328 research outputs found
Central Exclusive Scalar Luminosities from the Linked Dipole Chain Model gluon densities
We investigate the implication of uncertainties in the unintegrated gluon
distribution for the predictions for central exclusive production of scalars at
hadron colliders. We use parameterizations of the kT-unintegrated gluon density
obtained from the Linked Dipole Chain model, applying different options for the
treatment of non-leading terms. We find that the luminosity function for
central exclusive production is very sensitive to details of the transverse
momentum distribution of the gluon which, contrary to the kT-integrated
distribution, is not very well constrained experimentally
The non-forward BFKL amplitude and rapidity gap physics
We discuss the BFKL approach to processes with large momentum transferred
through a rapidity gap. The Mueller and Tang scheme to the BFKL non-forward
parton-parton elastic scattering amplitude at large , is extended to include
higher conformal spins. The new contributions are found to decrease with
increasing energy, as follows from the gluon reggeisation phenomenon, and to
vanish for asymptotically high energies. However, at moderate energies and high
, the higher conformal spins dominate the amplitude. We illustrate the
effects by studying the production of two high jets separated by a
rapidity gap at HERA energies. In a simplified framework, we find excellent
agreement with the HERA photoproduction data once we incorporate the rapidity
gap survival probability against soft rescattering effects. We emphasize that
measurements of the analogous process in electroproduction may probe different
summations over conformal spins.Comment: Latex, 14 pages, 3 figures; the final version to appear in Phys.
Lett. B; a short discussion of the Tevatron data added; a previously missing
factor of i^n introduced in eq. (13
Study of the Linked Dipole Chain Model in heavy quark production at the Tevatron
We present calculations of charm and beauty production at Tevatron within the
framework of kT-factorization, using the unintegrated gluon distributions as
obtained from the Linked Dipole Chain model. The analysis covers transverse
momentum and rapidity distributions and the azimuthal correlations between b
and bbar quarks (or rather muons from their decay) which are powerful tests for
the different unintegrated gluon distributions. We compare the theoretical
results with recent experimental data taken by D0 and CDF collaborations at the
Tevatron Run I and II.Comment: 16 page
Transverse polarization in inclusive quasi-real photoproduction at the current fragmentation
It is shown that the recent HERMES data on the transverse
polarization in the inclusive quasi-real photoproduction at can be
accommodated by the strange quark scattering model. Relations with the quark
recombination approach are discussed.Comment: 5 pages, 3 figures, accepted by Eur. Phys. J.
Self-help interventions for anxiety disorders: An overview.
Anxiety disorders are highly prevalent and are associated with a marked impairment in quality of life and a huge economic cost to society. Unfortunately, a considerable number of people who struggle with anxiety do not seek or receive adequate treatment. Self-help interventions have been proposed to constitute a relatively cheap, effective, efficient, and low-threshold intervention for anxiety disorders. This paper offers a critical discussion of their advantages and disadvantages and the evidence for their effectiveness. We conclude that guided self-help can play a major role in mental health care for patients with anxiety disorders. However, several research questions need to be answered before broad-scale dissemination is possible. The Internet will continue to play a prominent role in the further development of this field of research and clinical practice
Dynamics of Brane-World Cosmological Models
We show that generically the initial singularity is isotropic in spatially
homogeneous cosmological models in the brane-world scenario. We then argue that
it is plausible that the initial singularity is isotropic in typical brane
world cosmological models. Therefore, brane cosmology naturally gives rise to a
set of initial data that provide the conditions for inflation to subsequently
take place, thereby solving the initial conditions problem and leading to a
self--consistent and viable cosmology.Comment: Final version. To appear in Physical Revie
Decomposition of the QCD String into Dipoles and Unintegrated Gluon Distributions
We present the perturbative and non-perturbative QCD structure of the
dipole-dipole scattering amplitude in momentum space. The perturbative
contribution is described by two-gluon exchange and the non-perturbative
contribution by the stochastic vacuum model which leads to confinement of the
quark and antiquark in the dipole via a string of color fields. This QCD string
gives important non-perturbative contributions to high-energy reactions. A new
structure different from the perturbative dipole factors is found in the
string-string scattering amplitude. The string can be represented as an
integral over stringless dipoles with a given dipole number density. This
decomposition of the QCD string into dipoles allows us to calculate the
unintegrated gluon distribution of hadrons and photons from the dipole-hadron
and dipole-photon cross section via kT-factorization.Comment: 43 pages, 14 figure
Pairing and Density Correlations of Stripe Electrons in a Two-Dimensional Antiferromagnet
We study a one-dimensional electron liquid embedded in a 2D antiferromagnetic
insulator, and coupled to it via a weak antiferromagnetic spin exchange
interaction. We argue that this model may qualitatively capture the physics of
a single charge stripe in the cuprates on length- and time scales shorter than
those set by its fluctuation dynamics. Using a local mean-field approach we
identify the low-energy effective theory that describes the electronic spin
sector of the stripe as that of a sine-Gordon model. We determine its phases
via a perturbative renormalization group analysis. For realistic values of the
model parameters we obtain a phase characterized by enhanced spin density and
composite charge density wave correlations, coexisting with subleading triplet
and composite singlet pairing correlations. This result is shown to be
independent of the spatial orientation of the stripe on the square lattice.
Slow transverse fluctuations of the stripes tend to suppress the density
correlations, thus promoting the pairing instabilities. The largest amplitudes
for the composite instabilities appear when the stripe forms an antiphase
domain wall in the antiferromagnet. For twisted spin alignments the amplitudes
decrease and leave room for a new type of composite pairing correlation,
breaking parity but preserving time reversal symmetry.Comment: Revtex, 28 pages incl. 5 figure
Delivery of hepato-pancreato-biliary surgery during the COVID-19 pandemic: an European-African Hepato-Pancreato-Biliary Association (E-AHPBA) cross-sectional survey
Background: The extent of the COVID-19 pandemic and the resulting response has varied globally. The European and African Hepato-Pancreato-Biliary Association (E-AHPBA), the premier representative body for practicing HPB surgeons in Europe and Africa, conducted this survey to assess the impact of COVID-19 on HPB surgery. Methods: An online survey was disseminated to all E-AHPBA members to assess the effects of the pandemic on unit capacity, management of HPB cancers, use of COVID-19 screening and other aspects of service delivery. Results: Overall, 145 (25%) members responded. Most units, particularly in COVID-high countries (>100,000 cases) reported insufficient critical care capacity and reduced HPB operating sessions compared to COVID-low countries. Delayed access to cancer surgery necessitated alternatives including increased neoadjuvant chemotherapy for pancreatic cancer and colorectal liver metastases, and locoregional treatments for hepatocellular carcinoma. Other aspects of service delivery including COVID-19 screening and personal protective equipment varied between units and countries. Conclusion: This study demonstrates that the COVID-19 pandemic has had a profound adverse impact on the delivery of HPB cancer care across the continents of Europe and Africa. The findings illustrate the need for safe resumption of cancer surgery in a ânewâ normal world with screening of patients and staff for COVID-19
Bose-Einstein Correlations of Neutral and Charged Pions in Hadronic Z Decays
Bose-Einstein correlations of both neutral and like-sign charged pion pairs
are measured in a sample of 2 million hadronic Z decays collected with the L3
detector at LEP. The analysis is performed in the four-momentum difference
range 300 MeV < Q < 2 GeV. The radius of the neutral pion source is found to be
smaller than that of charged pions. This result is in qualitative agreement
with the string fragmentation model
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