345 research outputs found
Speckle interferometry of asteroids
This final report for NASA Contract NAGw-867 consists of abstracts of the first three papers in a series of four appearing in Icarus that were funded by the preceding contract NAGw-224: (1) Speckle Interferometry of Asteroids I. 433 Eros; (2) Speckle Interferometry of Asteroids II. 532 Herculina; (3) Speckle Interferometry of Asteroids III. 511 Davida and its Photometry; and the fourth abstract attributed to NAGw-867, (4) Speckle Interferometry of Asteroids IV. Reconstructed images of 4 Vesta; and a review of the results from the asteroid interferometry program at Steward Observatory prepared for the Asteroids II book, (5) Speckle Interferometry of Asteroids. Two papers on asteroids, indirectly related to speckle interferometry, were written in part under NAGw-867. One is in press and its abstract is included here: Photometric Geodesy of Main-Belt Asteroids. II. Analysis of Lightcurves for Poles, Periods and Shapes; and the other paper, Triaxial Ellipsoid Dimensions and Rotational Pole of 2 Pallas from Two Stellar Occultations, is included in full
Cluster adjacency properties of scattering amplitudes
We conjecture a new set of analytic relations for scattering amplitudes in
planar N=4 super Yang-Mills theory. They generalise the Steinmann relations and
are expressed in terms of the cluster algebras associated to Gr(4,n). In terms
of the symbol, they dictate which letters can appear consecutively. We study
heptagon amplitudes and integrals in detail and present symbols for previously
unknown integrals at two and three loops which support our conjecture.Comment: 6 pages, 3 figures. Symbols of integrals presented in four ancillary
files, as detailed in README.tx
Cluster adjacency beyond MHV
We explore further the notion of cluster adjacency, focussing on non-MHV
amplitudes. We extend the notion of adjacency to the BCFW decomposition of
tree-level amplitudes. Adjacency controls the appearance of poles, both
physical and spurious, in individual BCFW terms. We then discuss how this
notion of adjacency is connected to the adjacency already observed at the level
of symbols of scattering amplitudes which controls the appearance of branch cut
singularities. Poles and symbols become intertwined by cluster adjacency and we
discuss the relation of this property to the -equation which imposes
constraints on the derivatives of the transcendental functions appearing in
loop amplitudes.Comment: 51 pages, 25 figures, 4 table
Killing a Sacred Cow?
So your office sends out a weekly packet of seven stories to a list of editors every week. Quite an accomplishment! It looks real good on the annual report and in the office files
Speckle interferometry of asteroids
By studying the image two-dimensional power spectra or autocorrelations projected by an asteroid as it rotates, it is possible to locate its rotational pole and derive its three axes dimensions through speckle interferometry under certain assumptions of uniform, geometric scattering, and triaxial ellipsoid shape. However, in cases where images can be reconstructed, the need for making the assumptions is obviated. Furthermore, the ultimate goal for speckle interferometry of image reconstruction will lead to mapping albedo features (if they exist) as impact areas or geological units. The first glimpses of the surface of an asteroid were obtained from images of 4 Vesta reconstructed from speckle interferometric observations. These images reveal that Vesta is quite Moon-like in having large hemispheric-scale albedo features. All of its lightcurves can be produced from a simple model developed from the images. Although undoubtedly more intricate than the model, Vesta's lightcurves can be matched by a model with three dark and four bright spots. The dark areas so dominate one hemisphere that a lightcurve minimum occurs when the maximum cross-section area is visible. The triaxial ellipsoid shape derived for Vesta is not consistent with the notion that the asteroid has an equilibrium shape in spite of its having apparently been differentiated
The massless supersymmetric ladder with L rungs
We show that in the massless N=1 supersymmetric Wess-Zumino theory it is
possible to devise a computational strategy by which the x-space calculation of
the ladder 4-point correlators can be carried out without introducing any
regularization. As an application we derive a representation valid at all loop
orders in terms of conformal invariant integrals. We obtain an explicit
expression of the 3-loop ladder diagram for collinear external points.Comment: LaTeX, 17 pages, 8 figure
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