1,403 research outputs found
OT 060420: A Seemingly Optical Transient Recorded by All-Sky Cameras
We report on a ~5th magnitude flash detected for approximately 10 minutes by
two CONCAM all-sky cameras located in Cerro Pachon - Chile and La Palma -
Spain. A third all-sky camera, located in Cerro Paranal - Chile did not detect
the flash, and therefore the authors of this paper suggest that the flash was a
series of cosmic-ray hits, meteors, or satellite glints. Another proposed
hypothesis is that the flash was an astronomical transient with variable
luminosity. In this paper we discuss bright optical transient detection using
fish-eye all-sky monitors, analyze the apparently false-positive optical
transient, and propose possible causes to false optical transient detection in
all-sky cameras.Comment: 7 figures, 3 tables, accepted PAS
All-sky Relative Opacity Mapping Using Night Time Panoramic Images
An all-sky cloud monitoring system that generates relative opacity maps over
many of the world's premier astronomical observatories is described.
Photometric measurements of numerous background stars are combined with
simultaneous sky brightness measurements to differentiate thin clouds from sky
glow sources such as air glow and zodiacal light. The system takes a continuous
pipeline of all-sky images, and compares them to canonical images taken on
other nights at the same sidereal time. Data interpolation then yields
transmission maps covering almost the entire sky. An implementation of this
system is currently operating through the Night Sky Live network of CONCAM3s
located at Cerro Pachon (Chile), Mauna Kea (Hawaii), Haleakala (Hawaii), SALT
(South Africa) and the Canary Islands (Northwestern Africa).Comment: Accepted for publication in PAS
Mobility edge in lattice QCD
We determine the location of the mobility edge in the spectrum of
the hermitian Wilson operator on quenched ensembles. We confirm a theoretical
picture of localization proposed for the Aoki phase diagram. When
we also determine some key properties of the localized eigenmodes with
eigenvalues . Our results lead to simple tests for the
validity of simulations with overlap and domain-wall fermions.Comment: revtex, 4 pages, 1 figure, minor change
Running coupling and mass anomalous dimension of SU(3) gauge theory with two flavors of symmetric-representation fermions
We have measured the running coupling constant of SU(3) gauge theory coupled
to Nf=2 flavors of symmetric representation fermions, using the Schrodinger
functional scheme. Our lattice action is defined with hypercubic smeared links
which, along with the larger lattice sizes, bring us closer to the continuum
limit than in our previous study. We observe that the coupling runs more slowly
than predicted by asymptotic freedom, but we are unable to observe fixed point
behavior before encountering a first order transition to a strong coupling
phase. This indicates that the infrared fixed point found with the thin-link
action is a lattice artifact. The slow running of the gauge coupling permits an
accurate determination of the mass anomalous dimension for this theory, which
we observe to be small, gamma_m < 0.6, over the range of couplings we can
reach. We also study the bulk and finite-temperature phase transitions in the
strong coupling region.Comment: 17 pages, 16 figures. Substantial modifications to explain why the
fat-link result for the beta function supersedes our thin-link result; also
updated the phase diagram to reflect additional numerical work. Added
references. Final versio
On the induced gauge invariant mass
We derive a general expression for the gauge invariant mass (m_G) for an
Abelian gauge field, as induced by vacuum polarization, in 1+1 dimensions. From
its relation to the chiral anomaly, we show that m_G has to satisfy a certain
quantization condition. This quantization can be, on the other hand, explicitly
verified by using the exact general expression for the gauge invariant mass in
terms of the fermion propagator. This result is applied to some explicit
examples, exploring the possibility of having interesting physical situations
where the value of departs from its canonical value. We also study the
possibility of generalizing the results to the 2+1 dimensional case at finite
temperature, showing that there are indeed situations where a finite and
non-vanishing gauge invariant mass is induced.Comment: 18 pages, Latex, 3 figures (pstex
Quantum Energies of Interfaces
We present a method for computing the one-loop, renormalized quantum energies
of symmetrical interfaces of arbitrary dimension and codimension using
elementary scattering data. Internal consistency requires finite-energy sum
rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin
Chirality Correlation within Dirac Eigenvectors from Domain Wall Fermions
In the dilute instanton gas model of the QCD vacuum, one expects a strong
spatial correlation between chirality and the maxima of the Dirac eigenvectors
with small eigenvalues. Following Horvath, {\it et al.} we examine this
question using lattice gauge theory within the quenched approximation. We
extend the work of those authors by using weaker coupling, , larger
lattices, , and an improved fermion formulation, domain wall fermions. In
contrast with this earlier work, we find a striking correlation between the
magnitude of the chirality density, , and the
normal density, , for the low-lying Dirac eigenvectors.Comment: latex, 25 pages including 12 eps figure
Revisiting Current Strategies for Primary Prevention of Motorcycle Collisions in Jamaica
Motorcycle Road Traffic Collisions place a heavy burden on emergency medical services in Jamaica. We explore the existing strategies and legislative policies that may prevent or reduce the severity of these injuries in Jamaica. This is an important aspect of health care as it may minimize the impact of these preventable injuries on the limited resources of the health services.
Chiral Symmetry Restoration in the Schwinger Model with Domain Wall Fermions
Domain Wall Fermions utilize an extra space time dimension to provide a
method for restoring the regularization induced chiral symmetry breaking in
lattice vector gauge theories even at finite lattice spacing. The breaking is
restored at an exponential rate as the size of the extra dimension increases.
Before this method can be used in dynamical simulations of lattice QCD, the
dependence of the restoration rate to the other parameters of the theory and,
in particular, the lattice spacing must be investigated. In this paper such an
investigation is carried out in the context of the two flavor lattice Schwinger
model.Comment: LaTeX, 37 pages including 18 figures. Added comments regarding power
law fitting in sect 7. Also, few changes were made to elucidate the content
in sect. 5.1 and 5.3. To appear in Phys. Rev.
Ginsparg-Wilson Fermions: A study in the Schwinger Model
Qualitative features of Ginsparg-Wilson fermions, as formulated by Neuberger,
coupled to two dimensional U(1) gauge theory are studied. The role of the
Wilson mass parameter in changing the number of massless flavors in the theory
and its connection with the index of the Dirac operator is studied. Although
the index of the Dirac operator is not related to the geometric definition of
the topological charge for strong couplings, the two start to agree as soon as
one goes to moderately weak couplings. This produces the desired singularity in
the quenched chiral condensate which appears to be very difficult to reproduce
with staggered fermions. The fermion determinant removes the singularity and
reproduces the known chiral condensate and the meson mass within understandable
errors.Comment: Corrected a few typos and changed some references. Minor changes to
the conten
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