193 research outputs found
Odd C-P contributions to diffractive processes
We investigate contributions to diffractive scattering, which are odd under
C- and P-parity. Comparison of p- and p-p scattering indicates that
these odderon contributions are very small and we show how a diquark clustering
in the proton can explain this effect. A good probe for the odderon exchange is
the photo- and electroproduction of pseudo-scalar mesons. We concentrate on the
pi^0 and show that the quasi elastic pi^0-production is again strongly
suppressed for a diquark structure of the proton whereas the cross sections for
diffractive proton dissociation are larger by orders of magnitude and rather
independent of the proton structure.Comment: 18 pages, LaTex2e, graphicx package, 14 eps figures include
Diffractive color-dipole nucleon scattering
We determine the diffractive scattering amplitude of a color-dipole on a
nucleon using a non-perturbative model of QCD which contains only parameters
taken from low-energy physics. This allows to relate specific features of the
confinement mechanisms with diffractive electro-production processes and
structure functions. The agreement with phenomenological data is satisfactory.Comment: 7 pages, 5 eps-figures, uses eps
Decomposition of the QCD String into Dipoles and Unintegrated Gluon Distributions
We present the perturbative and non-perturbative QCD structure of the
dipole-dipole scattering amplitude in momentum space. The perturbative
contribution is described by two-gluon exchange and the non-perturbative
contribution by the stochastic vacuum model which leads to confinement of the
quark and antiquark in the dipole via a string of color fields. This QCD string
gives important non-perturbative contributions to high-energy reactions. A new
structure different from the perturbative dipole factors is found in the
string-string scattering amplitude. The string can be represented as an
integral over stringless dipoles with a given dipole number density. This
decomposition of the QCD string into dipoles allows us to calculate the
unintegrated gluon distribution of hadrons and photons from the dipole-hadron
and dipole-photon cross section via kT-factorization.Comment: 43 pages, 14 figure
Log(1/x) Gluon Distribution and Structure Functions in the Loop-Loop Correlation Model
We consider the interaction of the partonic fluctuation of a scalar
``photon'' with an external color field to calculate the leading and
next-to-leading order gluon distribution of the proton following the work done
by Dosch-Hebecker-Metz-Pirner. We relate these gluon distributions to the short
and long distance behavior of the cross section of an adjoint dipole scattering
off a proton. The leading order result is a constant while the next-to-leading
order result shows a ln(1/x) enhancement at small x. To get numerical results
for the gluon distributions at the initial scale Q^2_0=1.8 GeV^2, we compute
the adjoint dipole-proton cross section in the loop-loop correlation model.
Quark distributions at the same initial scale are parametrized according to
Regge theory. We evolve quark and gluon distributions to higher Q^2 values
using the DGLAP equation and compute charm and proton structure functions in
the small-x region for different Q^2 values.Comment: 13 pages, 10 figures,revised version,references added, typos
corrected, to be published in Eur. Phys. Journal
Two Photon Reactions at High Energies
Cross sections for the reactions gamma^(*) gamma^(*) --> hadrons and
gamma^(*) gamma^(*) --> 2 vector mesons are calculated as functions of energy
(sqrt(s) > 20 GeV) and photon virtualities. Good agreement with experiment is
obtained for the total hadronic cross section and, after allowing for a
valence-quark contribution from the hadronic part of the photon, with the
photon structure function at small x. The cross section for vector meson
production are shown to be experimentally accessible for moderate values of
Q^2. This is sufficient to probe the nature of the hard pomeron which has
recently been proposed.Comment: some changes in style, physics unchanged, final version to appear in
Phys.Rev.D, LaTeX2e, graphicx package, 15 eps-figures, 15p
Gamma(*)Gamma(*) reaction at high energies
The energy available for gamma(*)gamma(*) physics at LEP2 is opening a new
window on the study of diffractive phenomena, both non-perturbative and
perturbative. We discuss some of the uncertainties and problems connected with
the experimental measurements and their interpretation.Comment: 6 pages, 6 figures, submitted to proceedings of the Durham Collider
Workshop, 22-26 September 199
Local endothelial complement activation reverses endothelial quiescence, enabling t-cell homing, and tumor control during t-cell immunotherapy.
Cancer immunotherapy relies upon the ability of T cells to infiltrate tumors. The endothelium constitutes a barrier between the tumor and effector T cells, and the ability to manipulate local vascular permeability could be translated into effective immunotherapy. Here, we show that in the context of adoptive T cell therapy, antitumor T cells, delivered at high enough doses, can overcome the endothelial barrier and infiltrate tumors, a process that requires local production of C3, complement activation on tumor endothelium and release of C5a. C5a, in turn, acts on endothelial cells promoting the upregulation of adhesion molecules and T-cell homing. Genetic deletion of C3 or the C5a receptor 1 (C5aR1), and pharmacological blockade of C5aR1, impaired the ability of T cells to overcome the endothelial barrier, infiltrate tumors, and control tumor progression in vivo, while genetic chimera mice demonstrated that C3 and C5aR1 expression by tumor stroma, and not leukocytes, governs T cell homing, acting on the local endothelium. In vitro, endothelial C3 and C5a expressions were required for endothelial activation by type 1 cytokines. Our data indicate that effective immunotherapy is a consequence of successful homing of T cells in response to local complement activation, which disrupts the tumor endothelial barrier
Confining QCD Strings, Casimir Scaling, and a Euclidean Approach to High-Energy Scattering
We compute the chromo-field distributions of static color-dipoles in the
fundamental and adjoint representation of SU(Nc) in the loop-loop correlation
model and find Casimir scaling in agreement with recent lattice results. Our
model combines perturbative gluon exchange with the non-perturbative stochastic
vacuum model which leads to confinement of the color-charges in the dipole via
a string of color-fields. We compute the energy stored in the confining string
and use low-energy theorems to show consistency with the static quark-antiquark
potential. We generalize Meggiolaro's analytic continuation from parton-parton
to gauge-invariant dipole-dipole scattering and obtain a Euclidean approach to
high-energy scattering that allows us in principle to calculate S-matrix
elements directly in lattice simulations of QCD. We apply this approach and
compute the S-matrix element for high-energy dipole-dipole scattering with the
presented Euclidean loop-loop correlation model. The result confirms the
analytic continuation of the gluon field strength correlator used in all
earlier applications of the stochastic vacuum model to high-energy scattering.Comment: 65 pages, 13 figures, extended and revised version to be published in
Phys. Rev. D (results unchanged, 2 new figures, 1 new table, additional
discussions in Sec.2.3 and Sec.5, new appendix on the non-Abelian Stokes
theorem, old Appendix A -> Sec.3, several references added
Heavy Quarkonia: Wilson Area Law, Stochastic Vacuum Model and Dual QCD
The semirelativistic interaction in QCD can be simply expressed
in terms of the Wilson loop and its functional derivatives. In this approach we
present the potential up to order using the expressions for
the Wilson loop given by the Wilson Minimal Area Law (MAL), the Stochastic
Vacuum Model (SVM) and Dual QCD (DQCD). We confirm the original results given
in the different frameworks and obtain new contributions. In particular we
calculate up to order the complete velocity dependent potential in the
SVM. This allows us to show that the MAL model is entirely contained in the
SVM. We compare and discuss also the SVM and the DQCD potentials. It turns out
that in these two very different models the spin-orbit potentials show up the
same leading non-perturbative contributions and 1/r corrections in the
long-range limit.Comment: 29 pages, revtex, 1 figure(fig1.ps); replaced with the last version
that will appear in Phys. Rev. D (1March 1997); few misprints correcte
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