438 research outputs found
Galilean invariance and homogeneous anisotropic randomly stirred flows
The Ward-Takahashi (WT) identities for incompressible flow implied by
Galilean invariance are derived for the randomly forced Navier-Stokes equation
(NSE), in which both the mean and fluctuating velocity components are
explicitly present. The consequences of Galilean invariance for the vertex
renormalization are drawn from this identity.Comment: REVTeX 4, 4 pages, no figures. To appear as a Brief Report in the
Physical Review
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
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
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 focused“telescope”for seismic anisotropy in the subduction zone. We retrieve spatiallyconsistent splitting parameters (mean fast directionΦ: 74°, mean delay time∂t: 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 single‐station observations. The periodicity is characterized by a sawtooth patterninΦwith 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 ENE‐WSW 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 EAR‐1144568, EAR‐1144351, EAR‐1460291, and EAR‐1444275. 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 EAR‐1261681
Remark on charge conjugation in the non relativistic limit
We study the non relativistic limit of the charge conjugation operation in the context of the Dirac equation coupled to an electromagnetic field.
The limit is well defined and, as in the relativistic case, ,
(parity) and (time reversal) are the generators of a matrix group
isomorphic to a semidirect sum of the dihedral group of eight elements and
. The existence of the limit is supported by an argument based in quantum
field theory. Also, and most important, the limit exists in the context of
galilean relativity. Finally, if one complexifies the Lorentz group and
therefore the galilean spacetime , then the explicit form of the matrix
for allows to interpret it, in this context, as the complex
conjugation of the spatial coordinates: . This result is
natural in a fiber bundle description.Comment: 8 page
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
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 ∼10²−10³ 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_S⁻¹), 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 ∼ 25–80) at 1 Hz and depths of 50–100 km. At each of these sites, independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle, 1300–1450°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 1.5–5. Modifying models to include effects of H₂O and rheology-dependent grain size shows that the effects of water-enhanced dissipation and water-enhanced grain growth nearly cancel, so H₂O effects are modest. Therefore, high H₂O 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
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