Results for "Simon Praetorius"

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Orientational order on surfaces - the coupling of topology, geometry and dynamicsJul 21 2016We consider the numerical investigation of surface bound orientational order using unit tangential vector fields by means of a gradient-flow equation of a weak surface Frank-Oseen energy. The energy is composed of intrinsic and extrinsic contributions, ... More
Active crystals on a sphereFeb 14 2018Two-dimensional crystals on curved manifolds exhibit nontrivial defect structures. Here, we consider "active crystals" on a sphere, which are composed of self-propelled colloidal particles. Our work is based on a new phase-field-crystal-type model that ... More
Nematic liquid crystals on curved surfaces - a thin film limitSep 27 2017We consider a thin film limit of a Landau-de Gennes Q-tensor model. In the limiting process we observe a continuous transition where the normal and tangential parts of the Q-tensor decouple and various intrinsic and extrinsic contributions emerge. Main ... More
A Navier Stokes Phase Field Crystal Model for Colloidal SuspensionsOct 21 2013Jan 26 2015We develop a fully continuous model for colloidal suspensions with hydrodynamic interactions. The Navier Stokes Phase Field Crystal (NS-PFC) model combines ideas of dynamic density functional theory with particulate flow approaches and is derived in detail ... More
Development and Analysis of a Block-Preconditioner for the Phase-Field Crystal EquationJan 27 2015We develop a preconditioner for the linear system arising from a finite element discretization of the Phase Field Crystal (PFC) equation. The PFC model serves as an atomic description of crystalline materials on diffusive time scales and thus offers the ... More
Liquid crystalline growth within a phase-field crystal modelJan 09 2015By using a phase-field crystal (PFC) model, the liquid-crystal growth of the plastic triangular phase is simulated with emphasis on crystal shape and topological defect formation. The equilibrium shape of a plastic triangular crystal (PTC) grown from ... More
A mechanism for cell motility by active polar gelsDec 17 2014May 05 2015We analyse a generic motility model, with the motility mechanism arising by contractile stress due to the interaction of myosin and actin. A hydrodynamic active polar gel theory is used to model the cytoplasm of a cell and is combined with a Helfrich-type ... More
A mesoscopic field theoretical approach for active systemsApr 22 2016We introduce a mesocopic modeling approach for active systems. The continuum model allows to consider microscopic details as well as emerging macroscopic behavior and can be considered as a minimal continuum model to describe generic properties of active ... More
Structure and dynamics of interfaces between two coexisting liquid crystalline phasesFeb 01 2013The phase-field-crystal model is used to access the structure and thermodynamics of interfaces between two coexisting liquid crystalline phases in two spatial dimensions. Depending on the model parameters there is a variety of possible coexistences between ... More
Adaptive FEM with optimal convergence rates for a certain class of non-symmetric and possibly non-linear problemsOct 31 2012Feb 11 2013We analyze adaptive mesh-refining algorithms for conforming finite element discretizations of certain non-linear second-order partial differential equations. We allow continuous polynomials of arbitrary, but fixed polynomial order. The adaptivity is driven ... More
Rate optimal adaptive FEM with inexact solver for nonlinear operatorsNov 16 2016We prove convergence with optimal algebraic rates for an adaptive finite element method for nonlinear equations with strongly monotone operator. Unlike prior works, our analysis also includes the iterative and inexact solution of the arising nonlinear ... More
Influence of grain size and exchange interaction on the LLB modeling procedureJul 15 2016Reliably predicting bit-error rates in realistic heat-assisted magnetic recording simulations is a challenging task. Integrating the Landau-Lifshitz-Bloch (LLB) equation can reduce the computational effort to determine the magnetization dynamics in the ... More
Areal density optimizations for heat-assisted-magnetic recording of high density bit-patterned mediaDec 11 2015Heat-assisted-magnetic recording (HAMR) is hoped to be the future recording technique for high density storage devices. Nevertheless, there exist several realizations strategies. With a coarse-grained Landau-Lifshitz-Bloch (LLB) model we investigate in ... More
Molecular engineering of chiral colloidal liquid crystals using DNA origamiMay 24 2017Establishing precise control over the shape and the interactions of the microscopic building blocks is essential for design of macroscopic soft materials with novel structural, optical and mechanical properties. Here, we demonstrate robust assembly of ... More
A self-consistent spin-diffusion model for micromagneticsDec 17 2015Sep 16 2016We propose a three-dimensional micromagnetic model that dynamically solves the Landau-Lifshitz-Gilbert equation coupled to the full spin-diffusion equation. In contrast to previous methods, we solve for the magnetization dynamics and the electric potential ... More
Adaptive vertex-centered finite volume methods with convergence ratesAug 25 2015Mar 22 2016We consider the vertex-centered finite volume method with first-order conforming ansatz functions. The adaptive mesh-refinement is driven by the local contributions of the weighted-residual error estimator. We prove that the adaptive algorithm leads to ... More
Kondo screening and beyond: an x-ray absorption and dichroism study of CePt$_5$/Pt(111)Nov 08 2016We use x-ray absorption spectroscopy as well as its linear and circular magnetic dichroisms to characterize relevant interactions and energy scales in the surface intermetallic CePt$_5$/Pt(111). The experiments provide insight into crystal field splitting, ... More
A three-dimensional spin-diffusion model for micromagneticsOct 22 2014May 18 2015We implement a finite-element scheme that solves the Landau-Lifshitz-Gilbert equation coupled to a diffusion equation accounting for spin-polarized currents. The latter solves for the spin accumulation not only in magnetic materials but also in nonmagnetic ... More
The intrinsic torsion of SU(3) and G_2 structuresFeb 26 2002We analyse the relationship between the components of the intrinsic torsion of an SU(3) structure on a 6-manifold and a G_2 structure on a 7-manifold. Various examples illustrate the type of SU(3) structure that can arise as a reduction of a metric with ... More
On Estimating Many Means, Selection Bias, and the BootstrapNov 15 2013With recent advances in high throughput technology, researchers often find themselves running a large number of hypothesis tests (thousands+) and esti- mating a large number of effect-sizes. Generally there is particular interest in those effects estimated ... More
Polymer Collapse on Fluctuating Random SurfacesSep 05 1994Jan 12 1995The conformations of interacting linear polymers on a dynamical planar random lattice are studied using a random two-matrix model. An exact expression for the partition function of self-avoiding chains subject to attractive contact interactions of relative ... More
On Loop Equations In KdV Exactly Solvable String TheoryNov 30 1991The non-perturbative behaviour of macroscopic loop amplitudes in the exactly solvable string theories based on the KdV hierarchies is considered. Loop equations are presented for the real non-perturbative solutions living on the spectral half-line, allowed ... More
Effective Theories for Circuits and AutomataJun 28 2011Feb 20 2012Abstracting an effective theory from a complicated process is central to the study of complexity. Even when the underlying mechanisms are understood, or at least measurable, the presence of dissipation and irreversibility in biological, computational ... More
Volatility Swap Under the SABR ModelMar 25 2013The SABR model is shortly presented and the volatility swap explained. The fair value for a volatility swap is then computed using the usual theory in financial mathematics. An analytical solution using confluent hypergeometric functions is found. The ... More
Extending the Stable Model Semantics with More Expressive RulesAug 06 1999The rules associated with propositional logic programs and the stable model semantics are not expressive enough to let one write concise programs. This problem is alleviated by introducing some new types of propositional rules. Together with a decision ... More
One way cuts in oriented graphsDec 28 2007Nov 19 2010This paper has been withdrawn by the author.
(k+1)-sums versus k-sumsNov 19 2010Jun 08 2012A $k$-sum of a set $A\subseteq \mathbb{Z}$ is an integer that may be expressed as a sum of $k$ distinct elements of $A$. How large can the ratio of the number of $(k+1)$-sums to the number of $k$-sums be? Writing $k\wedge A$ for the set of $k$-sums of ... More
Summability of Superstring TheoryMar 11 1998Mar 20 1998Several arguments are given for the summability of the superstring perturbation series. Whereas the Schottky group coordinatization of moduli space may be used to provide refined estimates of large-order bosonic string amplitudes, the super-Schottky group ... More
Scalar Field Theory in Curved Space and the Definition of MomentumFeb 09 1997Dec 22 1997Some general remarks are made about the quantum theory of scalar fields and the definition of momentum in curved space. Special emphasis is given to field theory in anti-de Sitter space, as it represents a maximally symmetric space-time of constant curvature ... More
Metric Diophantine approximation with respect to planar distance functionsJan 27 2004We outline a proof of an analogue of Khintchine's Theorem in R^2, where the ordinary height is replaced by a distance function satisfying an irrationality condition as well as certain decay and symmetry conditions.
On the explanation for quantum statisticsNov 15 2005The concept of classical indistinguishability is analyzed and defended against a number of well-known criticisms, with particular attention to the Gibbs' paradox. Granted that it is as much at home in classical as in quantum statistical mechanics, the ... More
The Lattice Fermi SurfaceOct 08 2001The Nambu - Jona-Lasinio model in 2+1 dimensions is simulated for non-zero baryon chemical potential with a diquark source term. No evidence for a BCS condensate or gap is seen at high density; rather, critical behaviour with novel exponents is observed, ... More
Improving the Lattice QED ActionNov 24 1994Strongly coupled QED is a model whose physics is dominated by short-ranged effects. In order to assess which features of numerical simulations of the chiral phase transition are universal and which are not, we have formulated a quenched version of the ... More
Monte Carlo Study of the 3D Thirring ModelFeb 05 1997I review three different non-perturbative approaches to the three dimensional Thirring model: the 1/N_f expansion, Schwinger-Dyson equations, and Monte Carlo simulation. Simulation results are presented to support the existence of a non-perturbative fixed ... More
The growth rate and dimension theory of beta-expansionsAug 30 2012Oct 15 2012In a recent paper of Feng and Sidorov they show that for $\beta\in(1,\frac{1+\sqrt{5}}{2})$ the set of $\beta$-expansions grows exponentially for every $x\in(0,\frac{1}{\beta-1})$. In this paper we study this growth rate further. We also consider the ... More
A theorem of Poincaré-Hopf typeMay 28 2009We compute (algebraically) the Euler characteristic of a complex of sheaves with constructible cohomology. A stratified Poincar\'e-Hopf formula is then a consequence of the smooth Poincar\'e-Hopf theorem and of additivity of the Euler-Poincar\'e characteristic ... More
A Dolbeault Isomorphism Theorem in Infinite DimensionsSep 27 2005For a large class of separable Banach spaces, we prove the real analytic Dolbeault Isomorphism Theorem for open subsets.
Towards a Systematic Development Process of Optimization MethodsFeb 29 2016Jul 18 2016The ultimate goal of all optimization methods is to solve real-world problems. For a successful project execution, knowledge about optimization and the application has to be pooled. As it is too inefficient to highly train one person in both fields, a ... More
Fourth Moment Theorems for complex Gaussian approximationNov 02 2015We prove a bound for the Wasserstein distance between vectors of smooth complex random variables and complex Gaussians in the framework of complex Markov diffusion generators. For the special case of chaotic eigenfunctions, this bound can be expressed ... More
Top quark mass measurements with the CMS experiment at the LHCJul 18 2016Measurements of the top quark mass are presented, obtained from CMS data collected in proton proton collisions at the LHC at centre-of-mass energies of 7 TeV and 8 TeV. The mass of the top quark is measured using several methods and channels, including ... More
Automating QCD amplitudes with on-shell methodsMay 07 2016We review some of the modern approaches to scattering amplitude computations in QCD and their application to precision LHC phenomenology. We emphasise the usefulness of momentum twistor variables in parameterising general amplitudes.
Up to and beyond ninth order in opacity: Radiative energy loss with GLVApr 29 2008A new examination of the GLV all-orders opacity result for radiative energy loss is presented. The opacity expansion is shown to be a Dyson expansion of a Schrodinger-like (or diffusion) equation, a form also found in BDMPS-Z-ASW, AMY and Higher Twist ... More
Nuts have no hairAug 18 1995We show that the Riemannian Kerr solutions are the only Riemannian, Ricci-flat and asymptotically flat ${\rm C}^{2}$-metrics $g_{\mu\nu}$ on a 4-dimensional complete manifold ${\cal M}$ of topology ${\rm R}^{2} \times {\rm S}^{2}$ which have (at least) ... More
Brane Effective Actions, Kappa-Symmetry and ApplicationsOct 11 2011Nov 22 2011This is a review on brane effective actions, their symmetries and some of its applications. Its first part uncovers the Green-Schwarz formulation of single M- and D-brane effective actions focusing on kinematical aspects : the identification of their ... More
Extremal black holes, Holography & Coarse grainingJun 01 2011Jul 30 2011I review some of the concepts at the crossroads of gravitational thermodynamics, holography and quantum mechanics. First, the origin of gravitational thermodynamics due to coarse graining of quantum information is exemplified using the half-BPS sector ... More
The geometry of null rotation identificationsMar 21 2002Apr 16 2002The geometry of flat spacetime modded out by a null rotation (boost+rotation) is analysed. When embedding this quotient spacetime in String/M-theory, it still preserves one half of the original supersymmetries. Its connection with the BTZ black hole, ... More
Automorphisms as brane non-local transformationsOct 26 2000The relation among spacetime supersymmetry algebras and superbrane actions is further explored. It is proved that $SL(2,\bR)$ belongs to the automorphism group of the ${\cal N}=2$ D=10 type IIB SuperPoincar\'e algebra. Its SO(2) subgroup is identified ... More
Spreadsheet HellJan 21 2008This management paper looks at the real world issues faced by practitioners managing spreadsheets through the production phase of their life cycle. It draws on the commercial experience of several developers working with large corporations, either as ... More
Adiabatic limits of co-associative Kovalev-Lefschetz fibrationsMar 28 2016Apr 26 2016We study co-associative fibrations of G_{2}-manifolds. We propose that the adiabatic limit of this structure should be given locally by a maximal submanifold in a space of indefinite signature and set up global versions of the constructions.
Kähler-Einstein metrics and algebraic structures on limit spacesMar 28 2016This is an expository article, closely following the author's lecture at the 2014 Journal Differential Geometry conference.
Some integral curvature estimates for the Ricci flow in four dimensionsApr 10 2015We consider solutions (M,g(t)), 0 <= t <T, to Ricci flow on compact, four dimensional manifolds without boundary. We prove integral curvature estimates which are valid for any such solution. In the case that the scalar curvature is bounded and T is finite, ... More
Local smoothing results for the Ricci flow in dimensions two and threeSep 19 2012Jun 20 2013We present local estimates for solutions to the Ricci flow, without the assumption that the solution has bounded curvature. These estimates lead to a generalisation of one of the pseudolocality results of G.Perelman in dimension two.
On the unimodality of power transformations of positive stable densitiesFeb 19 2010Nov 15 2013Let $Z_\alpha$ be a positive $\alpha-$stable random variable and $r\in{\bf R}.$ We show the existence of an unbounded open domain $D$ in $[1/2,1]\times{\bf R}$ with a cusp at $(1/2,-1/2)$, characterized by the complete monotonicity of the function $F_{\alpha, ... More
Fonctions de Mittag-Leffler et processus de Lévy stables sans saut négatifApr 14 2009It is noticed that a certain transform of the Mittag-Leffler function Ea is completely monotone for a in [1,2]. Using the explicit expressions of its Bernstein density, an identity in law between suprema of completely asymmetric Levy a-stable processes. ... More
A Galois-Connection between Cattell's and Szondi's Personality ProfilesMay 05 2014We propose a computable Galois-connection between, on the one hand, Cattell's 16-Personality-Factor (16PF) Profiles, one of the most comprehensive and widely-used personality measures for non-psychiatric populations and their containing PsychEval Personality ... More
A multifractal zeta function for cookie cutter setsAug 13 2012Starting with the work of Lapidus and van Frankenhuysen a number of papers have introduced zeta functions as a way of capturing multifractal information. In this paper we propose a new multifractal zeta function and show that under certain conditions ... More
Retrieving the three-dimensional matter power spectrum and galaxy biasing parameters from lensing tomographyFeb 09 2012Apr 16 2012With the availability of galaxy distance indicators in weak lensing surveys, lensing tomography can be harnessed to constrain the three-dimensional (3D) matter power spectrum over a range of redshift and physical scale. By combining galaxy-galaxy lensing ... More
On dp-minimal ordered structuresSep 23 2009We show some basic facts about dp-minimal ordered structures. The main results are : dp-minimal groups are abelian-by-finite-exponent, in a divisible ordered dp-minimal group, any infinite set has non-empty interior, and any theory of pure tree is dp-minimal. ... More
Finding generically stable measuresSep 18 2010We discuss two constructions for obtaining generically stable Keisler measures in an NIP theory. First, we show how to symmetrize an arbitrary invariant measure to obtain a generically stable one from it. Next, we show that suitable sigma-additive probability ... More
Automorphisms of Salem degree 22 on supersingular K3 surfaces of higher Artin invariant - a short noteSep 08 2016We give a short proof that every supersingular K3 surface in odd characteristic has an automorphism of Salem degree 22. The proof relies on the case $\sigma=1$ and the cone theorem.
Restrictions of SL_3 Maass forms to maximal flat subspacesAug 04 2013Aug 26 2014Let \psi be a Hecke-Maass form on a cubic division algebra over \Q. We apply arithmetic amplification to improve the local bound for the L^2 norm of \psi restricted to maximal flat subspaces.
Alternatives for optimization in systems and control: convex and non-convex approachesMay 01 2012In this presentation, we will develop a short overview of main trends of optimization in systems and control, and from there outline some new perspectives emerging today. More specifically, we will focus on the current situation, where it is clear that ... More
On the distribution of powers of real numbers modulo 1Nov 18 2014Given a strictly increasing sequence of positive real numbers tending to infinity $(q_{n})_{n=1}^{\infty}$, and an arbitrary sequence of real numbers $(r_{n})_{n=1}^{\infty}.$ We study the set of $\alpha\in(1,\infty)$ for which $\lim_{n\to\infty}\|\alpha^{q_{n}}-r_{n}\|= ... More
NPPT Bound Entanglement ExistsAug 31 2006Every dXd bipartite system is shown to have a large family of undistillable states with nonpositive partial transpose (NPPT). This family subsumes the family of conjectured NPPT bound entangled Werner states. In particular, all one-copy undistillable ... More
A Relativistic Conical Function and its Whittaker LimitsNov 01 2011In previous work we introduced and studied a function $R(a_{+},a_{-},{\bf c};v,\hat{v})$ that is a generalization of the hypergeometric function ${}_2F_1$ and the Askey-Wilson polynomials. When the coupling vector ${\bf c}\in{\mathbb C}^4$ is specialized ... More
Controlling inclusive cross sections in parton shower + matrix element mergingNov 23 2012Dec 03 2012We propose an extension of matrix element plus parton shower merging at tree level to preserve inclusive cross sections obtained from the merged and showered sample. Implementing this constraint generates approximate next-to-leading order (NLO) contributions ... More
Diophantine approximation and the solubility of the Schroedinger equationOct 22 2002Apr 29 2003We characterise the set of periods for which number theoretical obstructions prevent us from finding periodic solutions of the Schroedinger equation on a two dimensional torus as well as the asymptotic occurrence of possible resonances.
Bootstrapping the Mazur--Orlicz--König theoremDec 25 2015In this paper, we give some extensions of K\"onig's extension of the Mazur-Orlicz theorem. These extensions include generalizations of a surprising recent result of Sun Chuanfeng, and generalizations to the product of more than two spaces of the "Hahn-Banach-Lagrange" ... More
Green functions for the Dirac operator under local boundary conditions and applicationsMar 07 2007In this paper, we define the Green function for the Dirac operator under two local boundary conditions: the condition associated with a chirality operator (also called the chiral bag boundary condition) and the $\MIT$ bag boundary condition. Then we give ... More
Constructive Gelfand duality for non-unital commutative C*-algebrasDec 05 2014Feb 03 2015We prove constructive versions of various usual results related to the Gelfand duality. Namely, that the constructive Gelfand duality extend to a duality between commutative nonunital C*-algebras and locally compact completely regular locales, that ideals ... More
Natural Entanglement in Bose-Einstein CondensatesOct 18 2001Every Bose-Einstein condensate is in a highly entangled state, as a consequence of the fact that the particles in a condensate are distributed over space in a coherent way. It is proved that any two regions within a condensate of finite particle number ... More
Towards Critical Physics in 2+1d with U(2N)-Invariant FermionsOct 14 2016Interacting theories of N relativistic fermion flavors in reducible spinor representations in 2+1 spacetime dimensions are formulated on a lattice using domain wall fermions (DWF), for which a U(2N) global symmetry is recovered in the limit that the wall ... More
How to determine a K3 surface from a finite automorphismApr 29 2016In this article we pursue the question when an automorphism determines a (complex) K3 surface up to isomorphism. We prove that if the automorphism is finite non-symplectic and the transcendental lattice small, then the isomorphism class of the K3 surface ... More
Double-pass variants for multi-shift BiCGstab(ell)Oct 13 2010In analogy to Neuberger's double-pass algorithm for the Conjugate Gradient inversion with multi-shifts we introduce a double-pass variant for BiCGstab(ell). One possible application is the overlap operator of QCD at non-zero chemical potential, where ... More
Query-driven Data Completeness Management (PhD Thesis)Nov 11 2014Apr 01 2015Knowledge about data completeness is essentially in data-supported decision making. In this thesis we present a framework for metadata-based assessment of database completeness. We discuss how to express information about data completeness and how to ... More
Average-Value Tverberg Partitions via Finite Fourier AnalysisJan 19 2015Jul 25 2016The long-standing topological Tverberg conjecture claimed, for any continuous map from the boundary of an $N(q,d):=(q-1)(d+1)$-simplex to $d$-dimensional Euclidian space, the existence of $q$ pairwise disjoint subfaces whose images have non-empty $q$-fold ... More
Meromorphic Szego functions and asymptotic series for Verblunsky coefficientsFeb 23 2005We prove that the Szeg\H{o} function, $D(z)$, of a measure on the unit circle is entire meromorphic if and only if the Verblunsky coefficients have an asymptotic expansion in exponentials. We relate the positions of the poles of $D(z)^{-1}$ to the exponential ... More
Mass Equidistribution for Automorphic Forms of Cohomological Type on GL_2Jun 16 2010Aug 13 2010We extend Holowinsky and Soundararajan's proof of quantum unique ergodicity for holomorphic Hecke modular forms on SL(2,Z), by establishing it for automorphic forms of cohomological type on GL_2 over an arbitrary number field which satisfy the Ramanujan ... More
Quasi-modularity of generalized sum-of-divisors functionsJun 16 2015Jul 24 2015In 1919, P. A. MacMahon studied generating functions for generalized divisor sums. In this paper, we provide a framework in which to view these generating functions in terms of Jacobi forms, and prove that they are quasi-modular forms.
Introduction to Modular FormsJul 04 2014We introduce the notion of modular forms, focusing primarily on the group PSL2Z. We further introduce quasi-modular forms, as wel as discuss their relation to physics and their applications in a variety of enumerative problems. These notes are based on ... More
A limit theorem for moments in space of the increments of Brownian local timeJun 24 2015Dec 01 2015We proof a limit theorem for moments in space of the increments of Brownian local time. As special cases for the second and third moments, previous results by Chen et al. (Ann. Prob. 38, 2010, no. 1) and Rosen (Stoch. Dyn. 11, 2011, no. 1), which were ... More
Optimal Convergence Rates and One-Term Edgeworth Expansions for Multidimensional Functionals of Gaussian FieldsMay 28 2013Nov 11 2013We develop techniques for determining the exact asymptotic speed of convergence in the multidimensional normal approximation of smooth functions of Gaussian fields. As a by-product, our findings yield exact limits and often give rise to one-term generalized ... More
Tropical linear spaces and tropical convexityMay 08 2015In classical geometry, a linear space is a space that is closed under linear combinations. In tropical geometry, it has long been a consensus that tropical varieties defined by valuated matroids are the tropical analogue of linear spaces. It is not difficult ... More
An almost-integral universal Vassiliev invariant of knotsMay 23 2001Sep 05 2002A `total Chern class' invariant of knots is defined. This is a universal Vassiliev invariant which is integral `on the level of Lie algebras' but it is not expressible as an integer sum of diagrams. The construction is motivated by similarities between ... More
Curves between Lipschitz and $C^1$ and their relation to geometric knot theoryFeb 29 2016In this article we investigate regular curves whose derivatives have vanishing mean oscillations. We show that smoothing these curves using a standard mollifier one gets regular curves again. We apply this result to solve a couple of open problems. We ... More
Exceptional digit frequencies and expansions in non-integer basesNov 28 2017In this paper we study the set of digit frequencies that are realised by elements of the set of $\beta$-expansions. The main result of this paper demonstrates that as $\beta$ approaches $1,$ the set of digit frequencies that occur amongst the set of $\beta$-expansions ... More
Non-Gaussianities in a two-field generalization of Natural InflationNov 23 2017We describe a two-field model that generalizes Natural Inflation, in which the inflaton is the pseudo-Goldstone boson of an approximate symmetry that is spontaneously broken, and the radial mode is dynamical. We analyze how the dynamics fundamentally ... More
The Maser-Starburst connection in NGC253Nov 07 2017NGC253 is one of the closest starburst galaxies to the Milky Way and as such it has been studied in detail across the electromagnetic spectrum. Recent observations have detected the first extragalactic class I methanol masers at 36 and 44 GHz and the ... More
Numerical study of the $2+1d$ Thirring model with U($2N$)-invariant fermionsAug 25 2017In 2+1 dimensions the global U($2N$) symmetry associated with massless Dirac fermions is broken to U($N)\otimes$U($N$) by a parity-invariant mass. I will show how to adapt the domain wall formulation to recover the U($2N$)-invariant limit in interacting ... More
The Spectral Gap of Sparse Random DigraphsAug 01 2017The second largest eigenvalue of a transition matrix $P$ has connections with many properties of the underlying Markov chain, and especially its convergence rate towards the stationary distribution. In this paper, we give an asymptotic upper bound for ... More
A remark on the group-completion theoremSep 07 2017Suppose that $M$ is a topological monoid satisfying $\pi_0M=\mathbb{N}$ to which the McDuff-Segal group-completion theorem applies. This implies that a certain map $f: \mathbb{M}_{\infty}\rightarrow \Omega BM$ defined on an infinite mapping telescope ... More
Resolving the observer reference class problem in cosmologyJul 14 2017The assumption that we are typical observers plays a core role in attempts to make multiverse theories empirically testable. A widely shared worry about this assumption is that it suffers from systematic ambiguity concerning the reference class of observers ... More
On the Computation of the Shannon Capacity of a Discrete Channel with NoiseJan 30 2017Jan 31 2017Muroga [M52] showed how to express the Shannon channel capacity of a discrete channel with noise [S49] as an explicit function of the transition probabilities. His method accommodates channels with any finite number of input symbols, any finite number ... More
A heteroclinic orbit connecting traveling waves pertaining to different nonlinearitiesJun 13 2017In this paper we consider a semilinear parabolic equation in an infinite cylinder. The spatially varying nonlinearity is such that it connects two (spatially independent) bistable nonlinearities in a compact set in space. We prove that, given such a setting, ... More
Silicon Technologies for the CLIC Vertex DetectorJun 01 2017CLIC is a proposed linear e+e- collider designed to provide particle collisions at center-of-mass energies of up to 3 TeV. Precise measurements of the properties of the top quark and the Higgs boson, as well as searches for Beyond the Standard Model physics ... More
Kitaev MaterialsJan 24 2017In transition-metal compounds with partially filled $4d$ and $5d$ shells spin-orbit entanglement, electronic correlations, and crystal-field effects conspire to give rise to a variety of novel forms of topological quantum matter. This includes Kitaev ... More
Wrong side of the tracks: Big Data and Protected CategoriesDec 15 2014Jun 24 2016When we use machine learning for public policy, we find that many useful variables are associated with others on which it would be ethically problematic to base decisions. This problem becomes particularly acute in the Big Data era, when predictions are ... More
Further solvable analogues of the Baer-Suzuki theorem and generation of nonsolvable groupsDec 11 2010Dec 14 2010Let $G$ be an almost simple group. We prove that if $x \in G$ has prime order $p \ge 5$, then there exists an involution $y$ such that $<x,y>$ is not solvable. Also, if $x$ is an involution then there exist three conjugates of $x$ that generate a nonsolvable ... More
Towards a Theory of GlueDec 17 2012We propose and study the notions of behaviour type and composition operator making a first step towards the definition of a formal framework for studying behaviour composition in a setting sufficiently general to provide insight into how the component-based ... More
Population genetics models of local ancestryFeb 22 2012Apr 25 2012Migrations have played an important role in shaping the genetic diversity of human populations. Understanding genomic data thus requires careful modeling of historical gene flow. Here we consider the effect of relatively recent population structure and ... More