63 research outputs found
T-duality and Generalized Complex Geometry
We find the explicit T-duality transformation in the phase space formulation
of the N=(1,1) sigma model. We also show that the T-duality transformation is a
symplectomorphism and it is an element of O(d,d). Further, we find the explicit
T-duality transformation of a generalized complex structure in this model. We
also show that the extended supersymmetry of the sigma model is preserved under
the T-duality.Comment: 18 pages; added references; published versio
Generalized Kahler Geometry from supersymmetric sigma models
We give a physical derivation of generalized Kahler geometry. Starting from a
supersymmetric nonlinear sigma model, we rederive and explain the results of
Gualtieri regarding the equivalence between generalized Kahler geometry and the
bi-hermitean geometry of Gates-Hull-Rocek.
When cast in the language of supersymmetric sigma models, this relation maps
precisely to that between the Lagrangian and the Hamiltonian formalisms.
We also discuss topological twist in this context.Comment: 18 page
The Great Circle Camera: A New Drift Scanning Instrument
We discuss the design, construction, and use of a new class of scanning
camera that eliminates a critical limitation of standard CCD drift-scan
observations. A standard scan, which involves no correction for the
differential drift rates and curved stellar paths across the field-of-view,
suffers from severe image degradation even when one observes at moderate
declinations. Not only does this effect limit the area of the sky over which
drift scanning is viable, but as detector sizes increase, CCD mosaics become
standard, and dome/telescope seeing improves, the area of sky for which
scanning is acceptable (image degradation \ltsim seeing) will be further
reduced unless some action is taken. By modifying the scan path (the path on
the sky traced by signal accumulated along a single CCD column) to lie along a
great circle on the sky rather than along a path of constant declination, image
degradation is minimized. In this paper, we discuss the design and
implementation of a stage that rotates and translates the CCD during a
drift-scan exposure so that the scan path is along a great circle on the sky.
Data obtained during the commissioning run of the Great Circle Camera at the
Las Campanas 1-m telescope are presented.Comment: Second attempt at a readable archival file. 7 pages (gzip'ed and
uuencoded postscript). A version of the preprint with Figures 2 and 3 can be
obtained from D. Zaritsky. Accepted for publication in PAS
Type IIB tensionless superstrings in a pp-wave background
We solve the tensionless string in a constant plane wave background and
obtain a hugely degenerate spectrum. This is the case for a large class of
plane wave backgrounds. We show that the solution can also be derived as a
consistent limit of the quantized tensile theory of IIB strings in a pp-wave.
This is in contrast to the situation for several other backgrounds.Comment: 1+17 pages, LaTeX, minor corrections, added new reference
Minding the Terrazzo Gap between Athletes and Nonathletes: Representativeness, Integration, and Academic Performance at the U.S. Air Force Academy
The tension between focusing on collegiate athletic or academic performance has persisted for decades. A recent study finds that recruited athletes in college athletic programs underperform academically, earning lower grades than predicted. It postulates that increased representativeness and integration efforts will enhance the academic value of college athletes’ experience. The U.S. Air Force Academy system presents a natural experiment of whether such efforts can affect student-athlete academic performance. In this setting, we find that student-athletes perform comparably to nonathletes after controlling for predicted academic performance
Courant-like brackets and loop spaces
We study the algebra of local functionals equipped with a Poisson bracket. We
discuss the underlying algebraic structures related to a version of the
Courant-Dorfman algebra. As a main illustration, we consider the functionals
over the cotangent bundle of the superloop space over a smooth manifold. We
present a number of examples of the Courant-like brackets arising from this
analysis.Comment: 20 pages, the version published in JHE
Sigma models with off-shell N=(4,4) supersymmetry and noncommuting complex structures
We describe the conditions for extra supersymmetry in N=(2,2) supersymmetric
nonlinear sigma models written in terms of semichiral superfields. We find that
some of these models have additional off-shell supersymmetry. The (4,4)
supersymmetry introduces geometrical structures on the target-space which are
conveniently described in terms of Yano f-structures and Magri-Morosi
concomitants. On-shell, we relate the new structures to the known
bi-hypercomplex structures.Comment: 20 pages; v2: significant corrections, clarifications, and
reorganization; v3: discussion of supersymmetry vs twisted supersymmetry
added, relevant signs corrected
Sub-electron noise charge-coupled devices
A charge coupled device designed for celestial spectroscopy has achieved readout noise as low as 0.6 electrons rms. A nondestructive output circuit was operated in a special manner to read a single pixel multiple times. Off-chip electronics averaged the multiple values, reducing the random noise by the square root of the number of readouts. Charge capacity was measured to be 500,000 electrons. The device format is 1600 pixels horizontal by 64 pixels vertical. Pixel size is 28 microns square. Two output circuits are located at opposite ends of the 1600 bit CCD register. The device was thinned and operated backside illuminated at -110 degrees C. Output circuit design, layout, and operation are described. Presented data includes the photon transfer curve, noise histograms, and bar-target images down to 3 electrons signal. The test electronics are described, and future improvements are discussed
Gauged (2,2) Sigma Models and Generalized Kahler Geometry
We gauge the (2,2) supersymmetric non-linear sigma model whose target space
has bihermitian structure (g, B, J_{\pm}) with noncommuting complex structures.
The bihermitian geometry is realized by a sigma model which is written in terms
of (2,2) semi-chiral superfields. We discuss the moment map, from the
perspective of the gauged sigma model action and from the integrability
condition for a Hamiltonian vector field. We show that for a concrete example,
the SU(2) x U(1) WZNW model, as well as for the sigma models with almost
product structure, the moment map can be used together with the corresponding
Killing vector to form an element of T+T* which lies in the eigenbundle of the
generalized almost complex structure. Lastly, we discuss T-duality at the level
of a (2,2) sigma model involving semi-chiral superfields and present an
explicit example.Comment: 33 page
First-order supersymmetric sigma models and target space geometry
We study the conditions under which N=(1,1) generalized sigma models support
an extension to N=(2,2). The enhanced supersymmetry is related to the target
space complex geometry. Concentrating on a simple situation, related to Poisson
sigma models, we develop a language that may help us analyze more complicated
models in the future. In particular, we uncover a geometrical framework which
contains generalized complex geometry as a special case.Comment: 1+19 pages, JHEP style, published versio
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