24,371 research outputs found
Two-point motional Stark effect diagnostic for Madison Symmetric Torus
A high-precision spectral motional Stark effect (MSE) diagnostic provides internal magnetic field measurements for Madison Symmetric Torus (MST) plasmas. Currently, MST uses two spatial views-on the magnetic axis and on the midminor (off-axis) radius, the latter added recently. A new analysis scheme has been developed to infer both the pitch angle and the magnitude of the magnetic field from MSE spectra. Systematic errors are reduced by using atomic data from atomic data and analysis structure in the fit. Reconstructed current density and safety factor profiles are more strongly and globally constrained with the addition of the off-axis radius measurement than with the on-axis one only
Analysis of dilepton production in Au+Au collisions at sqrt(s_NN)=200 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach
We address dilepton production in Au+Au collisions at sqrt(s_NN)=200 GeV by
employing the parton-hadron-string dynamics (PHSD) off-shell transport
approach. Within the PHSD one goes beyond the quasiparticle approximation by
solving generalized transport equations on the basis of the off-shell
Kadanoff-Baym equations for the Green's functions in the phase-space
representation. The approach consistently describes the full evolution of a
relativistic heavy-ion collision from the initial hard scatterings and string
formation through the dynamical deconfinement phase transition to the
quark-gluon plasma (QGP) as well as hadronization and to the subsequent
interactions in the hadronic phase. {With partons described in the PHSD by the
dynamical quasiparticle model (DQPM) - matched to reproduce lattice QCD results
in thermodynamic equilibrium} - we calculate, in particular, the dilepton
radiation from partonic interactions through the reactions q+qbar->gamma^*,
q+qbar->gamma^*+g and q+g->gamma^*+q (qbar+g->gamma^*+qbar) in the early stage
of relativistic heavy-ion collisions. By comparing our results to the data from
the PHENIX Collaboration, we study the relative importance of different
dilepton production mechanisms and point out the regions in phase space where
partonic channels are dominant. Furthermore, explicit predictions are presented
for dileptons within the acceptance of the STAR detector system and compared to
the preliminary data.Comment: 11 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:1107.340
Thermal photon production in high-energy nuclear collisions
We use a boost-invariant one-dimensional (cylindrically symmetric) fluid
dynamics code to calculate thermal photon production in the central rapidity
region of S+Au and Pb+Pb collisions at SPS energy ( GeV/nucleon).
We assume that the hot matter is in thermal equilibrium throughout the
expansion, but consider deviations from chemical equilibrium in the high
temperature (deconfined) phase. We use equations of state with a first-order
phase transition between a massless pion gas and quark gluon plasma, with
transition temperatures in the range MeV.Comment: revised, now includes a_1 contribution. revtex, 10 pages plus 4
figures (uuencoded postscript
LFV in semileptonic decays and conversion in nuclei in SUSY-seesaw
Here we review the main results of LFV in the semileptonic tau decays (), (), and () as well as in conversion in nuclei within SUSY-seesaw scenarios,
and compare our predictions with the present experimental boundsComment: Talk given by M. J. Herrero in SUSY08 conference, Seou
The locally covariant Dirac field
We describe the free Dirac field in a four dimensional spacetime as a locally
covariant quantum field theory in the sense of Brunetti, Fredenhagen and Verch,
using a representation independent construction. The freedom in the geometric
constructions involved can be encoded in terms of the cohomology of the
category of spin spacetimes. If we restrict ourselves to the observable algebra
the cohomological obstructions vanish and the theory is unique. We establish
some basic properties of the theory and discuss the class of Hadamard states,
filling some technical gaps in the literature. Finally we show that the
relative Cauchy evolution yields commutators with the stress-energy-momentum
tensor, as in the scalar field case.Comment: 36 pages; v2 minor changes, typos corrected, updated references and
acknowledgement
Color-octet mechanism and J/psi polarization at LEP
Polarized heavy quarkonium productions in decays are considered. We
find that polarizations of the produced quarkonia are independent of that of
the parent Z^0 provided that one considers the energy distribution or the total
production rate. Produced J/psi's via the color-octet and the color- singlet
mechanisms are expected to be 19% and 29% longitudinally polarized,
respectively. The energy dependence of eta_{1,8}(x)=\frac{dGamma_{1,8}^L}{dx}
/\frac{dGamma_{1,8}}{d x} is very sensitive to the production mechanism, and
therefore the measurement of \eta(x)_exp will be an independent probe of the
color-octet mechanism.Comment: 15 pages, minor changes, version to be published in Phys. Rev.
A criterion for the nature of the superconducting transition in strongly interacting field theories : Holographic approach
It is beyond the present techniques based on perturbation theory to reveal
the nature of phase transitions in strongly interacting field theories.
Recently, the holographic approach has provided us with an effective dual
description, mapping strongly coupled conformal field theories to classical
gravity theories. Resorting to the holographic superconductor model, we propose
a general criterion for the nature of the superconducting phase transition
based on effective interactions between vortices. We find "tricritical" points
in terms of the chemical potential for U(1) charges and an effective
Ginzburg-Landau parameter, where vortices do not interact to separate the
second order (repulsive) from the first order (attractive) transitions. We
interpret the first order transition as the Coleman-Weinberg mechanism, arguing
that it is relevant to superconducting instabilities around quantum
criticality.Comment: 7 pages, 7 figure
Ozone Response to Aircraft Emissions: Sensitivity Studies with Two-dimensional Models
Our first intercomparison/assessment of the effects of a proposed high-speed civil transport (HSCT) fleet on the stratosphere is presented. These model calculations should be considered more as sensitivity studies, primarily designed to serve the following purposes: (1) to allow for intercomparison of model predictions; (2) to focus on the range of fleet operations and engine specifications giving minimal environmental impact; and (3) to provide the basis for future assessment studies. The basic scenarios were chosen to be as realistic as possible, using the information available on anticipated developments in technology. They are not to be interpreted as a commitment or goal for environmental acceptability
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