS scale to lie above 100 TeV. To circumvent this
bound we propose a `mixed' scenario which localizes the third generation
fermions on the TeV brane and allows the lighter generations to propagate in
the full five-dimensional bulk. We show that this construction naturally
reproduces the observed m_c / m_t and m_s / m_b hierarchies. We explore the
signatures of this scenario in precision measurements and future high energy
collider experiments. We find that the region of parameter space that addresses
the hierarchies of fermion Yukawa couplings permits a Higgs boson with a mass
of 500 GeV and remains otherwise invisible at the LHC. However, the entire
parameter region consistent with electroweak precision data is testable at
future linear colliders. We briefly discuss possible constraints on this
scenario arising from flavor changing neutral currents.Comment: 44 pages, 20 ps files; VII, typos fixed and refs adde
Updated Constraints on the Minimal Supergravity Model
Recently, refinements have been made on both the theoretical and experimental
determinations of the i.) mass of the lightest Higgs scalar (m_h), ii.) relic
density of cold dark matter in the universe (Omega_CDM h^2), iii.) branching
fraction for radiative B decay BF(b \to s \gamma), iv.) muon anomalous magnetic
moment (a_\mu), and v.) flavor violating decay B_s \to \mu^+\mu^-. Each of
these quantities can be predicted in the MSSM, and each depends in a
non-trivial way on the spectra of SUSY particles. In this paper, we present
updated constraints from each of these quantities on the minimal supergravity
(mSUGRA) model as embedded in the computer program ISAJET. The combination of
constraints points to certain favored regions of model parameter space where
collider and non-accelerator SUSY searches may be more focussed.Comment: 20 pages, 6 figures. Version published in JHE
The SKA view of the Neutral Interstellar Medium in Galaxies
Two major questions in galaxy evolution are how star-formation on small
scales leads to global scaling laws and how galaxies acquire sufficient gas to
sustain their star formation rates. HI observations with high angular
resolution and with sensitivity to very low column densities are some of the
important observational ingredients that are currently still missing. Answers
to these questions are necessary for a correct interpretation of observations
of galaxy evolution in the high-redshift universe and will provide crucial
input for the sub-grid physics in hydrodynamical simulations of galaxy
evolutions. In this chapter we discuss the progress that will be made with the
SKA using targeted observations of nearby individual disk and dwarf galaxies.Comment: 22 pages, 4 figures, to appear as part of 'Neutral Hydrogen' in
Proceedings 'Advancing Astrophysics with the SKA (AASKA14)', PoS(AASKA14)12
The High Energy Telescope on EXIST
The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed next
generation multi-wavelength survey mission. The primary instrument is a High
Energy telescope (HET) that conducts the deepest survey for Gamma-ray Bursts
(GRBs), obscured-accreting and dormant Supermassive Black Holes and Transients
of all varieties for immediate followup studies by the two secondary
instruments: a Soft X-ray Imager (SXI) and an Optical/Infrared Telescope (IRT).
EXIST will explore the early Universe using high redshift GRBs as cosmic probes
and survey black holes on all scales. The HET is a coded aperture telescope
employing a large array of imaging CZT detectors (4.5 m^2, 0.6 mm pixel) and a
hybrid Tungsten mask. We review the current HET concept which follows an
intensive design revision by the HET imaging working group and the recent
engineering studies in the Instrument and Mission Design Lab at the Goddard
Space Flight Center. The HET will locate GRBs and transients quickly (<10-30
sec) and accurately (< 20") for rapid (< 1-3 min) onboard followup soft X-ray
and optical/IR (0.3-2.2 micron) imaging and spectroscopy. The broad energy band
(5-600 keV) and the wide field of view (~90 deg x 70 deg at 10% coding
fraction) are optimal for capturing GRBs, obscured AGNs and rare transients.
The continuous scan of the entire sky every 3 hours will establish a
finely-sampled long-term history of many X-ray sources, opening up new
possibilities for variability studies.Comment: 10 pages, 6 figures, 3 tables, SPIE conference proceedings (UV,
X-ray, and Gamma-Ray Space Instrumentation for Astronomy XVI, 7435-9
Inferring individual attributes from search engine queries and auxiliary information
Internet data has surfaced as a primary source for investigation of different
aspects of human behavior. A crucial step in such studies is finding a suitable
cohort (i.e., a set of users) that shares a common trait of interest to
researchers. However, direct identification of users sharing this trait is
often impossible, as the data available to researchers is usually anonymized to
preserve user privacy. To facilitate research on specific topics of interest,
especially in medicine, we introduce an algorithm for identifying a trait of
interest in anonymous users. We illustrate how a small set of labeled examples,
together with statistical information about the entire population, can be
aggregated to obtain labels on unseen examples. We validate our approach using
labeled data from the political domain.
We provide two applications of the proposed algorithm to the medical domain.
In the first, we demonstrate how to identify users whose search patterns
indicate they might be suffering from certain types of cancer. In the second,
we detail an algorithm to predict the distribution of diseases given their
incidence in a subset of the population at study, making it possible to predict
disease spread from partial epidemiological data
RooStatsCms: a tool for analyses modelling, combination and statistical studies
The RooStatsCms (RSC) software framework allows analysis modelling and
combination, statistical studies together with the access to sophisticated
graphics routines for results visualisation. The goal of the project is to
complement the existing analyses by means of their combination and accurate
statistical studies.Comment: Proceedings of the 11th Topical Seminar on Innovative Particle and
Radiation Detectors. 4 pages and 5 figure
Unique Identification of Graviton Exchange Effects in e^+ e^- Collisions
Many types of new physics can lead to contact interaction-like modifications
in e^+ e^- processes below direct production threshold. We examine the
possibility of uniquely identifying the effects of graviton exchange, which are
anticipated in many extra dimensional theories, from amongst this large set of
models by using the moments of the angular distribution of the final state
particles. In the case of the e^+ e^- --> f bar{f} process we demonstrate that
this technique allows for the unique identification of the graviton exchange
signature at the 5 sigma level for mass scales as high as 6 sqrt(s). The
extension of this method to the e^+ e^- --> W^+ W^- process is also discussed.Comment: 21 pages, 3 figs, LaTe
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