796 research outputs found
Proposals for Bottom Quark/Squark Renormalization in the Complex MSSM
We present a consistent renormalization of the top and bottom quark/squark
sector of the MSSM with complex parameters (cMSSM). Various renormalization
schemes are defined, analyzed analytically and tested numerically in the decays
Stop_2 -> Sbot_i H+/W+ (i = 1,2). No scheme is found that produces numerically
acceptable results over all the cMSSM parameter space, where problems occur
mostly already for real parameters. Two schemes are identified that show the
most robust behavior. A numerical analysis of the four partial stop decay
widths is performed in our "preferred" scheme, "m_b, A_b DRbar". The full
one-loop corrections to the corresponding partial decay widths are evaluated
including hard QED and QCD radiation. We find mostly modest corrections at the
one-loop level.Comment: 47 pages, 12 figure
Precision calculations for h->WW/ZZ->4 fermions in the Two-Higgs-Doublet Model with PROPHECY4F
We have calculated the next-to-leading-order electroweak and QCD corrections
to the decay processes h -> WW/ZZ -> 4 fermions of the light CP-even Higgs
boson h of various types of Two-Higgs-Doublet Models (Types I and II,
"lepton-specific" and "flipped" models). The input parameters are defined in
four different renormalization schemes, where parameters that are not directly
accessible by experiments are defined in the MSbar scheme. Numerical results
are presented for the corrections to partial decay widths for various benchmark
scenarios previously motivated in the literature, where we investigate the
dependence on the MSbar renormalization scale and on the choice of the
renormalization scheme in detail. We find that it is crucial to be precise with
these issues in parameter analyses, since parameter conversions between
different schemes can involve sizeable or large corrections, especially in
scenarios that are close to experimental exclusion limits or theoretical
bounds. It even turns out that some renormalization schemes are not applicable
in specific regions of parameter space. Our investigation of differential
distributions shows that corrections beyond the Standard Model are mostly
constant offsets induced by the mixing between the light and heavy CP-even
Higgs bosons, so that differential analyses of h -> 4f decay observables do not
help to identify Two-Higgs-Doublet Models. Moreover, the decay widths do not
significantly depend on the specific type of those models. The calculations are
implemented in the public Monte Carlo generator PROPHECY4F and ready for
application.Comment: 56 pages, 39 figure
Renormalization schemes for the Two-Higgs-Doublet Model and applications to h -> WW/ZZ -> 4fermions
We perform the renormalization of different types of Two-Higgs-Doublet Models
for the calculation of observables at next-to-leading order. In detail, we
suggest four different renormalization schemes based on on-shell
renormalization conditions as far as possible and on MSbar prescriptions for
the remaining field-mixing parameters where no distinguished on-shell condition
exists and make contact to existing schemes in the literature. In particular,
we treat the tadpole diagrams in different ways and discuss issues of gauge
independence and perturbative stability in the considered schemes. The
renormalization group equations for the MSbar parameters are solved in each
scheme, so that a consistent renormalization scale variation can be performed.
We have implemented all Feynman rules including counterterms and the
renormalization conditions into a FeynArts model file, so that amplitudes and
squared matrix elements can be generated automatically. As an application we
compute the decay of the light, CP-even Higgs boson of the Two-Higgs-Doublet
Model into four fermions at next-to-leading order. The comparison of different
schemes and the investigation of the renormalization scale dependence allows us
to test the perturbative consistency in each of the renormalization schemes,
and to get a better estimate of the theoretical uncertainty that arises due to
the truncation of the perturbation series.Comment: 44 pages, 8 figures, revised version, to appear in JHE
Dynamics of Strongly Deformed Polymers in Solution
Bead spring models for polymers in solution are nonlinear if either the
finite extensibility of the polymer, excluded volume effects or hydrodynamic
interactions between polymer segments are taken into account. For such models
we use a powerful method for the determination of the complete relaxation
spectrum of fluctuations at {\it steady state}. In general, the spectrum and
modes differ significantly from those of the linear Rouse model. For a tethered
polymer in uniform flow the differences are mainly caused by an inhomogeneous
distribution of tension along the chain and are most pronounced due to the
finite chain extensibility. Beyond the dynamics of steady state fluctuations we
also investigate the nonlinear response of the polymer to a {\em large sudden
change} in the flow. This response exhibits several distinct regimes with
characteristic decay laws and shows features which are beyond the scope of
single mode theories such as the dumbbell model.Comment: 7 pages, 3 figure
Supersymmetric Higgs Production in Vector-Boson Fusion
We present a full calculation of the supersymmetric NLO corrections to Higgs
boson production via vector-boson fusion. The supersymmetric QCD corrections
turn out to be significantly smaller than the electroweak ones. These
higher-order corrections are an important ingredient to a precision analysis of
the Higgs sector at the LHC.Comment: 6 pages; talk given at RADCOR 2009 - 9th International Symposium on
Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology), October 25 - 30 2009, Ascona, Switzerland, v2: reference
adde
Detection of risk factors for obesity in early childhood with quantile regression methods for longitudinal data
This article compares and discusses three different statistical methods for investigating risk factors for overweight and obesity in early childhood by means of the LISA study, a recent German birth cohort study with 3097 children. Since the definition of overweight and obesity is typically based on upper quantiles (90% and 97%) of the age specific body mass index (BMI) distribution, our aim was to model the influence of risk factors and age on these quantiles while as far as possible taking the longitudinal data structure into account. The following statistical regression models were chosen: additive mixed models, generalized additive models for location, scale and shape (GAMLSS), and distribution free quantile regression models. The methods were compared empirically by cross-validation and for the data at hand no model could be rated superior. Motivated by previous studies we explored whether there is an age-specific skewness of the BMI distribution. The investigated data does not suggest such an effect, even after adjusting for risk factors. Concerning risk factors, our results mainly confirm results obtained in previous studies. From a methodological point of view, we conclude that GAMLSS and distribution free quantile regression are promising approaches for longitudinal quantile regression, requiring, however, further extensions to fully account for longitudinal data structures
- …