Results for "Robert Hager"

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The nonlinear dispersion relation of geodesic acoustic modesSep 15 2011The energy input and frequency shift of geodesic acoustic modes (GAMs) due to turbulence in tokamak edge plasmas are investigated in numerical two-fluid turbulence studies. Surprisingly, the turbulent GAM dispersion relation is qualitatively equivalent ... More
Radial propagation of geodesic acoustic modesApr 24 2009Oct 21 2009The GAM group velocity is estimated from the ratio of the radial free energy flux to the total free energy applying gyrokinetic and two-fluid theory. This method is much more robust than approaches that calculate the group velocity directly and can be ... More
Verification of the global gyrokinetic stellarator code XGC-S for linear ion temperature gradient driven modesMay 14 2019XGC (X-point Gyrokinetic Code) is a whole-volume, total-f gyrokinetic particle-in-cell code developed for modelling tokamaks. In recent work, XGC has been extended to model more general 3D toroidal magnetic configurations, such as stellarators. These ... More
Perturbations of Jordan MatricesDec 06 2006We consider perturbations of a large Jordan matrix, either random and small in norm or of small rank. In both cases we show that most of the eigenvalues of the perturbed matrix are very close to a circle with centre at the origin. In the case of random ... More
Gradient-based methods for sparse recoveryDec 09 2009The convergence rate is analyzed for the SpaSRA algorithm (Sparse Reconstruction by Separable Approximation) for minimizing a sum $f (\m{x}) + \psi (\m{x})$ where $f$ is smooth and $\psi$ is convex, but possibly nonsmooth. It is shown that if $f$ is convex, ... More
Moment Preserving Constrained Resampling with Applications to Particle-in-Cell MethodsFeb 17 2017Oct 22 2017In simulations of partial differential equations using particle-in-cell (PIC) methods, it is often advantageous to resample the particle distribution function to increase simulation accuracy, reduce compute cost, and/or avoid numerical instabilities. ... More
Learning in an Uncertain World: Representing Ambiguity Through Multiple HypothesesDec 01 2016Aug 22 2017Many prediction tasks contain uncertainty. In some cases, uncertainty is inherent in the task itself. In future prediction, for example, many distinct outcomes are equally valid. In other cases, uncertainty arises from the way data is labeled. For example, ... More
Convergence rate for a Radau collocation method applied to unconstrained optimal controlAug 16 2015Sep 13 2015A local convergence rate is established for an orthogonal collocation method based on Radau quadrature applied to an unconstrained optimal control problem. If the continuous problem has a sufficiently smooth solution and the Hamiltonian satisfies a strong ... More
Lebesgue Constants Arising in a Class of Collocation MethodsJul 29 2015Sep 15 2015Estimates are obtained for the Lebesgue constants associated with the Gauss quadrature points on $(-1, +1)$ augmented by the point $-1$ and with the Radau quadrature points on either $(-1, +1]$ or $[-1, +1)$. It is shown that the Lebesgue constants are ... More
Recognizing Surgical Activities with Recurrent Neural NetworksJun 20 2016Jun 22 2016We apply recurrent neural networks to the task of recognizing surgical activities from robot kinematics. Prior work in this area focuses on recognizing short, low-level activities, or gestures, and has been based on variants of hidden Markov models and ... More
Verification of long wavelength electromagnetic modes with a gyrokinetic-fluid hybrid model in the XGC codeFeb 16 2017As an alternative option to kinetic electrons, the gyrokinetic total-f particle-in-cell (PIC) code XGC1 has been extended to the MHD/fluid type electromagnetic regime by combining gyrokinetic PIC ions with massless drift-fluid electrons analogous to Chen ... More
Optimizing ccNUMA locality for task-parallel execution under OpenMP and TBB on multicore-based systemsDec 30 2010Task parallelism as employed by the OpenMP task construct or some Intel Threading Building Blocks (TBB) components, although ideal for tackling irregular problems or typical producer/consumer schemes, bears some potential for performance bottlenecks if ... More
User Experience of the CoSTAR System for Instruction of Collaborative RobotsMar 23 2017How can we enable novice users to create effective task plans for collaborative robots? Must there be a tradeoff between generalizability and ease of use? To answer these questions, we conducted a user study with the CoSTAR system, which integrates perception ... More
A global-local approach for detecting hotspots in multiple-response regressionNov 08 2018We tackle modelling and inference for variable selection in regression problems with many predictors and many responses. We focus on detecting hotspots, i.e., predictors associated with several responses. Such a task is critical in statistical genetics, ... More
A Proof of Concept for Optimizing Task Parallelism by Locality QueuesFeb 11 2009Task parallelism as employed by the OpenMP task construct, although ideal for tackling irregular problems or typical producer/consumer schemes, bears some potential for performance bottlenecks if locality of data access is important, which is typically ... More
Toward a Science of Autonomy for Physical Science: HealthcareSep 19 2016In Star Wars Episode V, we see Luke Skywalker being repaired by a surgical robot. In the context of the movie, this doesn't seem surprising or disturbing. After all, it is a long, long time ago, in a galaxy far, far away. It would never happen here. Or ... More
Estimation Procedures for Robust Sensor ControlMar 27 2013Many robotic sensor estimation problems can characterized in terms of nonlinear measurement systems. These systems are contaminated with noise and may be underdetermined from a single observation. In order to get reliable estimation results, the system ... More
Introducing a Performance Model for Bandwidth-Limited Loop KernelsMay 06 2009We present a performance model for bandwidth limited loop kernels which is founded on the analysis of modern cache based microarchitectures. This model allows an accurate performance prediction and evaluation for existing instruction codes. It provides ... More
Eigenvalue asymptotics for randomly perturbed non-selfadjoint operatorsJan 16 2006May 04 2007We consider quite general $h$-pseudodifferential operators on $R^n$ with small random perturbations and show that in the limit of small $h$ the eigenvalues are distributed according to a Weyl law with a probabality that tends to 1. The first author has ... More
Event-Based Transverse Momentum ResummationApr 17 2019We have developed a framework for automated transverse momentum resummation for arbitrary electroweak final states based on reweighting tree-level events. It is fully differential in the kinematics of the electroweak final states, which facilitates a ... More
Unitarity in the Schroedinger Formalism of QFT in Curved Space-TimeJan 21 2019Jan 23 2019We review the general quantization of scalar fields in curved space-times and discuss the determination of the ground-state. We give an argument for the instability of the ground-state of a QFT in a semi-classical space-time of Bianchi-type I, by explicitly ... More
An ellipsoidal branch and bound algorithm for global optimizationDec 09 2009A branch and bound algorithm is developed for global optimization. Branching in the algorithm is accomplished by subdividing the feasible set using ellipses. Lower bounds are obtained by replacing the concave part of the objective function by an affine ... More
2D Crystal Shapes, Droplet Condensation and Exponential Slowing Down in Simulations of First-Order Phase TransitionsJan 18 2002Apr 14 2003Multicanonical ensemble simulations for the simulation of first-order phase transitions suffer from exponential slowing down. Monte Carlo autocorrelation times diverge exponentially with free energy barriers $\Delta F$, which in $L^d$ boxes grow as $L^{d-1}$. ... More
Choice of the uncritical manifold for dilute polymer solutionsDec 21 2004We discuss the dependence of the results of renormalized perturbation theory for dilute polymer solutions on the choice of the uncritical manifold where the perturbation series are evaluated. Special emphasis is given to the influence of polydispersity ... More
Theta-point behavior of diluted polymer solutions: Can one observe the universal logarithmic corrections predicted by field theory?Aug 31 1999In recent large scale Monte-Carlo simulations of various models of Theta-point polymers in three dimensions Grassberger and Hegger found logarithmic corrections to mean field theory with amplitudes much larger than the universal amplitudes of the leading ... More
An Active Set Algorithm for Nonlinear Optimization with Polyhedral ConstraintsJun 07 2016A polyhedral active set algorithm PASA is developed for solving a nonlinear optimization problem whose feasible set is a polyhedron. Phase one of the algorithm is the gradient projection method, while phase two is any algorithm for solving a linearly ... More
Inexact alternating direction multiplier methods for separable convex optimizationApr 08 2016Inexact alternating direction multiplier methods (ADMMs) are developed for solving general separable convex optimization problems with a linear constraint and with an objective that is the sum of smooth and nonsmooth terms. The approach involves linearized ... More
Projection algorithms for non-convex minimization, with application to sparse principal component analysisApr 16 2014Mar 30 2015We consider concave minimization problems over non-convex sets.Optimization problems with this structure arise in sparse principal component analysis. We analyze both a gradient projection algorithm and an approximate Newton algorithm where the Hessian ... More
The orbital and superhump periods of the deeply eclipsing dwarf nova SDSS J150240.98+333423.9May 18 2010During July 2009 we observed the first confirmed superoutburst of the eclipsing dwarf nova SDSS J150240.98+333423.9 using CCD photometry. The outburst amplitude was at least 3.9 magnitudes and it lasted at least 16 days. Superhumps having up to 0.35 peak-to-peak ... More
Effective Lifetimes of $B_s$ Decays and their Constraints on the $B_s^0$-$\bar B_s^0$ Mixing ParametersSep 23 2011Measurements of the effective lifetimes of $B_s$-meson decays, which only require untagged rate analyses, allow us to probe the width difference $\Delta\Gamma_s$ and the CP-violating phase $\phi_s$ of $B^0_s$-$\bar B^0_s$ mixing. We point out that the ... More
A Fresh Look at B_{s,d} -> pi pi, pi K, K K DecaysDec 03 2010Using updated measurements and SU(3)-breaking form factors, we have a detailed look at the B_d -> pi^+ pi^-, B_s -> K^+ K^- and B_d -> pi^\mp K^\pm, B_s -> pi^\pm K^\mp systems. The corresponding decays are related to each other by the U-spin symmetry ... More
An Expectation Maximization Framework for Yule-Simon Preferential Attachment ModelsOct 23 2017Sep 16 2018In this paper we develop an Expectation Maximization(EM) algorithm to estimate the parameter of a Yule-Simon distribution. The Yule-Simon distribution exhibits the "rich get richer" effect whereby an 80-20 type of rule tends to dominate. These distributions ... More
Holographic Renormalization for Asymptotically Lifshitz SpacetimesJul 28 2011Sep 07 2011A variational formulation is given for a theory of gravity coupled to a massive vector in four dimensions, with Asymptotically Lifshitz boundary conditions on the fields. For theories with critical exponent z=2 we obtain a well-defined variational principle ... More
Conditions for the importance of inelastic losses in photoemissionDec 04 2001It is shown that for materials near the metal insulator transition, inelastic losses can give rise to substantial changes on a scale of 10-100 meV in the observed lineshape compared to the intrinsic spectral function of an electron photoemitted from a ... More
Ohmic Losses in Valence-band Photoemission ExperimentsAug 14 2000Photoemission experiments involve the motion of an electron near a conducting surface. This necessarily generates heat by ohmic losses from eddy currents. This inelastic scattering of the electrons will result in a downward shift in observed spectra. ... More
Theory of Percolative Conduction in Polycrystaline High-temperature SuperconductorsNov 17 1998Jul 01 1999Conduction in bulk polycrystalline high-T$_c$ superconductors with relatively high critical currents has been shown to be percolative. This phenomenon is due to weak links at grain boundaries. These weak links are the major limiting factor for technological ... More
The Chern-Simons state for the non-diagonal Bianchi IX modelFeb 03 1998The Bianchi IX mixmaster model is quantized in its non-diagonal form, imposing spatial diffeomorphism, time reparametrization and Lorentz invariance as constraints on physical state vectors before gauge-fixing. The result turns out to be different from ... More
Exact quantum states for the diagonal Bianchi type IX model with negative cosmological constantMay 17 1996Quantum states of the diagonal Bianchi type IX model with negative cosmological constant $\Lambda$ are obtained by transforming the Chern-Simons solution in Ashtekar's variables to the metric representation. We apply our method developed earlier for $\Lambda>0$ ... More
Triad representation of the Chern-Simons state in quantum gravityMar 30 2000We investigate a triad representation of the Chern-Simons state of quantum gravity with a non-vanishing cosmological constant. It is shown that the Chern-Simons state, which is a well-known exact wavefunctional within the Ashtekar theory, can be transformed ... More
c-axis Josephson Tunneling in Twinned YBCO CrystalsJul 02 1999Jan 13 2000Josephson tunneling between YBCO and Pb with the current flowing along the c-axis of the YBCO is persumed to come from an s-wave component of the superconductivity of the YBCO. Experiments on multi-twin samples are not entirely consistent with this hypothesis. ... More
Theory of Josephson tunneling along the c-axis of YBCOMar 10 1998The existence of Josephson tunneling has been demonstrated between YBa$_2$Cu$_3$O$_{7-\delta}$ and Pb with the current flowing along the c-axis of YBa$_2$Cu$_3$O$_{7-\delta}$. This is presumed to come from an s-wave component of the superconductivity ... More
Physical states of Bianchi type IX quantum cosmologies described by the Chern-Simons functionalMar 18 1996A class of exact solutions of the Wheeler-DeWitt equation for diagonal Bianchi type IX cosmologies with cosmological constant is derived in the metric representation. This class consists of all the ``topological solutions'' which are associated with the ... More
In Pursuit of New Physics with B^0_s -> K^+K^-Nov 04 2010The B^0_s -> K^+K^- decay is the U-spin partner of B^0_d -> pi^+\pi^- and allows a determination of the angle gamma of the unitarity triangle of the Cabibbo-Kobayashi-Maskawa matrix. Using updated information on the branching ratio and the relevant hadronic ... More
Quantum phase transition in a 1D transport model with boson affected hopping: Luttinger liquid versus charge-density-wave behaviorNov 05 2008Feb 10 2009We solve a very general two-channel fermion-boson model describing charge transport within some background medium by means of a refined pseudo-site density matrix renormalization group (DMRG) technique. Performing a careful finite-size scaling analysis, ... More
Efficient multicore-aware parallelization strategies for iterative stencil computationsApr 10 2010Stencil computations consume a major part of runtime in many scientific simulation codes. As prototypes for this class of algorithms we consider the iterative Jacobi and Gauss-Seidel smoothers and aim at highly efficient parallel implementations for cache-based ... More
Temporal and Physical Reasoning for Perception-Based Robotic ManipulationOct 11 2017Accurate knowledge of object poses is crucial to successful robotic manipulation tasks, and yet most current approaches only work in laboratory settings. Noisy sensors and cluttered scenes interfere with accurate pose recognition, which is problematic ... More
Performance limitations for sparse matrix-vector multiplications on current multicore environmentsOct 26 2009The increasing importance of multicore processors calls for a reevaluation of established numerical algorithms in view of their ability to profit from this new hardware concept. In order to optimize the existent algorithms, a detailed knowledge of the ... More
An exact algorithm for graph partitioningDec 09 2009An exact algorithm is presented for solving edge weighted graph partitioning problems. The algorithm is based on a branch and bound method applied to a continuous quadratic programming formulation of the problem. Lower bounds are obtained by decomposing ... More
On the accuracy and usefulness of analytic energy models for contemporary multicore processorsMar 05 2018This paper presents refinements to the execution-cache-memory performance model and a previously published power model for multicore processors. The combination of both enables a very accurate prediction of performance and energy consumption of contemporary ... More
Information and Multi-Sensor CoordinationMar 27 2013The control and integration of distributed, multi-sensor perceptual systems is a complex and challenging problem. The observations or opinions of different sensors are often disparate incomparable and are usually only partial views. Sensor information ... More
A fast low-to-high mode bifurcation dynamics in a tokamak edge plasma gyrokinetic simulationJan 19 2017May 08 2017Transport barrier formation and its relation to sheared flows in fluids and plasmas are of fundamental interest in various natural and laboratory observations and of critical importance in achieving an economical energy production in a magnetic fusion ... More
Multicore-aware parallel temporal blocking of stencil codes for shared and distributed memoryDec 22 2009New algorithms and optimization techniques are needed to balance the accelerating trend towards bandwidth-starved multicore chips. It is well known that the performance of stencil codes can be improved by temporal blocking, lessening the pressure on the ... More
Multi-core architectures: Complexities of performance prediction and the impact of cache topologyOct 26 2009The balance metric is a simple approach to estimate the performance of bandwidth-limited loop kernels. However, applying the method to in-cache situations and modern multi-core architectures yields unsatisfactory results. This paper analyzes the in uence ... More
Towards Robot Task Planning From Probabilistic Models of Human SkillsFeb 15 2016We describe an algorithm for motion planning based on expert demonstrations of a skill. In order to teach robots to perform complex object manipulation tasks that can generalize robustly to new environments, we must (1) learn a representation of the effects ... More
A domain-specific language and matrix-free stencil code for investigating electronic properties of Dirac and topological materialsAug 31 2017May 07 2018We introduce PVSC-DTM (Parallel Vectorized Stencil Code for Dirac and Topological Materials), a library and code generator based on a domain-specific language tailored to implement the specific stencil-like algorithms that can describe Dirac and topological ... More
CAS-CNN: A Deep Convolutional Neural Network for Image Compression Artifact SuppressionNov 22 2016Lossy image compression algorithms are pervasively used to reduce the size of images transmitted over the web and recorded on data storage media. However, we pay for their high compression rate with visual artifacts degrading the user experience. Deep ... More
sharpDARTS: Faster and More Accurate Differentiable Architecture SearchMar 23 2019Neural Architecture Search (NAS) has been a source of dramatic improvements in neural network design, with recent results meeting or exceeding the performance of hand-tuned architectures. However, our understanding of how to represent the search space ... More
A Continuous Refinement Strategy for the Multilevel Computation of Vertex SeparatorsNov 22 2013The Vertex Separator Problem (VSP) on a graph is the problem of finding the smallest collection of vertices whose removal separates the graph into two disjoint subsets of roughly equal size. Recently, Hager and Hungerford [1] developed a continuous bilinear ... More
Data access optimizations for highly threaded multi-core CPUs with multiple memory controllersDec 14 2007Jan 28 2008Processor and system architectures that feature multiple memory controllers are prone to show bottlenecks and erratic performance numbers on codes with regular access patterns. Although such effects are well known in the form of cache thrashing and aliasing ... More
A Decentralized Multi-block ADMM for Demand-side Primary Frequency Control using Local Frequency MeasurementsSep 28 2015We consider demand-side primary frequency control in the power grid provided by smart and flexible loads: loads change consumption to match generation and help the grid while minimizing disutility for consumers incurred by consumption changes. The dual ... More
Dynamic Template Tracking and RecognitionApr 19 2012In this paper we address the problem of tracking non-rigid objects whose local appearance and motion changes as a function of time. This class of objects includes dynamic textures such as steam, fire, smoke, water, etc., as well as articulated objects ... More
A Decentralized Multi-block ADMM for Demand-side Primary Frequency Control using Local Frequency MeasurementsSep 28 2015Apr 06 2019We consider demand-side primary frequency control in the power grid provided by smart and flexible loads: loads change consumption to match generation and help the grid while minimizing disutility for consumers incurred by consumption changes. The dual ... More
Fluctuations of steps on crystal surfacesAug 24 2001Fluctuations of isolated and pairs of ascending steps of monoatomic height are studied in the framework of SOS models, using mainly Monte Carlo techniques. Below the roughening transistion of the surface, the profiles of long steps show the same scaling ... More
Best practices for HPM-assisted performance engineering on modern multicore processorsJun 17 2012Many tools and libraries employ hardware performance monitoring (HPM) on modern processors, and using this data for performance assessment and as a starting point for code optimizations is very popular. However, such data is only useful if it is interpreted ... More
LIKWID: Lightweight Performance ToolsApr 26 2011Jan 07 2013Exploiting the performance of today's microprocessors requires intimate knowledge of the microarchitecture as well as an awareness of the ever-growing complexity in thread and cache topology. LIKWID is a set of command line utilities that addresses four ... More
LIKWID: A lightweight performance-oriented tool suite for x86 multicore environmentsApr 26 2010Jun 30 2010Exploiting the performance of today's processors requires intimate knowledge of the microarchitecture as well as an awareness of the ever-growing complexity in thread and cache topology. LIKWID is a set of command-line utilities that addresses four key ... More
Electron confinement in graphene with gate-defined quantum dotsMar 19 2015Apr 20 2016We theoretically analyse the possibility to electrostatically confine electrons in circular quantum dot arrays, impressed on contacted graphene nanoribbons by top gates. Utilising exact numerical techniques, we compute the scattering efficiency of a single ... More
Note on Representing $\aleph_0$-categorical Linear OrdersNov 25 2015These notes find a canonical representation of the $\aleph_0$-categorical linear orders based on Joseph Rosenstein's description. A unique minimal representation, called the normal form, is obtained.
Theory of the Transition at 0.2 K in Ni-doped Bi2Sr2CaCu2O8Dec 06 1999A theory is put forward that the electronic phase transition at 0.2 K in Ni-doped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ is result of the formation of a spin density wave in the system of Ni impurities. The driving force for the transition is the exchange ... More
In Pursuit of New Physics with B DecaysMay 30 2011Decays of B mesons offer interesting probes to search for physics beyond the Standard Model. Thanks to the data taking at the LHC, we are at the beginning of a new era of precision B physics. I will discuss recent developments concerning the analyses ... More
Theoretical Overview of CP Violation in B-Meson DecayJun 13 2000After a brief look at CP violation in kaon decays, a short overview of CP violation in the $B$-meson system and of strategies to determine the angles of the unitarity triangles of the CKM matrix is given. Both general aspects and some recent developments ... More
New Strategies to Extract $β$ and $γ$ from $B_d\to π^+ π^-$ and $B_s\to K^+ K^-$Mar 23 1999The decays $B_d\to \pi^+ \pi^-$ and $B_s\to K^+ K^-$ are related to each other by interchanging all down and strange quarks, i.e. through the $U$-spin flavour symmetry of strong interactions. A completely general parametrization of the CP-violating observables ... More
Penguin Effects in $φ_{d,s}$ DeterminationsDec 12 2012The theoretical precision of the measurement of the $B^0_{d,s}$-$\bar B^0_{d,s}$ mixing phases $\phi_{d,s}$ through the benchmark decays $B^0_d\to J/\psi K_S$, $B^0_s\to J/\psi \phi$ and $B^0_s\to J/\psi f_0(980)$ is limited by doubly Cabibbo-suppressed ... More
Extracting gamma Through Flavour-Symmetry StrategiesJul 26 2002A brief overview of flavour-symmetry strategies to extract the angle gamma of the unitarity triangle is given, focusing on B --> pi K modes and the B_d --> pi^+ pi^-, B_s --> K^+ K^- system. We discuss also a variant of the latter approach for the e^+ ... More
Extracting $γ$ from $B_{s(d)}\to J/ψK_S$ and $B_{d(s)}\to D^{+}_{d(s)} D^{-}_{d(s)}$Mar 23 1999A completely general parametrization of the time-dependent decay rates of the modes $B_s\to J/\psi K_S$ and $B_d\to J/\psi K_S$ is given, which are related to each other through the $U$-spin flavour symmetry of strong interactions. Owing to the interference ... More
Graded skew Specht modules and cuspidal modules for Khovanov-Lauda-Rouquier algebras of affine type ADec 23 2014Nov 21 2015Kleshchev, Mathas and Ram (2012) gave a presentation for graded Specht modules over Khovanov-Lauda-Rouquier algebras of finite and affine type A. We show that this construction can be applied more generally to skew shapes to give a presentation of graded ... More
Computing ultra-precise eigenvalues of the Laplacian within polygonsFeb 27 2016The main difficulty in solving the Helmholtz equation within polygons is due to non-analytic vertices. By using a method nearly identical to that used by Fox, Henrici, and Moler in their 1967 paper; it is demonstrated that such eigenvalue calculations ... More
The Tunneling TransformNov 10 2014We supplement the Lorentz transform $L(v)$ with a new "Tunneling" transform $T(v)$. Application of this new transform to elementary quantum mechanics offers a novel, intuitive insight into the nature of quantum tunneling; in particular, the so called ... More
Gross-Pitaevskii Theory of the Rotating Bose GasOct 08 2001Apr 20 2002We study the Gross-Pitaevskii functional for a rotating two-dimensional Bose gas in a trap. We prove that there is a breaking of the rotational symmetry in the ground state; more precisely, for any value of the angular velocity and for large enough values ... More
Lengths of Periods and Seshadri Constants of Abelian VarietiesJun 13 1996The purpose of this note is to point out an elementary but somewhat surprising connection between the work of Buser and Sarnak on lengths of periods of abelian varieties and the Seshadri constants measuring the local positivity of theta divisors. The ... More
Hot Topics in Cold GasesAug 25 2009Since the first experimental realization of Bose-Einstein condensation in cold atomic gases in 1995 there has been a surge of activity in this field. Ingenious experiments have allowed us to probe matter close to zero temperature and reveal some of the ... More
Vortices and Spontaneous Symmetry Breaking in Rotating Bose GasesJan 02 2008We present a rigorous proof of the appearance of quantized vortices in dilute trapped Bose gases with repulsive two-body interactions subject to rotation, which was obtained recently in joint work with Elliott Lieb. Starting from the many-body Schroedinger ... More
Origin of the `He/N' and `Fe II' Spectral Classes of NovaeAug 02 2012The spectra of postoutburst novae display either He+N or Fe II lines as the most prominent non-Balmer lines at maximum light. Spectral diagnostics indicate physical conditions for 'He/N' spectra that are consistent with their origin in the white dwarf ... More
General boundary quantum field theory: Timelike hypersurfaces in Klein-Gordon theorySep 15 2005Mar 17 2006We show that the real massive Klein-Gordon theory admits a description in terms of states on various timelike hypersurfaces and amplitudes associated to regions bounded by them. This realizes crucial elements of the general boundary framework for quantum ... More
Renormalization for spin foam models of quantum gravityJan 20 2004We give an introductory account to the renormalization of models without metric background. We sketch the application to certain discrete models of quantum gravity such as spin foam models.
The general boundary approach to quantum gravityDec 17 2003We present an approach to quantum gravity based on the general boundary formulation of quantum mechanics, path integral quantization, spin foam models and renormalization.
Renormalization of Discrete Models without BackgroundDec 11 2002Feb 26 2003Conventional renormalization methods in statistical physics and lattice quantum field theory assume a flat metric background. We outline here a generalization of such methods to models on discretized spaces without metric background. Cellular decompositions ... More
Generalized Lattice Gauge Theory, Spin Foams and State Sum InvariantsOct 29 2001May 09 2002We construct a generalization of pure lattice gauge theory (LGT) where the role of the gauge group is played by a tensor category. The type of tensor category admissible (spherical, ribbon, symmetric) depends on the dimension of the underlying manifold ... More
Structure Theorem for Covariant Bundles on Quantum Homogeneous SpacesAug 06 2001May 10 2002The natural generalization of the notion of bundle in quantum geometry is that of bimodule. If the base space has quantum group symmetries one is particularly interested in bimodules covariant (equivariant) under these symmetries. Most attention has so ... More
Braided Quantum Field TheoryJun 29 1999Nov 15 2000We develop a general framework for quantum field theory on noncommutative spaces, i.e., spaces with quantum group symmetry. We use the path integral approach to obtain expressions for $n$-point functions. Perturbation theory leads us to generalised Feynman ... More
Reverse Engineering Quantum Field TheoryOct 02 2012An approach to the foundations of quantum theory is advertised that proceeds by "reverse engineering" quantum field theory. As a concrete instance of this approach, the general boundary formulation of quantum theory is outlined.
A "general boundary" formulation for quantum mechanics and quantum gravityJun 03 2003Oct 16 2003I propose to formalize quantum theories as topological quantum field theories in a generalized sense, associating state spaces with boundaries of arbitrary (and possibly finite) regions of space-time. I further propose to obtain such ``general boundary'' ... More
The Quantum Geometry of Spin and StatisticsAug 08 2000Apr 05 2001Both, spin and statistics of a quantum system can be seen to arise from underlying (quantum) group symmetries. We show that the spin-statistics theorem is equivalent to a unification of these symmetries. Besides covering the Bose-Fermi case we classify ... More
Analysis of a Zero of a Beta Function Using All-Orders Summation of DiagramsMay 14 2015Conventionally, one calculates a zero in a beta function by computing this function to a given loop order and solving for the zero. Here we discuss a different method which is applicable in theories where one can perform a partial diagrammatic summation ... More
On the Question of an Ultraviolet Zero of the Beta Function of the $λ(\vecφ^2)^2_4$ TheoryAug 13 2014We investigate the possibility of an ultraviolet (UV) zero in the $n$-loop beta function of a $\lambda (\vec{\phi}^2)^2$ field theory with an $N$-component scalar field, $\vec{\phi}$, in four spacetime dimensions, up to the level of $n=5$ loops. Although ... More
A quantum cellular automaton for universal quantum computationDec 06 2004I describe a quantum cellular automaton capable of performing universal quantum computation. The automaton has an elementary transition function that acts on Margolus cells of $2\times 2$ qubits, and both the ``quantum input'' and the program are encoded ... More
The second weight of generalized Reed-Muller codes in most casesFeb 01 2009Jun 30 2009The second weight of the Generalized Reed-Muller code of order $d$ over the finite field with $q$ elements is now known for $d <q$ and $d>(n-1)(q-1)$. In this paper, we determine the second weight for the other values of $d$ which are not multiple of ... More
Polarization Observables in $γN\to K\bar{K}N$Dec 10 2004Dec 10 2004We explore some of the rich structure of the polarization observables recently developed for processes like $\gamma N\to\pi\pi N$ and $\gamma N\to K \bar{K} N$ in the framework of a specific model for the latter process. Emphasis is placed on observables ... More
HQET and Form Factor Effects in $B\to K^{(*)}\ell^+\ell^-$Dec 07 1995We examine the rates for the exclusive decays $B\to K^{(*)}\ell^+\ell^-$. We use the scaling predictions of the heavy quark effective theory to extract the necessary form factors from fits to various combinations of data. These data include the $D\to ... More
Fixed-Parameter Algorithms for Computing Kemeny Scores - Theory and PracticeJan 22 2010The central problem in this work is to compute a ranking of a set of elements which is "closest to" a given set of input rankings of the elements. We define "closest to" in an established way as having the minimum sum of Kendall-Tau distances to each ... More