17,514 research outputs found
Violation of the Bjorken Sum Rule in QCD
We show that the Bjorken sum rule for the first moment of the polarized
nucleon structure function is not necessarily satisfied in QCD if the
axial anomaly is taken into account. We argue that nonperturbative QCD effects
should lead to a violation of the sum rule of the order of the percentage
isospin violation in current quark masses.Comment: 11 pages, no figures (several typos and a numerical error on pag. 5
corrected
Polarized Structure Functions with Neutrino Beams
We review the potential impact of neutrino data on the determination of the
spin structure of the nucleon. We show that a flavour decomposition of the
parton structure of the nucleon as required by present-day precision
phenomenology could only be achieved at a neutrino factory. We discuss how
neutrino scattering data would allow a full resolution of the nucleon spin
problem.Comment: 11 pages, 9 figures, plenary talk at SPIN200
Progress in perturbative QCD
We briefly summarize some recent theoretical developments in perturbative
QCD, emphasizing new ideas which have led to widening the domain of
applicability of perturbation theory. In particular, it is now possible to
calculate efficiently processes with many partons; the high order behavior of
perturbation theory can be at least partly understood by going beyond leading
twist accuracy; factorization with more than one hard scale (such as in DIS
with heavy quarks) can be made consistent with the renormalization group; and
large infrared logs can be resummed beyond the renormalization group. The use
of the renormalization group to resum large longitudinal scales may allow the
use of perturbation theory even in the absence of a large transverse scale.Comment: 10 pages Latex; summary of the theory WG at the DIS97 workshop; typo
on pag. 4 correcte
Polarized Structure Functions: a Theoretical Update
We review recent developments in the theory and phenomenology of polarized
structure functions. We summarize recent experimental data on the proton and
deuteron structure function , and their impact on the understanding of
polarized sum rules. Specifically, we discuss how accurate measurements of the
singlet and nonsinglet first moment of test perturbative and
nonperturbative QCD, and critically examine the way these measurements are
arrived at. We then discuss how the extraction of structure functions from the
data can be improved by means of a theoretical analysis of their and
dependence, and how, conversely, experimental information on this dependence
can be used to pin down the polarized parton content of the nucleon.Comment: 20 pages, plain TeX with epsf, 10 figures in compressed postscript.
Table 2 updated incorporating a recent correction to the NLO anomalous
dimensions of Mertig and van Neerve
Polarized Structure Functions: Theory and Phenomenology
We review the theory of polarized structure functions measured in
deep-inelastic lepton-nucleon scattering, focusing on the most recent
developments. We concentrate on the structure function , emphasizing the
phenomenological problems related to the extraction of the proton and neutron
from the data, and to the determination of its moments, especially
the first moment. In particular, we discuss the theoretical and experimental
uncertainties due to the dependence of the data, small and large
extrapolations, QCD loop corrections, higher twist corrections, and, in
connection to neutron experiments, nuclear effects. We also discuss the current
status of the sum rules satisfied by the first moment of and their
theoretical interpretation.Comment: 20 pages, 6 postscript figures (included), plain TeX, CERN-TH.7453/94
A few minor changes and a reference added around eqs.(3.8)-(3.12
An exotic k-essence interpretation of interactive cosmological models
We define a generalization of scalar fields with non-canonical kinetic term
which we call exotic k-essence or briefly, exotik. These fields are generated
by the global description of cosmological models with two interactive fluids in
the dark sector and under certain conditions, they correspond to usual
k-essences. The formalism is applied to the cases of constant potential and of
inverse square potential and also we develop the purely exotik version for the
modified holographic Ricci type of dark energy (MHR), where the equations of
state are not constant. With the kinetic function and the inverse
square potential we recover, through the interaction term, the identification
between k-essences and quintessences of exponential potential, already known
for Friedmann-Robertson-Walker and Bianchi type I geometries. Worked examples
are shown that include the self-interacting MHR and also models with crossing
of the phantom divide line (PDL).Comment: Revised version to be published in European Physical Journal
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