Results for "Ole Martin Brokstad"

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Towards autonomous ocean observing systems using Miniature Underwater Gliders with UAV deployment and recovery capabilitiesFeb 08 2019This paper presents preliminary results towards the development of an autonomous ocean observing system using Miniature Underwater Gliders (MUGs) that can operate with the support of Unmanned Aerial Vehicles (UAVs) and Unmanned Surface Vessels (USVs) ... More
50 Years of Bailey's lemmaOct 12 2009Oct 14 2009This is a paper published in 2001 based on a talk given in 1999 celebrating the 50th anniversary of W. N. Bailey's influential q-series paper "Identities of the Rogers-Ramanujan type". In no more than 13 pages I give a brief but reasonably complete overview ... More
The generalized Borwein conjecture. I. The Burge transformNov 27 2000Given an arbitrary ordered pair of coprime integers (a,b) we obtain a pair of identities of the Rogers--Ramanujan type. These identities have the same product side as the (first) Andrews--Gordon identity for modulus 2ab\pm 1, but an altogether different ... More
Refined q-trinomial coefficients and character identitiesMay 12 2000A refinement of the q-trinomial coefficients is introduced, which has a very powerful iterative property. This ``T-invariance'' is applied to derive new Virasoro character identities related to the exceptional simply-laced Lie algebras E_6,E_7 and E_8. ... More
Hall--Littlewood functions and the A_2 Rogers--Ramanujan identitiesOct 28 2004Jun 17 2005We prove an identity for Hall--Littlewood symmetric functions labelled by the Lie algebra A_2. Through specialization this yields a simple proof of the A_2 Rogers--Ramanujan identities of Andrews, Schilling and the author.
Partial-sum analogues of the Rogers-Ramanujan identitiesAug 28 2001Aug 26 2002A new type of polynomial analogue of the Rogers-Ramanujan identities is proven. Here the product-side of the Rogers-Ramanujan identities is replaced by a partial theta sum and the sum-side by a weighted sum over Schur polynomials.
Solitons in coupled atomic-molecular Bose-Einstein condensates in a trapMay 16 2006Mar 26 2008We consider coupled atomic-molecular Bose-Einstein condensate system in a quasi-one-dimensional trap. In the vicinity of a Feshbach resonance the system can reveal soliton-like behavior. We analyze bright soliton solutions for the system in the trap and ... More
Stochastic Market EfficiencyJan 24 2011It is argued that the simple trading strategy of leveraging or deleveraging an investment in the market portfolio cannot outperform the market. Such stochastic market efficiency places strong constraints on the possible stochastic properties of the market. ... More
The Bailey lemma and Kostka polynomialsJul 03 2002Using the theory of Kostka polynomials, we prove an A_{n-1} version of Bailey's lemma at integral level. Exploiting a new, conjectural expansion for Kostka numbers, this is then generalized to fractional levels, leading to a new expression for admissible ... More
The null hypothesis of common jumps in case of irregular and asynchronous observationsDec 19 2017This paper proposes novel tests for the absence of jumps in a univariate semimartingale and for the absence of common jumps in a bivariate semimartingale. Our methods rely on ratio statistics of power variations based on irregular observations, sampled ... More
Testing for simultaneous jumps in case of asynchronous observationsJun 23 2016This paper proposes a novel test for simultaneous jumps in a bivariate It\^o semimartingale when observation times are asynchronous and irregular. Inference is built on a realized correlation coefficient for the jumps of the two processes which is estimated ... More
Inhomogeneous lattice paths, generalized Kostka polynomials and A$_{n-1}$ supernomialsFeb 23 1998Dec 18 1998Inhomogeneous lattice paths are introduced as ordered sequences of rectangular Young tableaux thereby generalizing recent work on the Kostka polynomials by Nakayashiki and Yamada and by Lascoux, Leclerc and Thibon. Motivated by these works and by Kashiwara's ... More
Composition operators and embedding theorems for some function spaces of Dirichlet seriesFeb 09 2016Nov 19 2018We observe that local embedding problems for certain Hardy and Bergman spaces of Dirichlet series are equivalent to boundedness of a class of composition operators. Following this, we perform a careful study of such composition operators generated by ... More
Composition Operators on Bohr-Bergman Spaces of Dirichlet SeriesSep 10 2014Jun 15 2015For $\alpha \in \mathbb{R}$, let $\mathscr{D}_\alpha$ denote the scale of Hilbert spaces consisting of Dirichlet series $f(s) = \sum_{n=1}^\infty a_n n^{-s}$ that satisfy $\sum_{n=1}^\infty |a_n|^2/[d(n)]^\alpha < \infty$. The Gordon--Hedenmalm Theorem ... More
Modular Nekrasov-Okounkov formulasFeb 09 2019Using Littlewood's map, which decomposes a partition into its $r$-core and $r$-quotient, Han and Ji have shown that many well-known hook-length formulas admit modular analogues. In this paper we present a variant of the Han-Ji `multiplication theorem' ... More
A q-rious positivityMar 09 2010The $q$-binomial coefficients $\qbinom{n}{m}=\prod_{i=1}^m(1-q^{n-m+i})/(1-q^i)$, for integers $0\le m\le n$, are known to be polynomials with non-negative integer coefficients. This readily follows from the $q$-binomial theorem, or the many combinatorial ... More
Laws of large numbers for Hayashi-Yoshida-type functionalsMar 15 2018In high-frequency statistics and econometrics sums of functionals of increments of stochastic processes are commonly used and statistical inference is based on the asymptotic behaviour of these sums as the mesh of the observation times tends to zero. ... More
Dedekind's eta-function and Rogers-Ramanujan identitiesJan 11 2010Jan 22 2010We prove a q-series identity that generalises Macdonald's A_{2n}^{(2)} eta-function identity and the Rogers-Ramanujan identities. We conjecture our result to generalise even further to also include the Andrews-Gordon identities.
On Ladder Logic Bombs in Industrial Control SystemsFeb 17 2017In industrial control systems, devices such as Programmable Logic Controllers (PLCs) are commonly used to directly interact with sensors and actuators, and perform local automatic control. PLCs run software on two different layers: a) firmware (i.e. the ... More
Constant term identities and Poincare polynomialsSep 05 2012Apr 05 2013In 1982 Macdonald published his now famous constant term conjectures for classical root systems. This paper begins with the almost trivial observation that Macdonald's constant term identities admit an extra set of free parameters, thereby linking them ... More
Preheating in an Asymptotically Safe Quantum Field TheoryMar 08 2016We consider reheating in a class of asymptotically safe quantum field theories recently studied in \cite{Litim:2014uca, Litim:2015iea}. These theories allow for an inflationary phase in the very early universe. Inflation ends with a period of reheating. ... More
A Nekrasov-Okounkov formula for Macdonald polynomialsJun 15 2016Feb 19 2018We prove a Macdonald polynomial analogue of the celebrated Nekrasov-Okounkov hook-length formula from the theory of random partitions. As an application we obtain a proof of one of the main conjectures of Hausel and Rodriguez-Villegas from their work ... More
Analysis of the Diffuse Domain Method for second order elliptic boundary value problemsDec 17 2014The diffuse domain method for partial differential equations on complicated geometries recently received strong attention in particular from practitioners, but many fundamental issues in the analysis are still widely open. In this paper we study the diffuse ... More
Direct subsurface absorption of hydrogen on Pd(111)Dec 13 1995We summarize and discuss some of the available experimental and theoretical data important for understanding the role played by subsurface sites in dissociative chemisorption calculations for the H$_2$/Pd(111) system. Then we use a semi-empirical potential ... More
Volterra operators on Hardy spaces of Dirichlet seriesFeb 15 2016Nov 08 2016For a Dirichlet series symbol $g(s) = \sum_{n \geq 1} b_n n^{-s}$, the associated Volterra operator $\mathbf{T}_g$ acting on a Dirichlet series $f(s)=\sum_{n\ge 1} a_n n^{-s}$ is defined by the integral $f\mapsto -\int_{s}^{+\infty} f(w)g'(w)\,dw$. We ... More
Diffuse Interface Methods for Inverse Problems: Case Study for an Elliptic Cauchy ProblemJun 18 2015Jul 10 2015Many inverse problems have to deal with complex, evolving and often not exactly known geometries, e.g. as domains of forward problems modeled by partial differential equations. This makes it desirable to use methods which are robust with respect to perturbed ... More
Convolutional LSTM Networks for Subcellular Localization of ProteinsMar 06 2015Machine learning is widely used to analyze biological sequence data. Non-sequential models such as SVMs or feed-forward neural networks are often used although they have no natural way of handling sequences of varying length. Recurrent neural networks ... More
Logarithmic and complex constant term identitiesDec 14 2011Mar 04 2012In recent work on the representation theory of vertex algebras related to the Virasoro minimal models M(2,p), Adamovic and Milas discovered logarithmic analogues of (special cases of) the famous Dyson and Morris constant term identities. In this paper ... More
Discrete analogues of Macdonald-Mehta integralsJan 25 2016We consider discretisations of the Macdonald--Mehta integrals from the theory of finite reflection groups. For the classical groups, $\mathrm{A}_{r-1}$, $\mathrm{B}_r$ and $\mathrm{D}_r$, we provide closed-form evaluations in those cases for which the ... More
Spectral WallsMar 28 2019During defect-antidefect scattering, bound modes frequently disappear into the continuous spectrum before the defects themselves collide. This leads to a structural, nonperturbative change in the spectrum of small excitations. Sometimes the effect can ... More
Bond analysis of cobalt and iron based skutterudites: elongated lanthanum bonds in LaFe4P12Nov 12 2008Motivated by the possibility of further improving the thermoelectric properties of skutterudites we investigate charge transfer and bonding in this class of materials using density functional calculations. Results for the CoP3, CoSb3, LaFe4P12 and the ... More
Understanding adsorption of hydrogen atoms on grapheneAug 08 2008Adsorption of hydrogen atoms on a single graphite sheet (graphene) has been investigated by first-principles electronic structure means, employing plane-wave based, periodic density functional theory. A reasonably large 5x5 surface unit cell has been ... More
Theoretical analysis of oxygen vacancies in layered sodium cobaltate Na_xCoO_{2-δ}Nov 24 2011Nov 05 2012Sodium cobaltate with high Na content is a promising thermoelectric material. It has recently been reported that oxygen vacancies can alter the material properties, reducing its figure of merit. However, experimental data concerning the oxygen stoichiometry ... More
Amplitude noise and coherence degradation of femtosecond supercontinuum generation in all-normal-dispersion fibersFeb 04 2019Supercontinuum (SC) generation via femtosecond (fs) pumping in all-normal-dispersion (ANDi) fiber is predicted to offer completely coherent broadening mechanisms, potentially allowing for substantially reduced noise levels in comparison to those obtained ... More
I^K-convergenceSep 13 2011In this paper we introduce I^K-convergence which is a common generalization of the I^K-convergence of sequences, double sequences and nets. We show that many results that were shown before for these special cases are true for the I^K-convergence, too
Influence of isolated and clustered defects on electronic and dielectric properties of wustiteJan 20 2015The influence of intrinsic Fe defects in FeO (either single cation vacancies or prototypical 4:1 vacancy clusters) on the electronic and dielectric properties is studied within the density functional theory. The importance of local Coulomb interactions ... More
Can Image Enhancement be Beneficial to Find Smoke Images in Laparoscopic Surgery?Dec 27 2018Laparoscopic surgery has a limited field of view. Laser ablation in a laproscopic surgery causes smoke, which inevitably influences the surgeon's visibility. Therefore, it is of vital importance to remove the smoke, such that a clear visualization is ... More
Linear-optical generation of eigenstates of the two-site XY modelOct 04 2014Much of the anticipation accompanying the development of a quantum computer relates to its application to simulating dynamics of another quantum system of interest. Here we study the building blocks for simulating quantum spin systems with linear optics. ... More
A tight bound on the speed-up through storage for quickest multi-commodity flowsJun 18 2014Multi-commodity flows over time exhibit the non-intuitive property that letting flow wait can allow us to send flow faster overall. Fleischer and Skutella (IPCO~2002) show that the speed-up through storage is at most a factor of~$2$, and that there are ... More
On the representation of polyhedra by polynomial inequalitiesMar 26 2002Oct 24 2002A beautiful result of Br\"ocker and Scheiderer on the stability index of basic closed semi-algebraic sets implies, as a very special case, that every $d$-dimensional polyhedron admits a representation as the set of solutions of at most $d(d+1)/2$ polynomial ... More
Algorithmic Optimisations for Iterative Deconvolution MethodsApr 26 2013We investigate possibilities to speed up iterative algorithms for non-blind image deconvolution. We focus on algorithms in which convolution with the point-spread function to be deconvolved is used in each iteration, and aim at accelerating these convolution ... More
Open-closed modular operads, Cardy condition and string field theoryNov 26 2016We prove that the modular operad of diffeomorphism classes of Riemann surfaces with both `open' and `closed' boundary components, in the sense of string field theory, is the modular completion of its genus 0 part quotiented by the Cardy condition. We ... More
Neutralino Dark Matter and the CurvatonNov 30 2006Mar 09 2007We build a realistic model of curvaton cosmology, in which the energy content is described by radiation, WIMP dark matter and a curvaton component. We calculate the curvature and isocurvature perturbations, allowing for arbitrary initial density perturbations ... More
Role of the self-interaction error in studying chemisorption on graphene from first-principlesFeb 22 2010May 13 2010Adsorption of gaseous species, and in particular of hydrogen atoms, on graphene is an important process for the chemistry of this material. At the equilibrium geometry, the H atom is covalently bonded to a carbon that puckers out from the surface plane. ... More
Automatic Generation of Security Argument GraphsMay 29 2014Graph-based assessment formalisms have proven to be useful in the safety, dependability, and security communities to help stakeholders manage risk and maintain appropriate documentation throughout the system lifecycle. In this paper, we propose a set ... More
Detection of Unauthorized IoT Devices Using Machine Learning TechniquesSep 14 2017Security experts have demonstrated numerous risks imposed by Internet of Things (IoT) devices on organizations. Due to the widespread adoption of such devices, their diversity, standardization obstacles, and inherent mobility, organizations require an ... More
Solving systems of linear equations on a quantum computerFeb 05 2013Systems of linear equations are used to model a wide array of problems in all fields of science and engineering. Recently, it has been shown that quantum computers could solve linear systems exponentially faster than classical computers, making for one ... More
Probability as a physical motiveFeb 15 2007Apr 01 2007Recent theoretical progress in nonequilibrium thermodynamics, linking the physical principle of Maximum Entropy Production ("MEP") to the information-theoretical "MaxEnt" principle of scientific inference, together with conjectures from theoretical physics ... More
Greiter replies to Demler, Zhang, Meixner, and HankeMay 28 1997May 28 1997In a comment on my recent manuscript on the pi-particle [cond-mat/9705049], Demler et al. [cond-mat/9705191] argued that there is a correction to the chemical potential which enters the expression for the energy of the pi-particle given in [Demler and ... More
S=1 Spin Liquids: Broken Discrete Symmetries RestoredMar 13 2002We introduce a novel kind of spin liquid, the spin 1 chirality liquid, which provides a generic paradigm for a disordered spin 1 antiferromagnet in two dimensions. It supports spinon and holon excitations, which carry a chirality quantum number. These ... More
A Targeted Survey for HI Clouds in Galaxy GroupsMar 20 2001Five galaxy groups with properties similar to those of the Local Group have been surveyed for HI clouds with the Arecibo Telescope. In total 300 pointings have been observed on grids of approximately 2.5 x 1.5 Mpc centred on the groups. The 4.5 sigma ... More
Efficient formulation of the periodic corrections in Brouwer's gravity solutionJul 30 2014Mar 12 2015The periodic terms of Brouwer's gravity solution are reconstructed in a nonsingular set of variables which are derived from the well-known polar-nodal variables. This change does not affect the essence of the solution, which still keeps all the benefits ... More
LEO intermediary propagation as a feasible alternative to Brouwer's gravity solutionJun 09 2014Mar 11 2015The performance of Brouwer's gravity solution is compared with Deprit's second-order radial intermediary. Taking the main problem of the artificial satellite as the test model, that is perturbations are limited to the effects of the second zonal harmonic, ... More
A short note on vector bundles on curvesSep 21 2010Beauville and Laszlo give an interpretation of the affine Grassmannian for Gl_n over a field k as a moduli space of, loosely speaking, vector bundles over a projective curve together with a trivialization over the complement of a fixed closed point. In ... More
On the limiting absorption principle for Schröedinger HamiltoniansOct 13 2015May 03 2016We prove the limiting absorption principle and discuss the continuity properties of the boundary values of the resolvent for a class of form bounded perturbations of the Euclidean Laplacian $\Delta$ that covers both short and long range potentials with ... More
Global Fluctuations in General Beta Dyson Brownian MotionOct 25 2006We consider a system of diffusing particles on the real line in a quadratic external potential and with repulsive electrostatic interaction. The empirical measure process is known to converge weakly to a deterministic measure-valued process as the number ... More
Quasi-4-Connected ComponentsFeb 14 2016We introduce a new decomposition of a graphs into quasi-4-connected components, where we call a graph quasi-4-connected if it is 3-connected and it only has separations of order 3 that remove a single vertex. Moreover, we give a cubic time algorithm computing ... More
Sharp Bounds for Eigenvalues and Multiplicities on Surfaces of RevolutionApr 12 1996We find sharp upper bounds for the multiplicities and the numerical values of all the distinct eigenvalues on a surface of revolution diffeomorphic to the sphere.
Interplay of site and bond electron-phonon coupling in one dimensionOct 07 2016The interplay of bond and charge correlations is studied in a one-dimensional model with both Holstein and Su-Schrieffer-Heeger (SSH) couplings to quantum phonons. The problem is solved exactly by quantum Monte Carlo simulations. If one of the couplings ... More
Design and Status of IceCubeMay 01 2004IceCube is a kilometer-scale high energy neutrino detector that builds on the wealth of experience accumulated with its smaller predecessor, AMANDA. An international collaboration has begun construction of key components of the IceCube detector and deployment ... More
Curvature computations for a two-component Camassa-Holm equation with vorticitySep 02 2015In the present paper, a two-component Camassa-Holm (2CH) system with vorticity is studied as a geodesic flow on a suitable Lie group. The paper aims at presenting various details of the geometric formalism and a major result is the computation of the ... More
A Critique of the CAP TheoremSep 17 2015Sep 18 2015The CAP Theorem is a frequently cited impossibility result in distributed systems, especially among NoSQL distributed databases. In this paper we survey some of the confusion about the meaning of CAP, including inconsistencies and ambiguities in its definitions, ... More
A variance reduced estimator of the connected two-point function in the presence of a broken Z_2 symmetryDec 08 2015The exchange or geometric cluster algorithm allows us to define a variance reduced estimator of the connected two-point function in the presence of a broken Z_2-symmetry. We present first numerical tests for the improved Blume-Capel model on the simple ... More
Search for CP Violation in the Decay Z -> b (b bar) gAug 01 1996About three million hadronic decays of the Z collected by ALEPH in the years 1991-1994 are used to search for anomalous CP violation beyond the Standard Model in the decay Z -> b \bar{b} g. The study is performed by analyzing angular correlations between ... More
M-branes on U-foldsDec 27 2007We give a preliminary discussion of how the addition of extra coordinates in M-theory, which together with the original ones parametrise a U-fold, can serve as a tool for formulating brane dynamics with manifest U-duality. The redundant degrees of freedom ... More
Superspace Methods in String Theory, Supergravity and Gauge TheoryMay 18 2001In these two lectures, delivered at the XXXVII Karpacz Winter School, February 2001, I review some applications of superspace in various topics related to string theory and M-theory. The first lecture is mainly devoted to descriptions of brane dynamics ... More
World-volume fields and background coupling of branesJun 18 1998This is the written version of an invited talk delivered at the workshop ``Quantum gravity in the Southern Cone'' held in San Carlos de Bariloche, Argentina, January 7-10, 1998. After giving a brief introduction to the concept of branes and their role ... More
Aspects of D-brane actionsDec 14 1996A couple of issues concerning the effective dynamics of D-branes in string theory are discussed. Primarily, I am concerned with linearization of the actions by introduction of non-propagating fields and a full super- and kappa-symmetric description of ... More
T-duality and non-geometric solutions from double geometrySep 15 2014Although the introduction of generalised and extended geometry has been motivated mainly by the appearance of dualities upon reductions on tori, it has until now been unclear how (all) the duality transformations arise from first principles in extended ... More
Thoughts on Membranes, Matrices and Non-CommutativityOct 11 2004We review the passage from the supermembrane to matrix theory via a consistent truncation following a non-commutative deformation in light-cone gauge. Some indications are given that there should exist a generalisation of non-commutativity involving a ... More
Confinement at Weak CouplingNov 03 2005The free energy of U(N) and SU(N) gauge theory was recently found to be of order N^0 to all orders of a perturbative expansion about a center-symmetric orbit of vanishing curvature. Here I consider extended models for which this expansion is perturbatively ... More
Mass Generation in Continuum SU(2) Gauge Theory in Covariant Abelian GaugesSep 02 1999Jan 17 2000The local action of an SU(2) gauge theory in general covariant Abelian gauges and the associated equivariant BRST symmetry that guarantees the perturbative renormalizability of the model are given. I show that a global SL(2,R) symmetry of the model is ... More
Quantization in the Presence of Gribov AmbiguitiesOct 21 1998The non-perturbative validity of covariant BRST-quantization of gauge theories on compact Euclidean space-time manifolds is reviewed. BRST-quantization is related to the construction of a Topological Quantum Field Theory (TQFT) of Witten type on the gauge ... More
Systematic Study of Hadronic Molecules in the Heavy-Quark SectorMay 16 2014In this work we study the properties of hadronic molecules in the heavy-quark sector. These have become increasingly important since from the beginning of this century a large number of states have been measured that for different reasons do not fit the ... More
Filtration shrinkage, strict local martingales and the Föllmer measureNov 30 2011May 19 2014When a strict local martingale is projected onto a subfiltration to which it is not adapted, the local martingale property may be lost, and the finite variation part of the projection may have singular paths. This phenomenon has consequences for arbitrage ... More
Charge-Ordering Phenomena in One-Dimensional SolidsMay 13 2007As the dimensionality is reduced, the world becomes more and more interesting; novel and fascinating phenomena show up which call for understanding. Physics in one dimension is a fascinating topic for theory and experiment: for the former often a simplification, ... More
NNLO contributions to epsilon_K and rare kaon decaysSep 11 2009We discuss the theory prediction of epsilon_K and the rare K -> pi nu nu-bar decays and review the structure and current status of higher-order contributions to these flavour changing processes in the standard model in some detail. This includes the next-to-next-to-leading ... More
Concavity, Abel-transform and the Abel-inverse theorem in smooth complete toric varietiesMay 02 2007Mar 27 2009We extend the usual projective Abel-Radon transform to the larger context of a smooth complete toric variety X. We define and study toric concavity attached to an algebraic splitting vector bundle on X and we prove a toric version of the Abel-inverse ... More
Elementary thermodynamics of trapped particlesOct 12 2002I develop simple thermodynamic relations for a collection of noninteracting classical particles confined in a harmonic trap. The volume of such a trap is not a good thermodynamic variable, so conventional expressions of the first law of thermodynamics ... More
Performance potential for simulating spin models on GPUJan 07 2011Feb 20 2012Graphics processing units (GPUs) are recently being used to an increasing degree for general computational purposes. This development is motivated by their theoretical peak performance, which significantly exceeds that of broadly available CPUs. For practical ... More
Quantum geometry and quantum dynamics at the Planck scaleOct 15 2009Canonical quantum gravity provides insights into the quantum dynamics as well as quantum geometry of space-time by its implications for constraints. Loop quantum gravity in particular requires specific corrections due to its quantization procedure, which ... More
Quantum gravity, space-time structure, and cosmologyJun 12 2012A set of diverse but mutually consistent results obtained in different settings has spawned a new view of loop quantum gravity and its physical implications, based on the interplay of operator calculations and effective theory: Quantum corrections modify, ... More
Comment on "Quantum bounce and cosmic recall" [arXiv:0710.4543]Nov 17 2008A recently derived inequality on volume fluctuations of a bouncing cosmology, valid for states which are semiclassical long after the bounce, does not restrict pre-bounce fluctuations sufficiently strongly to conclude that the pre-bounce state was semiclassical ... More
How quantum is the big bang?May 08 2008When quantum gravity is used to discuss the big bang singularity, the most important, though rarely addressed, question is what role genuine quantum degrees of freedom play. Here, complete effective equations are derived for isotropic models with an interacting ... More
Dynamical coherent states and physical solutions of quantum cosmological bouncesMar 29 2007A new model is studied which describes the quantum behavior of transitions through an isotropic quantum cosmological bounce in loop quantum cosmology sourced by a free and massless scalar field. As an exactly solvable model even at the quantum level, ... More
Singularities and Quantum GravityFeb 27 2007Although there is general agreement that a removal of classical gravitational singularities is not only a crucial conceptual test of any approach to quantum gravity but also a prerequisite for any fundamental theory, the precise criteria for non-singular ... More
Universe scenarios from loop quantum cosmologyNov 18 2005Loop quantum cosmology is an application of recent developments for a non-perturbative and background independent quantization of gravity to a cosmological setting. Characteristic properties of the quantization such as discreteness of spatial geometry ... More
The Semiclassical Limit of Loop Quantum CosmologyMay 29 2001The continuum and semiclassical limits of isotropic, spatially flat loop quantum cosmology are discussed, with an emphasis on the role played by the Barbero-Immirzi parameter \gamma in controlling space-time discreteness. In this way, standard quantum ... More
Renormalization group flow of reduced string actionsSep 22 2005It has been argued that certain reduced actions play a role in AdS/CFT when comparing fast moving strings to long single trace operators in gauge theories. Such actions arise in two ways: as a limit of the string action and as a description of long single ... More
Spiky strings and single trace operators in gauge theoriesOct 24 2004Jun 24 2005We consider single trace operators of the form O_{m_1 ... m_n} = tr D_+^{m_1} F ... D_+^{m_n} F which are common to all gauge theories. We argue that, when all m_i are equal and large, they have a dual description as strings with cusps, or spikes, one ... More
Wilson loops and anomalous dimensions in cascading theoriesOct 03 2003Nov 07 2003We use light-like Wilson loops and the AdS/CFT correspondence to compute the anomalous dimensions of twist two operators in the cascading (Klebanov-Strassler) theory. The computation amounts to find a minimal surface in the UV region of the KS background ... More
A note on twist two operators in N=4 SYM and Wilson loops in Minkowski signatureOct 13 2002Nov 04 2002Recently the anomalous dimension of twist two operators in N=4 SYM theory was computed by Gubser, Klebanov and Polyakov in the limit of large 't Hooft coupling using semi-classical rotating strings in AdS_5. Here we reproduce their results for large angular ... More
The Origin of Fat TailsOct 16 2013May 16 2014We propose a random walk model of asset returns where the parameters depend on market stress. Stress is measured by, e.g., the value of an implied volatility index. We show that model parameters including standard deviations and correlations can be estimated ... More
The Coulomb branch of N=1 supersymmetric SU(N_c) x SU(N_c) gauge theoriesJul 08 1997Jan 26 1998We analyze the low energy behavior of N=1 supersymmetric gauge theories with SU(N_c) x SU(N_c) gauge group and a Landau-Ginzburg type superpotential. These theories contain fundamentals transforming under one of the gauge groups as well as bifundamental ... More
Geometrical theory of diffraction and spectral statisticsOct 06 1999We investigate the influence of diffraction on the statistics of energy levels in quantum systems with a chaotic classical limit. By applying the geometrical theory of diffraction we show that diffraction on singularities of the potential can lead to ... More
Billiard Systems in Three Dimensions: The Boundary Integral Equation and the Trace FormulaOct 31 1997We derive semiclassical contributions of periodic orbits from a boundary integral equation for three-dimensional billiard systems. We use an iterative method that keeps track of the composition of the stability matrix and the Maslov index as an orbit ... More
Parallel Magnetic Resonance ImagingJan 25 2015Jul 17 2015The main disadvantage of Magnetic Resonance Imaging (MRI) are its long scan times and, in consequence, its sensitivity to motion. Exploiting the complementary information from multiple receive coils, parallel imaging is able to recover images from under-sampled ... More
Templates and subtemplates of Rössler attractors from a bifurcation diagramFeb 24 2016We study the bifurcation diagram of the R\"ossler system. It displays the various dynamical regimes of the system (stable or chaotic) when a parameter is varied. We choose a diagram that exhibits coexisting attractors and banded chaos. We use the topological ... More
Dressing curvesAug 03 2015We present a loop group description for curves in $\mathbb{R}^3$, and apply it to classify the circletons: Circles dressed by simple factors.
The precise shape of the eigenvalue intensity for a class of non-selfadjoint operators under random perturbationsJan 31 2014Dec 20 2015We consider a non-selfadjoint $h$-differential model operator $P_h$ in the semiclassical limit ($h\rightarrow 0$) subject to small random perturbations. Furthermore, we let the coupling constant $\delta$ be $\exp\{-\frac{1}{Ch}\}\leq \delta \ll h^{\kappa}$ ... More