2,204 research outputs found
pi-/pi+ ratio in heavy ions collisions: Coulomb effect or chemical equilibration?
We calculate the pi-/pi+ ratio for Pb+Pb at CERN/SPS energies and for Au+Au
at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without
consideration of Coulomb effect an enhancement of this ratio at low mt is found
compatible with that observed in these experiments. Our calculations are based
on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which
described many other aspects of experimental data. In this model the observed
enhancement is a consequence of baryon and strangeness conservation and of
chemical equilibration of the system and is caused by the decay of produced
hyperons, which leads to a difference in the total number of positive and
negative pions as well. Based on the same approach, we also present results for
the pi-/pi+ ratio for S+S (CERN/SPS) collisions, where we find a similar
effect. The absence of the enhancement of the pi-/pi+ ratio in the S+S data
presented by the NA44 Collaboration, if confirmed, could indicate that chemical
equilibration has not yet been estabilished in this reaction.Comment: 8 pages and 2 figures, submmited to Phys. Lett. B. This reviewed
version (Nov.29,1996) contains more details about the model simulated
efficiency considering the experimental detection conditions. Other small
modifications were mad
Hydrodynamical analysis of single inclusive spectra and Bose-Einstein correlations for at 160 AGeV
We present the first analysis of preliminary data for at 160
using 3+1-dimensional relativistic hydrodynamics. We find excellent agreement
with the rapidity spectra of negative hadrons and the correlation measurements.
The data indicates a large amount of stopping; of the invariant energy
of the collision is thermalized and of the baryons are contained in the
central fireball. Within our model this implies that a quark-gluon-plasma of
lifetime 3.4 was formed.Comment: 13 pages, 5 Postscript figures (attached to this file as compressed
and uuencoded Postscript file
Upper Bound On Gluino Mass From Thermal Leptogenesis
Thermal leptogenesis requires the reheating temperature T_R \gsim 3\times
10^{9} GeV, which contradicts a recently obtained constraint on the reheating
temperature, T_R \lsim 10^6 GeV, for the gravitino mass of 100 GeV-10 TeV.
This stringent constraint comes from the fact that the hadronic decays of
gravitinos destroy very efficiently light elements produced by the Big-Bang
nucleosynthesis. However, it is not applicable if the gravitino is the lightest
supersymmetric particle (LSP). We show that this solution to the gravitino
problem works for the case where the next LSP is a scalar charged lepton or a
scalar neutrino. We point out that there is an upper bound on the gluino mass
as m_{\rm gluino} \lsim 1.8 TeV so that the energy density of gravitino does
not exceed the observed dark matter density .Comment: 11 pages, 3 figures. Minor corrections, new references added, to
appear in PL
Finger patterns produced by thermomagnetic instability in superconductors
A linear analysis of thermal diffusion and Maxwell equations is applied to
study the thermomagnetic instability in a type-II superconducting slab. It is
shown that the instability can lead to formation of spatially nonuniform
distributions of magnetic field and temperature. The distributions acquire a
finger structure with fingers perpendicular to the screening current direction.
We derive the criterion for the instability, and estimate its build-up time and
characteristic finger width. The fingering instability emerges when the
background electric field is larger than a threshold field, , and the
applied magnetic field exceeds a value . Numerical
simulations support the analytical results, and allow to follow the development
of the fingering instability beyond the linear regime. The fingering
instability may be responsible for the nucleation of dendritic flux patterns
observed in superconducting films using magneto-optical imaging.Comment: 8 pages, 6 figures, accepted to Phys. Rev. B; (new version: minor
changes
Primordial Non-Gaussianity in Models with Dark Matter Isocurvature Fluctuations
We investigate primordial non-Gaussianity and dark matter isocurvature
fluctuations in the modulated reheating and the curvaton scenarios. In these
scenarios, large non-Gaussianity can be generated, on the other hand, depending
on how dark matter is produced, too large isocurvature fluctuations can also
arise, which is inconsistent with current observations. In this paper, we study
this issue in a mixed scenario where the curvature fluctuations can also be
produced from the inflaton fluctuations as well as those from a light scalar
field such as the modulus and the curvaton. We show that primordial
fluctuations can be highly non-Gaussian without conflicting the current
constraint on isocurvature fluctuations for such mixed scenarios. However, if
the constraint on isocurvature fluctuations becomes severer as expected by the
Planck satellite, , a nonlinearity parameter for adiabatic
fluctuations, should be very small as , which would give
interesting implications for the generation mechanism of dark matter.
Non-Gaussianity from isocurvature fluctuations is also discussed in these
scenarios.Comment: 26 pages, 4 figures, accepted for publication in PR
The consequences of compromising the EU's free movement of persons principle on Swiss research: how to survive constrained access to regional funding
Between 2014 and 2016, Switzerland's access to some of the EU funding was limited after a referendum against mass immigration was accepted and the country refused to sign the free movement accord to the EU's newest member, Croatia. It is well documented that Switzerland has suffered from a drop in participation, funding and a decrease in consortium lead positions. However, there is no account of the consequences on institutional level. We therefore aimed at describing the immediate- and longer-term impact of the partial association status to the Swiss Tropical and Public Health Institute (Swiss TPH) and to identify key strategies for minimizing institutional damage during a limited access period to a key regional funding source. A quantitative analysis of the institute's grants database, from 2007 to 2019, did not show any clear trends related to the partial association status of Switzerland for funding and projects awarded. The qualitative outcomes changed along the timeline assessed; whereas in 2014 a range of negative effects were stated by Swiss TPH researchers, a survey conducted in 2019 with Swiss TPH applicants and project partners to Horizon 2020, revealed that most project leaders felt that the partial association did neither affect their external partners' willingness to collaborate nor Swiss TPH's role in the proposal or consortium. On the other hand, the institutional strategic goal of taking on consortia leads was delayed by several years as a direct consequence of the partial association. Also, the exclusion from European research networks and the lack of consultation of expertise by the European partner institutions was widely seen as damaging. A policy of favouring long-term partnerships over ad-hoc collaborations, along with constant and trustful communication, as immediate mitigation measure, helped averting some of the reputational and access damage. Moreover, the Swiss TPH business model based on a three-way strategy of research, education and services has proven highly viable allowing to build a large pool of potential funding sources internationally, resulting in relative resilience in terms of income lost
Large-order trend of the anomalous-dimensions spectrum of trilinear twist-3 quark operators
The anomalous dimensions of trilinear-quark operators are calculated at
leading twist by diagonalizing the one-gluon exchange kernel of the
renormalization-group type evolution equation for the nucleon distribution
amplitude. This is done within a symmetrized basis of Appell polynomials of
maximum degree for (up to order 400) by combining analytical and
numerical algorithms. The calculated anomalous dimensions form a degenerate
system, whose upper envelope shows asymptotically logarithmic behavior.Comment: 12 pages; 1 table; 4 figures as PS files; RevTex styl
Intrinsic Transverse Size Effect
Two recently proposed concepts to improve the perturbative calculation of
exclusive amplitudes, gluonic radiative corrections (Sudakov factor) and
confinement size effects (intrinsic transverse momentum) are combined to study
the neutron magnetic form factor in the space-like region. We find that nucleon
distribution amplitudes modelled on the basis of current QCD sum rules indicate
overlap with the existing data at the highest measured values of momentum
transfer. However, sizeable higher-order perturbative corrections (K-factor)
and/or higher-twist contributions cannot be excluded, although they may be
weaker than in the proton case.Comment: 12 pages LATEX, 4 figures as compressed uu-encoded PS-file, preprint
University of Wuppertal WU-B-94-16, University of Bochum RUB-TPII-04/94 (some
typos eliminated
Long-term Outcome after Surgical Closure of Atrial Septal Defect in Childhood with Extensive Assessment Including MRI Measurement of the Ventricles
Surgical closure of the secundum type of atrial septal defect (ASD) in childhood leads to excellent survival. However, relevant morbidity has been reported. Transcatheter closure of these defects has now become an alternative approach. To compare the results of the two different interventions, reliable data are needed on the long-term morbidity after defect closure with both methods. Patients were evaluated after a minimum of 10 years after surgical closure of an ASD in childhood. Assessment included analysis of perioperative data, interview, clinical examination, electrocardiogram, (ECG), 24-hour ECG, ergometry, chest radiograph, echocardiography, and MRI. A total of 66 patients underwent operation between 1971 and 1986 at our institution. Forty-eight of them (73%) were interviewed and 38 (58%) participated fully in the study program. Eighteen (27%) either refused to participate or were lost to follow-up. There were no substantial residual disorders, such as arrhythmias, right-sided heart dilatation, pulmonary hypertension, or reduced work capacity. Surgical closure of an ASD in childhood has an excellent long-term outcome. Surgical closure is thus the standard against which transcatheter closure needs to be measure
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