338 research outputs found
Instanton-Driven Saturation at Small x
We report on the interesting possibility of instanton-driven gluon saturation
in lepton-nucleon scattering at small Bjorken-x. Our results crucially involve
non-perturbative information from high-quality lattice simulations. The
conspicuous, intrinsic instanton size scale ~ 0.5 fm, as known from the
lattice, turns out to determine the saturation scale. A central result is the
identification of the ``colour glass condensate'' with the QCD-sphaleron state.Comment: 14 pages, 9 figure
QCD-Instantons and Saturation at Small x
We briefly report on the contribution of QCD-instantons to the phenomenon of
saturation in deep-inelastic scattering (DIS) at small Bjorken-x. The
explicitly known instanton gauge field serves as a concrete realization of an
underlying non-perturbative saturation mechanism associated with strong
classical fields. Two independent strategies were pursued, with consistent
results: On the one hand, an approach starting from instanton-perturbation
theory was considered and on the other hand, the scattering of a Wilson loop in
an instanton gauge field background. In both cases, the conspicuous, intrinsic
instanton size scale ~ 0.5 fm, as known from the lattice, turns out to
determine the saturation scale.Comment: 6 pages, 2 figures, presented at the Workshop on Strong and
Electroweak Matter (SEWM 2002), October 2-5, 2002, Heidelberg, German
Factorisation, Parton Entanglement and the Drell-Yan Process
We discuss the angular distribution of the lepton pair in the Drell-Yan
process, hadron+hadron -> \gamma^* X -> l^+ l^- X. This process gives
information on the spin-density matrix \rho^{(q,\bar{q})} of the annihilating
quark-antiquark pair in q+\bar{q} -> l^+ l^-. There is strong experimental
evidence that even for unpolarised initial hadrons \rho^{(q,\bar{q})} is
nontrivial, and therefore the quark-antiquark system is polarised. We discuss
the possibilities of a general \rho^{(q,\bar{q})} -which could be entangled-
and a factorising \rho^{(q,\bar{q})}. We argue that instantons may lead to a
nontrivial \rho^{(q,\bar{q})} of the type indicated by experiments.Comment: 14 pages, 2 figures, comments and references added; to appear in EPJ
Effective-Lagrangian approach to gamma gamma --> WW; II: Results and comparison with e+e- --> WW
We present a study of anomalous electroweak gauge-boson couplings which can
be measured in e+e- and gamma gamma collisions at a future linear collider like
ILC. We consider the gauge-boson sector of a locally SU(2) x U(1) invariant
effective Lagrangian with ten dimension-six operators added to the Lagrangian
of the Standard Model. These operators induce anomalous three- and
four-gauge-boson couplings and an anomalous gamma gamma H coupling. We
calculate the reachable sensitivity for the measurement of the anomalous
couplings in gamma gamma --> WW. We compare these results with the reachable
precision in the reaction e+e- --> WW on the one hand and with the bounds that
one can get from high-precision observables in Z decays on the other hand. We
show that one needs both the e+e- and the gamma gamma modes at an ILC to
constrain the largest possible number of anomalous couplings and that the
Giga-Z mode offers the best sensitivity for certain anomalous couplings.Comment: 25 pages, 1 figure, 7 tables, comments, references and a table added;
to appear in EPJ
Culture-Dependent Microbiome of the Ciona intestinalis Tunic: Isolation, Bioactivity Profiling and Untargeted Metabolomics
Ascidians and their associated microbiota are prolific producers of bioactive marine natural products. Recent culture-independent studies have revealed that the tunic of the solitary ascidian Cionaintestinalis (sea vase) is colonized by a diverse bacterial community, however, the biotechnological potential of this community has remained largely unexplored. In this study, we aimed at isolating the culturable microbiota associated with the tunic of C.intestinalis collected from the North and Baltic Seas, to investigate their antimicrobial and anticancer activities, and to gain first insights into their metabolite repertoire. The tunic of the sea vase was found to harbor a rich microbial community, from which 89 bacterial and 22 fungal strains were isolated. The diversity of the tunic-associated microbiota differed from that of the ambient seawater samples, but also between sampling sites. Fungi were isolated for the first time from the tunic of Ciona. The proportion of bioactive extracts was high, since 45% of the microbial extracts inhibited the growth of human pathogenic bacteria, fungi or cancer cell lines. In a subsequent bioactivity- and metabolite profiling-based approach, seven microbial extracts were prioritized for in-depth chemical investigations. Untargeted metabolomics analyses of the selected extracts by a UPLC-MS/MS-based molecular networking approach revealed a vast chemical diversity with compounds assigned to 22 natural product families, plus many metabolites that remained unidentified. This initial study indicates that bacteria and fungi associated with the tunic of C.intestinalis represent an untapped source of putatively new marine natural products with pharmacological relevance
Tailoring the frictional properties of granular media
A method of modifying the roughness of soda-lime glass spheres is presented,
with the purpose of tuning inter-particle friction. The effect of chemical
etching on the surface topography and the bulk frictional properties of grains
is systematically investigated. The surface roughness of the grains is measured
using white light interferometry and characterised by the lateral and vertical
roughness length scales. The underwater angle of repose is measured to
characterise the bulk frictional behaviour. We observe that the co-efficient of
friction depends on the vertical roughness length scale. We also demonstrate a
bulk surface roughness measurement using a carbonated soft drink.Comment: 10 pages, 17 figures, submitted to Phys. Rev.
Compatibility of phenomenological dipole cross sections with the Balitsky-Kovchegov equation
Phenomenological models of the dipole cross section that enters in the
description of for instance deep inelastic scattering at very high energies
have had considerable success in describing the available small-x data in both
the saturation region and the so-called extended geometric scaling (EGS)
region. We investigate to what extent such models are compatible with the
numerical solutions of the Balitsky-Kovchegov (BK) equation which is expected
to describe the nonlinear evolution in x of the dipole cross section in these
momentum regions. We find that in the EGS region the BK equation yields results
that are qualitatively different from those of phenomenological studies. In
particular, geometric scaling around the saturation scale is only obtained at
asymptotic rapidities. We find that in this limit, the anomalous dimension
\gamma(r,x) of phenomenological models approaches a limiting function that is
universal for a large range of initial conditions. At the saturation scale,
this function equals approximately 0.44, in contrast to the value 0.628
commonly used in the models. We further investigate the dependence of these
results on the starting distribution, the small-r limit of the anomalous
dimension for fixed rapidities and the x-dependence of the saturation scale.Comment: 14 pages, 8 figures. Extensive revisions, several new results, plots,
references and conclusions added; to appear in Phys.Rev.
Semiclassical Description of Tunneling in Mixed Systems: The Case of the Annular Billiard
We study quantum-mechanical tunneling between symmetry-related pairs of
regular phase space regions that are separated by a chaotic layer. We consider
the annular billiard, and use scattering theory to relate the splitting of
quasi-degenerate states quantized on the two regular regions to specific paths
connecting them. The tunneling amplitudes involved are given a semiclassical
interpretation by extending the billiard boundaries to complex space and
generalizing specular reflection to complex rays. We give analytical
expressions for the splittings, and show that the dominant contributions come
from {\em chaos-assisted}\/ paths that tunnel into and out of the chaotic
layer.Comment: 4 pages, uuencoded postscript file, replaces a corrupted versio
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