3,429 research outputs found
The supersymmetric Higgs sector and B-Bbar mixing for large tan beta
We match the Higgs sector of the most general flavour breaking and CP
violating minimal supersymmetric standard model (MSSM) onto a generic
two-Higgs-doublet model, paying special attention to the definition of tan beta
in the effective theory. In particular no tan beta-enhanced loop corrections
appear in the relation to tan beta defined in the DRbar scheme in the MSSM. The
corrections to the Higgs-mediated flavour-changing amplitudes which result from
this matching are especially relevant for the B_d and B_s mass differences
dM_s,d for minimal flavour violation, where the superficially leading
contribution vanishes. We give a symmetry argument to explain this cancellation
and perform a systematic study of all Higgs-mediated effects, including Higgs
loops. The corrections to dM_s are at most 7% for mu>0 and M_A < 600 if
constraints from other observables are taken into account. For mu<0 they can be
larger, but are always less than about 20%. Contrary to recent claims we do not
find numerically large contributions here, nor do we find any tan beta-enhanced
contributions from loop corrections to the Higgs potential in B^+ -> tau^+ nu
or B -> X_s gamma. We further update supersymmetric loop corrections to the
Yukawa couplings, where we include all possible CP-violating phases and correct
errors in the literature. The possible presence of CP-violating phases
generated by Higgs exchange diagrams is briefly discussed as well. Finally we
provide improved values for the bag factors P^VLL_1, P^LR_2, and P^SLL_1 at the
electroweak scale.Comment: 61 page
A priori convergence estimates for a rough Poisson-Dirichlet problem with natural vertical boundary conditions
Stents are medical devices designed to modify blood flow in aneurysm sacs, in
order to prevent their rupture. Some of them can be considered as a locally
periodic rough boundary. In order to approximate blood flow in arteries and
vessels of the cardio-vascular system containing stents, we use multi-scale
techniques to construct boundary layers and wall laws. Simplifying the flow we
turn to consider a 2-dimensional Poisson problem that conserves essential
features related to the rough boundary. Then, we investigate convergence of
boundary layer approximations and the corresponding wall laws in the case of
Neumann type boundary conditions at the inlet and outlet parts of the domain.
The difficulty comes from the fact that correctors, for the boundary layers
near the rough surface, may introduce error terms on the other portions of the
boundary. In order to correct these spurious oscillations, we introduce a
vertical boundary layer. Trough a careful study of its behavior, we prove
rigorously decay estimates. We then construct complete boundary layers that
respect the macroscopic boundary conditions. We also derive error estimates in
terms of the roughness size epsilon either for the full boundary layer
approximation and for the corresponding averaged wall law.Comment: Dedicated to Professor Giovanni Paolo Galdi 60' Birthda
Next-to-leading order QCD corrections to Z boson pair production via vector-boson fusion
Vector-boson fusion processes are an important tool for the study of
electroweak symmetry breaking at hadron colliders, since they allow to
distinguish a light Higgs boson scenario from strong weak boson scattering. We
here consider the channels WW->ZZ and ZZ->ZZ as part of electroweak Z boson
pair production in association with two tagging jets. We present the
calculation of the NLO QCD corrections to the cross sections for p p -> e+ e-
mu+ mu- + 2 jets and p p -> e+ e- nu_mu nubar_mu + 2 jets via vector-boson
fusion at order alpha_s alpha^6, which is performed in the form a NLO
parton-level Monte Carlo program. The corrections to the integrated cross
sections are found to be modest, while the shapes of some kinematical
distributions change appreciably at NLO. Residual scale uncertainties typically
are at the few percent level.Comment: 12 pages, 4 figure
Challenges to the development of antigen-specific breast cancer vaccines
Continued progress in the development of antigen-specific breast cancer vaccines depends on the identification of appropriate target antigens, the establishment of effective immunization strategies, and the ability to circumvent immune escape mechanisms. Methods such as T cell epitope cloning and serological expression cloning (SEREX) have led to the identification of a number target antigens expressed in breast cancer. Improved immunization strategies, such as using dendritic cells to present tumor-associated antigens to T lymphocytes, have been shown to induce antigen-specific T cell responses in vivo and, in some cases, objective clinical responses. An outcome of successful tumor immunity is the evolution of antigen-loss tumor variants. The development of a polyvalent breast cancer vaccine, directed against a panel of tumor-associated antigens, may counteract this form of immune escape
New insights into the dynamics of the glutathione-ascorbate redox system of plants
The Hallilwell-Asada-Foyer redox cascade (HAF) is viewed as a H2O2 detoxifying system with a great variety of responses against environmental changes. The functional consequences of these responses are interpreted intuitively because a systemic analysis of the inherent dynamic potential of the HAF is lacking. With the help of numerical modelling we show that in wheat roots parameter patterns are established which result in homeostatic states of HAF over a vast range of environmental changes. The reduced fractions glutathione (GSH) and ascorbate (ASC) remain on high levels even during dramatic changes in the enzyme activity ratios of glutathione reductase, dehydroascorbate reductase and ascorbat peroxidase. Necessarily their oxidised counterparts dithioglutathione (GSSG) and dehydroascorbate (DHA) stay in these buffered regions on very low concentration levels. Our modelling shows that redox ratios GSH/GSSG and ASC/DHA can be modified additionally via changes in NADPH/H2O2 ratios. Thus, the redox states of GSH and ASC can not simply be regarded as indicators for oxidative stress with respect to H2O2 levels. The involvement of the redox variables in other redox processes than the HAF reaction (redox proteome) and / or their utilisation in metabolism (protein modification, detoxification of xenobiotics) are viewed to cause system relaxations of the redox variables. The re-establishment of their homeostatic ratios follow time courses which are redox moiety specific and are balanced according to the existing parameter patterns. Despite of its detoxification function the HAF balances the glutathione / ascorbate redox state in cells according to the prevailing physiological conditions
Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint
Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc
Effect of polarized gluon distribution on spin asymmetries for neutral and charged pion production
A longitudinal double spin asymmetry for \pi^0 production has been measured
by the PHENIX collaboration. The asymmetry is sensitive to the polarized gluon
distribution and is indicated to be positive by theoretical predictions. We
study a correlation between behavior of the asymmetry and polarized gluon
distribution in neutral and charged pion production at RHIC.Comment: 7 pages, 5 eps figures, section added, typos corrected. to be
published in PR
Semileptonic weak Hamiltonian to in momentum-space subtraction schemes
The CKM unitarity precision test of the Standard Model requires a systematic
treatment of electromagnetic and strong corrections for semi-leptonic decays.
Electromagnetic corrections require the renormalization of a semileptonic
four-fermion operator. In this work we calculate the
perturbative scheme conversion between the
scheme and several momentum-space subtraction schemes, which can
also be implemented on the lattice. We consider schemes defined by MOM and SMOM
kinematics and emphasize the importance of the choice of projector for each
scheme. The conventional projector, that has been used in the literature for
MOM kinematics, generates QCD corrections to the conversion factor that do not
vanish for and which generate an artificial dependence on the
lattice matching scale that would only disappear after summing all orders of
perturbation theory. This can be traced to the violation of a Ward identity
that holds in tha limit. We show how to remedy this by judicious
choices of projector, and prove that the Wilson coefficients in those schemes
are free from pure QCD contributions. The resulting Wilson coefficients (and
operator matrix elements) have greatly reduced scale dependence. Our choice of
the scheme over the traditional -mass scheme is motivated by
the fact that, besides being more tractable at higher orders, unlike the latter
it allows for a transparent separation of scales. We exploit this to obtain
renormalization-group-improved leading-log and next-to-leading-log strong
corrections to the electromagnetic contributions and study the (QED-induced)
dependence on the lattice matching scale.Comment: 1+22 page
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