Results for "Tim Langen"

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Controlling Spin-flips of Molecules in an Electromagnetic TrapJun 09 2017Dec 07 2017Doubly dipolar molecules exhibit complex internal spin-dynamics when electric and magnetic fields are both applied. Near magnetic trap minima, these spin-dynamics lead to enhancements in Majorana spin-flip transitions by many orders of magnitude relative ... More
Enhancing radical molecular beams by skimmer coolingFeb 27 2018A high-intensity supersonic beam source has been a key component in studies of molecular collisions, molecule-surface interaction, chemical reactions, and precision spectroscopy. However, the molecular density available for experiments in a downstream ... More
Prethermalization and universal dynamics in near-integrable quantum systemsMar 30 2016Jul 02 2016We review the recent progress in the understanding of the relaxation of isolated near-integrable quantum many-body systems. Focusing on prethermalization and universal dynamics following a quench, we describe the experiments with ultracold atomic gases ... More
Ultracold atoms out of equilibriumAug 27 2014The relaxation of isolated quantum many-body systems is a major unsolved problem connecting statistical and quantum physics. Studying such relaxation processes remains a challenge despite considerable efforts. Experimentally, it requires the creation ... More
Optimal control of the self-bound dipolar droplet formation processMay 29 2019Dipolar Bose-Einstein condensates have recently attracted much attention in the world of quantum many body experiments. While the theoretical principles behind these experiments are typically supported by numerical simulations, the application of optimal ... More
Optical cycling of a cold barium monofluoride beam enabled by magnetic fieldsJun 20 2019We demonstrate buffer-gas cooling, high-resolution spectroscopy and cycling fluorescence of cold barium monofluoride (BaF) molecules. Our source produces an intense and internally cold molecular beam containing the different BaF isotopologues with a mean ... More
Optimal control of Bose-Einstein condensates in three dimensionsJul 27 2015Ultracold gases promise many applications in quantum metrology, simulation and computation. In this context, optimal control theory (OCT) provides a versatile framework for the efficient preparation of complex quantum states. However, due to the high ... More
Local relaxation and light-cone-like propagation of correlations in a trapped one-dimensional Bose gasDec 29 2013We describe the relaxation dynamics of a coherently split one-dimensional (1D) Bose gas in the harmonic approximation. A dephased, prethermalized state emerges in a light-cone-like evolution which is connected to the spreading of correlations with a characteristic ... More
Experimental demonstration of single-site addressability in a two-dimensional optical latticeMar 27 2009Oct 13 2009We demonstrate single site addressability in a two-dimensional optical lattice with 600 nm lattice spacing. After loading a Bose-Einstein condensate in the lattice potential we use a focused electron beam to remove atoms from selected sites. The patterned ... More
High Resolution Imaging of Single Atoms in a Quantum GasApr 30 2008Our knowledge on ultracold quantum gases is strongly influenced by our ability to probe these objects. In situ imaging combined with single atom sensitivity is an especially appealing scenario as it can provide direct information on the structure and ... More
Double light-cone dynamics establish thermal states in integrable 1D Bose gasesSep 18 2017We theoretically investigate the non-equilibrium dynamics in a quenched pair of 1D Bose gases with density imbalance. We describe the system using its low-energy effective theory, the Luttinger liquid model. In this framework the system shows strictly ... More
Local emergence of thermal correlations in an isolated quantum many-body systemMay 16 2013We experimentally demonstrate how thermal properties in an non-equilibrium quantum many- body system emerge locally, spread in space and time, and finally lead to the globally relaxed state. In our experiment, we quench a one-dimensional (1D) Bose gas ... More
On solving the quantum many-body problemMay 12 2015We experimentally study a pair of tunnel-coupled one-dimensional atomic superfluids, which realize the quantum sine-Gordon/massive Thirring models relevant for a wide variety of disciplines from particle to condensed-matter physics. From measured interference ... More
Transient supersolid properties in an array of dipolar quantum dropletsJan 23 2019Mar 08 2019We study theoretically and experimentally the emergence of supersolid properties in a dipolar Bose-Einstein condensate. The theory reveals a ground state phase diagram with three distinct regimes - a regular Bose-Einstein condensate, incoherent and coherent ... More
Striped states in a many-body system of tilted dipolesJun 28 2017Nov 28 2017We study theoretically and experimentally the behaviour of a strongly confined dipolar Bose-Einstein condensate, in the regime of quantum-mechanical stabilization by beyond-mean-field effects. Theoretically, we demonstrate that self-organized striped ... More
Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein CondensateApr 12 2018Jul 18 2018We present transport measurements on a dipolar superfluid using a Bose-Einstein condensate of Dy-162 with strong magnetic dipole-dipole interactions. By moving an attractive laser beam through the condensate we observe an anisotropy in superfluid flow. ... More
Transient supersolid properties in an array of dipolar quantum dropletsJan 23 2019We study theoretically and experimentally the emergence of supersolid properties in a dipolar Bose-Einstein condensate. The theory reveals a ground state phase diagram with three distinct regimes - a regular Bose-Einstein condensate, incoherent and coherent ... More
Degenerate Bose gases with uniform lossNov 18 2014Mar 21 2016We theoretically investigate a weakly-interacting degenerate Bose gas coupled to an empty Markovian bath. We show that in the universal phononic limit the system evolves towards an asymptotic state where an emergent temperature is set by the quantum noise ... More
Scissors mode of dipolar quantum droplets of dysprosium atomsDec 19 2017Mar 25 2018We report on the observation of the scissors mode of a single dipolar quantum droplet. The existence of this mode is due to the breaking of the rotational symmetry by the dipole-dipole interaction, which is fixed along an external homogeneous magnetic ... More
The Fate of the Higgs Mode in a Trapped Dipolar SupersolidJul 22 2019We theoretically investigate the spectrum of elementary excitations of a trapped dipolar quantum gas across the BEC-supersolid phase transition. Our calculations reveal the existence of distinct Higgs and Nambu-Goldstone modes that emerge from the softening ... More
Chiral Prethermalization in supersonically split condensatesFeb 26 2014We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a supersonic unzipping of a single condensate. We use the Lorentz invariance of the low energy sector of such systems to show that dephasing results in ... More
On solving quantum many-body problems by experimentMay 12 2015May 19 2017Knowledge of all correlation functions of a system is equivalent to solving the corresponding many-body problem. Already a finite set of correlation functions can be sufficient to describe a quantum many-body system if correlations factorise, at least ... More
Multimode dynamics and emergence of a characteristic length-scale in a one-dimensional quantum systemNov 22 2012We study the non-equilibrium dynamics of a coherently split one-dimensional (1d) Bose gas by measuring the full probability distribution functions of matter-wave interference. Observing the system on different length scales allows us to probe the dynamics ... More
Cooling of a one-dimensional Bose gasMay 18 2015Jun 17 2015We experimentally study the dynamics of a degenerate one-dimensional Bose gas that is subject to a continuous outcoupling of atoms. Although standard evaporative cooling is rendered ineffective by the absence of thermalizing collisions in this system, ... More
The low-energy Goldstone mode in a trapped dipolar supersolidJun 11 2019A supersolid is a counter-intuitive state of matter that combines the frictionless flow of a superfluid with the crystal-like periodic density modulation of a solid. Since the first prediction in the 1950s, experimental efforts to realize this state have ... More
Prethermalization in one-dimensional Bose gases: description by a stochastic Ornstein-Uhlenbeck processOct 31 2012Dec 21 2012We experimentally study the relaxation dynamics of a coherently split one-dimensional Bose gas using matterwave interference. Measuring the full probability distributions of interference contrast reveals the prethermalization of the system to a non-thermal ... More
Relaxation and Pre-thermalization in an Isolated Quantum SystemNov 30 2011Sep 26 2012Understanding relaxation processes is an important unsolved problem in many areas of physics. A key challenge in studying such non-equilibrium dynamics is the scarcity of experimental tools for characterizing their complex transient states. We employ ... More
On the sum of fourth powers of numbers in arithmetic progressionJul 29 2019We prove that the equation ${ (x - y)^4 + x^4 + (x + y)^4 = z^n }$ has no integer solutions ${ x, y, z}$ with ${ \gcd(x, y) = 1 }$ for all integers ${ n > 1 }$. We mainly use a modular approach with two Frey ${ \mathbb{Q} }$-curves defined over the field ... More
Black Hole Formation in Lovelock GravityAug 10 2014We first derive the Hamiltonian for Lovelock gravity and find that it takes the same form as in general relativity when written in terms of the Misner-Sharp mass function. We then minimally couple the action to matter fields to find Hamilton's equations ... More
Determining the CKM Parameter Vcd from nuN Charm ProductionAug 14 1997The formalism for extracting the CKM parameter $V_{cd}$ from $\nu N$ production of charm is discussed in some detail. The various model assumptions needed are clearly pointed out. A direct determination from neutrino induced dimuon production requires ... More
Unfolding algorithms and tests using RooUnfoldMay 05 2011The RooUnfold package provides a common framework to evaluate and use different unfolding algorithms, side-by-side. It currently provides implementations or interfaces for the Iterative Bayes, Singular Value Decomposition, and TUnfold methods, as well ... More
Search for Supersymmetric Neutral Higgs Bosons at the TevatronOct 26 2007Recent preliminary results obtained by the CDF and DO Collaborations on searches for Higgs bosons beyond the Standard Model at Run II of the Tevatron are discussed. The data, corresponding to integrated luminosities of up to 1 fb-1, are compared to theoretical ... More
General relativity as a two-dimensional CFTMay 21 2015The tree-level scattering amplitudes of general relativity encode the full non-linearity of the Einstein field equations. Yet remarkably compact expressions for these amplitudes have been found which seem unrelated to a perturbative expansion of the Einstein-Hilbert ... More
Routes to Open-Endedness in Evolutionary SystemsJun 05 2018Jul 17 2018This paper presents a high-level conceptual framework to help orient the discussion and implementation of open-endedness in evolutionary systems. Drawing upon work by Banzhaf et al., three different kinds of open-endedness are identified: exploratory, ... More
Requirements for Open-Ended Evolution in Natural and Artificial SystemsJul 27 2015Open-ended evolutionary dynamics remains an elusive goal for artificial evolutionary systems. Many ideas exist in the biological literature beyond the basic Darwinian requirements of variation, differential reproduction and inheritance. I argue that these ... More
Artificial Life and the Web: WebAL Comes of AgeJul 22 2014A brief survey is presented of the first 18 years of web-based Artificial Life ("WebAL") research and applications, covering the period 1995-2013. The survey is followed by a short discussion of common methodologies employed and current technologies relevant ... More
Devil's crevasse and macroscopic entanglement in two-component Bose-Einstein condensatesMay 22 2013Spin coherent states are the matter equivalent of optical coherent states, where a large number of two component particles form a macroscopic state displaying quantum coherence. Here we give a detailed study of entanglement generated between two spin-1/2 ... More
Radio Detection of Cosmic Rays -- Achievements and Future PotentialApr 18 2017When modern efforts for radio detection of cosmic rays started about a decade ago, hopes were high but the true potential was unknown. Since then, we have achieved a detailed understanding of the radio emission physics and have consequently succeeded ... More
Experimental summary of the $52^{\rm nd}$ Rencontres de Moriond session on Electroweak Interactions and Unified TheoriesJul 17 2017Jul 18 2017A summary, from an experimental perspective, of the $52^{\rm nd}$ Rencontres de Moriond session on Electroweak Interactions and Unified Theories is presented.
The CMS magnet test and cosmic challengeMay 13 2008The CMS detector is under construction for imminent operation at the Large Hadron Collider at CERN near Geneva, Switzerland. The installation and commissioning is performed in a surface hall. Thereafter, all the main heavy elements of the detector, the ... More
Searches for Leptoquarks with the D-Zero Detector at the TeVatronSep 08 2003The existence of leptoquarks (LQ), color-triplets of bosons with lepton and quark quantum numbers, is predicted by various theories beyond the Standard Model. This article summarizes the D-Zero Run I searches for the three different LQ generations in ... More
On the geometry of a class of invariant measures and a problem of AldousAug 16 2008In his 1985 survey of notions of exchangeability, Aldous introduced a form of exchangeability corresponding to the symmetries of the infinite discrete cube, and asked whether these exchangeable probability measures enjoy a representation theorem similar ... More
Lagrangian matching invariants for fibred four-manifolds: IIJun 02 2006Dec 19 2007In the second of a pair of papers, we complete the construction of Seiberg-Witten-like invariants for smooth four-manifolds equipped with broken fibrations, prove an index formula, and compute some examples.
Lagrangian matching invariants for fibred four-manifolds: IJun 02 2006Dec 19 2007In a pair of papers, we construct invariants for smooth four-manifolds equipped with `broken fibrations' - the singular Lefschetz fibrations of Auroux, Donaldson and Katzarkov - generalising the Donaldson-Smith invariants for Lefschetz fibrations. The ... More
Gluing and deformation of asymptotically cylindrical Calabi-Yau manifolds in complex dimension threeMar 27 2017We develop some consequences of the connection between Calabi-Yau structures and torsion-free $G_2$ structures on compact and asymptotically cylindrical six- and seven-dimensional manifolds. Firstly, we improve the known proof that matching asymptotically ... More
Explanation in Artificial Intelligence: Insights from the Social SciencesJun 22 2017Aug 15 2018There has been a recent resurgence in the area of explainable artificial intelligence as researchers and practitioners seek to make their algorithms more understandable. Much of this research is focused on explicitly explaining decisions or actions to ... More
Extensions of probability-preserving systems by measurably-varying homogeneous spaces and applicationsMay 05 2009Nov 11 2009We study a generalized notion of a homogeneous skew-product extension of a probability-preserving system in which the homogeneous space fibres are allowed to vary over the ergodic decomposition of the base. The construction of such extensions rests on ... More
There are no socialist primes less than 10^9Oct 23 2013Dec 05 2013There are no primes $p$ with $5<p<10^{9}$ for which $2!, 3!, \ldots, (p-1)!$ are all distinct modulo $p$; it is conjectured that there are no such primes.
Positive Polynomials and Sequential Closures of Quadratic ModulesJul 21 2008Let S be a basic closed semi-algebraic set in R^n and P the corresponding preordering in R[X_1,...,X_n]. We examine for which polynomials f there exist identities f+\ep q \in P for all \ep>0. These are precisely the elements of the sequential closure ... More
Non-conventional ergodic averages for several commuting actions of an amenable groupSep 17 2013Jun 19 2014Let $(X,\mu)$ be a probability space, $G$ a countable amenable group and $(F_n)_n$ a left F\o lner sequence in $G$. This paper analyzes the non-conventional ergodic averages \[\frac{1}{|F_n|}\sum_{g \in F_n}\prod_{i=1}^d (f_i\circ T_1^g\cdots T_i^g)\] ... More
Pleasant extensions retaining algebraic structure, IMay 05 2009Sep 07 2014In two recent papers we introduced some new techniques for constructing an extension of a probability-preserving system $T:\mathbb{Z}^d\curvearrowright (X,\mu)$ that enjoys certain desirable properties in connexion with the asymptotic behaviour of some ... More
Formal Semantics and Soundness of a Translation from Event-B Actions to SQL StatementsJun 08 2016The EventB2SQL tool translates Event-B models to persistent Java applications that store the state of the model in a relational database. Most Event-B assignments are translated directly to SQL database modification statements, which can then be executed ... More
Ergodic-theoretic implementations of the Roth density-increment argumentMay 27 2011Jul 21 2013We exhibit proofs of two ergodic-theoretic results in the study of multiple recurrence using an analog of the density-increment argument of Roth and Gowers: Furstenberg's Multiple Recurrence Theorem (which implies Szemer\'edi's Theorem), and a two-dimensional ... More
The sum of the unitary divisor functionDec 17 2013Jul 10 2014This article establishes a new upper bound on the function $\sigma^{*}(n)$, the sum of all coprime divisors of $n$. The article concludes with two questions concerning this function.
Euclidean-valued group cohomology is always reducedOct 11 2013Feb 16 2017If G is a countable discrete group acting linearly on a finite-dimensional vector space over any topological field, then the groups of coboundaries are closed for the product topology in all degrees, and hence the cohomology is reduced in all degrees. ... More
The structure of low-complexity Gibbs measures on product spacesOct 16 2018May 03 2019Let $K_1$, $\dots$, $K_n$ be bounded, complete, separable metric spaces. Let $\lambda_i$ be a Borel probability measure on $K_i$ for each $i$. Let $f:\prod_i K_i \to \mathbb{R}$ be a bounded and continuous potential function, and let $$\mu(d \mathbf{x})\ ... More
Multi-variate correlation and mixtures of product measuresSep 27 2018Nov 16 2018Total correlation (`TC') and dual total correlation (`DTC') are two classical way to quantify the correlation among an $n$-tuple of random variables. They both reduce to mutual information when $n=2$. The first part of this paper sets up the theory of ... More
Partial difference equations over compact Abelian groups, II: step-polynomial solutionsSep 13 2013Oct 25 2014This paper continues an earlier work on the structure of solutions to two classes of functional equation. Let $Z$ be a compact Abelian group and $U_1$, \ldots, $U_k \leq Z$ be closed subgroups. Given $f:Z\to\mathbb{T}$ and $w \in Z$, one defines the differenced ... More
Extendability of parallel sections in vector bundlesJul 07 2014Aug 26 2015We address the following question: Given a differentiable manifold $M$ what are the open subsets $U$ of $M$ such that, for all vector bundles $E$ over $M$ and all linear connections $\nabla$ on $E$, any $\nabla$-parallel section in $E$ defined on $U$ ... More
Dirichlet-to-Neumann operators on manifoldsSep 03 2019We consider the Dirichlet-to-Neumann operator associated to a strictly elliptic operator on the space $\mathrm{C}(\partial M)$ of continuous functions on the boundary $\partial M$ of a compact manifold $\overline{M}$ with boundary. We prove that it generates ... More
Quantum correlations in dilute dipolar quantum droplets beyond the extended Gross-Pitaevskii equationApr 23 2019Dipolar quantum droplets are exotic quantum objects that are self-bound due to the subtle balance of attraction, repulsion and quantum correlations. Here we present a systematic study of the critical atom number of these self-bound droplets, comparing ... More
Experimental Observation of a Generalized Gibbs EnsembleNov 26 2014The connection between the non-equilibrium dynamics of isolated quantum many-body systems and statistical mechanics is a fundamental open question. It is generally believed that the unitary quantum evolution of a sufficiently complex system leads to an ... More
Prethermalization Revealed by the Relaxation Dynamics of Full Distribution FunctionsDec 19 2012We detail the experimental observation of the non-equilibrium many-body phenomenon prethermalization. We study the dynamics of a rapidly and coherently split one-dimensional Bose gas. An analysis based on the use of full quantum mechanical probability ... More
The mildly nonlinear imprint of structure on the CMBDec 03 1999Dec 05 1999I outline some nonperturbative relativistic effects that arise from gravitational corrections to the Boltzmann equations. These may be important for the study of CMB temperature anisotropies, particularly their interpretation. These terms are not included ... More
Are pre-main-sequence stars older than we thought?Jul 14 2009We fit the colour-magnitude diagrams of stars between the zero-age main-sequence and terminal-age main sequence in young clusters and associations. The ages we derive are a factor 1.5 to 2 longer than the commonly used ages for these regions, which are ... More
A Structured Variational Auto-encoder for Learning Deep Hierarchies of Sparse FeaturesFeb 28 2016In this note we present a generative model of natural images consisting of a deep hierarchy of layers of latent random variables, each of which follows a new type of distribution that we call rectified Gaussian. These rectified Gaussian units allow spike-and-slab ... More
What Bell DidAug 08 2014On the 50th anniversary of Bell's monumental 1964 paper, there is still widespread misunderstanding about exactly what Bell proved. This misunderstanding derives in turn from a failure to appreciate the earlier arguments of Einstein, Podolsky and Rosen. ... More
Reply to WernerAug 08 2014Reinhard Werner authored a comment on my paper "What Bell Did", disputing the conclusion and argumentation of the paper. This is my reply.
Euclidean-valued group cohomology is always reducedOct 11 2013Nov 25 2013If G is a countable discrete group acting linearly on a finite-dimensional vector space over any topological field, then the groups of coboundaries are closed for the product topology in all degrees, and hence the cohomology is reduced in all degrees. ... More
The No-Boundary Probability for the Universe starting at the top of the hillApr 16 2007We use the Hartle-Hawking No-Boundary Proposal to make a comparison between the probabilities of the universe starting near, and at, the top of a hill in the effective potential. In the context of top-down cosmology, our calculation finds that the universe ... More
Correlation functions, null polygonal Wilson loops, and local operatorsOct 18 2011Jul 30 2012We consider the ratio of the correlation function of n+1 local operators over the correlator of the first n of these operators in planar N=4 super-Yang-Mills theory, and consider the limit where the first n operators become pairwise null separated. By ... More
Privacy Implications of Health Information Seeking on the WebApr 07 2014Mar 06 2015This article investigates privacy risks to those visiting health- related web pages. The population of pages analyzed is derived from the 50 top search results for 1,986 common diseases. This yielded a total population of 80,124 unique pages which were ... More
The LSST Data Processing Software Stack: Summer 2015 ReleaseNov 20 2015The Large Synoptic Survey Telescope (LSST) is an 8-m optical ground-based telescope being constructed on Cerro Pachon in Chile. LSST will survey half the sky every few nights in six optical bands. The data will be transferred to NCSA and within 60 seconds ... More
The structure of low-complexity Gibbs measures on product spacesOct 16 2018Mar 04 2019Let $K_1$, $\dots$, $K_n$ be bounded, complete, separable metric spaces. Let $\lambda_i$ be a Borel probability measure on $K_i$ for each $i$. Let $f:\prod_i K_i \to \mathbb{R}$ be a bounded and continuous potential function, and let $$\mu(d \mathbf{x})\ ... More
Homological properties of bigraded algebrasNov 24 2000Sep 23 2001We study the x- and y-regularity of a bigraded K-algebra R. These notions are used to study asymptotic properties of certain finitely generated bigraded modules. As an application we get for any equigenerated graded ideal I upper bounds for the number ... More
New results on event-by-event ratio fluctuations in Pb+Pb collisions at CERN SPS energiesJul 08 2011Event-by-event fluctuations of produced particle multiplicities are believed to be sensitive to a deconfinement phase transition and the critical point of strongly interacting matter. The NA49 collaboration has conducted a systematic study of various ... More
Event-by-Event Fluctuations and the Search for the Critical Point within the NA49 ExperimentOct 03 2009Nov 01 2009In heavy-ion collisions in the energy regime probed at the CERN SPS, experimental hints for the deconfinement phase transition have been seen in numerous inclusive hadronic observables. In order to further characterize this transition, and in the pursuit ... More
On the equivalence of the discrete nonlinear Schrödinger equation and the discrete isotropic Heisenberg magnetJun 28 1999The equivalence of the discrete isotropic Heisenberg magnet (IHM) model and the discrete nonlinear Schr\"odinger equation (NLSE) given by Ablowitz and Ladik is shown. This is used to derive the equivalence of their discretization with the one by Izergin ... More
A Geometric Embedding for Standard Analytic ModulesMar 28 2005Jun 11 2007In this manuscript we make a general study of the representations realized, for a reductive Lie group of Harish-Chandra class, on the compactly supported sheaf cohomology groups of an irreducible finite-rank polarized homogeneous vector bundle defined ... More
Discrete Hashimoto surfaces and a doubly discrete smokering flowJul 25 2000B\"acklund transformations for smooth and ``space discrete'' Hashimoto surfaces are discussed and a geometric interpretation is given. It is shown that the complex curvature of a discrete space curve evolves with the discrete nonlinear Schr\"odinger equation ... More
The elementary obstruction and the Weil restrictionDec 20 2007Mar 31 2009In this text we investigate the good behaviour of the elementary obstruction, introduced by Colliot-Thelene and Sansuc. This is an obstruction to the existence of a rational points on certain algebraic varieties. Assuming some conditions on the Picard ... More
Evolutionary Innovations and Where to Find Them: Routes to Open-Ended Evolution in Natural and Artificial SystemsJun 05 2018Feb 21 2019This paper presents a high-level conceptual framework to help orient the discussion and implementation of open-endedness in evolutionary systems. Drawing upon earlier work by Banzhaf et al., three different kinds of open-endedness are identified: exploratory, ... More
Radio detection of cosmic rays with the Auger Engineering Radio ArrayMay 13 2019The Auger Engineering Radio Array (AERA) complements the Pierre Auger Observatory with 150 radio-antenna stations measuring in the frequency range from 30 to 80 MHz. With an instrumented area of 17 km$^2$, the array constitutes the largest cosmic-ray ... More
The Labyrinth of Quantum LogicFeb 06 2018Quantum mechanics predicts many surprising phenomena, including the two-slit interference of electrons. It has often been claimed that these phenomena cannot be understood in classical terms. But the meaning of "classical" is often not precisely specified. ... More
Uniform stability of linear evolution equations, with applications to parallel transportsFeb 12 2015I prove the bistability of linear evolution equations $x' = A(t)x$ in a Banach space $E$, where the operator-valued function $A$ is of the form $A(t) = f'(t)G(t,f(t))$ for a binary operator-valued function $G$ and a scalar function $f$. The constant that ... More
Norm convergence of continuous-time polynomial multiple ergodic averagesMar 01 2011Jul 01 2016For a jointly measurable probability-preserving action $\tau:\mathbb{R}^D\curvearrowright (X,\mu)$ and a tuple of polynomial maps $p_i:\mathbb{R}\to \mathbb{R}^D$, $i=1,2,...,k$, the multiple ergodic averages \[ \frac{1}{T}\int_0^T (f_1\circ \tau^{p_1(t)})(f_2\circ ... More
RectangularityAug 08 2011We introduce a condition on arrays in some way maximally distinct from Latin square condition, as well as some other conditions on algebras, graphs and $0,1$-matrices. We show that these are essentially the same structures, generalising a similar collection ... More
Rational group ring elements with kernels having irrational dimensionSep 12 2009Mar 12 2013We prove that there are examples of finitely generated groups G together with group ring elements Q \in \bbQ G for which the von Neumann dimension \dim_{LG}\ker Q is irrational, so (in conjunction with other known results) answering a question of Atiyah. ... More
Behaviour of entropy under bounded and integrable orbit equivalenceApr 04 2016Nov 07 2016Let $G$ and $H$ be infinite finitely generated amenable groups. This paper studies two notions of equivalence between actions of such groups on standard Borel probability spaces. They are defined as stable orbit equivalences in which the associated cocycles ... More
Strictly elliptic operators with generalized Wentzell boundary conditions on continuous functions on manifolds with boundarySep 03 2019We prove that strictly elliptic operators with generalized Wentzell boundary conditions generate analytic semigroups of angle $\frac{\pi}{2}$ on the space of continuous function on a compact manifold with boundary.
On the regularity over positively graded algebrasDec 20 2006Aug 30 2007We study the relationship between the Tor-regularity and the local-regularity over a positively graded algebra defined over a field which coincide if the algebra is a standard graded polynomial ring. In this case both are characterizations of the so-called ... More
The geometry of model spaces for probability-preserving actions of sofic groupsDec 04 2015Jun 06 2016Bowen's notion of sofic entropy is a powerful invariant for classifying probability-preserving actions of sofic groups. It can be defined in terms of the covering numbers of certain metric spaces associated to such an action, the `model spaces'. The metric ... More
An Interesting Gadget for Chain Pair SimplificationJul 22 2016In this paper we present an interesting gadget based on the chain pair simplification problem under the discrete Fr\'echet distance (CPS-3F), which allows the construction of arbitrarily long paths that must be chosen in the simplification of the two ... More
Known Radio Pulsars Do Not Contribute to the Galactic Center Gamma-Ray ExcessSep 09 2015Observations using the Fermi Large Area Telescope (Fermi-LAT) have found a significant gamma-ray excess surrounding the center of the Milky Way (GC). One possible interpretation of this excess invokes gamma-ray emission from an undiscovered population ... More
Constraints on the Size of Extra Dimensions from the Orbital Evolution of the Black-Hole X-Ray Binary XTE J1118+480Dec 03 2008Sep 30 2009In a universe of the Randall-Sundrum type, black holes are unstable and emit gravitational modes in the extra dimension. This leads to dramatically shortened lifetimes of astrophysical black holes and to an observable change of the orbital period of black-hole ... More
Neutralino annihilation processes in the minimal supergravity modelJun 13 2008We study all tree-level neutralino annihilation processes concerning energy-dependence at the mSUGRA benchmark point SPS1a using tree-level calculators MadGraph and CompHEP as well as FormCalc. We further investigate the total tree-level neutralino annihilation ... More
Testing the No-Hair Theorem with Observations of Black Holes in the Electromagnetic SpectrumFeb 24 2016May 20 2016According to the general-relativistic no-hair theorem, astrophysical black holes depend only on their masses and spins and are uniquely described by the Kerr metric. Mass and spin are the first two multipole moments of the Kerr spacetime and completely ... More
Transient Alert Follow-up Planned for CCATFeb 05 2014CCAT is a sub-millimeter telescope to be built on Cerro Chajnantor in Chile near the ALMA site. The remote location means that all observing will be done by remote observers with the future goal of fully autonomous observing using a dynamic scheduler. ... More
The renaissance of radio detection of cosmic raysOct 25 2013Nearly 50 years ago, the first radio signals from cosmic ray air showers were detected. After many successful studies, however, research ceased not even 10 years later. Only a decade ago, the field was revived with the application of powerful digital ... More
Reimplementing the Hierarchical Data System using HDF5Feb 13 2015The Starlink Hierarchical Data System has been a very successful niche astronomy file format and library for over 30 years. Development of the library was frozen ten years ago when funding for Starlink was stopped and almost no-one remains who understands ... More