10,947 research outputs found
Anomalous Chiral Action from the Path-Integral
By generalizing the Fujikawa approach, we show in the path-integral
formalism: (1) how the infinitesimal variation of the fermion measure can be
integrated to obtain the full anomalous chiral action; (2) how the action
derived in this way can be identified as the Chern-Simons term in five
dimensions, if the anomaly is consistent; (3) how the regularization can be
carried out, so as to lead to the consistent anomaly and not to the covariant
anomaly. Our method uses Schwinger's ``proper-time'' representation of the
Green's function and the gauge invariant point-splitting technique. We find
that the consistency requirement and the point-splitting technique allow both
an anomalous and a non-anomalous action. In the end, the nature of the vacuum
determines whether we have an anomalous theory, or, a non-anomalous theoryComment: 28 page
Evolution of antiferromagnetic domains in the all-in-all-out ordered pyrochlore NdZrO
We report the observation of magnetic domains in the exotic,
antiferromagnetically ordered all-in-all-out state of NdZrO,
induced by spin canting. The all-in-all-out state can be realized by Ising-like
spins on a pyrochlore lattice and is established in NdZrO below
0.31 K for external magnetic fields up to 0.14 T. Two different spin
arrangements can fulfill this configuration which leads to the possibility of
magnetic domains. The all-in-all-out domain structure can be controlled by an
external magnetic field applied parallel to the [111] direction. This is a
result of different spin canting mechanism for the two all-in-all-out
configurations for such a direction of the magnetic field. The change of the
domain structure is observed through a hysteresis in the magnetic
susceptibility. No hysteresis occurs, however, in case the external magnetic
field is applied along [100].Comment: Accepted for publication in Phys. Rev. B, 6 pages, 6 figure
Isotope Effect in the Superfluid Density of HTS Cuprates: Stripes, Pseudogap and Impurities
Underdoped cuprates exhibit a normal-state pseudogap, and their spins and
doped carriers tend to spatially separate into 1- or 2-D stripes. Some view
these as central to superconductivity, others as peripheral and merely
competing. Using LaSrCuZnO we show that an oxygen
isotope effect in and in the superfluid density can be used to
distinguish between the roles of stripes and pseudogap and also to detect the
presence of impurity scattering. We conclude that stripes and pseudogap are
distinct, and both compete and coexist with superconductivity.Comment: Revised submission to PRL with added appendix on a possible isotope
effect in the effective mass, 4 pages, 3 figure
Evolutionary quantum cosmology in a gauge-fixed picture
We study the classical and quantum models of a flat
Friedmann-Robertson-Walker (FRW) space-time, coupled to a perfect fluid, in the
context of the consensus and a gauge-fixed Lagrangian frameworks. It is shown
that, either in the usual or in the gauge-fixed actions, the evolution of the
universe based on the classical cosmology represents a late time power law
expansion, coming from a big-bang singularity in which the scale factor goes to
zero for the standard matter, and tending towards a big-rip singularity in
which the scale factor diverges for the phantom fluid. We then employ the
familiar canonical quantization procedure in the given cosmological setting to
find the cosmological wave functions in the corresponding minisuperspace. Using
a gauge-fixed (reduced) Lagrangian, we show that, it may lead to a
Schr\"{o}dinger equation for the quantum-mechanical description of the model
under consideration, the eigenfunctions of which can be used to construct the
time dependent wave function of the universe. We use the resulting wave
function in order to investigate the possibility of the avoidance of classical
singularities due to quantum effects by means of the many-worlds and
ontological interpretation of quantum cosmology.Comment: 15 pages, 10 figures, typos corrected, Refs. adde
Magnetic field induced orientation of superconducting MgB crystallites determined by X-ray diffraction
X-ray diffraction studies of fine polycrystalline samples of MgB in the
superconducting state reveal that crystals orient with their \emph{c}-axis in a
plane normal to the direction of the applied magnetic field. The MgB
samples were thoroughly ground to obtain average grain size 5 - 10 m in
order to increase the population of free single crystal grains in the powder.
By monitoring Bragg reflections in a plane normal to an applied magnetic field
we find that the powder is textured with significantly stronger (\emph{0,0,l})
reflections in comparison to (\emph{h,k,0}), which remain essentially
unchanged. The orientation of the crystals with the \emph{ab}-plane parallel to
the magnetic field at all temperatures below demonstrates that the sign
of the torque under magnetic field does not alter, in disagreement with current
theoretical predictions
Rotated stripe order and its competition with superconductivity in LaSrCuO
We report the observation of a bulk charge modulation in
LaSrCuO (LSCO) with a characteristic in-plane wave-vector
of (0.236, ), with =0.011 r.l.u. The transverse shift of
the ordering wave-vector indicates the presence of rotated charge-stripe
ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond
direction. On cooling through the superconducting transition, we find an abrupt
change in the growth of the charge correlations and a suppression of the charge
order parameter indicating competition between the two orderings. Orthorhombic
LSCO thus helps bridge the apparent disparities between the behavior previously
observed in the tetragonal "214" cuprates and the orthorhombic yttrium and
bismuth-based cuprates and thus lends strong support to the idea that there is
a common motif to charge order in all cuprate families.Comment: 6 pages, 4 figue
Recent developments of MCViNE and its applications at SNS
MCViNE is an open source, object-oriented Monte Carlo neutron ray-tracing simulation software package. Its design allows for flexible, hierarchical representations of sophisticated instrument components such as detector systems, and samples with a variety of shapes and scattering kernels. Recently this flexible design has enabled several applications of MCViNE simulations at the Spallation Neutron Source (SNS) at Oak Ridge National Lab, including assisting design of neutron instruments at the second target station and design of novel sample environments, as well as studying effects of instrument resolution and multiple scattering. Here we provide an overview of the recent developments and new features of MCViNE since its initial introduction (Jiao et al 2016 Nucl. Instrum. Methods Phys. Res., Sect. A 810, 86–99), and some example applications
Antinociceptive, Anti-Inflammatory, and Antipyretic Activity of Mangrove Plants: A Mini Review
Mangrove plants are specialised plants that grow in the tidal coasts of tropic and subtropic regions of the world. Their unique ecology and traditional medicinal uses of mangrove plants have attracted the attention of researchers over the years, and as a result, reports on biological activity of mangrove plants have increased significantly in recent years. This review has been set out to compile and appraise the results on antinociceptive, anti-inflammatory, and antipyretic activity of mangrove plants. While the Web of Knowledge, Google Scholar, and PubMed were the starting points to gather information, other pieces of relevant published literature were also adequately explored for this purpose. A total of 29 reports on 17 plant species have been found to report such activities. While 19 reports were on the biological activity of the crude extracts, 10 reports identified the active compound(s) of various chemical classes of natural products including terpenes, steroids, and flavonoids. This review finds that antinociceptive, anti-inflammatory, and antipyretic activity appears to be widespread in mangrove plants
Quantum limits to center-of-mass measurements
We discuss the issue of measuring the mean position (center-of-mass) of a
group of bosonic or fermionic quantum particles, including particle number
fluctuations. We introduce a standard quantum limit for these measurements at
ultra-low temperatures, and discuss this limit in the context of both photons
and ultra-cold atoms. In the case of fermions, we present evidence that the
Pauli exclusion principle has a strongly beneficial effect, giving rise to a
1/N scaling in the position standard-deviation -- as opposed to a
scaling for bosons. The difference between the actual mean-position fluctuation
and this limit is evidence for quantum wave-packet spreading in the
center-of-mass. This macroscopic quantum effect cannot be readily observed for
non-interacting particles, due to classical pulse broadening. For this reason,
we also study the evolution of photonic and matter-wave solitons, where
classical dispersion is suppressed. In the photonic case, we show that the
intrinsic quantum diffusion of the mean position can contribute significantly
to uncertainties in soliton pulse arrival times. We also discuss ways in which
the relatively long lifetimes of attractive bosons in matter-wave solitons may
be used to demonstrate quantum interference between massive objects composed of
thousands of particles.Comment: 12 pages, 6 figures. Submitted to PRA. Revised to include more
references as well as a discussion of fermionic center-of-mas
- …