4,917 research outputs found
Techniques for QCD calculations by numerical integration
Calculations of observables in quantum chromodynamics are typically performed
using a method that combines numerical integrations over the momenta of final
state particles with analytical integrations over the momenta of virtual
particles. I describe the most important steps of a method for performing all
of the integrations numerically.Comment: 36 pages with 16 postscript figure
Chirality of tensor perturbations for complex values of the Immirzi parameter
In this paper we generalise previous work on tensor perturbations in a de
Sitter background in terms of Ashtekar variables to cover all complex values of
the Immirzi parameter gamma (previous work was restricted to imaginary gamma).
Particular attention is paid to the case of real gamma. Following the same
approach as in the imaginary case, we can obtain physical graviton states by
invoking reality and torsion free conditions. The Hamiltonian in terms of
graviton states has the same form whether gamma has a real part or not; however
changes occur for the vacuum energy and fluctuations. Specifically, we observe
a gamma dependent chiral asymmetry in the vacuum fluctuations only if gamma has
an imaginary part. Ordering prescriptions also change this asymmetry. We thus
present a measurable result for CMB polarisation experiments that could shed
light on the workings of quantum gravity.Comment: 6 pages, 1 figur
Successive Combination Jet Algorithm For Hadron Collisions
Jet finding algorithms, as they are used in and hadron collisions,
are reviewed and compared. It is suggested that a successive combination style
algorithm, similar to that used in physics, might be useful also in
hadron collisions, where cone style algorithms have been used previously.Comment: 18 pages plus four uuencoded postscript figures, REVTEX 3.0,
CERN-TH.6860/9
Searching For Anomalous Couplings
The capability of current and future measurements at low and high energy
colliders to probe for the existence of anomalous, CP conserving,
dipole moment-type couplings is examined. At present, constraints
on the universality of the tau charged and neutral current interactions as well
as the shape of the energy spectrum provide the strongest
bounds on such anomalous couplings. The presence of these dipole moments are
shown to influence, e.g., the extraction of from
decays and can lead to apparent violations of CVC expectations.Comment: 24 pages, 9 figure
Value of alpha_s from deep-inelastic-scattering data
We report the value of obtained from QCD analysis of
existing data on deep-inelastic scattering of charged leptons off proton and
deuterium and estimate its theoretical uncertainties with particular attention
paid to impact of the high-twist contribution to the deep-inelastic-scattering
structure functions. Taking into account the major uncertainties the value
is obtained. An extrapolation of the LO--NLO--NNLO
results to the higher orders makes it possible to estimate .Comment: 9 pages, LATEX, 4 figures (EPS). Talk given at 16th International
Baldin Seminar on High-Energy Physics Problems: Relativistic Nuclear Physics
and Quantum Chromodynamics (ISHEPP 16), Dubna, Russia, 10-15 Jun 200; v2:
typos corrected, layout improved, 2 references adde
Determination of the Strong Coupling \boldmath{\as} from hadronic Event Shapes and NNLO QCD predictions using JADE Data
Event Shape Data from annihilation into hadrons collected by the
JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used
to determine the strong coupling . QCD predictions complete to
next-to-next-to-leading order (NNLO), alternatively combined with resummed
next-to-leading-log-approximation (NNLO+NLLA) calculations, are used. The
combined value from six different event shape observables at the six JADE
centre-of-mass energies using the NNLO calculations is
= 0.1210 +/- 0.0007(stat.) +/- 0.0021(expt.) +/- 0.0044(had.)
+/- 0.0036(theo.) and with the NNLO+NLLA calculations the combined value is
= 0.1172 +/- 0.0006(stat.) +/- 0.0020(expt.) +/- 0.0035(had.) +/-
0.0030(theo.) . The stability of the NNLO and NNLO+NLLA results with respect to
missing higher order contributions, studied by variations of the
renormalisation scale, is improved compared to previous results obtained with
NLO+NLLA or with NLO predictions only. The observed energy dependence of
agrees with the QCD prediction of asymptotic freedom and excludes
absence of running with 99% confidence level.Comment: 9 pages, EPHJA style, 4 figures, corresponds to published version
with JADE author lis
Anthropic solution to the magnetic muon anomaly: the charged see-saw
We present models of new physics that can explain the muon g-2 anomaly in
accord with with the assumption that the only scalar existing at the weak scale
is the Higgs, as suggested by anthropic selection. Such models are dubbed
"charged see-saw" because the muon mass term is mediated by heavy leptons. The
electroweak contribution to the g-2 gets modified by order one factors, giving
an anomaly of the same order as the observed hint, which is strongly correlated
with a modification of the Higgs coupling to the muon.Comment: 21 pages, many equations despite the first word in the title. v3:
loop function G_WN corrected, conclusions unchange
Exclusive processes in position space and the pion distribution amplitude
We suggest to carry out lattice calculations of current correlators in
position space, sandwiched between the vacuum and a hadron state (e.g. pion),
in order to access hadronic light-cone distribution amplitudes (DAs). In this
way the renormalization problem for composite lattice operators is avoided
altogether, and the connection to the DA is done using perturbation theory in
the continuum. As an example, the correlation function of two electromagnetic
currents is calculated to the next-to-next-to-leading order accuracy in
perturbation theory and including the twist-4 corrections. We argue that this
strategy is fully competitive with direct lattice measurements of the moments
of the DA, defined as matrix elements of local operators, and offers new
insight in the space-time picture of hard exclusive reactions.Comment: 15 pages, 10 figure
Targeting atypical protein kinase C iota reduces viability in glioblastoma stem-like cells via a notch signaling mechanism
In a previous study, Protein Kinase C iota (PRKCI) emerged as an important candidate gene for glioblastoma (GBM) stem-like cell (GSC) survival. Here, we show that PKCι is overexpressed and activated in patient derived GSCs compared with normal neural stem cells and normal brain lysate, and that silencing of PRKCI in GSCs causes apoptosis, along with loss of clonogenicity and reduced proliferation. Notably, PRKCI silencing reduces tumor growth in vivo in a xenograft mouse model. PKCι has been intensively studied as a therapeutic target in non-small cell lung cancer, resulting in the identification of an inhibitor, aurothiomalate (ATM), which disrupts the PKCι/ERK signaling axis. However, we show that, although sensitive to pharmacological inhibition via a pseudosubstrate peptide inhibitor, GSCs are much less sensitive to ATM, suggesting that PKCι acts along a different signaling axis in GSCs. Gene expression profiling of PRKCI-silenced GSCs revealed a novel role of the Notch signaling pathway in PKCι mediated GSC survival. A proximity ligation assay showed that Notch1 and PKCι are in close proximity in GSCs. Targeting PKCι in the context of Notch signaling could be an effective way of attacking the GSC population in GBM
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