402 research outputs found
Quark and Gluon Orbital Angular Momentum and Spin in Hard Processes
We suggest a method of constructing gauge invariant quark and gluon
distributions that describe an abstract QCD observable and apply this method to
analyze angular momentum of a hadron. In addition to the known quark and gluon
polarized structure functions, we obtain gauge invariant distributions for
quark and gluon orbital angular momenta, and consider some basic properties of
these distributions and their moments.Comment: 16 pages, no figures, RevTe
Design and realisation of a MZI type polymer based high speed EO-modulator
We designed a 20 GHz Mach Zehnder interferometric EO-modulator based on a new developed polyesterimide. Measurements show a V/sub /spl pi// of 7.5 V, an insertion loss of 11 dB and an extinction ratio exceeding 20 dB for an interaction length of 2 cm
Universal structure of subleading infrared poles at strong coupling
Recently a concise expression for the subleading infrared singularity of
dimensional-regularized gauge theories has been proposed. For conformal
theories, such relation involves a universal eikonal contribution plus a
non-eikonal contribution, related to the subleading term in the anomalous
dimension of twist two operators with large spin. In this note we make use of
the AdS/CFT correspondence in order to check such conjecture at strong coupling
for the case of N=4 SYM.Comment: 13 page
Expression of rabbit IL-4 by recombinant myxoma viruses enhances virulence and overcomes genetic resistance to myxomatosis
AbstractRabbit IL-4 was expressed in the virulent standard laboratory strain (SLS) and the attenuated Uriarra (Ur) strain of myxoma virus with the aim of creating a Th2 cytokine environment and inhibiting the development of an antiviral cell-mediated response to myxomatosis in infected rabbits. This allowed testing of a model for genetic resistance to myxomatosis in wild rabbits that have undergone 50 years of natural selection for resistance to myxomatosis. Expression of IL-4 significantly enhanced virulence of both virulent and attenuated virus strains in susceptible (laboratory) and resistant (wild) rabbits. SLS-IL-4 completely overcame genetic resistance in wild rabbits. The pathogenesis of SLS-IL-4 was compared in susceptible and resistant rabbits. The results support a model for resistance to myxomatosis of an enhanced innate immune response controlling virus replication and allowing an effective antiviral cell-mediated immune response to develop in resistant rabbits. Expression of IL-4 did not overcome immunity to myxomatosis induced by immunization
Generelized Parton Distributions in light meson production
We analyze light meson electroproduction within the handbag model, where the
amplitude factorizes into Generelized Parton Distributions (GPDs) and a hard
scattering part. The cross sections and spin asymmetries for various vector and
pseudoscalar mesons are analyzed. We discuss what information on hadron
structure can be obtained from GPDs.Comment: Latex, 14 pages, 12 figures, Presented at the 5th joint International
HADRON STRUCTURE '11 Conference, June 27- July 1, 2011, Tatranska Strba
(Slovak Republic
An attempt to understand exclusive pi+ electroproduction
Hard exclusive pi+ electroproduction is investigated within the handbag
approach. The prominent role of the pion-pole contribution is demonstrated. It
is also shown that the experimental data require a twist-3 effect which ensues
from the helicity-flip generalized parton distribution H_T and the twist-3 pion
wave function. The results calculated from this handbag approach are compared
in detail with the experimental data on cross sections and spin asymmetries
measured with a polarized target. It is also commented on consequences of this
approach for exclusive \pi^0 and vector-meson electroproduction.Comment: 35 pages, 12 figures, using Latex, a number of additional comments
have been included in the text, e.g. in paragraph above (3) or at end of
sect.
Comments on operators with large spin
We consider high spin operators. We give a general argument for the
logarithmic scaling of their anomalous dimensions which is based on the
symmetries of the problem. By an analytic continuation we can also see the
origin of the double logarithmic divergence in the Sudakov factor. We show that
the cusp anomalous dimension is the energy density for a flux configuration of
the gauge theory on . We then focus on operators in super Yang Mills which carry large spin and SO(6) charge and show that in
a particular limit their properties are described in terms of a bosonic O(6)
sigma model. This can be used to make certain all loop computations in the
string theory.Comment: 33 pages, 1 figure,v2:reference to more recent work added, minor
correction
Factorization constraints for soft anomalous dimensions in QCD scattering amplitudes
We study the factorization of soft and collinear singularities in
dimensionally-regularized fixed-angle scattering amplitudes in massless gauge
theories. Our factorization is based on replacing the hard massless partons by
light-like Wilson lines, and defining gauge-invariant jet and soft functions in
dimensional regularization. In this scheme the factorized amplitude admits a
powerful symmetry: it is invariant under rescaling of individual Wilson-line
velocities. This symmetry is broken by cusp singularities in both the soft and
the eikonal jet functions. We show that the cancellation of these cusp
anomalies in any multi-leg amplitude imposes all-order constraints on the
kinematic dependence of the corresponding soft anomalous dimension, relating it
to the cusp anomalous dimension. For amplitudes with two or three hard partons
the solution is unique: the constraints fully determine the kinematic
dependence of the soft function. For amplitudes with four or more hard partons
we present a minimal solution where the soft anomalous dimension is a sum over
colour dipoles, multiplied by the cusp anomalous dimension. In this case
additional contributions to the soft anomalous dimension at three loops or
beyond are not excluded, but they are constrained to be functions of conformal
cross ratios of kinematic variables.Comment: v1: 35 pages, v2: minor changes - some clarifying remarks and
references added. Journal version (to appear in JHEP
Ioffe-time distributions instead of parton momentum distributions in description of deep inelastic scattering
We argue that parton distributions in coordinate space provide a more natural
object for nonperturbative methods compared to the usual momentum distributions
in which the physics of different longitudinal distances is being mixed. To
illustrate the advantages of the coordinate space formulation, we calculate the
coordinate space distributions for valence quarks in the proton using the QCD
sum rule approach. A remarkable agreement is found between the calculated and
the experimentally measured u-quark distribution up to light-cone distances
of order fm in the proton rest frame.
The calculation for valence d quarks gives much worse results; the reasons for
this discrepancy are discussed.Comment: 24 pages plus 13 pages with figures, requires epsf.sty, revised
version to appear in Phys.Rev.
Transverse momentum dependence in gluon distribution and fragmentation functions
We investigate the twist two gluon distribution functions for spin 1/2
hadrons, emphasizing intrinsic transverse momentum of the gluons. These
functions are relevant in leading order in the inverse hard scale in scattering
processes such as inclusive leptoproduction or Drell-Yan scattering, or more
general in hard processes in which at least two hadrons are involved. They show
up in azimuthal asymmetries. For future estimates of such observables, we
discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure
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