7,936 research outputs found
Gauge links, TMD-factorization, and TMD-factorization breaking
In this section, we discuss some basic features of transverse momentum
dependent, or unintegrated, parton distribution functions. In particular, when
these correlation functions are combined in a factorization formulae with hard
processes beyond the simplest cases, there are basic problems with universality
and factorization. We discuss some of these problems as well as the
opportunities that they offer.Comment: 9 pages, 10 figures Gluons and the quark sea at high energies:
distributions, polarization, tomograph
Scattered light mapping of protoplanetary disks
High-contrast scattered light observations have revealed the surface
morphology of several dozens of protoplanetary disks at optical and
near-infrared wavelengths. Inclined disks offer the opportunity to measure part
of the phase function of the dust grains that reside in the disk surface which
is essential for our understanding of protoplanetary dust properties and the
early stages of planet formation. We aim to construct a method which takes into
account how the flaring shape of the scattering surface of an (optically thick)
protoplanetary disk projects onto the image plane of the observer. This allows
us to map physical quantities (scattering radius and scattering angle) onto
scattered light images and retrieve stellar irradiation corrected (r^2-scaled)
images and dust phase functions. We apply the method on archival polarized
intensity images of the protoplanetary disk around HD 100546 that were obtained
with VLT/SPHERE in R'-band and VLT/NACO in H- and Ks-band. The brightest side
of the r^2-scaled R'-band polarized intensity image of HD 100546 changes from
the far to the near side of the disk when a flaring instead of a geometrically
flat disk surface is used for the r^2-scaling. The decrease in polarized
surface brightness in the scattering angle range of ~40-70 deg is likely a
result of the dust phase function and degree of polarization which peak in
different scattering angle regimes. The derived phase functions show part of a
forward scattering peak which indicates that large, aggregate dust grains
dominate the scattering opacity in the disk surface. Projection effects of a
protoplanetary disk surface need to be taken into account to correctly
interpret scattered light images. Applying the correct scaling for the
correction of stellar irradiation is crucial for the interpretation of the
images and the derivation of the dust properties in the disk surface layer.Comment: Accepted for publication in A&A, 6 pages, 3 figure
An interferometric study of the post-AGB binary 89 Herculis. II Radiative transfer models of the circumbinary disk
The presence of disks and outflows is widespread among post-AGB binaries. In
the first paper of this series, a surprisingly large fraction of optical light
was found to be resolved in the 89 Her post-AGB system. The data showed this
flux to arise from close to the central binary. Scattering off the inner rim of
the circumbinary disk, or in a dusty outflow were suggested as two possible
origins. With detailed dust radiative transfer models of the disk we aim to
discriminate between these two configurations. By including Herschel/SPIRE
photometry, we extend the SED such that it now fully covers UV to sub-mm
wavelengths. The MCMax radiative transfer code is used to create a large grid
of disk models. Our models include a self-consistent treatment of dust settling
as well as of scattering. A Si-rich composition with two additional opacity
sources, metallic Fe or amorphous C, are tested. The SED is fit together with
mid-IR (MIDI) visibilities as well as the optical and near-IR visibilities of
Paper I, to constrain the structure of the disk and in particular of its inner
rim. The near-IR visibility data require a smooth inner rim, here obtained with
a two-power-law parameterization of the radial surface density distribution. A
model can be found that fits all the IR photometric and interferometric data
well, with either of the two continuum opacity sources. Our best-fit passive
models are characterized by a significant amount of mm-sized grains, which are
settled to the midplane of the disk. Not a single disk model fits our data at
optical wavelengths though, the reason being the opposing constraints imposed
by the optical and near-IR interferometric data. A geometry in which a passive,
dusty, and puffed-up circumbinary disk is present, can reproduce all the IR but
not the optical observations of 89 Her. Another dusty, outflow or halo,
component therefore needs to be added to the system.Comment: 15 pages, in pres
Low velocity quantum reflection of Bose-Einstein condensates
We studied quantum reflection of Bose-Einstein condensates at normal
incidence on a square array of silicon pillars. For incident velocities of
2.5-26 mm/s observations agreed with theoretical predictions that the
Casimir-Polder potential of a reduced density surface would reflect slow atoms
with much higher probability. At low velocities (0.5-2.5 mm/s), we observed
that the reflection probability saturated around 60% rather than increasing
towards unity. We present a simple model which explains this reduced
reflectivity as resulting from the combined effects of the Casimir-Polder plus
mean field potential and predicts the observed saturation. Furthermore, at low
incident velocities, the reflected condensates show collective excitations.Comment: 4 figure
Single transverse-spin asymmetry for -meson production in semi-inclusive deep inelastic scattering
We study the single-transverse spin asymmetry for open charm production in
the semi-inclusive lepton-hadron deep inelastic scattering. We calculate the
asymmetry in terms of the QCD collinear factorization approach for mesons
at high enough , and find that the asymmetry is proportional to the
twist-three tri-gluon correlation function in the proton. With a simple model
for the tri-gluon correlation function, we estimate the asymmetry for both
COMPASS and eRHIC kinematics, and discuss the possibilities of extracting the
tri-gluon correlation function in these experiments.Comment: 13 pages, 7 figure
TMDlib and TMDplotter: library and plotting tools for transverse-momentum-dependent parton distributions
Transverse-momentum-dependent distributions (TMDs) are central in high-energy
physics from both theoretical and phenomenological points of view. In this
manual we introduce the library, TMDlib, of fits and parameterisations for
transverse-momentum-dependent parton distribution functions (TMD PDFs) and
fragmentation functions (TMD FFs) together with an online plotting tool,
TMDplotter. We provide a description of the program components and of the
different physical frameworks the user can access via the available
parameterisations.Comment: version 2, referring to TMDlib 1.0.2 - comments and references adde
Parton Distributions in Light-Cone Gauge: Where Are the Final-State Interactions?
We show that the final-state interaction effects in the single target spin
asymmetry discovered by Brodsky et al. can be reproduced by either a standard
light-cone gauge definition of the parton distributions with a prescription of
the light-cone singularities consistent with the light-cone gauge link, or a
modified light-cone gauge definition with a gauge link involving the gauge
potential at the spatial infinity.Comment: 9 pages, 2 figures, additional results are adde
Hadron mass corrections in semi-inclusive deep inelastic scattering
We derive mass corrections for semi-inclusive deep inelastic scattering of
leptons from nucleons using a collinear factorization framework which
incorporates the initial state mass of the target nucleon and the final state
mass of the produced hadron. The formalism is constructed specifically to
ensure that physical kinematic thresholds for the semi-inclusive process are
explicitly respected. A systematic study of the kinematic dependencies of the
mass corrections to semi-inclusive cross sections reveals that these are even
larger than for inclusive structure functions, especially at very small and
very large hadron momentum fractions. The hadron mass corrections compete with
the experimental uncertainties at kinematics typical of current facilities, and
will be important to efforts at extracting parton distributions or
fragmentation functions from semi-inclusive processes at intermediate energies.Comment: 22 pages, 6 figures; expanded discussion of kinematics and new
scaling variable; appendix comparing collinear frames included; version to
appear in JHE
Inverse Langmuir method for oligonucleotide microarray analysis
<p>Abstract</p> <p>Background</p> <p>An algorithm for the analysis of Affymetrix Genechips is presented. This algorithm, referred to as the Inverse Langmuir Method (ILM), estimates the binding of transcripts to complementary probes using DNA/RNA hybridization free energies, and the hybridization between partially complementary transcripts in solution using RNA/RNA free energies. The balance between these two competing reactions allows for the translation of background-subtracted intensities into transcript concentrations.</p> <p>Results</p> <p>To validate the ILM, it is applied to publicly available microarray data from a multi-lab comparison study. Here, microarray experiments are performed on samples which deviate only in few genes. The log<sub>2 </sub>fold change between these two samples, as obtained from RT-PCR experiments, agrees well with the log<sub>2 </sub>fold change as obtained with the ILM, indicating that the ILM determines changes in the expression level accurately. We also show that the ILM allows for the identification of outlying probes, as it yields independent concentration estimates per probe.</p> <p>Conclusion</p> <p>The ILM is robust and offers an interesting alternative to purely statistical algorithms for microarray data analysis.</p
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