Results for "S. A. Stern"

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Evidence for a Collisional Mechanism Affecting Kuiper Belt Object ColorsJun 08 2002The Kuiper Belt (KB) region of the solar system, stretching from 30 to at least 50 AU, contains Pluto-Charon, some ~105 Kuiper Belt Objects (KBOs) larger than 100 km in diameter, and myriad smaller bodies produced by collisions among KBOs (Farinella, ... More
Regarding the Accretion of 2003 VB12 (Sedna) and Like Bodies in Distant Heliocentric OrbitsApr 27 2004Oct 12 2004Recently, Brown et al. (2004) reported the exciting discovery of an ~800 km radius object, (90377) Sedna, on a distant, eccentric orbit centered at ~490 AU from the Sun. Here we undertake a first look exploring the feasibility of accreting this object ... More
Implications Regarding the Energetics Of the Collisional Formation of Kuiper Belt SatellitesJun 06 2002Recently, it has been discovered that at least 1% of Kuiper Belt Objects (KBOs) are accompanied by large satellites. Here we examine the energetics of KBO satellite formation via collisions, finding collisions require a dynamically excited Kuiper Belt. ... More
Ejecta Exchange, Color Evolution in the Pluto System, and Implications for KBOs and Asteroids with SatellitesMay 22 2008We examine the ability of impacts by Kuiper Belt debris to cause regolith exchange between objects in the Pluto system. We find that ejecta velocities from KB impacts are too low to escape from Pluto and Charon. However, ejecta can escape Nix and Hydra, ... More
4D Edge Currents from 5D Chern-Simons TheoryOct 28 1994A class of two dimensional conformal field theories is known to correspond to three dimensional Chern-Simons theory. Here we claim that there is an analogous class of four dimensional field theories corresponding to five dimensional Chern-Simons theory. ... More
First Constraints on Rings in the Pluto SystemAug 01 2006Oct 25 2006Simple theoretical calculations have suggested that small body impacts onto Pluto's newly discovered small satellites, Nix and Hydra, are capable of generating time-variable rings or dust sheets in the Pluto system. Using HST/ACS data obtained on 2006 ... More
Noncommutative Corrections to the Robertson-Walker metricAug 07 2008Upon applying Chamseddine's noncommutative deformation of gravity we obtain the leading order noncommutative corrections to the Robertson-Walker metric tensor. We get an isotropic inhomogeneous metric tensor for a certain choice of the noncommutativity ... More
Triton's surface age and impactor population revisited in light of Kuiper Belt fluxes: Evidence for small Kuiper Belt objects and recent geological activityOct 24 1999Neptune's largest satellite, Triton, is one of the most fascinating and enigmatic bodies in the solar system. Among its numerous interesting traits, Triton appears to have far fewer craters than would be expected if its surface was primordial. Here we ... More
Edge Currents and Vertex Operators for Chern-Simons GravityMay 20 1992We apply elementary canonical methods for the quantization of 2+1 dimensional gravity, where the dynamics is given by E. Witten's $ISO(2,1)$ Chern-Simons action. As in a previous work, our approach does not involve choice of gauge or clever manipulations ... More
Integrability of the Wess_Zumino-Witten model as a non-ultralocal theoryFeb 27 1996Mar 15 1996We consider the 2--dimensional Wess--Zumino--Witten (WZW) model in the canonical formalism introduced in a previous paper by two of us. Using an $r$--$s$ matrix approach to non--ultralocal field theories we find the Poisson algebra of monodromy matrices ... More
Searching for Charon's Atmosphere: Predictions for the New Horizons ApproachJun 12 2015May 30 2016Observations of Pluto's companion planet Charon have so far yielded no compelling evidence for a persistent atmosphere. However, with the upcoming encounter of New Horizons at the Pluto-Charon system, sensitivity to detection of a possible Charon atmosphere ... More
On the Size-Dependence of the Inclination Distribution of the Main Kuiper BeltNov 16 2000We present a new analysis of the currently available orbital elements for the known Kuiper belt objects. In the non-resonant, main Kuiper belt we find a statistically significant relationship between an object's absolute magnitude (H) and its inclination ... More
Remarks on an Exact Seiberg-Witten mapJul 27 2009Sep 20 2009We obtain the leading derivative corrections to an expression for the Seiberg-Witten map given by Banerjee and Yang and show how they affect the noncommutative deformation of the Maxwell action, as well as the matter coupling in noncommutative emergent ... More
Hamiltonian Approach to Poisson Lie T-DualityNov 30 1998The Hamiltonian formalism offers a natural framework for discussing the notion of Poisson Lie T-duality. This is because the duality is inherent in the Poisson structures alone and exists regardless of the choice of Hamiltonian. Thus one can pose alternative ... More
Non-constant Non-commutativity in 2d Field Theories and a New Look at Fuzzy MonopolesFeb 06 2006Apr 17 2006We write down scalar field theory and gauge theory on two-dimensional noncommutative spaces ${\cal M}$ with nonvanishing curvature and non-constant non-commutativity. Usual dynamics results upon taking the limit of ${\cal M}$ going to i) a commutative ... More
Relativistic Particles on Quantum Space-timeNov 04 2010Jan 31 2011We discuss alternatives to the usual quantization of relativistic particles which result in discrete spectra for position and time operators.
T-Duality for Coset ModelsMar 19 1999We construct dual Lagrangians for $G/H$ models in two space-time dimensions for arbitrary Lie groups $G$ and $H\subset G$. Our approach does not require choosing coordinates on $G/H$, and allows for a natural generalization to Lie-Poisson duality. For ... More
Bosonization and Current Algebra of Spinning StringsOct 02 1996We write down a general geometric action principle for spinning strings in $d$-dimensional Minkowski space, which is formulated without the use of Grassmann coordinates. Instead, it is constructed in terms of the pull-back of a left invariant Maurer-Cartan ... More
Noncommutative Point SourcesSep 24 2007We construct a perturbative solution to classical noncommutative gauge theory on ${\mathbb{R}}^{3}$ minus the origin using the Groenewald-Moyal star product. The result describes a noncommutative point charge. Applying it to the quantum mechanics of the ... More
Noncommutative Static Strings from Matrix ModelsApr 09 2014May 16 2014We examine the noncommutative cylinder solution to a matrix model with a Minkowski background metric. It can be regarded as the noncommutative analogue of a static circular string. Perturbations about the solution yield a tachyonic scalar field (and an ... More
Particle Classification and Dynamics in GL(2,C) GravityMar 05 2009May 14 2009A relatively simple approach to noncommutative gravity utilizes the gauge theory formulation of general relativity and involves replacing the Lorentz gauge group by a larger group. This results in additional field degrees of freedom which either must ... More
Particle-like solutions to classical noncommutative gauge theoryApr 19 2008Aug 07 2008We construct perturbative static solutions to the classical field equations of noncommutative U(1) gauge theory for the three cases: a) space-time noncommutativity, b) space-space noncommutativity and c) both a) and b). The solutions tend to the Coulumb ... More
Matrix Model Cosmology in Two Space-time DimensionsSep 27 2014Oct 10 2014We examine solutions to the classical IKKT matrix model equations in three space-time dimensions. Closed, open and static two-dimensional universes naturally emerge from such models in the commutative limit. We show that tachyonic modes are a generic ... More
Properties of Quantum Hall Skyrmions from AnomaliesDec 14 1997Mar 17 1998It is well known that the Fractional Quantum Hall Effect (FQHE) may be effectively represented by a Chern-Simons theory. In order to incorporate QH Skyrmions, we couple this theory to the topological spin current, and include the Hopf term. The cancellation ... More
On the Threshold of the Reionization EpochAug 04 2001Aug 23 2001Discovery of the cosmic reionization epoch would represent a significant milestone in cosmology. We present Keck spectroscopy of the quasar SDSS 1044-0125, at z = 5.73. The spectrum shows a dramatic increase in the optical depth at observed wavelengths ... More
Gauge Theories and Fibre Bundles - Applications to Particle DynamicsFeb 27 2017Mar 20 2017The underlying mathematical structures of gauge theories are known to be geometrical in nature and the local and global features of this geometry have been studied for a long time in mathematics under the name of fibre bundles. It is now understood that ... More
The Chern-Simons Source as a Conformal Family and Its Vertex OperatorsJan 23 1992In a previous work, a straightforward canonical approach to the source-free quantum Chern-Simons dynamics was developed. It makes use of neither gauge conditions nor functional integrals and needs only ideas known from QCD and quantum gravity. It gives ... More
Conformal Edge Currents in Chern-Simons TheoriesOct 30 1991We develop elementary canonical methods for the quantization of abelian and nonabelian Chern-Simons actions using well known ideas in gauge theories and quantum gravity. Our approach does not involve choice of gauge or clever manipulations of functional ... More
Outer Solar System Exploration: A Compelling and Unified Dual Mission Decadal Strategy for Exploring Uranus, Neptune, Triton, Dwarf Planets, and Small KBOs and CentaursJul 23 2018Aug 08 2018Laying the Vision and Voyages (V&V, National Research Council 2011) Decadal Survey 2013-2022 objectives against subsequent budget profiles reveals that separate missions to every desirable target in the Solar System are simply not realistic. In fact, ... More
Theory of interlayer tunneling in bi-layer quantum Hall ferromagnetsJun 28 2000Spielman et al. have recently observed a large zero-bias peak in the tunnel conductance of a bi-layer system in a quantum Hall ferromagnet state. We argue that disorder-induced topological defects in the pseudospin order parameter limit the peak size ... More
A classical analog to topological non-local quantum interference effectNov 23 2003The two main features of the Aharonov-Bohm effect are the topological dependence of accumulated phase on the winding number around the magnetic fluxon, and non-locality -- local observations at any intermediate point along the trajectories are not affected ... More
Current at a distance and resonant transparency in Weyl semimetalsAug 12 2015Oct 29 2015Surface Fermi arcs are the most prominent manifestation of the topological nature of Weyl semimetals. In the presence of a static magnetic field oriented perpendicular to the sample surface, their existence leads to unique inter-surface cyclotron orbits. ... More
Noncommutative BTZ Black Hole and Discrete TimeNov 22 2006Nov 23 2006We search for all Poisson brackets for the BTZ black hole which are consistent with the geometry of the commutative solution and are of lowest order in the embedding coordinates. For arbitrary values for the angular momentum we obtain two two-parameter ... More
Discovery of a Clustered Quasar Pair at z ~ 5: Biased Peaks in Early Structure FormationJun 20 2003We report a discovery of a quasar at z = 4.96 +- 0.03 within a few Mpc of the quasar SDSS 0338+0021 at z = 5.02 +- 0.02. The newly found quasar has the SDSS i and z magnitudes of ~ 21.2, and an estimated absolute magnitude M_B ~ -25.2. The projected separation ... More
Spectroscopic Confirmation of a Radio-Selected Galaxy Overdensity at z=1.11Jun 09 2003We report the discovery of a galaxy overdensity at z=1.11 associated with the z=1.110 high-redshift radio galaxy MG0442+0202. The group, CL0442+0202, was found in a near-infrared survey of z>1 radio galaxies undertaken to identify spatially-coincident ... More
A Perturbative Approach to Fuzzifying Field TheoriesFeb 01 2005Feb 09 2005We propose a procedure for computing noncommutative corrections to the metric tensor, and apply it to scalar field theory written on coordinate patches of smooth manifolds. The procedure involves finding maps to the noncommutative plane where differentiation ... More
Space-Time Noncommutativity from Particle MechanicsFeb 26 2004Mar 05 2004We exploit the reparametrization symmetry of a relativistic free particle to impose a gauge condition which upon quantization implies space-time noncommutativity. We show that there is an algebraic map from this gauge back to the standard `commuting' ... More
Absence of the Holographic Principle in Noncommutative Chern-Simons TheoryJul 20 2001Aug 17 2001We examine noncommutative Chern-Simons theory on a bounded spatial domain. We argue that upon `turning on' the noncommutativity, the edge observables, which characterized the commutative theory, move into the bulk. We show this to lowest order in the ... More
Dirac Operator on the Quantum SphereMar 23 2001Apr 02 2001We construct a Dirac operator on the quantum sphere $S^2_q$ which is covariant under the action of $SU_q(2)$. It reduces to Watamuras' Dirac operator on the fuzzy sphere when $q\to 1$. We argue that our Dirac operator may be useful in constructing $SU_q(2)$ ... More
Gauge Theory of the Star ProductMay 13 2007Sep 20 2007The choice of a star product realization for noncommutative field theory can be regarded as a gauge choice in the space of all equivalent star products. With the goal of having a gauge invariant treatment, we develop tools, such as integration measures ... More
Noncommutative $AdS^3$ with Quantized Cosmological ConstantNov 07 2005We examine a recent deformation of three-dimensional anti-deSitter gravity based on noncommutative Chern-Simons theory with gauge group $U(1,1)\times U(1,1)$. In addition to a noncommutative analogue of 3D gravity, the theory contains two addition gauge ... More
Scale Transformations on the Noncommutative Plane and the Seiberg-Witten MapJun 08 2004Jun 16 2004We write down three kinds of scale transformations {\tt i-iii)} on the noncommutative plane. {\tt i)} is the analogue of standard dilations on the plane, {\tt ii)} is a re-scaling of the noncommutative parameter $\theta$, and {\tt iii)} is a combination ... More
Edge States from Defects on the Noncommutative PlaneJul 23 2003Sep 16 2003We illustrate how boundary states are recovered when going from a noncommutative manifold to a commutative one with a boundary. Our example is the noncommutative plane with a defect, whose commutative limit was found to be a punctured plane - so here ... More
Fuzzy $CP^2$ Space-TimesDec 06 2016Jan 29 2017Four-dimensional manifolds with changing signature are obtained by taking the large $N$ limit of fuzzy $CP^2$ solutions to a Lorentzian matrix model. The regions of Lorentzian signature give toy models of closed universes which exhibit cosmological singularities. ... More
Dual InstantonsFeb 28 2000Aug 17 2000We show how to map the Belavin-Polyakov instantons of the O(3)-nonlinear $\sigma-$model to a dual theory where they then appear as nontopological solitons. They are stationary points of the Euclidean action in the dual theory, and moreover, the dual action ... More
A New Class of Two-Dimensional Noncommutative SpacesDec 23 2001Jan 05 2002We find an infinite number of noncommutative geometries which posses a differential structure. They generalize the two dimensional noncommutative plane, and have infinite dimensional representations. Upon applying generalized coherent states we are able ... More
Fuzzy $CP^2$ Space-TimesDec 06 2016Four-dimensional manifolds with changing signature are obtained by taking the large $N$ limit of fuzzy $CP^2$ solutions to a Lorentzian matrix model. The regions of Lorentzian signature give toy models of closed universes which exhibit cosmological singularities. ... More
Can classical wormholes stabilize the brane-anti-brane system?Sep 09 2003We investigate the static solutions of Callan and Maldecena and Gibbons to lowest order Dirac-Born-Infeld theory. Among them are charged wormhole solutions connecting branes to anti-branes. It is seen that there are no such solutions when the separation ... More
W-Infinity Algebras from Noncommutative Chern-Simons TheoryJun 11 2002May 16 2003We examine Chern-Simons theory written on a noncommutative plane with a `hole', and show that the algebra of observables is a nonlinear deformation of the $w_\infty$ algebra. The deformation depends on the level (the coefficient in the Chern-Simons action), ... More
Non-commutative $AdS_2/CFT_1$ duality: the case of massless scalar fieldsJul 16 2017Jan 18 2018We show how to construct correlators for the $CFT_1$ which is dual to non-commutative $AdS_2$ ($ncAdS_2$). We do it explicitly for the example of the massless scalar field on Euclidean $ncAdS_2$. $ncAdS_2$ is the quantization of $AdS_2$ that preserves ... More
A Comment on the Spectrum of H-MonopolesJul 17 1996We consider the question of ground states in the supersymmetric system that arises in the search for the missing H-monopole states. By studying the effective theory near certain singularities in the five-brane moduli space, we find the remaining BPS states ... More
Vacuum fluctuations of \bar{q}q and values of low-energy constantsJul 10 2000Aug 18 2000We discuss the influence of the vacuum fluctuations of \bar{q}q pairs on low-energy constants and condensates. The analysis of the Goldstone boson masses and decay constants shows that the three-flavour condensate and some low-energy constants are very ... More
The New Horizons Pluto Kuiper belt Mission: An Overview with Historical ContextSep 27 2007NASA's New Horizons (NH) Pluto-Kuiper belt (PKB) mission was launched on 19 January 2006 on a Jupiter Gravity Assist (JGA) trajectory toward the Pluto system for a 14 July 2015 closest approach; Jupiter closest approach occurred on 28 February 2007. It ... More
Snyder space revisitedAug 09 2011Oct 18 2011We examine basis functions on momentum space for the three dimensional Euclidean Snyder algebra. We argue that the momentum space is isomorphic to the SO(3) group manifold, and that the basis functions span either one of two Hilbert spaces. This implies ... More
Two-parameter deformation of the Poincaré algebraJan 11 1996We examine a two-parameter ($\hbar ,$ $\lambda $) deformation of the Poincar\`e algebra which is covariant under the action of $SL_q(2,C).$ When $\lambda \rightarrow 0$ it yields the Poincar\`e algebra, while in the $\hbar\rightarrow 0$ limit we recover ... More
Supersymmetric Extension of the Snyder AlgebraNov 16 2011Nov 23 2011We obtain a minimal supersymmetric extension of the Snyder algebra and study its representations. The construction differs from the general approach given in Hatsuda and Siegel ({\tt hep-th/0311002}), and does not utilize super-de Sitter groups. The spectra ... More
Growing Hair on the extremal $BTZ$ black holeMar 29 2017Apr 19 2017We show that the nonlinear $\sigma-$model in an asymptotically $AdS_3$ space-time admits a novel local symmetry. The field action is assumed to be quartic in the nonlinear $\sigma-$model fields and minimally coupled to gravity. The local symmetry transformation ... More
B fields from a Luddite perspectiveJan 14 2004In this talk we discuss the geometric realization of B fields and higher p-form potentials on a manifold M as connections on affine bundles over M. We realize D branes on M as special submanifolds of these affine bundles. As an application of this geometric ... More
Quantum Mechanical Mirror Symmetry, D Branes, and B FieldsSep 23 2002We construct quantum mechanical models which mimic many features of string theory. We use these models to gain improved descriptions of B fields and gerbes. We examine analogs of T duality, D branes, and mirror symmetry and derive quantum mechanical analogs ... More
Signature change in matrix model solutionsAug 23 2018Oct 18 2018Various classical solutions to lower dimensional IKKT-like Lorentzian matrix models are examined in their commutative limit. Poisson manifolds emerge in this limit, and their associated induced and effective metrics are computed. Signature change is found ... More
Spinning $σ$-model solitons in $2+1$ Anti-de Sitter spaceAug 17 2016Oct 15 2016We obtain numerical solutions for rotating topological solitons of the nonlinear $\sigma$-model in three-dimensional Anti-de Sitter space. Two types of solutions, $i)$ and $ii)$, are found. The $\sigma$-model fields are everywhere well defined for both ... More
Particle Dynamics on Snyder spaceOct 18 2011Mar 26 2012We examine Hamiltonian formalism on Euclidean Snyder space. The latter corresponds to a lattice in the quantum theory. For any given dynamical system, it may not be possible to identify time with a real number parametrizing the evolution in the quantum ... More
Coulomb drag between a metal and a Wigner crystalMar 14 2001We calculated the Coulomb drag contribution to the resistivity and the transresistivity for a double layer system, in which the passive layer is a Wigner crystal pinned by impurities, and the active one is a metal. We found that in quasi one dimensional ... More
Lie-Poisson Deformation of the Poincaré AlgebraMay 25 1995We find a one parameter family of quadratic Poisson structures on ${\bf R}^4\times SL(2,C)$ which satisfies the property {\it a)} that it is preserved under the Lie-Poisson action of the Lorentz group, as well as {\it b)} that it reduces to the standard ... More
Vortex shear effects in layered superconductorsSep 12 2002Motivated by recent transport and magnetization measurements in BSCCO samples [B. Khaykovich et. al., Phys. Rev. B 61, R9261 (2000)], we present a simple macroscopic model describing effects of inhomogeneous current distribution and shear in a layered ... More
Deformed Wong ParticlesApr 27 1993By generalizing the Feynman proof of the Lorentz force law, recently reported by Dyson, we derive equations of motion for particles possessing internal degrees of freedom $I^a$ which do not, in general, generate a finite algebra. We obtain consistency ... More
Mechanical D Branes and B FieldsOct 02 2003We represent B fields and higher p-form potentials on a manifold M as connections on affine bundles over M. We realize D branes on M as special submanifolds of these affine bundles. We check the physical relevance of this representation by showing that ... More
Geometry of minimal energy Yang-Mills connectionsAug 05 2008Aug 16 2008We study the converse to the statement that instantons are minimizers of the Yang--Mills energy in four dimensions. We show that given an energy minimizing connection, A, the curvature of A takes values in a subbundle of the adjoint bundle which decomposes ... More
Deformation Quantization of the Isotropic RotatorDec 14 1993We perform a deformation quantization of the classical isotropic rigid rotator. The resulting quantum system is not invariant under the usual $SU(2)\times SU(2)$ chiral symmetry, but instead $SU_{q^{-1}}(2) \times SU_q(2)$.
Hidden Quantum Group Symmetry in the Chiral ModelDec 12 1996We apply the SL(2,C) lattice Kac-Moody algebra of Alekseev, Faddeev and Semenov-Tian-Shansky to obtain a new lattice description of the SU(2) chiral model in two dimensions. The system has a global quantum group symmetry and it can be regarded as a deformation ... More
Bosonic Description of Spinning Strings in $2+1$ DimensionsJan 30 1996We write down a general action principle for spinning strings in 2+1 dimensional space-time without introducing Grassmann variables. The action is written solely in terms of coordinates taking values in the 2+1 Poincare group, and it has the usual string ... More
A Search for Vulcanoids with the STEREO Heliospheric ImagerJan 16 2013Interior to the orbit of Mercury, between 0.07 and 0.21 AU, is a dynamically stable region where a population of asteroids, known as Vulcanoids, may reside. We present the results from our search for Vulcanoids using archival data from the Heliospheric ... More
Current Algebra and Conformal Field Theory on a Figure EightApr 08 1993We examine the dynamics of a free massless scalar field on a figure eight network. Upon requiring the scalar field to have a well defined value at the junction of the network, it is seen that the conserved currents of the theory satisfy Kirchhoff's law, ... More
The Carbon Monoxide Abundance in Comet 103P/Hartley during the EPOXI FlybyApr 22 2011We report the detection of several emission bands in the CO Fourth Positive Group from comet 103P/Hartley during ultraviolet spectroscopic observations from the Hubble Space Telescope (HST) on 2010 November 4 near the time of closest approach by NASA's ... More
The Positions, Colors, and Photometric Variability of Pluto's Small Satellites from HST Observations 2005-2006Apr 29 2006May 02 2006Pluto's two small satellites, temporarily designated S/2005 P 1 and S/2005 P 2, were observed on four dates (15.1 and 18.1 May 2005, 15.7 February 2006, and 2.8 March 2006) using the Hubble Space Telescope's (HST) Advanced Camera for Surveys (ACS). Here ... More
Overview of the New Horizons Science PayloadSep 26 2007The New Horizons mission was launched on 2006 January 19, and the spacecraft is heading for a flyby encounter with the Pluto system in the summer of 2015. The challenges associated with sending a spacecraft to Pluto in less than 10 years and performing ... More
The New Horizons Kuiper Belt Extended MissionJun 21 2018The central objective of the New Horizons prime mission was to make the first exploration of Pluto and its system of moons. Following that, New Horizons has been approved for its first extended mission, which has the objectives of extensively studying ... More
The Fraction of High Redshift Galaxies in Deep Infrared Selected Field Galaxy SamplesFeb 25 2000Recent results on the incidence of red galaxies in a > 100 square arcminute field galaxy survey to K=20 and a K=22 survey of the Hubble Deep Field are presented. We argue that a simple photometric redshift indicator, based on J-K color and supported by ... More
Dissipationless transport in low density bilayer systemsAug 17 1999In a bilayer electronic system the layer index may be viewed as the z-component of an isospin-1/2. An XY isospin-ordered ferromagnetic phase was observed in quantum Hall systems and is predicted to exist at zero magnetic field at low density. This phase ... More
PHA*: Finding the Shortest Path with A* in An Unknown Physical EnvironmentJun 30 2011We address the problem of finding the shortest path between two points in an unknown real physical environment, where a traveling agent must move around in the environment to explore unknown territory. We introduce the Physical-A* algorithm (PHA*) for ... More
Orbits and photometry of Pluto's satellites: Charon, S/2005 P1 and S/2005 P2Dec 20 2005Mar 18 2006We present new astrometry of Pluto's three satellites from images taken of the Pluto system during 2002-3 with the High Resolution Camera (HRC) mode of the Advanced Camera for Surveys (ACS) instrument on the Hubble Space Telescope. The observations were ... More
The Pluto System After New HorizonsDec 15 2017The discovery of Pluto in 1930 presaged the discoveries of both the Kuiper Belt and ice dwarf planets, which are the third class of planets in our solar system. From the 1970s to the 19990s numerous fascinating attributes of the Pluto system were discovered, ... More
No Evidence for Periodic Variability in the Light Curve of Active Galaxy J0045+41Mar 02 2018Dorn-Wallenstein, Levesque, & Ruan recently presented the identification of a z=0.215 active galaxy located behind M31 and claimed the detection of multiple periodic variations in the object's light curve with as many as nine different periods. They interpreted ... More
Spin-Triplet Excitons in the $S=1/2$ Gapped Antiferromagnet BaCuSi$_2$O$_6$: Electron Paramagnetic Resonance StudiesJan 02 2006BaCuSi$_2$O$_6$, a $S=1/2$ quantum antiferromagnet with a double-layer structure of Cu$^{2+}$ ions in a distorted planar-rectangular coordination and with a dimerized spin singlet ground state, is studied by means of the electron paramagnetic resonance ... More
The Evolution of Star Formation Activity in Cluster Galaxies Over $0.15<z<1.5$Oct 05 2016We explore 7.5 billion years of evolution in the star formation activity of massive ($M_{\star}>10^{10.1}\,M_{\odot}$) cluster galaxies using a sample of 25 clusters over $0.15<z<1$ from the Cluster Lensing And Supernova survey with Hubble and 11 clusters ... More
Discovery of an Optically-Faint Quasar at z=5.70 and Implications for the Faint End of the Quasar Luminosity FunctionOct 17 2005We present observations of an optically-faint quasar, RD J114816.2+525339, discovered from deep multi-color observations of the field around the z = 6.42 quasar SDSS J1148+5251. The two quasars have a projected separation of 109 arcsec and both are outliers ... More
Results of a systematic search for outburst events in 1.4 million galaxiesOct 02 2018We present an analysis of nine years of Catalina Surveys optical photometry for 1.4 million spectroscopically confirmed SDSS galaxies. We find 717 outburst events that were not reported by ongoing transient surveys. These events have timescales ranging ... More
The FIRST Sample of Ultraluminous Infrared Galaxies at High Redshift I. Sample and Near-IR MorphologiesMay 31 2000We present a new sample of distant ultraluminous infrared galaxies. The sample was selected from a positional cross--correlation of the IRAS Faint Source Catalog with the FIRST database. Objects from this set were selected for spectroscopy by virtue of ... More
An X-ray Selected Galaxy Cluster at z=1.26Mar 24 1999We report the discovery of an X-ray luminous galaxy cluster at z=1.26. RXJ0848.9+4452 was selected as an X-ray cluster candidate in the ROSAT Deep Cluster Survey, on the basis of its spatial extent. Deep optical and near-IR imaging have revealed a galaxy ... More
Half-filled Landau level as a Fermi liquid of dipolar quasiparticlesDec 09 1998In this paper we study the relation between the conventional Fermion-Chern-Simons (FCS) theory of the half-filled Landau level (nu=1/2), and alternate descriptions that are based on the notion of neutral quasi-particles that carry electric dipole moments. ... More
Discovery of a Color-Selected Quasar at z=5.50Feb 17 2000We present observations of RD J030117+002025, a quasar at z=5.50 discovered from deep, multi-color, ground-based observations covering 74 square arcmin. This is the most distant quasar or AGN currently known. The object was targeted as an R-band dropout, ... More
NICMOS Imaging of the Dusty Microjansky Radio Source VLA J123642+621331 at z = 4.424Oct 04 1999We present the discovery of a radio galaxy at a likely redshift of z = 4.424 in one of the flanking fields of the Hubble Deep Field. Radio observations with the VLA and MERLIN centered on the HDF yielded a complete sample of microjansky radio sources, ... More
A Radio Galaxy at z=5.19Apr 21 1999We report the discovery of the most distant known AGN, the radio galaxy TN J0924-2201 at z = 5.19. The radio source was selected from a new sample of ultra-steep spectrum (USS) sources, has an extreme radio spectral index alpha_365MHz^1.4GHz = -1.63, ... More
A New Einstein Cross: A Highly Magnified, Intrinsically Faint Lyman-Alpha Emitter at z=2.7Jun 08 2006We report the discovery of a new Einstein cross at redshift z_S = 2.701 based on Lyman-alpha emission in a cruciform configuration around an SDSS luminous red galaxy (z_L = 0.331). The system was targeted as a possible lens based on an anomalous emission ... More
Radio Properties of z>4 Optically-Selected QuasarsJan 22 2000We report on two programs to address differential evolution between the radio-loud and radio-quiet quasar populations at high (z>4) redshift. Both programs entail studying the radio properties of optically-selected quasars. First, we have observed 32 ... More
An IR-Selected Galaxy Cluster at z=1.27Sep 07 1997Sep 09 1997We report the discovery of a galaxy cluster at z=1.27. ClG J0848+4453 was found in a near-IR field survey as a high density region of objects with very red J-K colors. Optical spectroscopy of a limited number of 24 < R < 25 objects in the area shows that ... More
Time-resolved Dynamics of the Spin Hall EffectMay 30 2008The generation and manipulation of carrier spin polarization in semiconductors solely by electric fields has garnered significant attention as both an interesting manifestation of spin-orbit physics as well as a valuable capability for potential spintronics ... More
Drift and Diffusion of Spins Generated by the Spin Hall EffectJun 28 2007Electrically generated spin accumulation due to the spin Hall effect is imaged in n-GaAs channels using Kerr rotation microscopy, focusing on its spatial distribution and time-averaged behavior in a magnetic field. Spatially-resolved imaging reveals that ... More
Morphological Evolution in High Redshift Radio Galaxies and the Formation of Giant Elliptical GalaxiesMar 03 1998We present deep near-IR images of high redshift radio galaxies obtained with NIRC on the Keck I telescope. In most cases, the near-IR data sample rest wavelengths at ~4000 Angstroms, free of strong emission lines. At z > 3, the rest frame optical morphologies ... More
A Polarimetric Search for Hidden Quasars in Three Radio Selected Ultraluminous Infrared GalaxiesDec 05 1998We have carried out a spectropolarimetric search for hidden broad-line quasars in three ultraluminous infrared galaxies (ULIRGs) discovered in the positional correlations between sources detected in deep radio surveys and the IRAS Faint Source Catalog. ... More