23,791 research outputs found
Real Forms of Non-abelian Toda Theories and their W-algebras
We consider real forms of Lie algebras and embeddings of sl(2) which are
consistent with the construction of integrable models via Hamiltonian
reduction. In other words: we examine possible non-standard reality conditions
for non-abelian Toda theories. We point out in particular that the usual
restriction to the maximally non-compact form of the algebra is unnecessary,
and we show how relaxing this condition can lead to new real forms of the
resulting W-algebras. Previous results for abelian Toda theories are recovered
as special cases. The construction can be extended straightforwardly to deal
with osp(1|2) embeddings in Lie superalgebras. Two examples are worked out in
detail, one based on a bosonic Lie algebra, the other based on a Lie
superalgebra leading to an action which realizes the N=4 superconformal
algebra.Comment: 11 pages, LaTex; minor errors corrected, extra references adde
Improved Semileptonic Form Factor Calculations in Lattice QCD
We investigate the computational efficiency of two stochastic based
alternatives to the Sequential Propagator Method used in Lattice QCD
calculations of heavy-light semileptonic form factors. In the first method, we
replace the sequential propagator, which couples the calculation of two of the
three propagators required for the calculation, with a stochastic propagator so
that the calculations of all three propagators are independent. This method is
more flexible than the Sequential Propagator Method but introduces stochastic
noise. We study the noise to determine when this method becomes competitive
with the Sequential Propagator Method, and find that for any practical
calculation it is competitive with or superior to the Sequential Propagator
Method. We also examine a second stochastic method, the so-called ``one-end
trick", concluding it is relatively inefficient in this context. The
investigation is carried out on two gauge field ensembles, using the
non-perturbatively improved Wilson-Sheikholeslami-Wohlert action with N_f=2
mass-degenerate sea quarks. The two ensembles have similar lattice spacings but
different sea quark masses. We use the first stochastic method to extract
-improved, matched lattice results for the semileptonic form
factors on the ensemble with lighter sea quarks, extracting f_+(0)
Protocol for electrophysiological monitoring of carotid endarterectomies.
Near zero stroke rates can be achieved in carotid endarterectomy (CEA) surgery with selective shunting and electrophysiological neuromonitoring. though false negative rates as high as 40% have been reported. We sought to determine if improved training for interpretation of the monitoring signals can advance the efficacy of selective shunting with electrophysiological monitoring across multiple centers, and determine if other factors could contribute to the differences in reports. Processed and raw beta band (12.5-30 Hz) electroencephalogram (EEG) and median and tibial nerve somatosensory evoked potentials (SSEP) were monitored in 668 CEA cases at six surgical centers. A decrease in amplitude of 50% or more in any EEG or SSEP channel was the criteria for shunting or initiating a neuroprotective protocol. A reduction of 50% or greater in the beta band of the EEG or amplitude of the SSEP was observed in 150 cases. No patient showed signs of a cerebral infarct after surgery. Selective shunting based on EEG and SSEP monitoring can reduce CEA intraoperative stroke rate to a near zero level if trained personnel adopted standardized protocols. We also found that the rapid administration of a protective stroke protocol by attending anesthesiologists was an important aspect of this success rate
Conserved charges and supersymmetry in principal chiral and WZW models
Conserved and commuting charges are investigated in both bosonic and
supersymmetric classical chiral models, with and without Wess-Zumino terms. In
the bosonic theories, there are conserved currents based on symmetric invariant
tensors of the underlying algebra, and the construction of infinitely many
commuting charges, with spins equal to the exponents of the algebra modulo its
Coxeter number, can be carried out irrespective of the coefficient of the
Wess-Zumino term. In the supersymmetric models, a different pattern of
conserved quantities emerges, based on antisymmetric invariant tensors. The
current algebra is much more complicated than in the bosonic case, and it is
analysed in some detail. Two families of commuting charges can be constructed,
each with finitely many members whose spins are exactly the exponents of the
algebra (with no repetition modulo the Coxeter number). The conserved
quantities in the bosonic and supersymmetric theories are only indirectly
related, except for the special case of the WZW model and its supersymmetric
extension.Comment: LaTeX; 49 pages; v2: minor changes and additions to text and ref
The organic chemistry in the innermost, infalling envelope of the Class 0 protostar L483
Context: The protostellar envelopes, outflow and large-scale chemistry of
Class~0 and Class~I objects have been well-studied, but while previous works
have hinted at or found a few Keplerian disks at the Class~0 stage, it remains
to be seen if their presence in this early stage is the norm. Likewise, while
complex organics have been detected toward some Class~0 objects, their
distribution is unknown as they could reside in the hottest parts of the
envelope, in the emerging disk itself or in other components of the
protostellar system, such as shocked regions related to outflows.
Aims: In this work, we aim to address two related issues regarding
protostars: when rotationally supported disks form around deeply embedded
protostars and where complex organic molecules reside in such objects.
Methods: We observed the deeply embedded protostar, L483, using Atacama Large
Millimeter/submillimeter Array (ALMA) Band~7 data from Cycles~1 and 3 with a
high angular resolution down to ~0.1 (20~au) scales.
Results: We find that the kinematics of CS~-- and
HCN~-- are best fitted by the velocity profile from infall under
conservation of angular momentum and not by a Keplerian profile. The spatial
extents of the observed complex organics are consistent with an estimated ice
sublimation radius of the envelope at ~50~au, suggesting that the complex
organics exist in the hot corino of L483.
Conclusions: We find that L483 does not harbor a Keplerian disk down to at
least ~au in radius. Instead, the innermost regions of L483 are undergoing
a rotating collapse. This result highlights that some Class~0 objects contain
only very small disks, or none at all, with the complex organic chemistry
taking place on scales inside the hot corino of the envelope, in a region
larger than the emerging disk.Comment: 19 pages, 11 figure
Spectral Measures and Generating Series for Nimrep Graphs in Subfactor Theory II: SU(3)
We complete the computation of spectral measures for SU(3) nimrep graphs
arising in subfactor theory, namely the SU(3) ADE graphs associated with SU(3)
modular invariants and the McKay graphs of finite subgroups of SU(3). For the
SU(2) graphs the spectral measures distill onto very special subsets of the
semicircle/circle, whilst for the SU(3) graphs the spectral measures distill
onto very special subsets of the discoid/torus. The theory of nimreps allows us
to compute these measures precisely. We have previously determined spectral
measures for some nimrep graphs arising in subfactor theory, particularly those
associated with all SU(2) modular invariants, all subgroups of SU(2), the
torus, SU(3), and some SU(3) graphs.Comment: 38 pages, 21 figure
Low-mass Star Formation: Observations
I briefly review recent observations of regions forming low mass stars. The
discussion is cast in the form of seven questions that have been partially
answered, or at least illuminated, by new data. These are the following: where
do stars form in molecular clouds; what determines the IMF; how long do the
steps of the process take; how efficient is star formation; do any theories
explain the data; how are the star and disk built over time; and what chemical
changes accompany star and planet formation. I close with a summary and list of
open questions.Comment: Proceedings of Computational Star Formation Conference, Barcelon
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