6,098 research outputs found
The fate of the Wilson-Fisher fixed point in non-commutative \phi^4
In this article we study non-commutative vector sigma model with the most
general \phi^4 interaction on Moyal-Weyl spaces. We compute the 2- and 4-point
functions to all orders in the large N limit and then apply the approximate
Wilson renormalization group recursion formula to study the renormalized
coupling constants of the theory. The non-commutative Wilson-Fisher fixed point
interpolates between the commutative Wilson-Fisher fixed point of the Ising
universality class which is found to lie at zero value of the critical coupling
constant a_* of the zero dimensional reduction of the theory, and a novel
strongly interacting fixed point which lies at infinite value of a_*
corresponding to maximal non-commutativity beyond which the two-sheeted
structure of a_* as a function of the dilation parameter disappears.Comment: 19 pages, 7 figures, v2:one reference adde
First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe
We perform a first principles calculation of the anomalous Hall effect in
ferromagnetic bcc Fe. Our theory identifies an intrinsic contribution to the
anomalous Hall conductivity and relates it to the k-space Berry phase of
occupied Bloch states. The theory is able to account for both dc and
magneto-optical Hall conductivities with no adjustable parameters.Comment: 4 pages, 6 figures, author list correcte
Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice
We investigate a recent proposal to construct chiral gauge theories on the
lattice using domain wall fermions. We restrict ourselves to the finite volume
case, in which two domain walls are present, with modes of opposite chirality
on each of them. We couple the chiral fermions on only one of the domain walls
to a gauge field. In order to preserve gauge invariance, we have to add a
scalar field, which gives rise to additional light mirror fermion and scalar
modes. We argue that in an anomaly free model these extra modes would decouple
if our model possesses a so-called strong coupling symmetric phase. However,
our numerical results indicate that such a phase most probably does not exist.
---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6
Staggered Fermions and Gauge Field Topology
Based on a large number of smearing steps, we classify SU(3) gauge field
configurations in different topological sectors. For each sector we compare the
exact analytical predictions for the microscopic Dirac operator spectrum of
quenched staggered fermions. In all sectors we find perfect agreement with the
predictions for the sector of topological charge zero, showing explicitly that
the smallest Dirac operator eigenvalues of staggered fermions at presently
realistic lattice couplings are insensitive to gauge field topology. On the
smeared configurations, eigenvalues clearly separate out from the rest
on configurations of topological charge , and move towards zero in
agreement with the index theorem.Comment: LaTeX, 10 page
Effect of Perennial Ryegrass Cultivars on the Fatty Acid Composition in Milk of Stall-Fed Cows
Herbage provides bulk feed for ruminants and plant lipids, especially C18:3, are a major source of benefical fatty acids (FA) in milk. There are very few direct comparisons allowing a precise evaluation of the effects of the basal forage diet on milk FA composition. Grass quality differences can affect rumen metabolism and there could be opportunities to change the composition of ruminant products through choice of grass cultivar. To test this hypothesis, six cultivars were fed to dairy cows in a stall-feeding trial with fresh grass to evaluate the effect of grass cultivar on rumen VFA and milk FA composition during the growing season
Observation of a parity oscillation in the conductance of atomic wires
Using a scanning tunnel microscope or mechanically controlled break
junctions, atomic contacts of Au, Pt and Ir are pulled to form chains of atoms.
We have recorded traces of conductance during the pulling process and averaged
these for a large amount of contacts. An oscillatory evolution of conductance
is observed during the formation of the monoatomic chain suggesting a
dependence on even or odd numbers of atoms forming the chain. This behaviour is
not only present in the monovalent metal Au, as it has been previously
predicted, but is also found in the other metals which form chains suggesting
it to be a universal feature of atomic wires
Observation of electronic and atomic shell effects in gold nanowires
The formation of gold nanowires in vacuum at room temperature reveals a
periodic spectrum of exceptionally stable diameters. This is identified as
shell structure similar to that which was recently discovered for alkali metals
at low temperatures. The gold nanowires present two competing `magic' series of
stable diameters, one governed by electronic structure and the other by the
atomic packing.Comment: 4 pages, 4 figure
Determination of humidity and temperature fluctuations based on MOZAIC data and parametrisation of persistent contrail coverage for general circulation models
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