48 research outputs found
Renormalization-Group Improved Prediction for Higgs Production at Hadron Colliders
We use renormalization-group methods in effective field theory to improve the
theoretical prediction for the cross section for Higgs-boson production at
hadron colliders. In addition to soft-gluon resummation at NNNLL, we also resum
enhanced contributions of the form (C_A\pi\alpha_s)^n, which arise in the
analytic continuation of the gluon form factor to time-like momentum transfer.
This resummation is achieved by evaluating the matching corrections arising at
the Higgs-boson mass scale at a time-like renormalization point \mu^2<0,
followed by renormalization-group evolution to \mu^2>0. We match our resummed
result to NNLO fixed-order perturbation theory and give numerical predictions
for the total production cross section as a function of the Higgs-boson mass.
Resummation effects are significant even at NNLO, where our improved
predictions for the cross sections at the Tevatron and the LHC exceed the
fixed-order predictions by about 13% and 8%, respectively, for m_H=120 GeV. We
also discuss the application of our technique to other time-like processes such
as Drell-Yan production, e^+ e^- --> hadrons, and hadronic decays of the Higgs
boson.Comment: 35 pages, 6 figures; v2: update to MSTW2008 PDFs, detailed comparison
with moment-space formalism; v3: typo in equation (A.3) correcte
Forward-Backward and Charge Asymmetries in the Standard Model
This talk reviews the Standard Model predictions for the top-quark forward
backward and charge asymmetries measured at the Tevatron and at the LHC.Comment: 8 pages, 2 figures. Proceedings of CKM 2012, the 7th International
Workshop on the CKM Unitarity Triangle, University of Cincinnati, USA, 28
September - 2 October 201
Updated Predictions for Higgs Production at the Tevatron and the LHC
We present updated predictions for the total cross section for Higgs boson
production through gluon fusion at hadron colliders. In addition to
renormalization-group improvement at next-to-next-to-next-to-leading
logarithmic accuracy, we incorporate the two-loop electroweak corrections,
which leads to the most precise predictions at present. Numerical results are
given for Higgs masses between 115 GeV and 200 GeV at the Tevatron with
\sqrt{s}=1.96 TeV and the LHC with \sqrt{s}=7-14 TeV.Comment: 8 pages, 2 figures. v2: combined PDF+alpha_s uncertainties included;
results using NNPDF2.0 added; upgrade CTEQ6.6->CT1
Enabling Logic Computation Between Ta/CoFeB/MgO Nanomagnets
Dipolar coupled magnets proved to have the potential to be capable of successfully performing digital computation in a highly parallel way. For that, nanomagnet-based computation requires precise control of the domain wall nucleation from a well-localized region of the magnet. Co/Pt and Co/Ni multilayer stacks were successfully used to demonstrate a variety of computing devices. However, Ta/CoFeB/MgO appears more promising, thanks to the lower switching field required to achieve a full magnetization reversal, reduced thickness (less than 10 nm), and its compatibility with magnetic tunnel junctions. In this work, the switch of the information is achieved through the application of a magnetic field, which allows to scale more the nanomagnets with respect to current-driven magnetization reversal-based devices and to go toward 3-D structures. We experimentally demonstrate that Ga ions can be used to tune the energy landscape of the structured magnets to provide signal directionality and achieve a distinct logic computation. We prove that it is possible to define the artificial nucleation center (ANC) in different structures with two irradiation steps and that this approach can enable logic computation in ultrathin films by dipolar interaction. Moreover, different from previous studies, the results coming from the irradiation analysis are then used for real logic devices. We present the experimental demonstration of a set of fully working planar inverters, showing that it is possible to reach a coupling field between the input and the output, which is strong enough to reliably implement logic operations. Micromagnetic simulations are used to study the nucleation center's effectiveness with respect to its position in the magnet and to support the experiments. Our results open the path to the development of more efficient nanomagnet-based logic circuits
Experimental Demonstration of a Rowland Spectrometer for Spin Waves
We experimentally demonstrate the operation of a spin-wave Rowland
spectrometer. In the proposed device geometry, spin waves are coherently
excited on a diffraction grating and form an interference pattern that
spatially separates spectral components of the incoming signal. The diffraction
grating was created by focused-ion-beam irradiation, which was found to locally
eliminate the ferrimagnetic properties of YIG, without removing the material.
We found that in our experiments spin waves were created by an indirect
mechanism, by exploiting nonlinear resonance between the grating and the
coplanar waveguide. Our work paves the way for complex spin-wave optic devices
-- chips that replicate the functionality of integrated optical devices on a
chip-scale.Comment: 7 pages, 5 figures, presented at Joint European Magnetic Symposia
(JEMS) 202
Controlling Domain-Wall Nucleation in Ta/CoFeB/MgO Nanomagnets via Local Ga+ Ion Irradiation
Comprehensive control of the domain wall nucleation process is crucial for
spin-based emerging technologies ranging from random-access and storage-class
memories over domain-wall logic concepts to nanomagnetic logic. In this work,
focused Ga+ ion-irradiation is investigated as an effective means to control
domain-wall nucleation in Ta/CoFeB/MgO nanostructures. We show that analogously
to He+ irradiation, it is not only possible to reduce the perpendicular
magnetic anisotropy but also to increase it significantly, enabling new,
bidirectional manipulation schemes. First, the irradiation effects are assessed
on film level, sketching an overview of the dose-dependent changes in the
magnetic energy landscape. Subsequent time-domain nucleation characteristics of
irradiated nanostructures reveal substantial increases in the anisotropy fields
but surprisingly small effects on the measured energy barriers, indicating
shrinking nucleation volumes. Spatial control of the domain wall nucleation
point is achieved by employing focused irradiation of pre-irradiated magnets,
with the diameter of the introduced circular defect controlling the coercivity.
Special attention is given to the nucleation mechanisms, changing from a
Stoner-Wohlfarth particle's coherent rotation to depinning from an anisotropy
gradient. Dynamic micromagnetic simulations and related measurements are used
in addition to model and analyze this depinning-dominated magnetization
reversal
RG-improved single-particle inclusive cross sections and forward-backward asymmetry in production at hadron colliders
We use techniques from soft-collinear effective theory (SCET) to derive
renormalization-group improved predictions for single-particle inclusive (1PI)
observables in top-quark pair production at hadron colliders. In particular, we
study the top-quark transverse-momentum and rapidity distributions, the
forward-backward asymmetry at the Tevatron, and the total cross section at
NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed
order. We also perform a detailed analysis of power corrections to the leading
terms in the threshold expansion of the partonic hard-scattering kernels. We
conclude that, although the threshold expansion in 1PI kinematics is
susceptible to numerically significant power corrections, its predictions for
the total cross section are in good agreement with those obtained by
integrating the top-pair invariant-mass distribution in pair invariant-mass
kinematics, as long as a certain set of subleading terms appearing naturally
within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table
Association of growth with neurodevelopment in extremely low gestational age infants: a population-based analysis.
To assess the association between postnatal growth and neurodevelopment at the age of 2 years in extremely low gestational age newborns (ELGAN, < 28 weeks' gestation). Retrospective population-based cohort study including all live born ELGAN in 2006-2012 in Switzerland. Growth parameters (weight, length, head circumference, body mass index) were assessed at birth, at hospital discharge home, and 2-year follow-up (FU2). Unadjusted and adjusted regression models assessed associations between growth (birth to hospital discharge and birth to FU2) and neurodevelopment at FU2. A total of 1244 infants (mean GA 26.5 ± 1.0 weeks, birth weight 853 ± 189 g) survived to hospital discharge and were included in the analyses. FU2 was documented for 1049 (84.3%) infants. The mean (± SD) mental and a psychomotor development index at 2FU were 88.9 (± 18.0) and 86.9 (± 17.7), respectively. Moderate or severe neurodevelopmental impairment was documented in 23.2% of patients. Changes of z-scores between birth and discharge and between birth and FU2 for weight were - 1.06 (± 0.85) and - 0.140 (± 1.15), for length - 1.36 (± 1.34), and - 0.40 (± 1.33), for head circumference - 0.61 (± 1.04) and - 0.76 (± 1.32) as well as for BMI 0.22 (± 3.36) and - 0.006 (± 1.45). Unadjusted and adjusted analyses showed that none of the four growth parameters was significantly associated with any of the three outcome parameters of neurodevelopment. This was consistent for both time intervals.
CONCLUSION
In the present population-based cohort of ELGAN, neither growth between birth and hospital discharge nor between birth and FU2 were significantly associated with neurodevelopment at age of 2 years.
WHAT IS KNOWN
• Studies assessing the association between growth and neurodevelopment in extremely low gestational age newborns (28 weeks' gestation) show conflicting results.
WHAT IS NEW
• Neither growth between birth and hospital discharge nor between birth and corrected age of 2 years were significantly associated with neurodevelopment at age of 2 years. • The role of postnatal growth as a predictor of neurodevelopmental outcome during infancy might be smaller than previously assumed
Bacterial tolerance to host-exuded specialized metabolites structures the maize root microbiome.
Plants exude specialized metabolites from their roots, and these compounds are known to structure the root microbiome. However, the underlying mechanisms are poorly understood. We established a representative collection of maize root bacteria and tested their tolerance against benzoxazinoids (BXs), the dominant specialized and bioactive metabolites in the root exudates of maize plants. In vitro experiments revealed that BXs inhibited bacterial growth in a strain- and compound-dependent manner. Tolerance against these selective antimicrobial compounds depended on bacterial cell wall structure. Further, we found that native root bacteria isolated from maize tolerated the BXs better compared to nonhost Arabidopsis bacteria. This finding suggests the adaptation of the root bacteria to the specialized metabolites of their host plant. Bacterial tolerance to 6-methoxy-benzoxazolin-2-one (MBOA), the most abundant and selective antimicrobial metabolite in the maize rhizosphere, correlated significantly with the abundance of these bacteria on BX-exuding maize roots. Thus, strain-dependent tolerance to BXs largely explained the abundance pattern of bacteria on maize roots. Abundant bacteria generally tolerated MBOA, while low abundant root microbiome members were sensitive to this compound. Our findings reveal that tolerance to plant specialized metabolites is an important competence determinant for root colonization. We propose that bacterial tolerance to root-derived antimicrobial compounds is an underlying mechanism determining the structure of host-specific microbial communities