433 research outputs found
Perturbation theory for the two-dimensional abelian Higgs model in the unitary gauge
In the unitary gauge the unphysical degrees of freedom of spontaneously
broken gauge theories are eliminated. The Feynman rules are simpler than in
other gauges, but it is non-renormalizable by the rules of power counting. On
the other hand, it is formally equal to the limit of the
renormalizable R-gauge. We consider perturbation theory to one-loop
order in the R-gauge and in the unitary gauge for the case of the
two-dimensional abelian Higgs model. An apparent conflict between the unitary
gauge and the limit of the R-gauge is resolved, and it is
demonstrated that results for physical quantities can be obtained in the
unitary gauge.Comment: 15 pages, LaTeX2e, uses the feynmf package, formulations correcte
Symmetry Breaking in the Schr\"odinger Representation for Chern-Simons Theories
This paper discusses the phenomenon of spontaneous symmetry breaking in the
Schr\"odinger representation formulation of quantum field theory. The analysis
is presented for three-dimensional space-time abelian gauge theories with
either Maxwell, Maxwell-Chern-Simons, or pure Chern-Simons terms as the gauge
field contribution to the action, each of which leads to a different form of
mass generation for the gauge fields.Comment: 16pp, LaTeX , UCONN-94-
SKS Splitting Beneath Mount St. Helens: Constraints on Subslab Mantle Entrainment
Observations of seismic anisotropy can provide direct constraints on the character of mantleflow in subduction zones, critical for our broader understanding of subduction dynamics. Here wepresent over 750 new SKS splitting measurements in the vicinity of Mount St. Helens in the Cascadiasubduction zone using a combination of stations from the iMUSH broadband array and Cascades VolcanoObservatory network. This provides the highest density of splitting measurements yet available inCascadia, acting as a focusedâtelescopeâfor seismic anisotropy in the subduction zone. We retrieve spatiallyconsistent splitting parameters (mean fast directionÎŚ: 74°, mean delay timeât: 1.0 s) with the azimuthaloccurrence of nulls in agreement with the fast direction of splitting. When averaged across the array, a90° periodicity in splitting parameters as a function of back azimuth is revealed, which has not beenrecovered previously with singleâstation observations. The periodicity is characterized by a sawtooth patterninÎŚwith a clearly defined 45° trend. We present new equations that reproduce this behavior based uponknown systematic errors when calculating shear wave splitting from data with realistic seismic noise.The corrected results suggest a single layer of anisotropy with an ENEâWSW fast axis parallel to the motionof the subducting Juan de Fuca plate; in agreement with predictions for entrained subslab mantleflow. Thesplitting pattern is consistent with that seen throughout Cascadia, suggesting that entrainment of theunderlying asthenosphere with the subducting slab is coherent and widespread.The broadband seismic component of the iMUSH project was supported by National Science Foundation grants EARâ1144568, EARâ1144351, EARâ1460291, and EARâ1444275. CME acknowledges support from the Australian Research Council (DE190100062). We thank the 2017 IRIS undergraduate summer intern
program for providing support to A. W. to work with E. A. W. at the University of Washington. The facilities of IRIS Data Services, and specifically the IRIS Data Management Center, were used for access to waveforms, related metadata, and/or derived products used in this study. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the National Science Foundation under Cooperative Agreement EARâ1261681
Reconciling mantle attenuation-temperature relationships from seismology, petrology, and laboratory measurements
Seismic attenuation measurements provide a powerful tool for sampling mantle properties. Laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt-free rocks, but require âź10²â10Âł extrapolations in grain size to mantle conditions; also, the effects of water and melt are not well understood. At the same time, body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation (Q_SâťÂš), affording an opportunity for calibration. We reanalyze seismic data sets that sample arc and back-arc mantle in Central America, the Marianas, and the Lau Basin, confirming very high attenuation (Q_S âź 25â80) at 1 Hz and depths of 50â100 km. At each of these sites, independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle, 1300â1450°C. The Q_S measurements correlate inversely with the petrologically inferred temperatures, as expected. However, dry attenuation models predict Q_S too high by a factor of 1.5â5. Modifying models to include effects of HâO and rheology-dependent grain size shows that the effects of water-enhanced dissipation and water-enhanced grain growth nearly cancel, so HâO effects are modest. Therefore, high HâO in the arc source region cannot explain the low Q_S, nor in the back arc where lavas show modest water content. Most likely, the high attenuation reflects the presence of melt, and some models of melt effects come close to reproducing observations. Overall, body wave Q_S can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs
Worldline Path Integrals for Fermions with General Couplings
We derive a worldline path integral representation for the effective action
of a multiplet of Dirac fermions coupled to the most general set of
matrix-valued scalar, pseudoscalar, vector, axial vector and antisymmetric
tensor background fields. By representing internal degrees of freedom in terms
of worldline fermions as well, we obtain a formulation which manifestly
exhibits chiral gauge invariance.Comment: 17 pages, Plain Tex, no macros needed; corrections to references and
to a formul
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Abnormal movements in critical care patients with brain injury: a diagnostic approach
Abnormal movements are frequently encountered in patients with brain injury hospitalized in intensive care units (ICUs), yet characterization of these movements and their underlying pathophysiology is difficult due to the comatose or uncooperative state of the patient. In addition, the available diagnostic approaches are largely derived from outpatients with neurodegenerative or developmental disorders frequently encountered in the outpatient setting, thereby limiting the applicability to inpatients with acute brain injuries. Thus, we reviewed the available literature regarding abnormal movements encountered in acutely ill patients with brain injuries. We classified the brain injury into the following categories: anoxic, vascular, infectious, inflammatory, traumatic, toxic-metabolic, tumor-related and seizures. Then, we identified the abnormal movements seen in each category as well as their epidemiologic, semiologic and clinicopathologic correlates. We propose a practical paradigm that can be applied at the bedside for diagnosing abnormal movements in the ICU. This model seeks to classify observed abnormal movements in light of various patient-specific factors. It begins with classifying the patientâs level of consciousness. Then, it integrates the frequency and type of each movement with the availability of ancillary diagnostic tests and the specific etiology of brain injury
Worldline Path Integrals for Fermions with Scalar, Pseudoscalar and Vector Couplings
A systematic derivation is given of the worldline path integrals for the
effective action of a multiplet of Dirac fermions interacting with general
matrix-valued classical background scalar, pseudoscalar, and vector gauge
fields. The first path integral involves worldline fermions with antiperiodic
boundary conditions on the worldline loop and generates the real part of the
one loop (Euclidean) effective action. The second path integral involves
worldline fermions with periodic boundary conditions and generates the
imaginary part of the (Euclidean) effective action, i.e. the phase of the
fermion functional determinant. Here we also introduce a new regularization for
the phase of functional determinants resembling a heat-kernel regularization.
Compared to the known special cases, our worldline Lagrangians have a number of
new interaction terms; the validity of some of these terms is checked in
perturbation theory. In particular, we obtain the leading order contribution
(in the heavy mass expansion) to the Wess-Zumino-Witten term, which generates
the chiral anomaly.Comment: 23 pages, Plain Tex, no macros needed, some minor changes and some
references adde
Charges on Strange Quark Nuggets in Space
Since Witten's seminal 1984 paper on the subject, searches for evidence of
strange quark nuggets (SQNs) have proven unsuccessful. In the absence of
experimental evidence ruling out SQNs, the validity of theories introducing
mechanisms that increase their stability should continue to be tested. To
stimulate electromagnetic SQN searches, particularly space searches, we
estimate the net charge that would develop on an SQN in space exposed to
various radiation baths (and showers) capable of liberating their less strongly
bound electrons, taking into account recombination with ambient electrons. We
consider, in particular, the cosmic background radiation, radiation from the
sun, and diffuse galactic and extragalactic -ray backgrounds. A
possible dramatic signal of SQNs in explosive astrophysical events is noted.Comment: CitationS added, new subsection added, more discussion, same
numerical result
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