2,051 research outputs found
Higgs transitions of spin ice
Frustrated magnets such as spin ice exhibit Coulomb phases, where
correlations have power-law forms at long distances. Applied perturbations can
cause ordering transitions which cannot be described by the usual Landau
paradigm, and are instead naturally viewed as Higgs transitions of an emergent
gauge theory. Starting from a classical statistical model of spin ice, it is
shown that a variety of possible phases and transitions can be described by
this approach. Certain cases are identified where continuous transitions are
argued to be likely; the predicted critical behavior may be tested in
experiments or numerical simulations.Comment: 23 pages, 10 figures; v2: published version with minor changes;
ancillary file "Figures3D.nb" is a Mathematica (v7) notebook containing
figures as rotatable 3D graphics (see http://www.wolfram.com/cdf-player/ for
a free viewer
A gravity survey on the southern and central parts of the Isle of man
The Bouguer anomalies on the Isle of Man have been calculated from a network of 365 stations. The results ofrock density measurements made in the laboratory are stated. The main features shown by the gravity survey of the southern and central parts of the island are two elongated negative anomalies, centered at Foxdale and Dhoon. They are shown to be shallow in origin and it is suggested that they are due to the prensence of two large granite bodies lower in density than the surrounding Manx Slates and only represented at the surface by small outcrops. These two granites are apparently steep sided and lie on a north-east to south-west 'axis' but are not connected. The negative anomaly seen in part in the extreme South-west of the island is probably due to arise on the Poxdale granite. The elongated shape of the granites revealed by the survey can be correlated with the zones of metamorphism, the distribution of the mineral veins and the "anticline of cleavage". Comparing the mass of land above sea level with the mass deficiency due to the granites the southern and central parts of the Isle of Man are found to be under-compensated. A residual gravity map of the Peel area was prepared and it revealed a negative anomaly which is probably due to the baain of lower density Peel Sandstones. The louguer anomalies are found generally to be high on the Isle of Man. This emphasises the fact that the Irish Sea seems to be an area of large positive anomalies for gradients have also been observed on the mainland. No definite conclusion has been reached as to the cause of this Irish Sea anomaly or, indeed, that it has only one cause
Optimal Image Reconstruction in Radio Interferometry
We introduce a method for analyzing radio interferometry data which produces
maps which are optimal in the Bayesian sense of maximum posterior probability
density, given certain prior assumptions. It is similar to maximum entropy
techniques, but with an exact accounting of the multiplicity instead of the
usual approximation involving Stirling's formula. It also incorporates an Occam
factor, automatically limiting the effective amount of detail in the map to
that justified by the data. We use Gibbs sampling to determine, to any desired
degree of accuracy, the multi-dimensional posterior density distribution. From
this we can construct a mean posterior map and other measures of the posterior
density, including confidence limits on any well-defined function of the
posterior map.Comment: 41 pages, 11 figures. High resolution figures 8 and 9 available at
http://www.astro.uiuc.edu/~bwandelt/SuttonWandelt200
Hidden unity in the quantum description of matter
We introduce an algebraic framework for interacting quantum systems that
enables studying complex phenomena, characterized by the coexistence and
competition of various broken symmetry states of matter. The approach unveils
the hidden unity behind seemingly unrelated physical phenomena, thus
establishing exact connections between them. This leads to the fundamental
concept of {\it universality} of physical phenomena, a general concept not
restricted to the domain of critical behavior. Key to our framework is the
concept of {\it languages} and the construction of {\it dictionaries} relating
them.Comment: 10 pages 2 psfigures. Appeared in Recent Progress in Many-Body
Theorie
Explicit Construction of the Massive Supersymmetry Multiplets on Spacetime
A systematic method of constructing supersymmetry multiples of second quantized fields is given for the massive case and for any spin, starting from the irreducible representations of the Poincaré Lie superalgebra. This allows a full understanding of the nature of the auxiliary fields
Tensor network states and algorithms in the presence of a global SU(2) symmetry
The benefits of exploiting the presence of symmetries in tensor network
algorithms have been extensively demonstrated in the context of matrix product
states (MPSs). These include the ability to select a specific symmetry sector
(e.g. with a given particle number or spin), to ensure the exact preservation
of total charge, and to significantly reduce computational costs. Compared to
the case of a generic tensor network, the practical implementation of
symmetries in the MPS is simplified by the fact that tensors only have three
indices (they are trivalent, just as the Clebsch-Gordan coefficients of the
symmetry group) and are organized as a one-dimensional array of tensors,
without closed loops. Instead, a more complex tensor network, one where tensors
have a larger number of indices and/or a more elaborate network structure,
requires a more general treatment. In two recent papers, namely (i) [Phys. Rev.
A 82, 050301 (2010)] and (ii) [Phys. Rev. B 83, 115125 (2011)], we described
how to incorporate a global internal symmetry into a generic tensor network
algorithm based on decomposing and manipulating tensors that are invariant
under the symmetry. In (i) we considered a generic symmetry group G that is
compact, completely reducible and multiplicity free, acting as a global
internal symmetry. Then in (ii) we described the practical implementation of
Abelian group symmetries. In this paper we describe the implementation of
non-Abelian group symmetries in great detail and for concreteness consider an
SU(2) symmetry. Our formalism can be readily extended to more exotic symmetries
associated with conservation of total fermionic or anyonic charge. As a
practical demonstration, we describe the SU(2)-invariant version of the
multi-scale entanglement renormalization ansatz and apply it to study the low
energy spectrum of a quantum spin chain with a global SU(2) symmetry.Comment: 32 pages, 37 figure
Unitary Irreducible Representations of Lie Supergroups
Each Lie supergroup can be considered as equivalent to a certain family of Lie groups. The unitary irreducible representations of Lie supergroups are examined using this equivalence, with particular reference to the super Poincaré group
Station-Keeping Requirements for Constellations of Free-Flying Collectors Used for Astronomical Imaging in Space
The accuracy requirements on station-keeping for constellations of
free-flying collectors coupled as (future) imaging arrays in space for
astrophysics applications are examined. The basic imaging element of these
arrays is the two-element interferometer. Accurate knowledge of two quantities
is required: the \textit{projected baseline length}, which is the distance
between the two interferometer elements projected on the plane tranverse to the
line of sight to the target; and the \textit{optical path difference}, which is
the difference in the distances from that transverse plane to the beam
combiner. ``Rules-of-thumb'' are determined for the typical accuracy required
on these parameters. The requirement on the projected baseline length is a
\textit{knowledge} requirement and depends on the angular size of the targets
of interest; it is generally at a level of half a meter for typical stellar
targets, decreasing to perhaps a few centimeters only for the widest attainable
fields of view. The requirement on the optical path difference is a
\textit{control} requirement and is much tighter, depending on the bandwidth of
the signal; it is at a level of half a wavelength for narrow (few %) signal
bands, decreasing to for the broadest bandwidths expected
to be useful. Translation of these requirements into engineering requirements
on station-keeping accuracy depends on the specific details of the collector
constellation geometry. Several examples are provided to guide future
application of the criteria presented here. Some implications for the design of
such collector constellations and for the methods used to transform the
information acquired into images are discussed.Comment: 13 pages, 6 figures, accepted 6/29/07 for the August 2007 issue of
PAS
Uncoupling of T Cell Receptor Zeta Chain Function during the Induction of Anergy by the Superantigen, Staphylococcal Enterotoxin A
Staphylococcus aureus enterotoxins have immunomodulatory properties. In this study, we show that Staphylococcal enterotoxin A (SEA) induces a strong proliferative response in a murine T cell clone independent of MHC class II bearing cells. SEA stimulation also induces a state of hypo-responsiveness (anergy). We characterized the components of the T cell receptor (TCR) during induction of anergy by SEA. Most interestingly, TCR zeta chain phosphorylation was absent under SEA anergizing conditions, which suggests an uncoupling of zeta chain function. We characterize here a model system for studying anergy in the absence of confounding costimulatory signals
Lorentz contraction, Bell's spaceships, and rigid body motion in special relativity
The meaning of Lorentz contraction in special relativity and its connection
with Bell's spaceships parable is discussed. The motion of Bell's spaceships is
then compared with the accelerated motion of a rigid body. We have tried to
write this in a simple form that could be used to correct students'
misconceptions due to conflicting earlier treatments.Comment: Modified the discussion in Sec. 2. This version to be published in
European Journal of Physic
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