238 research outputs found
Worldline Casting of the Stochastic Vacuum Model and Non-Perturbative Properties of QCD: General Formalism and Applications
The Stochastic Vacuum Model for QCD, proposed by Dosch and Simonov, is fused
with a Worldline casting of the underlying theory, i.e. QCD. Important,
non-perturbative features of the model are studied. In particular,
contributions associated with the spin-field interaction are calculated and
both the validity of the loop equations and of the Bianchi identity are
explicitly demonstrated. As an application, a simulated meson-meson scattering
problem is studied in the Regge kinematical regime. The process is modeled in
terms of the "helicoidal" Wilson contour along the lines introduced by Janik
and Peschanski in a related study based on a AdS/CFT-type approach. Working
strictly in the framework of the Stochastic Vacuum Model and in a semiclassical
approximation scheme the Regge behavior for the Scattering amplitude is
demonstrated. Going beyond this approximation, the contribution resulting from
boundary fluctuation of the Wilson loop contour is also estimated.Comment: 37 pages, 1 figure. Final version to appear in Phys.Rev.
Evolving text classification rules with genetic programming
We describe a novel method for using genetic programming to create compact classification rules using combinations of N-grams (character strings). Genetic programs acquire fitness by producing rules that are effective classifiers in terms of precision and recall when evaluated against a set of training documents. We describe a set of functions and terminals and provide results from a classification task using the Reuters 21578 dataset. We also suggest that the rules may have a number of other uses beyond classification and provide a basis for text mining applications
Worldline Approach to Forward and Fixed Angle fermion-fermion Scattering in Yang-Mills Theories at High Energies
Worldline techniques are employed to study the general behaviour of the
fermion-fermion collision amplitude at very high energies in a non-abelian
gauge field theory for the forward and fixed angle scattering cases. A central
objective of this work is to demonstrate the simplicity by which the worldline
methodology isolates that sector of the full theory which carries the soft
physics, relevant to each process. Anomalous dimensions pertaining to a given
soft sector are identified and subseuently used to facilitate the
renormalization group running of the respective four point functions. Gluon
reggeization is achieved for forward, while Sudakov suppression is established
for fixed angle scattering.Comment: 28 pages, 10 figures in three file
Gauge (non-)invariant Green functions of Dirac fermions coupled to gauge fields
We develop a unified approach to both infrared and ultraviolet asymptotics of
the fermion Green functions in the condensed matter systems that allow for an
effective description in the framework of the Quantum Electrodynamics. By
applying a path integral representation to the previously suggested form of the
physical electron propagator we demonstrate that in the massless case this
gauge invariant function features a "stronger-than-a-pole" branch-cut
singularity instead of the conjectured Luttinger-like behavior. The obtained
results alert one to the possibility that construction of physically relevant
amplitudes in the effective gauge theories might prove more complex than
previously thought
Theoretical evidence for a tachyonic ghost state contribution to the gluon propagator in high energy, forward quark-quark `scattering'
Implications stemming from the inclusion of non-perturbative, confinining
effects, as contained in the Stochastic Vacuum Model of Dosch and Simonov, are
considered in the context of a, hypothetical, quark-quark `scattering process'
in the Regge kinematical region. In a computation wherein the non-perturbative
input enters as a correction to established perturbative results, a careful
treatment of infrared divergencies is shown to imply the presence of an
effective propagator associated with the existence of a linear term in the
static potential. An equivalent statement is to say that the modified gluonic
propagator receives contribution from a tachyonic ghost state, an occurence
which is fully consistent with earlier such suggestions made in the context of
low energy QCD phenomenology.Comment: 14 page
Two different quasiparticle scattering rates in vortex line liquid phase of layered d-wave superconductors
We carry out a quantum mechanical analysis of the behavior of nodal
quasiparticles in the vortex line liquid phase of planar d-wave
superconductors. Applying a novel path integral technique we calculate a number
of experimentally relevant observables and demonstrate that in the low-field
regime the quasiparticle scattering rates deduced from photoemission and
thermal transport data can be markedly different from that extracted from
tunneling, specific heat, superfluid stiffness or spin-lattice relaxation time.Comment: Latex, 4 pages, no figure
Power corrections to the transition form factor and pion distribution amplitudes
Employing the standard hard-scattering approach and the running coupling
method we calculate a class of power-suppressed corrections to the electromagnetic transition form
factor (FF) arising from the end-point
integration regions. In the investigations we use a hard-scattering amplitude
of the subprocess , symmetrized under
exchange important for exclusive
processes containing two external photons. In the computations the pion model
distribution amplitudes (DA's) with one and two non-asymptotic terms are
employed. The obtained predictions are compared with the CLEO data and
constraints on the DA parameters and at the
normalization point are extracted. Further restrictions on
the pion DA's are deduced from the experimental data on the electromagnetic FF
.Comment: 23 pages, 6 figures; the version published in Phys. Rev. D69, 094010
(2004
Expression of Foxp3 in colorectal cancer but not in Treg cells correlates with disease progression in patients with colorectal cancer
Background: Regulatory T cells (Treg) expressing the transcription factor forkhead-box protein P3 (Foxp3) have been identified to counteract anti-tumor immune responses during tumor progression. Besides, Foxp3 presentation by cancer cells itself may also allow them to evade from effector T-cell responses, resulting in a survival benefit of the tumor. For colorectal cancer (CRC) the clinical relevance of Foxp3 has not been evaluated in detail. Therefore the aim of this study was to study its impact in colorectal cancer (CRC).
Methods and Findings: Gene and protein analysis of tumor tissues from patients with CRC was performed to quantify the expression of Foxp3 in tumor infiltrating Treg and colon cancer cells. The results were correlated with clinicopathological parameters and patients overall survival. Serial morphological analysis demonstrated Foxp3 to be expressed in cancer cells. High Foxp3 expression of the cancer cells was associated with poor prognosis compared to patients with low Foxp3 expression. In contrast, low and high Foxp3 level in tumor infiltrating Treg cells demonstrated no significant differences in overall patient survival.
Conclusions: Our findings strongly suggest that Foxp3 expression mediated by cancer cells rather than by Treg cells contribute to disease progression
Taming Landau singularities in QCD perturbation theory: The analytic approach 2.0
The aim of this topical article is to outline the fundamental ideas
underlying the recently developed Fractional Analytic Perturbation Theory
(FAPT) of QCD and present its main calculational tools together with key
applications. For this, it is first necessary to review previous methods to
apply QCD perturbation theory at low spacelike momentum scales, where the
influence of the Landau singularities becomes inevitable. Several concepts are
considered and their limitations are pointed out. The usefulness of FAPT is
discussed in terms of two characteristic hadronic quantities: the
perturbatively calculable part of the pion's electromagnetic form factor in the
spacelike region and the Higgs-boson decay into a pair in the
timelike region. In the first case, the focus is on the optimization of the
prediction with respect to the choice of the renormalization scheme and the
dependence on the renormalization and the factorization scales. The second case
serves to show that the application of FAPT to this reaction reaches already at
the four-loop level an accuracy of the order of 1%, avoiding difficulties
inherent in the standard perturbative expansion. The obtained results are
compared with estimates from fixed-order and contour-improved QCD perturbation
theory. Using the brand-new Higgs mass value of about 125 GeV, measured at the
Large Hadron Collider (CERN), a prediction for is extracted.Comment: v3: 23 pages, 7 figures, Invited topical article published in
Particles and Nuclei with update using the CERN Higgs discovery. Abridged
version presented as plenary talk at International Conference on
Renormalization Group and Related Topics (RG 2008), Dubna, Russia, September
1 - 5, 2008. v4 typo in Eq. (3) correcte
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