Results for "John H. Livingston"

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Age Determination in Upper Scorpius with Eclipsing BinariesJan 16 2019The Upper Scorpius OB association is the nearest region of recent massive star formation and thus an important benchmark for investigations concerning stellar evolution and planet formation timescales. We present nine EBs in Upper Scorpius, three of which ... More
A Characteristic Transmission Spectrum dominated by H$_{2}$O applies to the majority of HST/WFC3 exoplanet observationsDec 01 2015Apr 01 2016Currently, 19 transiting exoplanets have published transmission spectra obtained with the Hubble/WFC3 G141 near-IR grism. Using this sample, we have undertaken a uniform analysis incorporating measurement-error debiasing of the spectral modulation due ... More
Spitzer Observations of Hotspots in Radio LobesSep 04 2012We have carried out a systematic search with Spitzer Warm Mission and archival data for infrared emission from the hotspots in radio lobes that have been described by Hardcastle et al. (2004). These hotspots have been detected with both radio and X-ray ... More
Ground-based Transit Observation of the Habitable-zone Super-Earth K2-3dOct 05 2016Nov 25 2016We report the first ground-based transit observation of K2-3d, a 1.5 R_Earth planet supposedly within the habitable zone around a bright M-dwarf host star, using the Okayama 188 cm telescope and the multi(grz)-band imager MuSCAT. Although the depth of ... More
Optimization of infrared and magnetic shielding of superconducting TiN and Al coplanar microwave resonatorsAug 22 2016We present a systematic study of the effects of shielding on the internal quality factors (Qi) of Al and TiN microwave resonators designed for use in quantum coherent circuits. Measurements were performed in an adiabatic demagnetization refrigerator, ... More
Ground-based Transit Observation of the Habitable-zone super-Earth K2-3dOct 05 2016We report the first ground-based transit observation of K2-3d, a 1.5 R_Earth planet supposedly within the habitable zone around a bright M-dwarf host star, using the Okayama 188-cm telescope and the multi(grz)-band imager MuSCAT. Although the depth of ... More
The Stonehenge Technique. A new method for aligning coherent bremsstrahlung radiatorsSep 10 2008This paper describes a new technique for the alignment of crystal radiators used to produce high energy, linearly polarized photons via coherent bremsstrahlung scattering at electron beam facilities. In these experiments the crystal is mounted on a goniometer ... More
Concordances from connected sums of torus knots to L-space knotsJul 20 2017Aug 05 2017If a knot is a nontrivial connected sum of positive torus knots, then it is not concordant to an L-space knot.
The slicing number of a knotJun 07 2002Dec 16 2002An open question asks if every knot of 4-genus g_s can be changed into a slice knot by g_s crossing changes. A counterexample is given.
The concordance genus of knotsJul 19 2001Jan 13 2004In knot concordance three genera arise naturally, g(K), g_4(K), and g_c(K): these are the classical genus, the 4-ball genus, and the concordance genus, defined to be the minimum genus among all knots concordant to K. Clearly 0 <= g_4(K) <= g_c(K) <= g(K). ... More
Null-homologous unknottingsFeb 14 2019Every knot can be unknotted with two generalized twists; this was first proved by Ohyama. Here we prove that any knot of genus g can be unknotted with 2g null-homologous twists and that there exist genus g knots that cannot be unknotted with fewer than ... More
Knot reversal and mutation act non-trivially on the concordance group of topologically slice knotsApr 26 2019We construct a topologically slice knot that is not smoothly concordant to its reverse. Moreover, we show that string reversal induces a nontrivial involution on the quotient of the concordance group of topologically slice knots modulo the subgroup generated ... More
Null-homologous unknottingsFeb 14 2019Mar 25 2019Every knot can be unknotted with two generalized twists; this was first proved by Ohyama. Here we prove that any knot of genus g can be unknotted with 2g null-homologous twists and that there exist genus g knots that cannot be unknotted with fewer than ... More
Chiral smoothings of knotsSep 20 2018Nov 04 2018Given knots K and J, one can ask whether a single smoothing of a crossing in a diagram for K can convert it into a diagram for J. As an interesting example, Zekovic discovered that the torus knot T(2,5) can be converted into T(2,-5) with a single smoothing. ... More
Signature functions of knotsSep 03 2017The signature function of a knot is an integer-valued step function on the unit circle in the complex plane. Necessary and sufficient conditions for a function to be the signature function of a knot are presented.
Computations of the Ozsvath-Szabo knot concordance invariantNov 04 2003May 20 2004Ozsvath and Szabo have defined a knot concordance invariant tau that bounds the 4-ball genus of a knot. Here we discuss shortcuts to its computation. We include examples of Alexander polynomial one knots for which the invariant is nontrivial, including ... More
Splitting the concordance group of algebraically slice knotsMay 26 2003Oct 23 2003As a corollary of work of Ozsvath and Szabo [math.GT/0301149], it is shown that the classical concordance group of algebraically slice knots has an infinite cyclic summand and in particular is not a divisible group.
Notes on the knot concordance invariant UpsilonNov 30 2014Jan 19 2015The knot concordance invariant Upsilon, recently defined by Ozsvath, Stipsicz, and Szabo, takes values in the group of piecewise linear functions on the closed interval [0,2]. This paper presents a description of one approach to defining Upsilon and of ... More
Signature invariants related to the unknotting numberOct 28 2017Jun 12 2018New lower bounds on the unknotting number of a knot are constructed from the classical knot signature function. These bounds can be twice as strong as previously known signature bounds. They can also be stronger than known bounds arising from Heegaard ... More
Splitting numbers of links and the four-genusSep 14 2016The splitting number of a link is the minimum number of crossing changes between distinct components that is required to convert the link into a split link. We provide a bound on the splitting number in terms of the four-genus of related knots.
Four-manifolds of large negative deficiencyFeb 03 2003Oct 21 2003For every N > 0 there exists a group of deficiency less than -N that arises as the fundamental group of a smooth homology 4-sphere and also as the fundamental group of the complement of a compact contractible submanifold of the 4-sphere. A group is the ... More
Seifert forms and concordanceJan 04 2001Sep 05 2002If a knot K has Seifert matrix V_K and has a prime power cyclic branched cover that is not a homology sphere, then there is an infinite family of non-concordant knots having Seifert matrix V_K.
Order 2 Algebraically Slice KnotsAug 13 1998Nov 20 1999The concordance group of algebraically slice knots is the subgroup of the classical knot concordance group formed by algebraically slice knots. Results of Casson and Gordon and of Jiang showed that this group contains in infinitely generated free (abelian) ... More
Observations on Lickorish knotting of contractible 4-manifoldsNov 06 2001Lickorish has constructed large families of contractible 4--manifolds that have knotted embeddings in the 4--sphere and has also shown that every finitely presented perfect group with balanced presentation occurs as the fundamental group of the complement ... More
Maps of surface groups to finite groups with no simple loops in the kernelFeb 20 2000Let $F_g$ denote the closed orientable surface of genus $g$. What is the least order finite group, $G_g$, for which there is a homomorphism $\psi$ from $\pi_1(F_g)$ to $G_g$ so that no nontrivial simple closed curve on $F_g$ represents an element in Ker($\psi$)? ... More
Mass Constraints of the WASP-47 Planetary System from Radial VelocitiesDec 14 2016We report precise radial velocity (RV) measurements of WASP-47, a G star that hosts three transiting planets in close proximity (a hot Jupiter, a super-Earth and a Neptune-sized planet) and a non-transiting planet at 1.4 AU. Through a joint analysis of ... More
K2-66b and K2-106b: Two extremely hot sub-Neptune-size planets with high densitiesMay 09 2017We report precise mass and density measurements of two extremely hot sub-Neptune-size planets from the K2 mission using radial velocities, K2 photometry, and adaptive optics imaging. K2-66 harbors a close-in sub-Neptune-sized (2.49$^{+0.34}_{-0.24} R_\oplus$) ... More
Planetary Candidates from K2 Campaign 16Mar 12 2018May 23 2018Given that Campaign 16 of the K2 mission is one of just two K2 campaigns observed so far in "forward-facing" mode, which enables immediate follow-up observations from the ground, we present a catalog of interesting targets identified through photometry ... More
60 Validated Planets from K2 Campaigns 5-8Oct 09 2018We present a uniform analysis of 155 candidates from the second year of NASA's $K2$ mission (Campaigns 5-8), yielding 60 statistically validated planets spanning a range of properties, with median values of $R_p$ = 2.5 $R_\oplus$, $P$ = 7.1 d, $T_\mathrm{eq}$ ... More
The photospheric solar oxygen project: III. Investigation of the centre-to-limb variation of the 630nm [OI]-NiI blendJun 02 2015The solar photospheric abundance of oxygen is still a matter of debate. For about ten years some determinations have favoured a low oxygen abundance which is at variance with the value inferred by helioseismology. Among the oxygen abundance indicators, ... More
The photospheric solar oxygen project: IV. 3D-NLTE investigation of the 777 nm triplet linesAug 14 2015The solar photospheric oxygen abundance is still widely debated. Adopting the solar chemical composition based on the "low" oxygen abundance, as determined with the use of three-dimensional (3D) hydrodynamical model atmospheres, results in a well-known ... More
A new solar signal: Average maximum sunspot magnetic fields independent of activity cycleApr 11 2016Over the past five years, 2010-2015, we have observed, in the near infrared (IR), the maximum magnetic field strengths for 4145 sunspot umbrae. Herein we distinguish field strengths from field flux. (Most solar magnetographs measure flux). Maximum field ... More
Knot Concordance and TorsionNov 30 1999Let K be a knot in the 3-sphere with 2-fold branched covering space M. If for some prime p congruent to 3 mod 4 the p-torsion in the first homology of M is cyclic with odd exponent, then K is of infinite order in the knot concordance group. As one application, ... More
An involutive upsilon knot invariantOct 23 2017Using the theory of involutive Heegaard Floer knot theory developed by Hendricks-Manolescu, we define two involutive analogs of the Upsilon knot concordance invariant of Ozsvath-Stipsicz-Szabo. These involutive invariants are piecewise linear functions ... More
Beam-foil Spectroscopy of the 1s2s2p23p 6L-1s2p33p 6P Transitions in O IV, F V and Ne VIApr 01 2004We present observations of VUV transitions between doubly excited sextet states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+, (FH)+ and Ne+ beam with a solid carbon target. Some observed lines are assigned to the 1s2s2p23p 6L-1s2p33p ... More
1s2s2p23d 6L - 1s2p33d 6D, L=F, D, P Transitions in O IV, F V and Ne VIApr 01 2004We present observations of VUV transitions between doubly excited sextet states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+ beam with a solid carbon target. We also studied spectra obtained previously of F V and Ne VI. Some observed ... More
Concordance and MutationDec 21 1999Nov 27 2001We provide a framework for studying the interplay between concordance and positive mutation and identify some of the basic structures relating the two. The fundamental result in understanding knot concordance is the structure theorem proved by Levine: ... More
Doubly slice knots with low crossing numberApr 13 2015A knot in the three-sphere is doubly slice if it is the cross-section of an unknotted two-sphere in the four-sphere. For low-crossing knots, the most complete work to date gives a classification of doubly slice knots through 9 crossings. We extend that ... More
Ozsvath-Szabo and Rasmussen invariants of doubled knotsMay 17 2005Mar 10 2009Let \nu be any integer-valued additive knot invariant that bounds the smooth 4-genus of a knot K, |\nu(K)| <= g_4(K), and determines the 4-ball genus of positive torus knots, \nu(T_{p,q}) = (p-1)(q-1)/2. Either of the knot concordance invariants of Ozsvath-Szabo ... More
The geography problem for 4-manifolds with specified fundamental groupAug 03 2006Oct 10 2006For any given finitely presented group G there exists a closed oriented 4-manifold with fundamental group G. What pairs of integers can occur as the signature and Euler characteristic of such a 4-manifold? The first part of this paper develops general ... More
The Hausmann-Weinberger 4-manifold invariant of abelian groupsJul 08 2003Sep 27 2003The Hausmann-Weinberger invariant of a group G is the minimal Euler characteristic of a closed orientable 4-manifold M with fundamental group G. We compute this invariant for finitely generated free abelian groups and estimate the invariant for all finitely ... More
Solar cycle variation in Sun-as-a-star Ca II 854.2 nm bisectorsMay 17 2011The bisector of the strong chromospheric Ca II 854.2 nm line has an inverse-C shape the cause of which is not yet fully understood. We show that the amplitude of the bisector in Sun-as-a-star observations exhibits a solar cycle variation with smaller ... More
Stabilizing Four-Torsion in Classical Knot ConcordanceJul 31 2009Let $M_K$ be the 2-fold branched cover of a knot $K in $S^3$. If $H_1(M_K) = {\bf Z}_3 \oplus {\bf Z}_{3^{2i}} \oplus G$ where 3 does not divide the order of $G$ then $K$ is not of order 4 in the concordance group. This obstruction detects infinite new ... More
Heegaard Floer homology and rational cuspidal curvesApr 03 2013We apply the methods of Heegaard Floer homology to identify topological properties of complex curves in the complex projective plane. As one application, we resolve an open conjecture that constrains the Alexander polynomial of the link of the singular ... More
Semigroups, d-invariants and deformations of cuspidal singular points of plane curvesMay 13 2013Aug 01 2014We apply Heegaard Floer homology to study deformations of singularities of plane algebraic curves. Our main result provides an obstruction to the existence of a deformation between two singularities. Generalizations include the case of multiple singularities. ... More
Obstructing 4-torsion in the classical knot concordance groupFeb 15 1998We prove that if the order of the first homology of the 2-fold branched cover of a knot K in the 3-sphere is given by pm where p is a prime congruent to 3 mod 4 and gcd(p,m) =1, then K is of infinite order in the knot concordance group. This provides ... More
EPIC 211964830: A transiting multi-planet system in the Praesepe open clusterSep 06 2018Planet host stars with well-constrained ages provide a rare window to the time domain of planet formation and evolution. The NASA K2 mission has enabled the discovery of the vast majority of known planets transiting stars in clusters, providing a valuable ... More
K2-264: A transiting multi-planet system in the Praesepe open clusterSep 06 2018Feb 14 2019Planet host stars with well-constrained ages provide a rare window to the time domain of planet formation and evolution. The NASA K2 mission has enabled the discovery of the vast majority of known planets transiting stars in clusters, providing a valuable ... More
Three Small Planets Transiting a Hyades StarOct 19 2017Feb 15 2018We present the discovery of three small planets transiting K2-136 (LP 358 348, EPIC 247589423), a late K dwarf in the Hyades. The planets have orbital periods of $7.9757 \pm 0.0011$, $17.30681^{+0.00034}_{-0.00036}$, and $25.5715^{+0.0038}_{-0.0040}$ ... More
Three Small Super-Earths Transiting the nearby star GJ 9827Sep 05 2017Nov 01 2017We report on the discovery of three transiting planets around GJ~9827. The planets have radii of 1.75$_{-0.12}^{+0.11 }$, 1.36$_{- 0.09 }^{+ 0.09}$, and 2.10$_{- 0.15 }^{+ 0.15 }$~R$_{\oplus}$, and periods of 1.20896, 3.6480, and 6.2014 days, respectively. ... More
K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen ScientistsFeb 07 2019Observations from the Kepler and K2 missions have provided the astronomical community with unprecedented amounts of data to search for transiting exoplanets and other astrophysical phenomena. Here, we present K2-288, a low-mass binary system (M2.0 +/- ... More
Spitzer transit follow-up of planet candidates from the K2 missionJan 17 2019We present precision 4.5 $\mu$m Spitzer transit photometry of eight planet candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01, K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four sub-Neptunes and two ... More
The K2-138 System: A Near-Resonant Chain of Five Sub-Neptune Planets Discovered by Citizen ScientistsJan 11 2018Jan 20 2018K2-138 is a moderately bright (V = 12.2, K = 10.3) main sequence K-star observed in Campaign 12 of the NASA K2 mission. It hosts five small (1.6-3.3R_Earth) transiting planets in a compact architecture. The periods of the five planets are 2.35 d, 3.56 ... More
44 Validated Planets from K2 Campaign 10Jun 29 2018We present 44 validated planets from the 10$^\mathrm{th}$ observing campaign of the NASA $K2$ mission, as well as high resolution spectroscopy and speckle imaging follow-up observations. These 44 planets come from an initial set of 72 vetted candidates, ... More
K2-155: A Bright Metal-Poor M Dwarf with Three Transiting Super-EarthsJan 22 2018Jan 24 2018We report on the discovery of three transiting super-Earths around K2-155 (EPIC 210897587), a relatively bright early M dwarf ($V=12.81$ mag) observed during Campaign 13 of the NASA K2 mission. To characterize the system and validate the planet candidates, ... More
Sommerfeld Fine-Structure Formula for Two-Body AtomsJun 23 2012Mar 20 2013For relativistic atomic two-body systems such as the hydrogen atom, positronium, and muon-proton bound states, a two-body generalisation of the single-particle Sommerfeld fine-structure formula for the relativistic bound-state energies is found. The two-body ... More
On Mediating Supersymmetry Breaking in D-brane ModelsJan 17 2001We consider the 3+1 visible sector to live on a Hanany-Witten D-brane construction in type IIA string theory. The messenger sector consists of stretched strings from the visible brane to a hidden D6-brane in the extra spatial dimensions. In the open string ... More
Multicharge SuperstringsJul 22 2013There are an infinite number of type IIB superstrings in ten dimensions, called (p,q) strings, that are labeled by two distinct string charges. They can form string junctions and string networks. These are the key to understanding the Coulomb branch BPS ... More
The Early History of String Theory and SupersymmetryJan 04 2012This lecture presents a brief overview of the early history of string theory and supersymmetry. It describes how the S-matrix theory program for understanding the strong nuclear force evolved into superstring theory, which is a promising framework for ... More
Recent Progress in AdS/CFTJul 28 2009The study of AdS/CFT (or gauge/gravity) duality has been one of the most active and illuminating areas of research in string theory over the past decade. The scope of its relevance and the insights it is providing seem to be ever expanding. In this talk ... More
The Scientific Contributions of Joel ScherkApr 03 2009Joel Scherk (1946--1980) was an important early contributor to the development of string theory. Together with various collaborators, he made numerous profound and influential contributions to the subject throughout the decade of the 1970s. On the occasion ... More
String Theory Origins of SupersymmetryNov 09 2000The string theory introduced in early 1971 by Ramond, Neveu, and myself has two-dimensional world-sheet supersymmetry. This theory, developed at about the same time that Golfand and Likhtman constructed the four-dimensional super-Poincar\'e algebra, motivated ... More
String Theory: The Early YearsJul 14 2000Jul 26 2000Lenny Susskind has made many important contributions to theoretical physics during the past 35 years. In this talk I will discuss the early history of string theory (1968-72) emphasizing Susskind's contributions.
Lectures on Superstring and M Theory DualitiesJul 25 1996Sep 23 1996These lectures begin by reviewing the evidence for S duality of the toroidally compactified heterotic string in 4d that was obtained in the period 1992--94. Next they review recently discovered dualities that relate all five of the 10d superstring theories ... More
Anomaly-Free Supersymmetric Models in Six DimensionsDec 09 1995Dec 11 1995The conditions for the cancellation of all gauge, gravitational, and mixed anomalies of $N=1$ supersymmetric models in six dimensions are reviewed and illustrated by a number of examples. Of particular interest are models that cannot be realized perturbatively ... More
Dilaton-Axion SymmetrySep 29 1992The heterotic string compactified on a six-torus is described by a low-energy effective action consisting of N=4 supergravity coupled to N=4 super Yang-Mills, a theory that was studied in detail many years ago. By explicitly carrying out the dimensional ... More
Reminiscences of Collaborations with Joel ScherkJul 14 2000I had the privilege of collaborating with Joel Scherk on three separate occasions: in 1970 at Princeton, in 1974 at Caltech, and in 1978-79 at the Ecole Normale Superieure. In this talk I give some reminiscences of these collaborations.
From Superstrings to M TheoryJul 18 1998Aug 16 1998In the strong coupling limit type IIA superstring theory develops an eleventh dimension that is not apparent in perturbation theory. This suggests the existence of a consistent 11d quantum theory, called M theory, which is approximated by 11d supergravity ... More
Remarks on the M5-BraneJul 11 1997The fivebrane of M theory -- the M5-brane -- is an especially interesting object. It plays a central role in a geometric understanding of the Seiberg-Witten solution of N=2 D=4 gauge theories as well as in certain new 6d quantum theories. The low energy ... More
An SL(2,Z) Multiplet of Type IIB SuperstringsAug 25 1995Jun 10 1997An SL(2, Z) family of string solutions of type IIB supergravity in ten dimensions is constructed. The solutions are labeled by a pair of relatively prime integers, which characterize charges of the three-form field strengths. The string tensions depend ... More
Classical Symmetries of Some Two-Dimensional Models Coupled to GravityJun 11 1995Aug 24 1995This paper is a sequel to one in which we examined the affine symmetry algebras of arbitrary classical principal chiral models and symmetric space models in two dimensions. It examines the extension of those results in the presence of gravity. The main ... More
A generalization of Jaynes' principle: an information-theoretic interpretation of the minimum principles of quantum mechanics and gravitationJan 18 2000By considering the "kinetic-energy" term of the minimum principle for the Schr\"{o}dinger equation as a measure of information, that minimum principle is viewed as a statistical estimation procedure, analogous to the manner in which Jaynes ({\it Phys. ... More
The Boltzmann/Shannon entropy as a measure of correlationJan 17 2000IIt is demonstrated that the entropy of statistical mechanics and of information theory, $S({\bf p}) = -\sum p_i \log p_i $ may be viewed as a measure of correlation. Given a probability distribution on two discrete variables, $p_{ij}$, we define the ... More
A new and simpler noncommutative central sets theoremOct 06 2014Mar 13 2015Using dynamics, Furstenberg defined the concept of a central subset of positive integers and proved several powerful combinatorial properties of central sets. Later using the algebraic structure of the Stone-\v{C}ech compactification, Bergelson and Hindman, ... More
Solution of the Scalar Coulomb Bethe-Salpeter EquationJun 12 2000Jan 10 2001A relativistic two-body wave equation, local in configuration space, is derived from the Bethe-Salpeter equation for two scalar particles bound by a scalar Coulomb interaction. The two-body bound-state wave equation is solved analytically, giving a two-body ... More
Vortices under S-dualityAug 26 2002We investigate a system of 1,3, and 7-branes in type IIB string theory. We identify the 1-brane with the vortex of the Abelian Higgs model. We claim that in the S-dual, the theory on the 3-brane confines electric flux which we identify with the fundamental ... More
BPS Soliton Solutions of a D3-brane ActionMay 29 2014Jul 07 2014The world-volume action of a probe D3-brane in $AdS_5 \times S^5$ with $N$ units of flux has the field content, symmetries, and dualities of the $U(1)$ factor of ${\cal N} = 4$ $U(N+1)$ super Yang--Mills theory, spontaneously broken to $U(N) \times U(1)$ ... More
Some Recent Progress in AdS/CFTJun 08 2010Much of modern string theory research concerns AdS/CFT duality, or more generally, gauge/gravity duality. The main subjects are a) Testing and understanding such dualities by exploring how they work for systems with a lot of supersymmetry b) Constructing ... More
Status of Superstring and M-TheoryDec 07 2008Dec 22 2008The first lecture gives a colloquium-level overview of string theory and M-theory. The second lecture surveys various attempts to construct a viable model of particle physics. A recently proposed approach, based on F-theory, is emphasized.
Anomaly Cancellation: A Retrospective From a Modern PerspectiveJul 09 2001The mechanism by which gauge and gravitational anomalies cancel in certain string theories is reviewed. The presentation is aimed at theorists who do not necessarily specialize in string theory.
New Formulation of the Type IIB Superstring Action in $AdS_5 \times S^5$Jun 25 2015Jul 28 2016Previous studies of the type IIB superstring in an ${AdS_5 \times S^5}$ background are based on a description of the superspace geometry as the quotient space $PSU(2,2|4)/SO(4,1) \times SO(5)$. This paper develops an alternative approach in which the ... More
Introduction to Superstring TheoryAug 09 2000These four lectures, addressed to an audience of graduate students in experimental high energy physics, survey some of the basic concepts in string theory. The purpose is to convey a general sense of what string theory is and what it has achieved. Since ... More
The Status of String TheoryNov 05 1997Nov 06 1997There have been many remarkable developments in our understanding of superstring theory in the past few years, a period that has been described as ``the second superstring revolution.'' Several of them are discussed here. The presentation is intended ... More
The M Theory Five-BraneJun 26 1997BPS saturated p-branes play an important role in recent progress in understanding superstring theory and M theory. One approach to understanding the dynamics of p-branes is to formulate an effective (p+1)-dimensional world-volume theory. The construction ... More
Coupling a Self-Dual Tensor to Gravity in Six DimensionsJan 03 1997A recent result concerning interacting theories of self-dual tensor gauge fields in six dimensions is generalized to include coupling to gravity. The formalism makes five of the six general coordinate invariances manifest, whereas the sixth one requires ... More
Self-Dual Superstring in Six DimensionsApr 27 1996A free superstring with chiral N=2 supersymmetry in six dimensions is proposed. It couples to a two-form gauge field with a self-dual field strength. Compactification to four dimensions on a two-torus gives a strongly coupled N=4 four-dimensional gauge ... More
Notes on Feige's gumball machines problemAug 25 2009We give a detailed proof, in the identically distributed case, of a conjecture of Feige about the maximum probability that the sum of n independent non-negative integer valued random variables, each of mean 1, exceeds n. The general case is reduced to ... More
A dynamical characterization of C setsDec 04 2011Furstenberg, using tools from topological dynamics, defined the notion of a central subset of positive integers, and proved a powerful combinatorial theorem about such sets. Using the algebraic structure of the Stone-\v{C}ech compactification, this combinatorial ... More
Interpretation of Infrared Vibration-Rotation Spectra of Interstellar and Circumstellar MoleculesFeb 20 2013Infrared vibration-rotation lines can be valuable probes of interstellar and circumstellar molecules, especially symmetric molecules, which have no pure rotational transitions. But most such observations have been interpreted with an isothermal absorbing ... More
Resolving the Formation of ProtogalaxiesApr 25 2008Cosmic structure originated from minute density perturbations in an almost homogeneous universe. The first stars are believed to be very massive and luminous, providing the first ionizing radiation and heavy elements to the universe and forming 100 million ... More
String Theory SymmetriesMar 20 1995A brief review of the status of duality symmetries in string theory is presented. The evidence is accumulating rapidly that an enormous group of duality symmetries, including perturbative T dualities and non-perturbative S-dualities, underlies string ... More
Classical Symmetries of Some Two-Dimensional ModelsMar 11 1995Mar 27 1995It is well-known that principal chiral models and symmetric space models in two-dimensional Minkowski space have an infinite-dimensional algebra of hidden symmetries. Because of the relevance of symmetric space models to duality symmetries in string theory, ... More
Comments on Superstring Interactions in a Plane-Wave BackgroundAug 26 2002Sep 03 2002The three string vertex for Type IIB superstrings in a maximally supersymmetric plane-wave background is investigated. Specifically, we derive a factorization theorem for the Neumann coefficients that generalizes a flat-space result that was obtained ... More
Some Properties of Type I' String TheoryJul 08 1999Jul 26 1999The T-dual formulation of Type I superstring theory, sometimes called Type I' theory, has a number of interesting features. Here we review some of them including the role of D0-branes and D8-branes in controlling possible gauge symmetry enhancement.
Evidence for Non-perturbative String SymmetriesNov 24 1994Nov 29 1994String theory appears to admit a group of discrete field transformations -- called $S$ dualities -- as exact non-perturbative quantum symmetries. Mathematically, they are rather analogous to the better-known $T$ duality symmetries, which hold perturbatively. ... More
Gauge Theories on the Coulomb branchAug 05 2014We construct the world-volume action of a probe D3-brane in $AdS_5 \times S^5$ with $N$ units of flux. It has the field content, symmetries, and dualities of the $U(1)$ factor of ${\cal N} =4$ $U(N+1)$ super Yang--Mills theory, spontaneously broken to ... More
String Theory: Progress and ProblemsFeb 27 2007Mar 05 2007String theory builds on the great legacy of Yukawa and Tomonaga: New degrees of freedom and control of the UV are two important themes. This talk will give an overview of some of the progress and some of the unsolved problems that characterize string ... More
Superconformal Chern-Simons TheoriesNov 06 2004Nov 23 2004We explore the possibilities for constructing Lagrangian descriptions of three-dimensional superconformal classical gauge theories that contain a Chern-Simons term, but no kinetic term, for the gauge fields. Classes of such theories with N = 1 and N = ... More
The Three-String Vertex for a Plane-Wave BackgroundDec 23 2003The three string vertex for Type IIB superstrings in a maximally supersymmetric plane-wave background can be constructed in a light-cone gauge string field theory formalism. The detailed formula contains certain Neumann coefficients, which are functions ... More
Linking numbers and boundaries of varietiesAug 03 2000The intersection index at a common point of two analytic varieties of complementary dimensions in $\Bbb C^n$ is positive. This observation, which has been called a ``cornerstone'' of algebraic geometry ([GH, p.~62]), is a simple consequence of the fact ... More