4,176 research outputs found
Higher twists in deep inelastic scattering
We perform an exploratory study of higher twist contributions to deep
inelastic scattering. We estimate the size of two major sources of higher
twist, namely absorptive corrections and the vector meson dominance (VMD)
contribution. We find that they give a sizeable higher twist component of F_2.
For example at x = 0.01 it is about 8% (17%) at Q^2 = 10 GeV^2 (4 GeV^2),
reaching up to 27% at x = 10^{-4} and Q^2 = 4 GeV^2. At the smaller x value the
largest contribution comes from absorptive corrections, while at the larger
values of x the VMD term dominates.Comment: The sign of the gluon rescattering twist-4 component has been
corrected and the manuscript modified accordingl
Simultaneous QCD analysis of diffractive and inclusive DIS data
We perform a NLO QCD analysis of deep-inelastic scattering data, in which we
account for absorptive corrections. These corrections are determined from a
simultaneous analysis of diffractive deep-inelastic data. The absorptive
effects are found to enhance the size of the gluon distribution at small x,
such that a negative input gluon distribution at Q^2 = 1 GeV^2 is no longer
required. We discuss the problem that the gluon distribution is valence-like at
low scales, whereas the sea quark distribution grows with decreasing x. Our
study hints at the possible importance of power corrections for Q^2 \simeq 1--2
GeV^2.Comment: 11 pages, 3 figures. Version published as a Rapid Communication in
Phys. Rev.
The intercept of the BFKL pomeron from Forward Jets at HERA
Recently the H1 and ZEUS collaborations have presented cross sections for DIS
events with a forward jet. The BFKL formalism is able to produce an excellent
fit to these data. The extracted intercept of the hard pomeron suggests that
when all higher order corrections are taken into account the cross section will
still rise very rapidly as expected for low dynamics.Comment: 10 pages, one figure, accepted for publication in PL
The Two-Component Non-Perturbative Pomeron and the G-Universality
In this communication we present a generalization of the Donnachie-Landshoff
model inspired by the recent discovery of a 2-component Pomeron in LLA-QCD by
Bartels, Lipatov and Vacca. In particular, we explore a new property, not
present in the usual Regge theory - the G-Universality - which signifies the
independence of one of the Pomeron components on the nature of the initial and
final hadrons. The best description of all the forward hadron-hadron, gamma-
gamma and gamma-proton data is obtained when G-universailty is imposed.
Moreover, the maximal (ln)**2 behaviour of the hadron amplitude, first
established by Heisenberg, is clearly favoured by the data.Comment: 5 pages, 2 tables, talk at the International Workshop on Diffraction
in High-Energy Physics "Diffraction 2000", Cetraro, Italy, September 2-7,
200
The effective action and the triple Pomeron vertex
We study integrations over light-cone momenta in the gauge invariant
effective action of high energy QCD. A regularization mechanism which allows
for the evaluation of the longitudinal integrations is presented. After a
rederivation of the reggeized gluon and the BFKL-equation from the effective
action, we study the 1-3 and 2-4 reggeized gluon transition vertex of QCD
Reggeon field theory and discuss their connection with the usual triple Pomeron
vertex of perturbative QCD.Comment: Talk given at the 3rd International Hadron Structure '09 Conference,
Tatranska Strba, Slovakia, 30 Aug - 3 Sep 2009; 4 pages, 16 figure
Atlantic Water advection and glacier responses at the margins of Svalbard since the deglaciation
Atlantic Water (AW) advection plays an important role in climatic, oceanographic and environmental conditions in the Arctic. Situated along the only deep connection between the Atlantic and the Arctic oceans, the Svalbard Archipelago is an ideal location to reconstruct the past AW advection history and document its linkage with local glacier dynamics. In the framework of this thesis, three sediment cores from the northern margins of Svalbard were chosen covering up to 15,500 years. Multi-proxy based reconstructions (applying benthic foraminiferal assemblages, sediment properties and geochemical tracers) revealed a rapid retreat of the ice sheet covering Svalbard during the deglaciation, closely connected to AW inflow. While conditions during the early Holocene were warmer than today when AW caused open waters and retreated glaciers, Arctic Water gained influence at the transition to the mid-Holocene, whereas glaciers re-advanced during the late Holocene
High Energy Behavior of a Six-Point R-Current Correlator in N=4 Supersymmetric Yang-Mills Theory
We study the high energy limit of a six-point R-current correlator in N=4
supersymmetric Yang-Mills theory for finite N_c. We make use of the framework
of perturbative resummation of large logarithms of the energy. More
specifically, we apply the (extended) generalized leading logarithmic
approximation. We find that the same conformally invariant two-to-four gluon
vertex occurs as in non-supersymmetric Yang-Mills theory. As a new feature we
find a direct coupling of the four-gluon t-channel state to the R-current
impact factor.Comment: 47 page
Physics at Low x
The QCD expectations concerning the deep inelastic lepton - hadron scattering
at low and their phenomenological implications for HERA are summarised.
Theoretical predictions for the structure function based on the
leading log resummation are presented and compared with the results
obtained from the Altarelli-Parisi equations. Theoretical predictions are
confronted with the recent data from HERA. The role of studying the final
states in deep inelastic scattering for revealing the dynamics at low is
emphasised and some dedicated measurements like deep inelastic plus jet events,
transverse energy flow and dijet production in deep inelastic scattering are
discussed.Comment: 16 pages, 8 figures, review talk presented at the Workshop "QCD94",
7-13 July 1994, Montpellier, France (to appear in the Proceedings of the
Workshop), Krak\'ow INP report N0 1681/PH, hard copies of the figures
available on request from the author at [email protected]
Regularized Newton Methods for X-ray Phase Contrast and General Imaging Problems
Like many other advanced imaging methods, x-ray phase contrast imaging and
tomography require mathematical inversion of the observed data to obtain
real-space information. While an accurate forward model describing the
generally nonlinear image formation from a given object to the observations is
often available, explicit inversion formulas are typically not known. Moreover,
the measured data might be insufficient for stable image reconstruction, in
which case it has to be complemented by suitable a priori information. In this
work, regularized Newton methods are presented as a general framework for the
solution of such ill-posed nonlinear imaging problems. For a proof of
principle, the approach is applied to x-ray phase contrast imaging in the
near-field propagation regime. Simultaneous recovery of the phase- and
amplitude from a single near-field diffraction pattern without homogeneity
constraints is demonstrated for the first time. The presented methods further
permit all-at-once phase contrast tomography, i.e. simultaneous phase retrieval
and tomographic inversion. We demonstrate the potential of this approach by
three-dimensional imaging of a colloidal crystal at 95 nm isotropic resolution.Comment: (C)2016 Optical Society of America. One print or electronic copy may
be made for personal use only. Systematic reproduction and distribution,
duplication of any material in this paper for a fee or for commercial
purposes, or modifications of the content of this paper are prohibite
Thermo-optical interactions in a dye-microcavity photon Bose-Einstein condensate
Superfluidity and Bose-Einstein condensation are usually considered as two
closely related phenomena. Indeed, in most macroscopic quantum systems, like
liquid helium, ultracold atomic Bose gases, and exciton-polaritons,
condensation and superfluidity occur in parallel. In photon Bose-Einstein
condensates realized in the dye microcavity system, thermalization does not
occur by direct interaction of the condensate particles as in the above
described systems, i.e. photon-photon interactions, but by absorption and
re-emission processes on the dye molecules, which act as a heat reservoir.
Currently, there is no experimental evidence for superfluidity in the dye
microcavity system, though effective photon interactions have been observed
from thermo-optic effects in the dye medium. In this work, we theoretically
investigate the implications of effective thermo-optic photon interactions, a
temporally delayed and spatially non-local effect, on the photon condensate,
and derive the resulting Bogoliubov excitation spectrum. The calculations
suggest a linear photon dispersion at low momenta, fulfilling the Landau's
criterion of superfluidity . We envision that the temporally delayed and
long-range nature of the thermo-optic photon interaction offer perspectives for
novel quantum fluid phenomena.Comment: 21 pages, 5 figure
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