1,842 research outputs found
The spin density matrix of top quark pairs produced in electron-positron annihilation including QCD radiative corrections
We calculate the spin density matrix of top quark pairs for the reaction
to order . As an application we show
next-to-leading order results for a variety of spin observables for the
system. These include the top quark and antiquark polarizations and
spin-spin correlations as a function of the center-of-mass energy
and of the top quark scattering angle for arbitrary longitudinal polarization
of the electron/positron beam.Comment: 26 pages, 13 Postscript figures, uses REVTE
Polarization and spin correlations of top quarks at a future e+ e- linear collider
We discuss the polarization and spin correlations of top quarks produced
above threshold at a future linear collider, including QCD radiative
corrections.Comment: 11 pages (LaTeX), 16 Postscript figure. Contribution to the
International Workshop on "Symmetry and Spin", PRAHA-SPIN99, Prague, Czech
Republic, September 5 -12, 199
Effects of Higgs sector CP violation in top-quark pair production at the LHC
A striking manifestation of CP violation in the electroweak symmetry breaking
sector would be the existence of neutral Higgs boson(s) with undefined CP
parity. We analyse signatures of such a boson, with a mass of about 300 GeV or
larger, produced in high energy proton-proton collisions at LHC energies in its
top-quark antitop-quark decay channel. The large irreducible
background is taken into account. We propose, both for the dilepton and the
lepton + jets decay channels of , several correlations and asymmetries
with which (Higgs sector) CP violation can be traced. We show that for
judiciously chosen cuts on the invariant mass these CP observables
yield, for an LHC integrated luminosity of 100 , statistically
significant signals for a range of Higgs boson masses and Yukawa couplings.Comment: 36 pages, 25 Postscript figure
Exploring local quantum many-body relaxation by atoms in optical superlattices
We establish a setting - atoms in optical superlattices with period 2 - in
which one can experimentally probe signatures of the process of local
relaxation and apparent thermalization in non-equilibrium dynamics without the
need of addressing single sites. This opens up a way to explore the convergence
of subsystems to maximum entropy states in quenched quantum many-body systems
with present technology. Remarkably, the emergence of thermal states does not
follow from a coupling to an environment, but is a result of the complex
non-equilibrium dynamics in closed systems. We explore ways of measuring the
relevant signatures of thermalization in this analogue quantum simulation of a
relaxation process, exploiting the possibilities offered by optical
superlattices.Comment: 4 pages, 3 figures, version to published in Physical Review Letter
QCD Corrections to Decay Distributions of Neutral Higgs Bosons with (In)definite CP Parity
We compute the order QCD corrections to the density matrix for the
decay of a neutral Higgs boson with (in)definite CP parity into a quark
antiquark pair, respectively the QED corrections for the decay into a pair of
charged leptons. We classify and calculate single spin asymmetries and
spin-spin correlations which are generated by the scalar and pseudoscalar
Yukawa couplings. These spin effects can be traced in
and, for heavy Higgs bosons, in . We also calculate
resulting correlations among the final states and estimate, for the respective
decay modes, the number of events needed to measure the Yukawa couplings with
these correlations at the 3 sigma level.Comment: 32 pages, REVTeX, uses: psfig,amssym,aps,preprint 14 ps figure
A posteriori agreement as a quality measure for readability prediction systems
All readability research is ultimately concerned with the research question whether it is possible for a prediction system to automatically determine the level of readability of an unseen text. A significant problem for such a system is that readability might depend in part on the reader. If different readers assess the readability of texts in fundamentally different ways, there is insufficient a priori agreement to justify the correctness of a readability prediction system based on the texts assessed by those readers. We built a data set of readability assessments by expert readers. We clustered the experts into groups with greater a priori agreement and then measured for each group whether classifiers trained only on data from this group exhibited a classification bias. As this was found to be the case, the classification mechanism cannot be unproblematically generalized to a different user group
An intact signal peptide on dengue virus E protein enhances immunogenicity for CD8+ T cells and antibody when expressed from modified vaccinia Ankara
Dengue is a global public health concern and this is aggravated by a lack of vaccines or antiviral therapies. Despite the well-known role of CD8(+) T cells in the immunopathogenesis of Dengue virus (DENV), only recent studies have highlighted the importance of this arm of the immune response in protection against the disease. Thus, the majority of DENV vaccine candidates are designed to achieve protective titers of neutralizing antibodies, with less regard for cellular responses. Here, we used a mouse model to investigate CD8(+) T cell and humoral responses to a set of potential DENV vaccines based on recombinant modified vaccinia virus Ankara (rMVA). To enable this study, we identified two CD8(+) T cell epitopes in the DENV-3 E protein in C57BL/6 mice. Using these we found that all the rMVA vaccines elicited DENV-specific CD8(+) T cells that were cytotoxic in vivo and polyfunctional in vitro. Moreover, vaccines expressing the E protein with an intact signal peptide sequence elicited more DENV-specific CD8(+) T cells than those expressing E proteins in the cytoplasm. Significantly, it was these same ER-targeted E protein vaccines that elicited antibody responses. Our results support the further development of rMVA vaccines expressing DENV E proteins and add to the tools available for dengue vaccine development.Parts of this work were supported by the InstitutoNacional de Ciência e Tecnologia de Vacinas–INCTV (National Insti-tute of Science and Technology of Vaccines) and by a FAPEMIGPPM grant (CBB, PPM-00461-11). BRQ was a CAPES/PDSE fellow-ship recipient (8815-11-9). FGF is a CNPq fellowship recipient. DCTis an ARC Future Fellow (FT110100310)
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