10,076 research outputs found
On Locality, Holography and Unfolding
We study the functional class and locality problems in the context of
higher-spin theories and Vasiliev's equations. A locality criterion that is
sufficient to make higher-spin theories well-defined as field theories on
Anti-de-Sitter space is proposed. This criterion identifies admissible
pseudo-local field redefinitions which preserve AdS/CFT correlation functions
as we check in the 3d example. Implications of this analysis for known
higher-spin theories are discussed. We also check that the cubic coupling
coefficients previously fixed in 3d at the action level give the correct CFT
correlation functions upon computing the corresponding Witten diagrams.Comment: 36 pages, LaTex. References added, typos corrected. Final version to
appear in JHE
Beyond Diophantine Wannier diagrams: Gap labelling for Bloch-Landau Hamiltonians
It is well known that, given a purely magnetic Landau Hamiltonian with a
constant magnetic field which generates a magnetic flux per unit
area, then any spectral island consisting of infinitely
degenerate Landau levels carries an integrated density of states
. Wannier later discovered a similar Diophantine
relation expressing the integrated density of states of a gapped group of bands
of the Hofstadter Hamiltonian as a linear function of the magnetic field flux
with integer slope.
We extend this result to a gap labelling theorem for any Bloch-Landau
operator which also has a bounded -periodic electric
potential. Assume that has a spectral island which remains
isolated from the rest of the spectrum as long as lies in a compact
interval . Then on such
intervals, where the constant while .
The integer is the Chern marker of the spectral projection onto the
spectral island . This result also implies that the Fermi projection
on , albeit continuous in in the strong topology, is nowhere
continuous in the norm topology if either or and is
rational.
Our proofs, otherwise elementary, do not use non-commutative geometry but are
based on gauge covariant magnetic perturbation theory which we briefly review
for the sake of the reader. Moreover, our method allows us to extend the
analysis to certain non-covariant systems having slowly varying magnetic
fields.Comment: 20 pages, no figures. Appendix C added. Final version accepted for
publication in Journal of the European Mathematical Societ
Role of cardiac resynchronization therapy in the development of new-onset atrial fibrillation: A single-center prospective study.
Albeit several studies examined the association between cardiac resynchronization therapy (CRT) and atrial fibrillation (AF) in heart failure (HF), results are still unclear and quite conflicting. We thereby designed a single-center prospective study to determine whether CRT has a favorable effect on the incidence of new-onset AF in a homogeneous population of patients with non-ischemic idiopathic dilated cardiomyopathy and severe heart failure HF. We enrolled 58 patients, AF naïve when received CRT. After 1 year of follow-up our population was subdivided into responders (72.4%) and non (27.6%), so to compare the incidence of AF after 1, 2 and 3 years of follow-up in these two groups. Already after 1 year, there is a significant (p<0.05) difference in new-onset AF in non-responder patients respect to responders (18.2% vs 3.3%). These data are confirmed at 2 year (33.3% vs 12.2%) and 3 year (50.0% vs 15.0%) follow-up. In particular, at 3 year follow-up, non-responders have an increased risk to develop new-onset AF (OR=5.67, 95% confidence interval = 1.36-23.59, p=0.019). The present work suggests a possible favorable role of this non-pharmacological therapy, on the prevention of AF
Nano-Hertz Gravitational Waves Searches with Interferometric Pulsar Timing Experiments
We estimate the sensitivity to nano-Hertz gravitational waves of pulsar
timing experiments in which two highly-stable millisecond pulsars are tracked
simultaneously with two neighboring radio telescopes that are referenced to the
same time-keeping subsystem (i.e. "the clock"). By taking the difference of the
two time-of-arrival residual data streams we can exactly cancel the clock noise
in the combined data set, thereby enhancing the sensitivity to gravitational
waves. We estimate that, in the band () Hz, this
"interferometric" pulsar timing technique can potentially improve the
sensitivity to gravitational radiation by almost two orders of magnitude over
that of single-telescopes. Interferometric pulsar timing experiments could be
performed with neighboring pairs of antennas of the forthcoming large arraying
projects.Comment: Paper submitted to Phys. Rev. Letters. It is 9 pages long, and
includes 2 figure
Learning Features that Predict Cue Usage
Our goal is to identify the features that predict the occurrence and
placement of discourse cues in tutorial explanations in order to aid in the
automatic generation of explanations. Previous attempts to devise rules for
text generation were based on intuition or small numbers of constructed
examples. We apply a machine learning program, C4.5, to induce decision trees
for cue occurrence and placement from a corpus of data coded for a variety of
features previously thought to affect cue usage. Our experiments enable us to
identify the features with most predictive power, and show that machine
learning can be used to induce decision trees useful for text generation.Comment: 10 pages, 2 Postscript figures, uses aclap.sty, psfig.te
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