1,253 research outputs found
Two-Loop Beta Functions Without Feynman Diagrams
Starting from a consistency requirement between T-duality symmetry and
renormalization group flows, the two-loop metric beta function is found for a
d=2 bosonic sigma model on a generic, torsionless background. The result is
obtained without Feynman diagram calculations, and represents further evidence
that duality symmetry severely constrains renormalization flows.Comment: 4 pp., REVTeX. Added discussion on scheme (in)dependence; final
version to appear in Phys. Rev. Let
Rotating Dilaton Black Holes
It is shown that an arbitrarily small amount of angular momentum can
qualitatively change the properties of extremal charged black holes coupled to
a dilaton. In addition, the gyromagnetic ratio of these black holes is computed
and an exact rotating black string solution is presented.Comment: 14 page
T-Duality For String in Horava-Lifshitz Gravity
We continue our study of the Lorentz breaking string theories. These theories
are defined as string theory with modified Hamiltonian constraint which breaks
the Lorentz symmetry of target space-time. We analyze properties of this theory
in the target space-time that possesses isometry along one direction. We also
derive the T-duality rules for Lorentz breaking string theories and show that
they are the same as that of Buscher's T-duality for the relativistic strings.Comment: 17 pages, references adde
Michelson Interferometry with the Keck I Telescope
We report the first use of Michelson interferometry on the Keck I telescope
for diffraction-limited imaging in the near infrared JHK and L bands. By using
an aperture mask located close to the f/25 secondary, the 10 m Keck primary
mirror was transformed into a separate-element, multiple aperture
interferometer. This has allowed diffraction-limited imaging of a large number
of bright astrophysical targets, including the geometrically complex dust
envelopes around a number of evolved stars. The successful restoration of these
images, with dynamic ranges in excess of 200:1, highlights the significant
capabilities of sparse aperture imaging as compared with more conventional
filled-pupil speckle imaging for the class of bright targets considered here.
In particular the enhancement of the signal-to-noise ratio of the Fourier data,
precipitated by the reduction in atmospheric noise, allows high fidelity
imaging of complex sources with small numbers of short-exposure images relative
to speckle. Multi-epoch measurements confirm the reliability of this imaging
technique and our whole dataset provides a powerful demonstration of the
capabilities of aperture masking methods when utilized with the current
generation of large-aperture telescopes. The relationship between these new
results and recent advances in interferometry and adaptive optics is briefly
discussed.Comment: Accepted into Publications of the Astronomical Society of the
Pacific. To appear in vol. 112. Paper contains 10 pages, 8 figure
Differential geometry with a projection: Application to double field theory
In recent development of double field theory, as for the description of the
massless sector of closed strings, the spacetime dimension is formally doubled,
i.e. from D to D+D, and the T-duality is realized manifestly as a global O(D,D)
rotation. In this paper, we conceive a differential geometry characterized by a
O(D,D) symmetric projection, as the underlying mathematical structure of double
field theory. We introduce a differential operator compatible with the
projection, which, contracted with the projection, can be covariantized and may
replace the ordinary derivatives in the generalized Lie derivative that
generates the gauge symmetry of double field theory. We construct various gauge
covariant tensors which include a scalar and a tensor carrying two O(D,D)
vector indices.Comment: 1+22 pages, No figure; a previous result on 4-index tensor removed,
presentation improve
An Equivalence Between Momentum and Charge in String Theory
It is shown that for a translationally invariant solution to string theory,
spacetime duality interchanges the momentum in the symmetry direction and the
axion charge per unit length. As one application, we show explicitly that
charged black strings are equivalent to boosted (uncharged) black strings. The
extremal black strings (which correspond to the field outside of a fundamental
macroscopic string) are equivalent to plane fronted waves describing strings
moving at the speed of light.Comment: 10 page
Supersymmetric String Waves
We present plane-wave-type solutions of the lowest order superstring
effective action which have unbroken space-time supersymmetries. They describe
dilaton, axion and gauge fields in a stringy generalization of the Brinkmann
metric. Some conspiracy between the metric and the axion field is required. We
show that there exists a special class of these solutions, for which
stringy corrections to the effective on-shell action, to the
equations of motion (and therefore to the solutions themselves), and to the
supersymmetry transformations vanish. We call these solutions supersymmetric
string waves (SSW).Comment: 19 pages, LaTeX, SU-ITP-92-30 and UG-10/9
Vitamin D status and supplementation in adult patients receiving extracorporeal membrane oxygenation
The prevalence of vitamin D deficiency in critical illness is known to be high and associated with adverse clinical outcomes. Patients receiving extracorporeal membrane oxygenation (ECMO) may be at increased risk of vitamin D deficiency due to high severity of acute illness. Challenges with drug dosing in ECMO patients are recognised due to increased volume of distribution and drug absorption to circuit components. To describe the prevalence of vitamin D deficiency in ECMO patients and the effect of intramuscular dosing of cholecalciferol on levels of vitamin D metabolites, and to compare these data with intensive care unit (ICU) patients not receiving ECMO, two prospective studies were performed sequentially: an observational study of 100 consecutive ICU patients and an interventional study assessing effects of intramuscular cholecalciferol in 50 ICU patients. The subgroup of patients who required ECMO support in each of these studies was analysed and compared to patients who did not receive ECMO. Twenty-four ECMO patients, 12 from the observational study and 12 from the interventional study (who received intramuscular cholecalciferol) were studied-21/24 (88%) ECMO patients were vitamin D deficient at baseline compared to 65/126 (52%) of non-ECMO patients (P=0.006). Of the 12 ECMO patients who received cholecalciferol, six patients (50%) achieved correction of deficiency compared to 36/38 (95%) non-ECMO patients (P=0.001). The prevalence of vitamin D deficiency is higher in ECMO patients compared to other critically ill adults. Correction of deficiency with single dose cholecalciferol is not reliable;higher or repeated doses should be considered to correct deficiency
Two-Vierbein Formalism for String-Inspired Axionic Gravity
Using independent left and right vierbeins to describe graviton plus axion as
suggested by string mechanics, O(d,d) duality can be realized linearly.Comment: 14 pg., (uuencoded dvi file; fixed uuencoding so file is unprotected)
ITP-SB-93-
A Two-loop Test of Buscher's T-duality I
We study the two loop quantum equivalence of sigma models related by
Buscher's T-duality transformation. The computation of the two loop
perturbative free energy density is performed in the case of a certain
deformation of the SU(2) principal sigma model, and its T-dual, using
dimensional regularization and the geometric sigma model perturbation theory.
We obtain agreement between the free energy density expressions of the two
models.Comment: 28 pp, Latex, references adde
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