237 research outputs found
The Fading of Symmetry Non-restoration at Finite Temperature
The fate of symmetries at high temperature determines the dynamics of the
very early universe. It is conceivable that temperature effects favor symmetry
breaking instead of restoration. Concerning global symmetries, the non-linear
sigma model is analyzed in detail. For spontaneously broken gauge symmetries,
we propose the gauge boson magnetic mass as a ``flag'' for symmetry
(non)-restoration. We consider several cases: the standard model with one and
two Higgs doublets in the perturbative regime, and the case of a strongly
interacting Higgs sector. The latter is done in a model independent way with
the tools provided by chiral Lagrangians. Our results clearly point towards
restoration, a pattern consistent with recent lattice computations for global
symmetries. In addition, we explicitly verify invariance for gauge
theories at finite temperature.Comment: 28 pages, Latex2e, 28 figures, two typos corrected, conclusions
remain unchange
The dynamical origin of the refinement of the Gribov-Zwanziger theory
In recent years, the Gribov-Zwanziger action was refined by taking into
account certain dimension 2 condensates. In this fashion, one succeeded in
bringing the gluon and the ghost propagator obtained from the GZ model in
qualitative and quantitative agreement with the lattice data. In this paper, we
shall elaborate further on this aspect. First, we shall show that more
dimension 2 condensates can be taken into account than considered so far and,
in addition, we shall give firm evidence that these condensates are in fact
present by discussing the effective potential. It follows thus that the
Gribov-Zwanziger action dynamically transforms itself into the refined version,
thereby showing that the continuum nonperturbative Landau gauge fixing, as
implemented by the Gribov-Zwanziger approach, is consistent with lattice
simulations.Comment: 36 pages, 4 figure
Indirect lattice evidence for the Refined Gribov-Zwanziger formalism and the gluon condensate in the Landau gauge
We consider the gluon propagator at various lattice sizes and
spacings in the case of pure SU(3) Yang-Mills gauge theories using the Landau
gauge fixing. We discuss a class of fits in the infrared region in order to
(in)validate the tree level analytical prediction in terms of the (Refined)
Gribov-Zwanziger framework. It turns out that an important role is played by
the presence of the widely studied dimension two gluon condensate
. Including this effect allows to obtain an acceptable fit up to
1 \'{a} 1.5 GeV, while corroborating the Refined Gribov-Zwanziger prediction
for the gluon propagator. We also discuss the infinite volume extrapolation,
leading to the estimate . As a byproduct, we can
also provide the prediction obtained at
the renormalization scale .Comment: 17 pages, 10 figures, updated version, accepted for publication in
Phs.Rev.
Drake Antarctic Agile Meteor Radar (DrAAMER) First Results: Configuration and Comparison of Mean and Tidal Wind and Gravity Wave Momentum Flux Measurements with SAAMER
A new-generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1degS) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8degS). Motivations for the radars include the "hotspot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contribute most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from approx.20 to >70 m/s. In contrast, the diurnal tide and various planetary waves achieve maximum winds of approx.10 to 20 m/s. Monthly-mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below approx.85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this "hotspot"
apeNEXT: A multi-TFlops Computer for Simulations in Lattice Gauge Theory
We present the APE (Array Processor Experiment) project for the development
of dedicated parallel computers for numerical simulations in lattice gauge
theories. While APEmille is a production machine in today's physics simulations
at various sites in Europe, a new machine, apeNEXT, is currently being
developed to provide multi-Tflops computing performance. Like previous APE
machines, the new supercomputer is largely custom designed and specifically
optimized for simulations of Lattice QCD.Comment: Poster at the XXIII Physics in Collisions Conference (PIC03),
Zeuthen, Germany, June 2003, 3 pages, Latex. PSN FRAP15. Replaced for adding
forgotten autho
CCC meets ICU: Redefining the role of critical care of cancer patients
<p>Abstract</p> <p>Background</p> <p>Currently the majority of cancer patients are considered ineligible for intensive care treatment and oncologists are struggling to get their patients admitted to intensive care units. Critical care and oncology are frequently two separate worlds that communicate rarely and thus do not share novel developments in their fields. However, cancer medicine is rapidly improving and cancer is eventually becoming a chronic disease. Oncology is therefore characterized by a growing number of older and medically unfit patients that receive numerous novel drug classes with unexpected side effects.</p> <p>Discussion</p> <p>All of these changes will generate more medically challenging patients in acute distress that need to be considered for intensive care. An intense exchange between intensivists, oncologists, psychologists and palliative care specialists is warranted to communicate the developments in each field in order to improve triage and patient treatment. Here, we argue that "critical care of cancer patients" needs to be recognized as a medical subspecialty and that there is an urgent need to develop it systematically.</p> <p>Conclusion</p> <p>As prognosis of cancer improves, novel therapeutic concepts are being introduced and more and more older cancer patients receive full treatment the number of acutely ill patients is growing significantly. This development a major challenge to current concepts of intensive care and it needs to be redefined who of these patients should be treated, for how long and how intensively.</p
Dpes massless QCD have vacuum energy?
It is widely thought that this question has a positive answer, but we argue
that the support for this belief from both experiment and theory is weak or
nonexistent. We then list some of the ramifications of a negative answer.Comment: 8 pages, no figures, version to appear in NJ
Formalism for dilepton production via virtual photon bremsstrahlung in hadronic reactions
We derive a set of new formulas for various distributions in dilepton
production via virtual photon bremsstrahlung from pseudoscalar mesons and
unpolarized spin-one-half fermions. These formulas correspond to the leading
and sub-leading terms in the Low-Burnett-Kroll expansion for real photon
bremsstrahlung. The relation of our leading-term formulas to previous works is
also shown. Existing formulas are examined in the light of Lorentz covariance
and gauge invariance. Numerical comparison is made in a simple example, where
an "exact" formula and real photon data exist. The results reveal large
discrepancies among different bremsstrahlung formulas. Of all the leading-term
bremsstrahlung formulas, the one derived in this work agrees best with the
exact formula. The issues of M_T-scaling and event generators are also
addressed.Comment: 37 pages, RevTeX, epsf.sty, 10 embedded figure
The apeNEXT project
Numerical simulations in theoretical high-energy physics (Lattice QCD) require huge computing resources. Several generations of massively parallel computers optimised for these applications have been developed within the APE (array processor experiment) project. Large prototype systems of the latest generation, apeNEXT, are currently being assembled and tested. This contribution explains how the apeNEXT architecture is optimised for Lattice QCD, provides an overview of the hardware and software of apeNEXT, and describes its new features, like the SPMD programming model and the C compiler
Renormalisation constants of quark bilinears in lattice QCD with four dynamical Wilson quarks
We present preliminary results of the non-perturbative computation of the
RI-MOM renormalisation constants in a mass-independent scheme for the action
with Iwasaki glue and four dynamical Wilson quarks employed by ETMC. Our
project requires dedicated gauge ensembles with four degenerate sea quark
flavours at three lattice spacings and at several values of the standard and
twisted quark mass parameters. The RI-MOM renormalisation constants are
obtained from appropriate O(a) improved estimators extrapolated to the chiral
limit.Comment: 7 pages, 8 figures, Talk presented at the XXIX International
Symposium on Lattice Field Theory (Lattice 2011), July 10-16, 2011, Squaw
Valley, Lake Tahoe, California, US
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