1,191 research outputs found
Strong coupling expansion for Yang-Mills theory at finite temperature
Euclidean strong coupling expansion of the partition function is applied to
lattice Yang-Mills theory at finite temperature, i.e. for lattices with a
compactified temporal direction. The expansions have a finite radius of
convergence and thus are valid only for , where
denotes the nearest singularity of the free energy on the real axis. The
accessible temperature range is thus the confined regime up to the
deconfinement transition. We have calculated the first few orders of these
expansions of the free energy density as well as the screening masses for the
gauge groups SU(2) and SU(3). The resulting free energy series can be summed up
and corresponds to a glueball gas of the lowest mass glueballs up to the
calculated order. Our result can be used to fix the lower integration constant
for Monte Carlo calculations of the thermodynamic pressure via the integral
method, and shows from first principles that in the confined phase this
constant is indeed exponentially small. Similarly, our results also explain the
weak temperature dependence of glueball screening masses below , as
observed in Monte Carlo simulations. Possibilities and difficulties in
extracting from the series are discussed.Comment: 7 pages, 3 figures, 1 tables, corrected typo
The RHMC algorithm for theories with unknown spectral bounds
The Rational Hybrid Monte Carlo (RHMC) algorithm extends the Hybrid Monte
Carlo algorithm for lattice QCD simulations to situations involving fractional
powers of the determinant of the quadratic Dirac operator. This avoids the
updating increment () dependence of observables which plagues the Hybrid
Molecular-dynamics (HMD) method. The RHMC algorithm uses rational
approximations to fractional powers of the quadratic Dirac operator. Such
approximations are only available when positive upper and lower bounds to the
operator's spectrum are known. We apply the RHMC algorithm to simulations of 2
theories for which a positive lower spectral bound is unknown: lattice QCD with
staggered quarks at finite isospin chemical potential and lattice QCD with
massless staggered quarks and chiral 4-fermion interactions (QCD). A
choice of lower bound is made in each case, and the properties of the RHMC
simulations these define are studied. Justification of our choices of lower
bounds is made by comparing measurements with those from HMD simulations, and
by comparing different choices of lower bounds.Comment: Latex(Revtex 4) 25 pages, 8 postscript figure
Overlap Dirac operator at nonzero chemical potential and random matrix theory
We show how to introduce a quark chemical potential in the overlap Dirac
operator. The resulting operator satisfies a Ginsparg-Wilson relation and has
exact zero modes. It is no longer gamma_5-hermitian, but its nonreal
eigenvalues still occur in pairs. We compute the spectral density of the
operator on the lattice and show that, for small eigenvalues, the data agree
with analytical predictions of nonhermitian chiral random matrix theory for
both trivial and nontrivial topology.Comment: 4 pages, 2 figure
Mapping the phase diagram of strongly interacting matter
We employ a conformal mapping to explore the thermodynamics of strongly
interacting matter at finite values of the baryon chemical potential .
This method allows us to identify the singularity corresponding to the critical
point of a second-order phase transition at finite , given information
only at . The scheme is potentially useful for computing thermodynamic
properties of strongly interacting hot and dense matter in lattice gauge
theory. The technique is illustrated by an application to a chiral effective
model.Comment: 5 pages, 3 figures; published versio
WIMP Dark Matter and the QCD Equation of State
Weakly Interacting Massive Particles (WIMPs) of mass m freeze out at a
temperature T_f ~ m/25, i.e. in the range 400 MeV -- 40 GeV for a particle in
the typical mass range 10 -- 1000 GeV. The WIMP relic density, which depends on
the effective number of relativistic degrees of freedom at T_f, may be measured
to better than 1% by Planck, warranting comparable theoretical precision.
Recent theoretical and experimental advances in the understanding of high
temperature QCD show that the quark gluon plasma departs significantly from
ideal behaviour up to temperatures of several GeV, necessitating an improvement
of the cosmological equation of state over those currently used. We discuss how
this increases the relic density by approximately 1.5 -- 3.5% in benchmark
mSUGRA models, with an uncertainly in the QCD corrections of 0.5 -- 1 %. We
point out what further work is required to achieve a theoretical accuracy
comparable with the expected observational precision, and speculate that the
effective number of degrees of freedom at T_f may become measurable in the
foreseeable future.Comment: 4pp, 2figs. More info including Matlab scripts used to generate
equation of state curves at
http://www.pact.cpes.sussex.ac.uk/arXiv/hep-ph/0501232
Evidence for O(2) universality at the finite temperature transition for lattice QCD with 2 flavours of massless staggered quarks
We simulate lattice QCD with 2 flavours of massless quarks on lattices of
temporal extent N_t=8, to study the finite temperature transition from hadronic
matter to a quark-gluon plasma. A modified action which incorporates an
irrelevant chiral 4-fermion interaction is used, which allows simulations at
zero quark mass. We obtain excellent fits of the chiral condensates to the
magnetizations of a 3-dimensional O(2) spin model on lattices small enough to
model the finite size effects. This gives predictions for correlation lengths
and chiral susceptibilities from the corresponding spin-model quantities. These
are in good agreement with our measurements over the relevant range of
parameters. Binder cumulants are measured, but the errors are too large to draw
definite conclusions. From the properties of the O(2) spin model on the
relatively small lattices with which we fit our `data', we can see why earlier
attempts to fit staggered lattice data to leading-order infinite-volume scaling
functions, as well as finite size scaling studies, failed and led to erroneous
conclusions.Comment: 27 pages, Latex with 10 postscript figures. Some of the discussions
have been expanded to satisfy a referee. Typographical errors were correcte
Use of recurrence quantification analysis to examine associations between changes in text structure across an expressive writing intervention and reductions in distress symptoms in women wth breast cancer
The current study presents an exploratory analysis of using Recurrence Quantification Analysis (RQA) to analyze text data from an Expressive Writing Intervention (EWI) for Danish women treated for Breast Cancer. The analyses are based on the analysis of essays from a subsample with the average age 54.6 years (SD = 9.0), who completed questionnaires for cancer-related distress (IES) and depression symptoms (BDI-SF). The results show a significant association between an increase in recurrent patterns of text structure from first to last writing session and a decrease in cancer-related distress at 3 months post-intervention. Furthermore, the change in structure from first to last essay displayed a moderate, but significant correlation with change in cancer-related distress from baseline to 9 months post-intervention. The results suggest that changes in recurrence patterns of text structure might be an indicator of cognitive restructuring that leads to amelioration of cancer-specific distress
Using TPACK to examine teacher professional development for online and blended learning
Given the current rise of educational technology, more and more teachers are able to deliver their courses partially or fully online. This demands a new way of looking at teaching and learning, and raises many questions (e.g. how to become an online teacher). Therefore, many institutions and professionals try to meet such demands by offering professional development initiatives, aiming to provide teachers with new knowledge, skills, and attitudes towards teaching in an online setting. The technological, pedagogical, and content knowledge (TPACK) framework provides meaningful insights into teachers' necessary knowledge requirements for technology integration. Using the TPACK framework, this paper presents an overview and first analysis of the emphases placed by different teacher professional development approaches. This study will investigate the teacher professional development approaches of research articles by conducting a content analysis of each article, and by comparing the teacher professional development approaches. The analysis consists of sorting the textual data into different categories, and identifying different patterns and themes, which will be held against the TPACK framework. This is done for each individual study (within-case analysis) and between the studies (cross-case analysis). Furthermore, the initial results of this study will be discussed and the first recommendations for future research and practice will be formulated. Moreover, the results can be beneficial for practitioners involved in teacher professional development with regard to online and blended learning, to guide the design, development, implementation, and evaluation of a professional development approach. Therefore, the findings of this article can be of use to teachers, institutions, and professionals who wish to gain more insight into the current trends of existing professional development approaches, and provide them with a more thorough understanding of the initiatives that support teachers to become effective in online and blended learning. Further research could investigate if there is a link between the addressed TPACK elements in a teacher professional development approach and the retained results
补贴作为应对市场失灵的手段:欧盟国家援助政策对中国的启示
This paper discusses the role of subsidies in correcting market failures from the perspective of EU State aid policy. In recent years, one can notice a clear shift towards a 'more economic approach’ and a stronger focus on efficiency by the European Commission. However, this stronger focus on efficiency with regard to a politically sensitive area such as State aid is not self-evident, and also raises the question why other jurisdictions do not have a similar control on market intervention by States (US) or provinces (China). It also raises the question whether controlling the efficiency of government spending should be a task of the EU rathert han Member States. The aim of this paper is therefore to critically assess the changing goals of EU State aid policy, from market integration and equity to efficiency and fiscal discipline. Possible implications for China, in the form of a stricter control on subsidies,are also discussed
String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields
We present clear numerical evidence for string breaking in three-dimensional
SU(2) gauge theory with fundamental bosonic matter through a mixing analysis
between Wilson loops and meson operators representing bound states of a static
source and a dynamical scalar. The breaking scale is calculated in the
continuum limit. In units of the lightest glueball we find . The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results
and conclusions unchange
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