2,073 research outputs found
Using the Hopf Algebra Structure of QFT in Calculations
We employ the recently discovered Hopf algebra structure underlying
perturbative Quantum Field Theory to derive iterated integral representations
for Feynman diagrams. We give two applications: to massless Yukawa theory and
quantum electrodynamics in four dimensions.Comment: 28 p, Revtex, epsf for figures, minor changes, to appear in
Phys.Rev.
Unknotting the polarized vacuum of quenched QED
A knot-theoretic explanation is given for the rationality of the quenched QED
beta function. At the link level, the Ward identity entails cancellation of
subdivergences generated by one term of the skein relation, which in turn
implies cancellation of knots generated by the other term. In consequence, each
bare three-loop diagram has a rational Laurent expansion in the Landau gauge,
as is verified by explicit computation. Comparable simplification is found to
occur in scalar electrodynamics, when computed in the Duffin-Kemmer-Petiau
formalism.Comment: 11 pages, LaTe
Two-loop two-point functions with masses: asymptotic expansions and Taylor series, in any dimension
In all mass cases needed for quark and gluon self-energies, the two-loop
master diagram is expanded at large and small , in dimensions, using
identities derived from integration by parts. Expansions are given, in terms of
hypergeometric series, for all gluon diagrams and for all but one of the quark
diagrams; expansions of the latter are obtained from differential equations.
Pad\'{e} approximants to truncations of the expansions are shown to be of great
utility. As an application, we obtain the two-loop photon self-energy, for all
, and achieve highly accelerated convergence of its expansions in powers of
or , for .Comment: 25 pages, OUT--4102--43, BI--TP/92--5
Dimensional renormalization: ladders to rainbows
Renormalization factors are most easily extracted by going to the massless
limit of the quantum field theory and retaining only a single momentum scale.
We derive factors and renormalized Green functions to all orders in
perturbation theory for rainbow graphs and vertex (or scattering diagrams) at
zero momentum transfer, in the context of dimensional renormalization, and we
prove that the correct anomalous dimensions for those processes emerge in the
limit D -> 4.Comment: RevTeX, no figure
A faint galaxy redshift survey to B=24
Using the multislit LDSS-2 spectrograph on the {\it William Herschel
Telescope} we have completed a redshift survey in the magnitude range which has produced 73 redshifts representing a 73\% complete sample
uniformly-selected from four deep fields at high Galactic latitude. The survey
extends out to and includes the highest redshift galaxy () yet
discovered in a field sample. The median redshift, \zmed=0.46, and form of
the redshift distribution constitute compelling evidence against simple
luminosity evolution as an explanation of the large excess of faint galaxies
(2--4 no-evolution) seen in this magnitude range. Rather we
identify the excess population as blue objects with and \,
luminosities similar to local galaxies indicating a dramatic decrease in
the density of such objects over the last Hubble time, confirming the trends
found in brighter redshift surveys. We also find a marked absence of {\it very}
low redshift galaxies (0.1) at faint limits, severely constraining any
significant steepening of the local field galaxy luminosity function at low
luminosities.Comment: uuencoded compressed postscript. The preprint are also available at
URL http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Master integrals for massive two-loop Bhabha scattering in QED
We present a set of scalar master integrals (MIs) needed for a complete
treatment of massive two-loop corrections to Bhabha scattering in QED,
including integrals with arbitrary fermionic loops. The status of analytical
solutions for the MIs is reviewed and examples of some methods to solve MIs
analytically are worked out in more detail. Analytical results for the pole
terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge
Review of a Small-scale Pelagic Longline Fishery off Northeastern Brazil
The annual catches of four small longliners operating off northeast Brazil from 1983 to 1997 were examined across different areas and locations. The total catch comprised tunas (30%), sharks (54%), billfishes (12%), and other fish species (4%). Fishing strategy and annual composition of catches showed large spatial and temporal variabilities with the dominant catches alternating among yellowfin tuna,
Thunnus albacares; gray sharks, Carcharhinus spp.; and blue shark, Prionace glauca. Catches of blue and gray sharks
showed a significant interaction among seamounts, with gray sharks occurring in maximum abundance around those seamounts
that had relatively deep summits and low-sloping depth profiles. Results are discussed in terms of the various factors that may have influenced distribution of effort
Detecting the Gravitational Redshift of Cluster Gas
We examine the gravitational redshift of radiation emitted from within the
potential of a cluster. Spectral lines from the intracluster medium (ICM) are
redshifted in proportion to the emission-weighted mean potential along the line
of sight, amounting to approximately 50 km/s at a radius of 100 kpc/h, for a
cluster dispersion of 1200 km/s. We show that the relative redshifts of
different ionization states of metals in the ICM provide a unique probe of the
three-dimensional matter distribution. An examination of the reported peculiar
velocities of cD galaxies in well studied Abell clusters reveals they are
typically redshifted by an average of km/s. This can be achieved by
gravity with the addition of a steep central potential associated with the cD
galaxy. Note that in general gravitational redshifts cause a small overestimate
of the recessional velocities of clusters by an average of 20 km/s.Comment: 6 pages, 3 figures, accepted to the Astrophysical Journal Letter
Hong Kong International Violence Against Women Survey
Final Report of the 2006 Hong Kong IVAW
Evaluation of antimicrobial efficacy in shelter cats with upper respiratory infection: a prospective study
Feline Upper-Respiratory Infection (URI) is commonplace in most animal shelters, and its endemic presence is problematic for the animals as well as for veterinarians and other shelter personnel. Despite the fact that viruses are responsible for the majority of these infections, many cats with URI in shelters are still treated with antibiotics. Antibiotic treatment in the absence of bacterial infection and the overuse of antibiotics can lead to antibiotic resistance among feline populations. The aim of this research was to compare duration and severity of URI in shelter cats treated with and without antibiotics. Cats showing clinical symptoms were randomly assigned to two groups, one receiving antibiotic treatment and the other receiving no antibiotics. Cats were monitored daily and the severity of their ocular and nasal symptoms scored on a numerical scale. The duration of their clinical symptoms was also recorded. Pharyngeal swabs were taken from some of the study population to determine whether or not bacterial infection was present. The mean severity and duration scores and standard deviations were calculated for each group and an unpaired t-test performed. No significant difference in the severity of URI and the duration of the illness was found in cats who did and did not receive antibiotic treatment. These findings support the need to change the protocol for treatment of feline URI in order to improve the quality of care provided to the shelter cats. Furthermore, these findings provided additional evidence to support the need for enhanced antibiotic stewardship in both veterinary and human medicine
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