186 research outputs found
Quantitative comparison of filtering methods in lattice QCD
We systematically compare filtering methods used to extract topological
excitations (like instantons, calorons, monopoles and vortices) from lattice
gauge configurations, namely APE-smearing and spectral decompositions based on
lattice Dirac and Laplace operators. Each of these techniques introduces
ambiguities, which can invalidate the interpretation of the results. We show,
however, that all these methods, when handled with care, reveal very similar
topological structures. Hence, these common structures are free of ambiguities
and faithfully represent infrared degrees of freedom in the QCD vacuum. As an
application we discuss an interesting power-law for the clusters of filtered
topological charge.Comment: 6 pages, 18 plots in 5 figures; final version as published in EPJ A;
section 4 was adde
Hadron Properties with FLIC Fermions
The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of
nonperturbative O(a)-improvement in lattice fermion actions offering near
continuum results at finite lattice spacing. It provides computationally
inexpensive access to the light quark mass regime of QCD where chiral
nonanalytic behaviour associated with Goldstone bosons is revealed. The
motivation and formulation of FLIC fermions, its excellent scaling properties
and its low-lying hadron mass phenomenology are presented.Comment: 29 pages, 13 figures, 6 tables. Contribution to lecure notes in 2nd
Cairns Topical Workshop on Lattice Hadron Physics 2003 (LHP 2003), Cairns,
Australia, 22-30 Jul 200
Excited Baryons in Lattice QCD
We present first results for the masses of positive and negative parity
excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action
and a fat-link irrelevant clover (FLIC) fermion action in which only the
irrelevant operators are constructed with APE-smeared links. The results are in
agreement with earlier calculations of N^* resonances using improved actions
and exhibit a clear mass splitting between the nucleon and its chiral partner.
An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a
small mass splitting. The study of different Lambda interpolating fields
suggests a similar splitting between the lowest two Lambda1/2^- octet states.
However, the empirical mass suppression of the Lambda^*(1405) is not evident in
these quenched QCD simulations, suggesting a potentially important role for the
meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating
fields.Comment: Correlation matrix analysis performed. Increased to 400
configurations. 22 pages, 13 figures, 15 table
Topological Structure of the QCD Vacuum Revealed by Overlap Fermions
Overlap fermions preserve a remnant of chiral symmetry on the lattice. They
are a powerful tool to investigate the topological structure of the vacuum of
Yang-Mills theory and full QCD. Recent results concerning the localization of
topological charge and the localization and local chirality of the overlap
eigenmodes are reported. The charge distribution is radically different, if a
spectral cut-off for the Dirac eigenmodes is applied. The density q(x) is
changing from the scale-a charge density (with full lattice resolution) to the
ultraviolet filtered charge density. The scale-a density, computed on the Linux
cluster of LRZ, has a singular, sign-coherent global structure of co-dimension
1 first described by the Kentucky group. We stress, however, the cluster
properties of the UV filtered topological density resembling the instanton
picture. The spectral cut-off can be mapped to a bosonic smearing procedure.
The UV filtered field strength reveals a high degree of (anti)selfduality at
"hot spots" of the action. The fermionic eigenmodes show a high degree of local
chirality. The lowest modes are seen to be localized in low-dimensional
space-time regions.Comment: 13 pages, 11 figures, accepted to appear in the Proceedings of "HLRB,
KONWIHR and Linux-Cluster: Review, Results and Future Projects Workshop",
Leibniz Rechenzentrum Munich, December 200
The self-dual gauge fields and the domain wall fermion zero modes
A new type of gauge fixing of the Coulomb gauge domain wall fermion system
that reduces the fluctuation of the effective running coupling and the
effective mass of arbitrary momentum direction including the region outside the
cylinder cut region is proposed and tested in the
gauge configurations of RBC/UKQCD collaboration.
The running coupling at the lowest momentum point does not show infrared
suppression and compatible with the experimental data extracted from the JLab
collaboration. The source of the fluctuation of the effective mass near
momentum 0.6GeV region is expected to be due to the domain wall fermion
zero modes.Comment: 12 pages 2 figures, extended arguments and references adde
Conserved Quantities in Background Independent Theories
We discuss the difficulties that background independent theories based on
quantum geometry encounter in deriving general relativity as the low energy
limit. We follow a geometrogenesis scenario of a phase transition from a
pre-geometric theory to a geometric phase which suggests that a first step
towards the low energy limit is searching for the effective collective
excitations that will characterize it. Using the correspondence between the
pre-geometric background independent theory and a quantum information
processor, we are able to use the method of noiseless subsystems to extract
such coherent collective excitations. We illustrate this in the case of locally
evolving graphs.Comment: 11 pages, 3 figure
Numerical study of lattice index theorem usingimproved cooling and overlap fermions
We investigate topological charge and the index theorem on finite lattices
numerically. Using mean field improved gauge field configurations we calculate
the topological charge Q using the gluon field definition with -improved cooling and an -improved field strength tensor
. We also calculate the index of the massless overlap fermion
operator by directly measuring the differences of the numbers of zero modes
with left- and right--handed chiralities. For sufficiently smooth field
configurations we find that the gluon field definition of the topological
charge is integer to better than 1% and furthermore that this agrees with the
index of the overlap Dirac operator, i.e., the Atiyah-Singer index theorem is
satisfied. This establishes a benchmark for reliability when calculating
lattice quantities which are very sensitive to topology.Comment: 15 pages, 1 figure
Ten steps or climbing a mountain: A study of Australian health professionals' perceptions of implementing the baby friendly health initiative to protect, promote and support breastfeeding
Background: The Baby Friendly Hospital (Health) Initiative (BFHI) is a global initiative aimed at protecting,
promoting and supporting breastfeeding and is based on the ten steps to successful breastfeeding. Worldwide,
over 20,000 health facilities have attained BFHI accreditation but only 77 Australian hospitals (approximately 23%)
have received accreditation. Few studies have investigated the factors that facilitate or hinder implementation of
BFHI but it is acknowledged this is a major undertaking requiring strategic planning and change management
throughout an institution. This paper examines the perceptions of BFHI held by midwives and nurses working in
one Area Health Service in NSW, Australia.
Methods: The study used an interpretive, qualitative approach. A total of 132 health professionals, working across four maternity units, two neonatal intensive care units and related community services, participated in 10 focus groups. Data were analysed using thematic analysis.
Results: Three main themes were identified: âBelief and Commitmentâ; âInterpreting BFHIâ and âClimbing a
Mountainâ. Participants considered the BFHI implementation a high priority; an essential set of practices that would
have positive benefits for babies and mothers both locally and globally as well as for health professionals. It was
considered achievable but would take commitment and hard work to overcome the numerous challenges including a number of organisational constraints. There were, however, differing interpretations of what was required to attain BFHI accreditation with the potential that misinterpretation could hinder implementation.
A model described by Greenhalgh and colleagues on adoption of innovation is drawn on to interpret the findings.
Conclusion: Despite strong support for BFHI, the principles of this global strategy are interpreted differently by
health professionals and further education and accurate information is required. It may be that the current
processes used to disseminate and implement BFHI need to be reviewed. The findings suggest that there is a
contradiction between the broad philosophical stance and best practice approach of this global strategy and the
tendency for health professionals to focus on the ten steps as a set of tasks or a checklist to be accomplished. The
perceived procedural approach to implementation may be contributing to lower rates of breastfeeding
continuation
Loop quantum gravity: the first twenty five years
This is a review paper invited by the journal "Classical ad Quantum Gravity"
for a "Cluster Issue" on approaches to quantum gravity. I give a synthetic
presentation of loop gravity. I spell-out the aims of the theory and compare
the results obtained with the initial hopes that motivated the early interest
in this research direction. I give my own perspective on the status of the
program and attempt of a critical evaluation of its successes and limits.Comment: 24 pages, 3 figure
- âŠ