409 research outputs found
Two-Parton Contribution to the Heavy-Quark Forward-Backward Asymmetry in NNLO QCD
Forward-backward asymmetries, , are important observables for the
determination of the neutral-current couplings of heavy quarks in inclusive
heavy quark production, . In view of the
measurement perspectives on at a future linear collider, precise
predictions of are required for massive quarks. We compute the
contribution of the final state to to order \as^2 in
the QCD coupling. We provide general formulae, and we show that this
contribution to is infrared-finite. We evaluate these two-parton
contributions for and quarks on and near the resonance, and for
quarks above threshold. Moreover, near the threshold we obtain, by
expanding in the heavy-quark velocity , an expression for to order \as^2 and NNLL in . This quantity is equal, to this
order in , to the complete forward-backward asymmetry .Comment: latex, 26 pages, 2 tables, 17 figure
Angular Correlations in Top Quark Pair Production and Decay at Hadron Colliders
We show how to observe sizable angular correlations between the decay
products of the top quark and those of the anti-top quark in top quark pair
production and decay at hadron colliders. These correlations result from the
large asymmetry in the rate for producing like-spin versus unlike-spin top
quark pairs provided the appropriate spin axes are used. The effects of new
physics at production or decay on these correlations are briefly discussed.Comment: 34 pages, revtex, including 12 uuencoded postscript figure
Top Production in Hadron-Hadron Collisions and Anomalous Top-Gluon Couplings
We discuss the influence of anomalous tbar-t-G couplings on total and
differential tbar-t production cross sections in hadron-hadron collisions. We
study in detail the effects of a chromoelectric and a chromomagnetic dipole
moment, d' and \mu', of the top quark. In the d'-\mu' plane, we find a whole
region where the anomalous couplings give a zero net contribution to the total
top production rate. In differential cross sections, the anomalous moments have
to be quite sizable to give measurable effects. We estimate the values of d'
and \mu' which are allowed by the present Tevatron experimental results on top
production. A chromoelectric dipole moment of the top violates CP invariance.
We discuss a simple CP-odd observable which allows for a direct search for CP
violation in top production.Comment: footnote pg. 4 changed, acknowledgments extende
Heavy-Quark Form Factors and Threshold Cross Section at O(\alpha_S^2)
During the last year, analytic expressions for the two-loop QCD corrections
to the form factors for the vector, axial-vector, scalar and pseudo-scalar
vertices involving a pair of heavy quarks, , were calculated. The
results are valid for arbitrary momentum transfer and mass of the heavy quarks.
These form factors have a number of applications, including anomalous
couplings, the cross section, and the
forward-backward asymmetry of heavy quarks. Here the threshold
cross section is presented with some new second order axial vector
contributions.Comment: 5 pages. Presented at the International Europhysics Conference on
High Energy Physics (HEP2005), July 21-27 2005, Lisboa, Portuga
Large Electric Dipole Moments of Heavy Leptons
In many models of CP violation, the electric dipole moments (EDMs) of leptons
scale as the cube of the lepton mass. In these models, the EDM of a 100 GeV
heavy lepton would be a billion times greater than that of the muon, and could
be as large as a 0.01 e-fermi. In other models, in which the heavy leptons have
different properties from the lighter generations, a similarly large EDM can be
obtained. A large EDM could dominate the electromagnetic properties of heavy
leptons. The angular distribution and production cross-section of both charged
and neutral heavy leptons with large dipole moments is calculated and
discussed. The interesting possibility that a heavy neutrino with a large EDM
could leave an ionization track in a drift chamber is investigated.Comment: Discussion expanded extensively to include model-dependence of
results. Calculations unchanged. Note Added To Acknowledgments: This paper is
dedicated to the memory of Nathan Isgu
Electroweak dipole moment form factors of the top quark in supersymmetry
The CP violating electric and weak dipole moment form factors of the top
quark appear in the process . We present a complete
analysis of these dipole moment form factors within the Minimal Supersymmetric
Standard Model with complex parameters. We include gluino, chargino, and
neutralino exchange in the loop of the and
vertex. We give the analytic expressions and present numerical results.Comment: originally 19 pages LaTeX with 14 figures included. In the
replacement we have 1) updated some references, 2) added acknowledgements, 3)
modified the plots according to small numerical errors, 4) added 12 new plots
for \tan\beta = 3 together with the corresponding figure caption
CP Violation in the Top-Quark Pair Production at a Next Linear Collider
We provide a detailed, model-independent, study for CP violation effects due
to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment
(WDM) in the top-quark pair production via and two-photon annihilation
at a next linear collider (NLC). There are two methods in detecting CP
violation effects in these processes. One method makes use of measurements of
various spin correlations in the final decay products of the produced top-quark
pair, while the other is to measure various CP-odd polarization asymmetry
effects of the initial states. In the case only the first method can
be used, and in the case both methods can be employed. We
provide a complete classification of angular correlations of the and
decay products under CP and CP\tilde{T} which greatly faciliate CP
tests in the mode. Concentrating on the second method with the Compton
back-scattered high-energetic laser light off the electron or positron beam in
the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial
polarization configurations and apply them to investigating CP-violating
effects due to the top-quark EDM. With a typical set of experimental parameters
at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM
in the mode and the two-photon mode. Some model expectation values of
the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st
CP Violation in Semileptonic Decays with Unpolarized Beams
CP violating signals in semileptonic decays are studied. These can be
observed in decays of unpolarized single 's even if their rest frame
cannot be reconstructed. No beam polarization is required. The importance of
the two meson channel, in particular the final state is emphasized.Comment: Latex, 17 pages, 2 figures. The complete paper, including figures, is
also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ ,
or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Two-Loop QCD Corrections to the Heavy Quark Form Factors: Anomaly Contributions
We present closed analytic expressions for the order triangle
diagram contributions to the matrix elements of the singlet and non-singlet
axial vector currents between the vacuum and a quark-antiquark state. We have
calculated these vertex functions for arbitrary momentum transfer and for four
different sets of internal and external quark masses. We show that both the
singlet and non-singlet vertex functions satisfy the correct chiral Ward
identities. Using the exact expressions for the finite axial vector form
factors, we check the quality and the convergence of expansions at production
threshold and for asymptotic energies.Comment: 24 pages, 6 figure
Efficient chemotherapy of rat glioblastoma using Doxorubicin-loaded PLGA nanoparticles with different stabilizers
Background: Chemotherapy of glioblastoma is largely ineffective as the blood-brain barrier (BBB) prevents entry of most anticancer agents into the brain. For an efficient treatment of glioblastomas it is necessary to deliver anti-cancer drugs across the intact BBB. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with poloxamer 188 hold great promise as drug carriers for brain delivery after their intravenous injection. In the present study the anti-tumour efficacy of the surfactant-coated doxorubicin-loaded PLGA nanoparticles against rat glioblastoma 101/8 was investigated using histological and immunohistochemical methods. Methodology: The particles were prepared by a high-pressure solvent evaporation technique using 1% polyvinylalcohol (PLGA/PVA) or human serum albumin (PLGA/HSA) as stabilizers. Additionally, lecithin-containing PLGA/HSA particles (Dox-Lecithin-PLGA/HSA) were prepared. For evaluation of the antitumour efficacy the glioblastoma-bearing rats were treated intravenously with the doxorubicin-loaded nanoparticles coated with poloxamer 188 using the following treatment regimen: 3×2.5 mg/kg on day 2, 5 and 8 after tumour implantation; doxorubicin and poloxamer 188 solutions were used as controls. On day 18, the rats were sacrificed and the antitumour effect was determined by measurement of tumour size, necrotic areas, proliferation index, and expression of GFAP and VEGF as well as Isolectin B4, a marker for the vessel density. Conclusion: The results reveal a considerable anti-tumour effect of the doxorubicin-loaded nanoparticles. The overall best results were observed for Dox-Lecithin-PLGA/HSA. These data demonstrate that the poloxamer 188-coated PLGA nanoparticles enable delivery of doxorubicin across the blood-brain barrier in the therapeutically effective concentrations
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