2,206 research outputs found
The exclusive rare decays B -> K l(bar) l and B_c -> D(D*) l(bar) l in a relativistic quark model
We study the exclusive rare decay B -> K l(bar) l. We calculate the relevant
form factors within a relativistic constituent quark model, for the first time
without employing the impulse approximation. The calculated form factors are
used to evaluate differential decay rates and polarization observables. We
present results on the q2-dependence of a set of observables with and without
long-distance contributions. A similar analysis is done for the exclusive rare
decays B_c -> D (D*) l(bar) l with special emphasis on the cascade decay B_c ->
D* (-> D pi) l(bar) l. We derive a four-fold angular decay distribution for
this process in terms of helicity amplitudes including lepton mass effects. The
four-fold angular decay distribution allows to define a number of physical
observables which are amenable to measurement. We compare our results with the
results of other studies.Comment: 28 pages, 12 figure
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Tumor necrosis factor-alpha regulates the expression of inducible costimulator receptor ligand on CD34+ progenitor cells during differentiation into antigen presenting cells
The inducible costimulator receptor (ICOS) is a third member of the CD28 receptor family that regulates T cell activation and function. ICOS binds to a newly identified ligand on antigen presenting cells different from the CD152 ligands CD80 and CD86. We used soluble ICOSIg and a newly developed murine anti-human ICOS ligand (ICOSL) monoclonal antibody to further characterize the ICOSL during ontogeny of antigen presenting cells. In a previous study, we found that ICOSL is expressed on monocytes, dendritic cells, and B cells. To define when ICOSL is first expressed on myeloid antigen presenting cells, we examined ICOSL expression on CD34 cells in bone marrow. We found that CD34bright cells regardless of their myeloid commitment were ICOSL , whereas ICOSL was first expressed when CD34 expression diminished and the myeloid marker CD33 appeared
Amplitude analysis of hadron decays
We provide succinct covariant amplitude decompositions of 2-body weak
hadronic decays, with which to compare data, including exclusive rates,
helicity amplitudes and polarizations. For weak decays, the systematic
dependence of these amplitudes on masses and quantum numbers of participating
particles are determined within a factor of about two by the CKM angles and the
Fermi constant so theoretical models need to be much more accurate if they are
to be convincing.Comment: 31 pages, RevTe
Semi-naive dimensional renormalization
We propose a treatment of in dimensional regularization which is
based on an algebraically consistent extension of the Breitenlohner-Maison-'t
Hooft-Veltman (BMHV) scheme; we define the corresponding minimal
renormalization scheme and show its equivalence with a non-minimal BMHV scheme.
The restoration of the chiral Ward identities requires the introduction of
considerably fewer finite counterterms than in the BMHV scheme. This scheme is
the same as the minimal naive dimensional renormalization in the case of
diagrams not involving fermionic traces with an odd number of , but
unlike the latter it is a consistent scheme. As a simple example we apply our
minimal subtraction scheme to the Yukawa model at two loops in presence of
external gauge fields.Comment: 28 pages, 3 figure
Perspectives of Nuclear Physics in Europe: NuPECC Long Range Plan 2010
The goal of this European Science Foundation Forward Look into the future of Nuclear Physics is to bring together
the entire Nuclear Physics community in Europe to formulate a coherent plan of the best way to develop the field in
the coming decade and beyond.<p></p>
The primary aim of Nuclear Physics is to understand the origin, evolution, structure and phases of strongly interacting matter, which constitutes nearly 100% of the visible matter in the universe. This is an immensely important and challenging task that requires the concerted effort of scientists working in both theory and experiment, funding agencies, politicians and the public.<p></p>
Nuclear Physics projects are often “big science”, which implies large investments and long lead times. They need careful forward planning and strong support from policy makers. This Forward Look provides an excellent tool to achieve this. It represents the outcome of detailed scrutiny by Europe’s leading experts and will help focus the views of the scientific community on the most promising directions in the field and create the basis for funding agencies to provide adequate support.<p></p>
The current NuPECC Long Range Plan 2010 “Perspectives of Nuclear Physics in Europe” resulted from consultation
with close to 6 000 scientists and engineers over a period of approximately one year. Its detailed recommendations
are presented on the following pages. For the interested public, a short summary brochure has been produced to
accompany the Forward Look.<p></p>
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Overcoming the slowing down of flat-histogram Monte Carlo simulations: Cluster updates and optimized broad-histogram ensembles
We study the performance of Monte Carlo simulations that sample a broad histogram in energy by determining the mean first-passage time to span the entire energy space of d-dimensional ferromagnetic Ising/Potts models. We first show that flat-histogram Monte Carlo methods with single-spin flip updates such as the Wang-Landau algorithm or the multicanonical method perform suboptimally in comparison to an unbiased Markovian random walk in energy space. For the d=1, 2, 3 Ising model, the mean first-passage time τ scales with the number of spins N=Ld as τ∝N2Lz. The exponent z is found to decrease as the dimensionality d is increased. In the mean-field limit of infinite dimensions we find that z vanishes up to logarithmic corrections. We then demonstrate how the slowdown characterized by z\u3e0 for finite d can be overcome by two complementary approaches—cluster dynamics in connection with Wang-Landau sampling and the recently developed ensemble optimization technique. Both approaches are found to improve the random walk in energy space so that τ∝N2 up to logarithmic corrections for the d=1, 2 Ising model
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