64 research outputs found
Topological gauge fixing
We implement the metric-independent Fock-Schwinger gauge in the abelian
quantum Chern-Simons field theory defined in . The expressions
of the various components of the propagator are determined. Although the gauge
field propagator differs from the Gauss linking density, we prove that its
integral along two oriented knots is equal to the linking number
Testing the Technicolor Interpretation of the CDF Dijet Excess at the 8-TeV LHC
Under the assumption that the dijet excess seen by the CDF Collaboration near
150 Gev in Wjj production is due to the lightest technipion of the low-scale
technicolor process , we study its observability in
LHC detectors for 8 TeV collisions and 20 inverse femtobarns of integrated
luminosity. We describe interesting new kinematic tests that can provide
independent confirmation of this LSTC hypothesis. We show that cuts similar to
those employed by CDF, and recently by ATLAS, cannot confirm the dijet signal.
We propose cuts tailored to the LSTC hypothesis and its backgrounds at the LHC
that may reveal . Observation of the
isospin-related channel and of in the
and modes will be important
confirmations of the LSTC interpretation of the CDF signal. The
channel is experimentally cleaner than and its rate is known from
by phase space. It can be discovered or excluded with the collider
data expected by the end of 2012. The channel is
cleanest of all and its rate is determined from and the LSTC parameter
. This channel and are discussed as a
function of .Comment: 28 pages, 27 figures, submitted to PRD. arXiv admin note: substantial
text overlap with arXiv:1201.439
Testing the Technicolor Interpretation of CDF's Dijet Excess at the LHC
Under the assumption that the dijet excess seen by the CDF Collaboration near
150 Gev in Wjj production is due to the lightest technipion of the low-scale
technicolor process , we study its observability in
LHC detectors with 1--20 inverse femtobarns of data. We describe interesting
new kinematic tests that can provide independent confirmation of this LSTC
hypothesis. We find that cuts similar to those employed by CDF, and recently by
ATLAS, cannot confirm the dijet signal. We propose cuts tailored to the LSTC
hypothesis and its backgrounds at the LHC that may reveal . Observation of the isospin-related channel and of in the three lepton plus neutrino and dilepton plus dijet modes
will be important confirmations of the LSTC interpretation of the CDF signal.
The channel is experimentally cleaner than and its rate is
known from by phase space. It can be discovered or excluded with the
collider data expected in 2012. The channel is
cleanest of all and its rate is determined from and the LSTC parameter
. This channel and are discussed as
a function of .Comment: 24 pages, 24 figure
A new critical study of photon production in hadronic collisions
In the light of the new prompt photon data collected by PHENIX at RHIC and by
D0 at the run II of the Tevatron, we revisit the world prompt photon data, both
inclusive and isolated, in hadronic collisions, and compare them with the NLO
QCD calculations implemented in the Monte Carlo programme JETPHOX.Comment: 19 pages; 12 figure
Modern Feynman Diagrammatic One-Loop Calculations
In this talk we present techniques for calculating one-loop amplitudes for
multi-leg processes using Feynman diagrammatic methods in a semi-algebraic
context. Our approach combines the advantages of the different methods allowing
for a fast evaluation of the amplitude while monitoring the numerical stability
of the calculation. In phase space regions close to singular kinematics we use
a method avoiding spurious Gram determinants in the calculation. As an
application of our approach we report on the status of the calculation of the
amplitude for the process .Comment: 10 pages, 2 figures; contribution to the proceedings of the CPP2010
Workshop, 23-25 Sep. 2010, KEK, Tsukuba, Japa
Cross section of isolated prompt photons in hadron-hadron collisions
We consider the production of isolated prompt photons in hadronic collisions.
We present a general discussion in QCD perturbation theory of the isolation
criterion used by hadron collider experiments. The isolation criterion is
implemented in a computer programme of the Monte Carlo type, which evaluates
the production cross section at next-to-leading order accuracy in perturbative
QCD. The calculation includes both the direct and the fragmentation components
of the cross section, without any approximation of the dependence on the radius
R of the isolation cone. We examine the scale dependence of the isolated cross
section, the sensitivity of the cross section to the values of the isolation
parameters, and we provide a quantitative comparison between the full R
dependence and its small-R approximation.Comment: 29 pages, 1 figure, few comments slightly expanded, results
unchanged, misprints correcte
An algebraic/numerical formalism for one-loop multi-leg amplitudes
We present a formalism for the calculation of multi-particle one-loop
amplitudes, valid for an arbitrary number N of external legs, and for massive
as well as massless particles. A new method for the tensor reduction is
suggested which naturally isolates infrared divergences by construction. We
prove that for N>4, higher dimensional integrals can be avoided. We derive many
useful relations which allow for algebraic simplifications of one-loop
amplitudes. We introduce a form factor representation of tensor integrals which
contains no inverse Gram determinants by choosing a convenient set of basis
integrals. For the evaluation of these basis integrals we propose two methods:
An evaluation based on the analytical representation, which is fast and
accurate away from exceptional kinematical configurations, and a robust
numerical one, based on multi-dimensional contour deformation. The formalism
can be implemented straightforwardly into a computer program to calculate
next-to-leading order corrections to multi-particle processes in a largely
automated way.Comment: 71 pages, 7 figures, formulas for rank 6 pentagons added in Appendix
Recent Progress in the Golem Project
We report on the current status of the Golem project which aims at the
construction of a general one-loop evaluator for matrix elements. We construct
the one-loop matrix elements from Feynman diagrams in a highly automated way
and provide a library for the reduction and numerically stable evaluation of
the tensor integrals involved in this approach. Furthermore, we present
applications to physics processes relevant for the LHC.Comment: 7 pages, 4 figures, contrib. to proceedings of "Loops and Legs in
Quantum Field Theory", 10th DESY Workshop on Elementary Particle Theory,
25-30 April 2010, Woerlitz, German
Portrait of blood-derived extracellular vesicles in patients with Parkinson's disease.
The production of extracellular vesicles (EV) is a ubiquitous feature of eukaryotic cells but pathological events can affect their formation and constituents. We sought to characterize the nature, profile and protein signature of EV in the plasma of Parkinson's disease (PD) patients and how they correlate to clinical measures of the disease. EV were initially collected from cohorts of PD (n = 60; Controls, n = 37) and Huntington's disease (HD) patients (Pre-manifest, n = 11; manifest, n = 52; Controls, n = 55) - for comparative purposes in individuals with another chronic neurodegenerative condition - and exhaustively analyzed using flow cytometry, electron microscopy and proteomics. We then collected 42 samples from an additional independent cohort of PD patients to confirm our initial results. Through a series of iterative steps, we optimized an approach for defining the EV signature in PD. We found that the number of EV derived specifically from erythrocytes segregated with UPDRS scores corresponding to different disease stages. Proteomic analysis further revealed that there is a specific signature of proteins that could reliably differentiate control subjects from mild and moderate PD patients. Taken together, we have developed/identified an EV blood-based assay that has the potential to be used as a biomarker for PD
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