20,215 research outputs found
Exploration of the MSSM with Non-Universal Higgs Masses
We explore the parameter space of the minimal supersymmetric extension of the
Standard Model (MSSM), allowing the soft supersymmetry-breaking masses of the
Higgs multiplets, m_{1,2}, to be non-universal (NUHM). Compared with the
constrained MSSM (CMSSM) in which m_{1,2} are required to be equal to the soft
supersymmetry-breaking masses m_0 of the squark and slepton masses, the Higgs
mixing parameter mu and the pseudoscalar Higgs mass m_A, which are calculated
in the CMSSM, are free in the NUHM model. We incorporate accelerator and dark
matter constraints in determining allowed regions of the (mu, m_A), (mu, M_2)
and (m_{1/2}, m_0) planes for selected choices of the other NUHM parameters. In
the examples studied, we find that the LSP mass cannot be reduced far below its
limit in the CMSSM, whereas m_A may be as small as allowed by LEP for large tan
\beta. We present in Appendices details of the calculations of
neutralino-slepton, chargino-slepton and neutralino-sneutrino coannihilation
needed in our exploration of the NUHM.Comment: 92 pages LaTeX, 32 eps figures, final version, some changes to
figures pertaining to the b to s gamma constrain
Scalar Mass Bounds in Two Supersymmetric Extended Electroweak Gauge Models
In two recently proposed supersymmetric extended electroweak gauge models,
the reduced Higgs sector at the 100-GeV energy scale consists of only two
doublets, but they have quartic scalar couplings different from those of the
minimal supersymmetric standard model. In the SU(2) X SU(2) X U(1) model, there
is an absolute upper bound of about 145 GeV on the mass of the lightest neutral
scalar boson. In the SU(3) X U(1) model, there is only a parameter-dependent
upper bound which formally goes to infinity in a particular limitComment: 9 pages (6 figures not included), UCRHEP-T128 (July 1994
Numerical evaluation of one-loop QCD amplitudes
We present the publicly available program NGluon allowing the numerical
evaluation of primitive amplitudes at one-loop order in massless QCD. The
program allows the computation of one-loop amplitudes for an arbitrary number
of gluons. The focus of the present article is the extension to one-loop
amplitudes including an arbitrary number of massless quark pairs. We discuss in
detail the algorithmic differences to the pure gluonic case and present cross
checks to validate our implementation. The numerical accuracy is investigated
in detail.Comment: Talk given at ACAT 2011 conference in London, 5-9 Septembe
Recommended from our members
Bacterial pathogens and resistance causing community acquired paediatric bloodstream infections in low- and middle-income countries: a systematic review and meta-analysis
Background
Despite a high mortality rate in childhood, there is limited evidence on the causes and outcomes of paediatric bloodstream infections from low- and middle-income countries (LMICs). We conducted a systematic review and meta-analysis to characterize the bacterial causes of paediatric bloodstream infections in LMICs and their resistance profile.
Methods
We searched Pubmed and Embase databases between January 1st 1990 and October 30th 2019, combining MeSH and free-text terms for âsepsisâ and âlow-middle-income countriesâ in children. Two reviewers screened articles and performed data extraction to identify studies investigating children (1âmonth-18âyears), with at least one blood culture. The main outcomes of interests were the rate of positive blood cultures, the distribution of bacterial pathogens, the resistance patterns and the case-fatality rate. The proportions obtained from each study were pooled using the Freeman-Tukey double arcsine transformation, and a random-effect meta-analysis model was used.
Results
We identified 2403 eligible studies, 17 were included in the final review including 52,915 children (11 in Africa and 6 in Asia). The overall percentage of positive blood culture was 19.1% [95% CI: 12.0â27.5%]; 15.5% [8.4â24.4%] in Africa and 28.0% [13.2â45.8%] in Asia. A total of 4836 bacterial isolates were included in the studies; 2974 were Gram-negative (63.9% [52.2â74.9]) and 1858 were Gram-positive (35.8% [24.9â47.5]). In Asia, Salmonella typhi (26.2%) was the most commonly isolated pathogen, followed by Staphylococcus aureus (7.7%) whereas in Africa, S. aureus (17.8%) and Streptococcus pneumoniae (16.8%) were predominant followed by Escherichia coli (10.7%). S. aureus was more likely resistant to methicillin in Africa (29.5% vs. 7.9%), whereas E. coli was more frequently resistant to third-generation cephalosporins (31.2% vs. 21.2%), amikacin (29.6% vs. 0%) and ciprofloxacin (36.7% vs. 0%) in Asia. The overall estimate for case-fatality rate among 8 studies was 12.7% [6.6â20.2%]. Underlying conditions, such as malnutrition or HIV infection were assessed as a factor associated with bacteraemia in 4 studies each.
Conclusions
We observed a marked variation in pathogen distribution and their resistance profiles between Asia and Africa. Very limited data is available on underlying risk factors for bacteraemia, patterns of treatment of multidrug-resistant infections and predictors of adverse outcomes
B-Meson Observables in the Maximally CP-Violating MSSM with Minimal Flavour Violation
Additional sources of CP violation in the MSSM may affect B-meson mixings and
decays, even in scenarios with minimal flavour violation (MFV). We formulate
the maximally CP-violating and minimally flavour-violating (MCPMFV) variant of
the MSSM, which has 19 parameters, including 6 phases that violate CP. We then
develop a manifestly flavour-covariant effective Lagrangian formalism for
calculating Higgs-mediated FCNC observables in the MSSM at large tan(beta), and
analyze within the MCPMFV framework FCNC and other processes involving B
mesons. We include a new class of dominant subleading contributions due to
non-decoupling effects of the third-generation quarks. We present illustrative
numerical results that include effects of the CP-odd MCPMFV parameters on Higgs
and sparticle masses, the B_s and B_d mass differences, and on the decays B_s
--> mu+ mu-, B_u --> tau nu and b --> s gamma. We use these results to derive
illustrative constraints on the MCPMFV parameters imposed by D0, CDF, BELLE and
BABAR measurements of B mesons, demonstrating how a potentially observable
contribution to the CP asymmetry in the b --> s gamma decay may arise in the
MSSM with MCPMFV.Comment: 47 pages, 8 eps figures, comments and references added, accepted for
publication in Physical Review D, Eq.(3.2) correcte
Direct Detection of Dark Matter in the MSSM with Non-Universal Higgs Masses
We calculate dark matter scattering rates in the minimal supersymmetric
extension of the Standard Model (MSSM), allowing the soft
supersymmetry-breaking masses of the Higgs multiplets, m_{1,2}, to be
non-universal (NUHM). Compared with the constrained MSSM (CMSSM) in which
m_{1,2} are required to be equal to the soft supersymmetry-breaking masses m_0
of the squark and slepton masses, we find that the elastic scattering cross
sections may be up to two orders of magnitude larger than values in the CMSSM
for similar LSP masses. We find the following preferred ranges for the
spin-independent cross section: 10^{-6} pb \ga \sigma_{SI} \ga 10^{-10} pb, and
for the spin-dependent cross section: 10^{-3} pb \ga \sigma_{SD}, with the
lower bound on \sigma_{SI} dependent on using the putative constraint from the
muon anomalous magnetic moment. We stress the importance of incorporating
accelerator and dark matter constraints in restricting the NUHM parameter
space, and also of requiring that no undesirable vacuum appear below the GUT
scale. In particular, values of the spin-independent cross section another
order of magnitude larger would appear to be allowed, for small \tan \beta, if
the GUT vacuum stability requirement were relaxed, and much lower cross-section
values would be permitted if the muon anomalous magnetic moment constraint were
dropped.Comment: 30 pages LaTeX, 40 eps figure
Waves on Noncommutative Spacetime and Gamma-Ray Bursts
Quantum group Fourier transform methods are applied to the study of processes
on noncommutative Minkowski spacetime . A natural
wave equation is derived and the associated phenomena of {\it in vacuo}
dispersion are discussed. Assuming the deformation scale is of the
order of the Planck length one finds that the dispersion effects are large
enough to be tested in experimental investigations of astrophysical phenomena
such as gamma-ray bursts. We also outline a new approach to the construction of
field theories on the noncommutative spacetime, with the noncommutativity
equivalent under Fourier transform to non-Abelianness of the `addition law' for
momentum in Feynman diagrams. We argue that CPT violation effects of the type
testable using the sensitive neutral-kaon system are to be expected in such a
theory.Comment: 25 page
Time-Dependent Vacuum Energy Induced by D-Particle Recoil
We consider cosmology in the framework of a `material reference system' of D
particles, including the effects of quantum recoil induced by closed-string
probe particles. We find a time-dependent contribution to the cosmological
vacuum energy, which relaxes to zero as for large times . If
this energy density is dominant, the Universe expands with a scale factor . We show that this possibility is compatible with recent
observational constraints from high-redshift supernovae, and may also respect
other phenomenological bounds on time variation in the vacuum energy imposed by
early cosmology.Comment: 14 pages LATEX, no figure
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