51 research outputs found
Charged and Pseudoscalar Higgs production at a Muon Collider
We consider single charged Higgs () and pseudoscalar Higgs ()
production in association with a gauge boson at colliders. We find
that the tree-level t-channel and s-channel contributions to are enhanced for large values of , allowing
sizeable cross-sections whose analogies at colliders would be very
small. These processes provide attractive new ways of producing such particles
at colliders and are superior to the conventional methods in
regions of parameter space.Comment: 11 pages Latex, 5 figures, formulae added in sections 2.2 and 2.3,
extra discussion in section 2.3, references adde
Associated charged Higgs and W boson production in the MSSM at the CERN Large Hadron Collider
We investigate the viability of observing charged Higgs bosons (H^+/-)
produced in association with W bosons at the CERN Large Hadron Collider, using
the leptonic decay H^+ -> tau^+ nu_tau and hadronic W-decay, within different
scenarios of the Minimal Supersymmetric Standard Model (MSSM) with both real
and complex parameters. Performing a parton level study we show how the
irreducible Standard Model background from W+2 jets can be controlled by
applying appropriate cuts and find that the size of a possible signal depends
on the cuts needed to suppress QCD backgrounds and misidentifications. In the
standard maximal mixing scenario of the MSSM we find a viable signal for large
tan(beta) and intermediate H^+/- masses (~m_t) when using optimistic cuts
whereas for more pessimistic ones we only find a viable signal for very large
tan(beta) (>~50). We have also investigated a special class of MSSM scenarios
with large mass-splittings among the heavy Higgs bosons where the cross-section
can be resonantly enhanced by factors up to one hundred, with a strong
dependence on the CP-violating phases. Even so we find that the signal after
cuts remains small except for small masses (~< m_t) with optimistic cuts.
Finally, in all the scenarios we have investigated we have only found small
CP-asymmetries.Comment: 28 pages, 12 figures, version to appear in Euro. Phys. J.
Higgs-Boson Production Induced by Bottom Quarks
Bottom quark-induced processes are responsible for a large fraction of the
LHC discovery potential, in particular for supersymmetric Higgs bosons.
Recently, the discrepancy between exclusive and inclusive Higgs boson
production rates has been linked to the choice of an appropriate bottom
factorization scale. We investigate the process kinematics at hadron colliders
and show that it leads to a considerable decrease in the bottom factorization
scale. This effect is the missing piece needed to understand the corresponding
higher order results. Our results hold generally for charged and for neutral
Higgs boson production at the LHC as well as at the Tevatron. The situation is
different for single top quark production, where we find no sizeable
suppression of the factorization scale. Turning the argument around, we can
specify how large the collinear logarithms are, which can be resummed using the
bottom parton picture.Comment: 18 page
Supersymmetric Electroweak Corrections to Charged Higgs Boson Production in Association with a Top Quark at Hadron Colliders
We calculate the and supersymmetric electroweak corrections to the cross section
for the charged Higgs boson production in association with a top quark at the
Tevatron and the LHC. These corrections arise from the quantum effects which
are induced by potentially large Yukawa couplings from the Higgs sector and the
chargino-top(bottom)-sbottom(stop) couplings,
neutralino-top(bottom)-stop(sbottom) couplings and charged Higgs-stop-sbottom
couplings. They can decrease or increase the cross section depending on
but are not very sensitive to the mass of the charged Higgs boson
for high . At low the corrections decrease the total
cross sections significantly, which exceed -12% for below
at both the Tevatron and the LHC, but for the
corrections can become very small at the LHC. For high
these corrections can decrease or increase the total cross sections, and the
magnitude of the corrections are at most a few percent at both the Tevatron and
the LHC.Comment: 28 pages including 4 eps figure
Charged Higgs Boson Production in Bottom-Gluon Fusion
We compute the complete next-to-leading order SUSY-QCD corrections for the
associated production of a charged Higgs boson with a top quark via
bottom-gluon fusion. We investigate the applicability of the bottom parton
description in detail. The higher order corrections can be split into real and
virtual corrections for a general two Higgs doublet model and into additional
massive supersymmetric loop contributions. We find that the perturbative
behavior is well under control. The supersymmetric contributions consist of the
universal bottom Yukawa coupling corrections and non-factorizable diagrams.
Over most of the relevant supersymmetric parameter space the Yukawa coupling
corrections are sizeable, while the remaining supersymmetric loop contributions
are negligible.Comment: 18 pages, v2: some discussions added, v3: published versio
Prospects for heavy supersymmetric charged Higgs boson searches at hadron colliders
We investigate the production of a heavy charged Higgs boson at hadron
colliders within the context of the MSSM. A detailed study is performed for all
important production modes and basic background processes for the
t\bar{t}b\bar{b} signature. In our analysis we include effects of initial and
final state showering, hadronization, and principal detector effects. For the
signal production rate we include the leading SUSY quantum effects at high
\tan\beta>~ mt/mb. Based on the obtained efficiencies for the signal and
background we estimate the discovery and exclusion mass limits of the charged
Higgs boson at high values of \tan\beta. At the upgraded Tevatron the discovery
of a heavy charged Higgs boson (MH^+ >~ 200 GeV) is impossible for the
tree-level cross-section values. However, if QCD and SUSY effects happen to
reinforce mutually, there are indeed regions of the MSSM parameter space which
could provide 3\sigma evidence and, at best, 5\sigma charged Higgs boson
discovery at the Tevatron for masses M_H^+<~ 300 GeV and M_H^+<~ 250 GeV,
respectively, even assuming squark and gluino masses in the (500-1000) GeV
range. On the other hand, at the LHC one can discover a H^+ as heavy as 1 TeV
at the canonical confidence level of 5\sigma; or else exclude its existence at
95% C.L. up to masses ~ 1.5 TeV. Again the presence of SUSY quantum effects can
be very important here as they may shift the LHC limits by a few hundred GeV.Comment: Latex2e, 44 pages, 15 figures, 6 tables, uses JHEP3.sty, axodraw.sty.
Comments added. Discussion on QCD factors clarified. Added discussion on
uncertainties. Change of presentation of Tables 4 and 5 and Fig.6. Results
and conclusions unchanged. Version accepted in JHE
Isospin dependence of electromagnetic transition strengths among an isobaric triplet
Electric quadrupole matrix elements, M, for the J=2→0, ΔT=0, T=1 transitions across the A=46 isobaric multiplet Cr-V-Ti have been measured at GSI with the FRS-LYCCA-AGATA setup. This allows direct insight into the isospin purity of the states of interest by testing the linearity of M with respect to T. Pairs of nuclei in the T=1 triplet were studied using identical reaction mechanisms in order to control systematic errors. The M values were obtained with two different methodologies: (i) a relativistic Coulomb excitation experiment was performed for Cr and Ti; (ii) a “stretched target” technique was adopted here, for the first time, for lifetime measurements in V and Ti. A constant value of M across the triplet has been observed. Shell-model calculations performed within the fp shell fail to reproduce this unexpected trend, pointing towards the need of a wider valence space. This result is confirmed by the good agreement with experimental data achieved with an interaction which allows excitations from the underlying sd shell. A test of the linearity rule for all published data on complete T=1 isospin triplets is presented.Peer Reviewe
Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990-2015: A systematic analysis for the Global Burden of Disease Study 2015
Background: The Global Burden of Diseases, Injuries, and Risk Factors Study 2015 provides an up-to-date synthesis of the evidence for risk factor exposure and the attributable burden of disease. By providing national and subnational assessments spanning the past 25 years, this study can inform debates on the importance of addressing risks in context.
Methods: We used the comparative risk assessment framework developed for previous iterations of the Global Burden of Disease Study to estimate attributable deaths, disability-adjusted life-years (DALYs), and trends in exposure by age group, sex, year, and geography for 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks from 1990 to 2015. This study included 388 risk-outcome pairs that met World Cancer Research Fund-defined criteria for convincing or probable evidence. We extracted relative risk and exposure estimates from randomised controlled trials, cohorts, pooled cohorts, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. We developed a metric that allows comparisons of exposure across risk factors—the summary exposure value. Using the counterfactual scenario of theoretical minimum risk level, we estimated the portion of deaths and DALYs that could be attributed to a given risk. We decomposed trends in attributable burden into contributions from population growth, population age structure, risk exposure, and risk-deleted cause-specific DALY rates. We characterised risk exposure in relation to a Socio-demographic Index (SDI).
Findings: Between 1990 and 2015, global exposure to unsafe sanitation, household air pollution, childhood underweight, childhood stunting, and smoking each decreased by more than 25%. Global exposure for several occupational risks, high body-mass index (BMI), and drug use increased by more than 25% over the same period. All risks jointly evaluated in 2015 accounted for 57·8% (95% CI 56·6–58·8) of global deaths and 41·2% (39·8–42·8) of DALYs. In 2015, the ten largest contributors to global DALYs among Level 3 risks were high systolic blood pressure (211·8 million [192·7 million to 231·1 million] global DALYs), smoking (148·6 million [134·2 million to 163·1 million]), high fasting plasma glucose (143·1 million [125·1 million to 163·5 million]), high BMI (120·1 million [83·8 million to 158·4 million]), childhood undernutrition (113·3 million [103·9 million to 123·4 million]), ambient particulate matter (103·1 million [90·8 million to 115·1 million]), high total cholesterol (88·7 million [74·6 million to 105·7 million]), household air pollution (85·6 million [66·7 million to 106·1 million]), alcohol use (85·0 million [77·2 million to 93·0 million]), and diets high in sodium (83·0 million [49·3 million to 127·5 million]). From 1990 to 2015, attributable DALYs declined for micronutrient deficiencies, childhood undernutrition, unsafe sanitation and water, and household air pollution; reductions in risk-deleted DALY rates rather than reductions in exposure drove these declines. Rising exposure contributed to notable increases in attributable DALYs from high BMI, high fasting plasma glucose, occupational carcinogens, and drug use. Environmental risks and childhood undernutrition declined steadily with SDI; low physical activity, high BMI, and high fasting plasma glucose increased with SDI. In 119 countries, metabolic risks, such as high BMI and fasting plasma glucose, contributed the most attributable DALYs in 2015. Regionally, smoking still ranked among the leading five risk factors for attributable DALYs in 109 countries; childhood underweight and unsafe sex remained primary drivers of early death and disability in much of sub-Saharan Africa.
Interpretation: Declines in some key environmental risks have contributed to declines in critical infectious diseases. Some risks appear to be invariant to SDI. Increasing risks, including high BMI, high fasting plasma glucose, drug use, and some occupational exposures, contribute to rising burden from some conditions, but also provide opportunities for intervention. Some highly preventable risks, such as smoking, remain major causes of attributable DALYs, even as exposure is declining. Public policy makers need to pay attention to the risks that are increasingly major contributors to global burden.
Funding: Bill & Melinda Gates Foundation
Erratum: Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017
Interpretation: By quantifying levels and trends in exposures to risk factors and the resulting disease burden, this assessment offers insight into where past policy and programme efforts might have been successful and highlights current priorities for public health action. Decreases in behavioural, environmental, and occupational risks have largely offset the effects of population growth and ageing, in relation to trends in absolute burden. Conversely, the combination of increasing metabolic risks and population ageing will probably continue to drive the increasing trends in non-communicable diseases at the global level, which presents both a public health challenge and opportunity. We see considerable spatiotemporal heterogeneity in levels of risk exposure and risk-attributable burden. Although levels of development underlie some of this heterogeneity, O/E ratios show risks for which countries are overperforming or underperforming relative to their level of development. As such, these ratios provide a benchmarking tool to help to focus local decision making. Our findings reinforce the importance of both risk exposure monitoring and epidemiological research to assess causal connections between risks and health outcomes, and they highlight the usefulness of the GBD study in synthesising data to draw comprehensive and robust conclusions that help to inform good policy and strategic health planning
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