Results for "Tom Economou"

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Equilibrium balking strategies for a clearing queueing system in alternating environmentDec 23 2011We consider a Markovian clearing queueing system, where the customers are accumulated according to a Poisson arrival process and the server removes all present customers at the completion epochs of exponential service cycles. This system may represent ... More
Equilibrium balking strategies in the single server Markovian queue with catastrophesJul 12 2011We consider a Markovian queue subject to Poisson generated catastrophes. Whenever a catastrophe occurs, all customers are forced to abandon the system, the server is rendered inoperative and an exponential repair time is set on. We assume that the arriving ... More
Spin-photon entanglement interfaces in silicon carbide defect centersAug 11 2016Optically active spins in solid-state systems can be engineered to emit photons that are entangled with the spin in the solid. This allows for applications such as quantum communications, quantum key distribution, and distributed quantum computing. Recently, ... More
Generation of arbitrary all-photonic graph states from quantum emittersNov 15 2018May 10 2019We present protocols to generate arbitrary photonic graph states from quantum emitters that are in principle deterministic. We focus primarily on two-dimensional cluster states of arbitrary size due to their importance for measurement-based quantum computing. ... More
Long-distance entangling gates between quantum dot spins mediated by a superconducting resonatorFeb 15 2019Recent experimental work with silicon qubits has shown that it is possible, using an inhomogeneous magnetic field, to strongly couple modes of a microwave resonator to the spin of a single electron trapped in a double quantum dot. This suggests the possibility ... More
Fast Two-Qubit Gates in Semiconductor Quantum Dots using a Photonic MicrocavityApr 23 2012Jan 22 2013Implementations for quantum computing require fast single- and multi-qubit quantum gate operations. In the case of optically controlled quantum dot qubits theoretical designs for long-range two- or multi-qubit operations satisfying all the requirements ... More
A Bayesian Approach to Constraint Based Causal InferenceOct 16 2012We target the problem of accuracy and robustness in causal inference from finite data sets. Some state-of-the-art algorithms produce clear output complete with solid theoretical guarantees but are susceptible to propagating erroneous decisions, while ... More
A Dynamic Model of Streamer Coupling for High Pressure DischargesJul 18 2010A streamer coupling theory is developed to describe the formation of homogenous emission, and the high moving speed of emission patterns in high pressure discharges. By considering the effects of both electron diffusion and electronic drift in the streamer ... More
Inductive Construction of 2-Connected Graphs for Calculating the Virial CoefficientsJul 28 2009Jul 15 2010In this paper we give a method for constructing systematically all simple 2-connected graphs with n vertices from the set of simple 2-connected graphs with n-1 vertices, by means of two operations: subdivision of an edge and addition of a vertex. The ... More
Dynamic Anapole in Metasurfaces made of Sculptured CylindersMay 04 2019We present all-dielectric polaritonic metasurfaces consisting of properly sculptured cylinders to sustain the dynamic anapole, i.e. a non-radiating alternating current distribution. One way for the anapole to emerge, is by combining modes based on the ... More
A Logical Characterization of Constraint-Based Causal DiscoveryFeb 14 2012We present a novel approach to constraint-based causal discovery, that takes the form of straightforward logical inference, applied to a list of simple, logical statements about causal relations that are derived directly from observed (in)dependencies. ... More
A shorter proof of Lemma A.6 (arXiv:1005.0768)Jun 21 2012For the convenience of readers of the article {\em No-arbitrage pricing under systemic risk: accounting for cross-ownership} (Fischer, 2012, arXiv:1005.0768), a full proof of Lemma A.5 and a shorter proof of Lemma A.6 of that paper are provided.
Constructing Q-Fano 3-folds à la Prokhorov & ReidOct 06 2016We generalise a construction by Prokhorov & Reid of two families of Q-Fano 3-folds of index 2 to obtain five more families of Q-Fano 3-folds; four of index 2 and one of index 3. Two of the families constructed have the same Hilbert series and we study ... More
The structure theory of set addition revisitedDec 03 2012In this article we survey some of the recent developments in the structure theory of set addition.
Green's sumset problem at density one halfMar 29 2010Dec 02 2010We investigate the size of subspaces in sumsets and show two main results. First, if A is a subset of F_2^n with density at least 1/2 - o(n^{-1/2}) then A+A contains a subspace of co-dimension 1. Secondly, if A is a subset of F_2^n with density at least ... More
Three-term arithmetic progressions and sumsetsNov 10 2006Apr 01 2010Suppose that G is an abelian group and A is a finite subset of G containing no three-term arithmetic progressions. We show that |A+A| >> |A|(log |A|)^{1/3-\epsilon} for all \epsilon>0.
Additive structures in sumsetsMay 18 2006Apr 01 2010Suppose that A is a subset of the integers {1,...,N} of density a. We provide a new proof of a result of Green which shows that A+A contains an arithmetic progression of length exp(ca(log N)^{1/2}) for some absolute c>0. Furthermore we improve the length ... More
A statistical approach to covering lemmasOct 22 2016We discuss a statistical variant of Ruzsa's covering lemma and use it to show that if G is an Abelian group of bounded exponent and A in G has |A+A| < K|A| then the subgroup generated by A has size at most exp(O(K log^22K))|A|, where the constant in the ... More
An analytic approach to a weak non-Abelian Kneser-type theoremDec 03 2012We prove the following result due to Hamidoune using an analytic approach. Suppose that A is a subset of a finite group G with |AA^{-1}| \leq (2-\varepsilon)|A|. Then there is a subgroup H of G and a set X of size O_\varepsilon(1) such that A \subset ... More
Algebraicity and Asymptotics: An explosion of BPS indices from algebraic generating seriesJun 08 2016It is an observation of Kontsevich and Soibelman that generating series that produce certain (generalized) Donaldson Thomas invariants are secretly algebraic functions over the rationals. From a physical perspective this observation arises naturally for ... More
Power spectrum sensitivity of raster-scanned CMB experiments in the presence of 1/f noiseFeb 22 2007Sep 24 2007We investigate the effects of 1/f noise on the ability of a particular class of Cosmic Microwave Background experiments to measure the angular power spectrum of temperature anisotropy. We concentrate on experiments that operate primarily in raster-scan ... More
Sampling Generative Networks: Notes on a Few Effective TechniquesSep 14 2016Sep 16 2016We introduce several techniques for sampling and visualizing the latent spaces of generative models. Replacing linear interpolation with spherical linear interpolation prevents diverging from a model's prior distribution and produces sharper samples. ... More
Scattering diagrams, Hall algebras and stability conditionsMar 01 2016Nov 11 2016To any quiver with relations we associate a consistent scattering diagram taking values in the motivic Hall algebra of its category of representations. We show that the chamber structure of this scattering diagram coincides with the natural chamber structure ... More
A new strain energy function for the hyperelastic modelling of ligaments and tendons based on fascicle microstructureOct 02 2015A new strain energy function for the hyperelastic modelling of ligaments and tendons based on the geometrical arrangement of their fibrils is derived. The distribution of the crimp angles of the fibrils is used to determine the stress-strain response ... More
Interlacements and the Wired Uniform Spanning ForestDec 28 2015Oct 18 2016We extend the Aldous-Broder algorithm to generate the wired uniform spanning forests (WUSFs) of infinite, transient graphs. We do this by replacing the simple random walk in the classical algorithm with Sznitman's random interlacement process. We then ... More
General Graph Identification By HashingDec 22 2015A method for identifying graphs using MD5 hashing is presented. This allows fast graph equality comparisons and can also be used to facilitate graph isomorphism testing. The graphs can be labeled or unlabeled. The method identifies vertices by hashing ... More
The bijection between projective indecomposable and simple modulesOct 14 2014For modules over a finite-dimensional algebra, there is a canonical one-to-one correspondence between the projective indecomposable modules and the simple modules. In this purely expository note, we take a straight-line path from the definitions to this ... More
Conformal invariance of the 3D self-avoiding walkOct 25 2013We show that if the three dimensional self-avoiding walk (SAW) is conformally invariant, then one can compute the hitting densities for the SAW in a half space and in a sphere. We test these predictions by Monte Carlo simulations and find excellent agreement, ... More
Dyck Words and Multi-Quark Primitive AmplitudesApr 29 2013I study group theory (Kleiss-Kuijf) relations between purely multi-quark primitive amplitudes at tree level, and prove that they reduce the number of independent primitives to (n-2)!/(n/2)!, where n is the number of quarks plus antiquarks, in the case ... More
Sets of beta-expansions and the Hausdorff Measure of Slices through FractalsJul 08 2013We study natural measures on sets of beta-expansions and on slices through self similar sets. In the setting of beta-expansions, these allow us to better understand the measure of maximal entropy for the random beta-transformation and to reinterpret a ... More
On the Conservativity of Some Functors in Motivic Homotopy TheoryJun 24 2015Feb 23 2016Given a 0-connective motivic spectrum $E \in SH(k)$ over a perfect field k, we determine $h_0$ of the associated motive $M E \in DM(k)$ in terms of $\pi_0 (E)$. Using this we show that if k has finite 2-\'etale cohomological dimension, then the functor ... More
The Scenery Flow for Self-Affine MeasuresMay 07 2015We describe the scaling scenery associated to Bernoulli measures supported on separated self-affine sets under the condition that certain projections of the measure are absolutely continuous.
The Generalized Slices of Hermitian K-TheoryOct 05 2016We compute the generalized slices (as defined by Spitzweck-{\O}stv{\ae}r) of the motivic spectrum KO (representing hermitian K-theory) in terms of motivic cohomology and (a version of) generalized motivic cohomology, obtaining good agreement with the ... More
Notions of Möbius inversionJan 02 2012Oct 07 2012M\"obius inversion, originally a tool in number theory, was generalized to posets for use in group theory and combinatorics. It was later generalized to categories in two different ways, both of which are useful. We provide a unifying abstract framework. ... More
Generalized Enrichment for Categories and MulticategoriesJan 29 1999In this paper we answer the question: `what kind of a structure can a general multicategory be enriched in?' The answer is, in a sense to be made precise, that a multicategory of one type can be enriched in a multicategory of the type one level up. In ... More
Basic BicategoriesOct 04 1998A concise guide to very basic bicategory theory, from the definition of a bicategory to the coherence theorem.
General Operads and MulticategoriesOct 08 1998Notions of `operad' and `multicategory' abound. This work provides a single framework in which many of these various notions can be expressed. Explicitly: given a monad * on a category S, we define the term `(S,*)-multicategory', subject to certain conditions ... More
Stability conditions on a non-compact Calabi-Yau threefoldSep 02 2005Feb 28 2006We study the space of stability conditions $\Stab(X)$ on the non-compact Calabi-Yau threefold $X$ which is the total space of the canonical bundle of $\PP^2$. We give a combinatorial description of an open subset of $\Stab(X)$ and state a conjecture relating ... More
Flops and derived categoriesSep 06 2000This paper contains some applications of Fourier-Mukai techniques to the birational geometry of threefolds. In particular, we prove that birational Calabi-Yau threefolds have equivalent derived categories. To do this we show how flops arise naturally ... More
Algebraic and Affine Pattern AvoidanceMar 15 2013We investigate various connections between the 0-Hecke monoid, Catalan monoid, and pattern avoidance in permutations, providing new tools for approaching pattern avoidance in an algebraic framework. In particular, we characterize containment of a class ... More
Hall algebras and curve-counting invariantsFeb 23 2010We use Joyce's theory of motivic Hall algebras to prove that reduced Donaldson-Thomas curve-counting invariants on Calabi-Yau threefolds coincide with stable pair invariants, and that the generating functions for these invariants are Laurent expansions ... More
Twisted cyclic cohomology of the quantum SU(2)Mar 11 2004May 13 2004Withdrawn. Generalized and subsumed by math.QA/0405249
The State of Matrix TheoryJun 24 1997This is a brief description of what has been accomplished and what remains to be done in the construction of a nonperturbative formulation of "The Theory Formerly Known as String". It is culled from two short talks given by the author at SUSY 97 and Strings ... More
Monte Carlo Tests of SLE Predictions for the 2D Self-Avoiding WalkDec 21 2001The conjecture that the scaling limit of the two-dimensional self-avoiding walk (SAW) in a half plane is given by the stochastic Loewner evolution (SLE) with $\kappa=8/3$ leads to explicit predictions about the SAW. A remarkable feature of these predictions ... More
Regularity and nearness theorems for families of local Lie groupsJun 14 2012In this work, we prove three types of results with the strategy that, together, the author believes these should imply the local version of Hilbert's Fifth problem. In a separate development, we construct a nontrivial topology for rings of map germs on ... More
Testing the Boundary Conditions of General Relativity Near the Earth-Sun Saddle PointJun 07 1998Jun 03 1999We suggest that a satellite with a stable atomic clock on board be sent through the Earth-Sun gravitational saddle point to experimentally determine whether Nature prefers static solutions of the field equations of General Relativity, such as the standard ... More
Conformal invariance predictions for the three-dimensional self-avoiding walkAug 20 2014Dec 23 2014If the three dimensional self-avoiding walk (SAW) is conformally invariant, then one can compute the hitting densities for the SAW in a half-space and in a sphere. The ensembles of SAW's used to define these hitting densities involve walks of arbitrary ... More
Speech Coding, Speech Interfaces and IoT - Opportunities and ChallengesNov 14 2018Recent speech and audio coding standards such as 3GPP Enhanced Voice Services match the foreseeable needs and requirements in transmission of speech and audio, when using current transmission infrastructure and applications. Trends in Internet-of-Things ... More
Locality of the critical probability for transitive graphs of exponential growthAug 27 2018Around 2008, Schramm conjectured that the critical probabilities for Bernoulli bond percolation satisfy the following continuity property: If $(G_n)_{n\geq 1}$ is a sequence of transitive graphs converging locally to a transitive graph $G$ and $\limsup_{n\to\infty} ... More
Using weighting algorithms to refine source direction determinations in all-sky gravitational wave burst searches with two-detector networksMay 03 2018I explore the possibility of resurrecting an old, non-Bayesian computational approach for inferring the source direction of a gravitational wave from the output of a two-detector network. The method gives the beam pattern response functions and time delay, ... More
Affine Grassmannians in A^1-algebraic topologyJan 25 2018Mar 25 2019Let k be a field. Denote by Spc(k)_* the unstable, pointed motivic homotopy category and by Omega_Gm: Spc(k)_* \to Spc(k)_* the Gm-loops functor. For a k-group G, denote by Gr_G the affine Grassmannian of G. If G is isotropic reductive, we provide a canonical ... More
Knot types of generalized Kirchhoff rodsAug 30 2017Kirchhoff energy is a classical functional on the space of arclength-parameterized framed curves whose critical points approximate configurations of springy elastic rods. We introduce a generalized functional on the space of framed curves of arbitrary ... More
Long time thermal asymptotics of nonlinear Luttinger liquid from inverse scatteringAug 07 2017I derive a Fredholm determinant for the thermal correlator of vertex operators with a conformally invariant density matrix and nonlinear time evolution. Using the method of nonlinear steepest descent I find the long time asymptotics at finite temperature. ... More
Measuring technological complexity - Current approaches and a new measure of structural complexityAug 24 2017Mar 09 2018The paper reviews two prominent approaches for the measurement of technological complexity: the method of reflection and the assessment of technologies' combinatorial difficulty. It discusses their central underlying assumptions and identifies potential ... More
Rigidity in etale motivic stable homotopy theoryOct 18 2018For a scheme X, denote by SH(X_et^hyp) the stabilization of the hypercompletion of its etale infty-topos, and by SH_et(X) the localization of the stable motivic homotopy category SH(X) at the (desuspensions of) etale hypercovers. For a stable infty-category ... More
Magnification Spaces: A nonstandard approach to inverse mapping theoremsJul 20 2012This paper develops an infinitesimal order of magnitude coupled with overflow technique that allows nonnumerical proofs of nondegenerate and degenerate inverse mapping theorems for mappings minimally regular at a point. This approach is used first to ... More
Minimal elements of stopping time $σ$-algebrasDec 12 2011Jun 19 2012We show how minimal elements of a stopping time $\sigma$-algebra can be expressed in terms of the minimal elements of the $\sigma$-algebra of the underlying filtration. This facilitates an intuitive interpretation of stopping time $\sigma$-algebras. An ... More
Stopping times are hitting times: a natural representationDec 07 2011Jun 19 2012There exists a simple, didactically useful one-to-one relationship between stopping times and adapted c\`agl\`ad (LCRL) processes that are non-increasing and take the values 0 and 1 only. As a consequence, stopping times are always hitting times.
On Multiple and Polynomial Recurrent extensions of infinite measure preserving transformationsMar 30 2007Mar 11 2009We prove that multiple-recurrence and polynomial-recurrence of invertible infinite measure preserving transformations are both properties which pass to extensions.
A Fast Algorithm for Simulating the Chordal Schramm-Loewner EvolutionJul 29 2005Apr 24 2007The Schramm-Loewner evolution (SLE) can be simulated by dividing the time interval into N subintervals and approximating the random conformal map of the SLE by the composition of N random, but relatively simple, conformal maps. In the usual implementation ... More
Finding rational points on elliptic curves using 6-descent and 12-descentNov 23 2007We explain how recent work on 3-descent and 4-descent for elliptic curves over Q can be combined to search for generators of the Mordell-Weil group of large height. As an application we show that every elliptic curve of prime conductor in the Stein-Watkins ... More
Minimisation and reduction of 5-coverings of elliptic curvesDec 21 2011We consider models for genus one curves of degree 5, which arise in explicit 5-descent on elliptic curves. We prove a theorem on the existence of minimal models with the same invariants as the minimal model of the Jacobian elliptic curve and give an algorithm ... More
Renormalization group maps for Ising models in lattice gas variablesMay 15 2009May 27 2010Real space renormalization group maps, e.g., the majority rule transformation, map Ising type models to Ising type models on a coarser lattice. We show that each coefficient of the renormalized Hamiltonian in the lattice gas variables depends on only ... More
A primer on reflexivity and price dynamics under systemic riskJan 27 2013A simple quantitative example of a reflexive feedback process and the resulting price dynamics after an exogenous price shock to a financial network is presented. Furthermore, an outline of a theory that connects financial reflexivity, which stems from ... More
No-arbitrage pricing under cross-ownershipMay 05 2010We generalize Merton's asset valuation approach to systems of multiple financial firms where cross-ownership of equities and liabilities is present. The liabilities, which may include debts and derivatives, can be of differing seniority. We derive equations ... More
Primitive Characters and Permutation Characters of Solvable GroupsSep 09 2007Aug 10 2008Let X be an irreducible, primitive complex character of the finite solvable group G, and let X* denote the complex conjugate character. If the degree X(1) is odd, then we show how to associate to X in a unique way, a conjugacy class of subgroups U of ... More
Uniformizable and realcompact bornological universesSep 28 2009Bornological universes were introduced some time ago by Hu and obtained renewed interest in recent articles on convergence in hyperspaces and function spaces and optimization theory. One of Hu's results gives us a necessary and sufficient condition for ... More
Diffusions in random environment and ballistic behaviorSep 23 2005Sep 26 2005This article is accepted for publication in the "Annals I.H.P. Prob. & Stat.". We investigate the ballistic behavior of diffusions in random environment. We introduce conditions in the spirit of (T) and (T') of the discrete setting, cf. Sznitman \cite{szn01}, ... More
The Hessian of a genus one curveOct 12 2006Nov 30 2010We continue our development of the invariant theory of genus one curves with the aim of computing certain twists of the universal family of elliptic curves parametrised by the modular curve X(n) for n = 2,3,4,5. Our construction makes use of a covariant ... More
The invariants of a genus one curveOct 10 2006It was first pointed out by Weil that we can use classical invariant theory to compute the Jacobian of a genus one curve. The invariants required for curves of degree n = 2,3,4 were already known to the nineteenth centuary invariant theorists. We have ... More
On the Crepant Resolution Conjecture in the Local CaseOct 13 2008In this paper we analyze four examples of birational transformations between local Calabi-Yau 3-folds: two crepant resolutions, a crepant partial resolution, and a flop. We study the effect of these transformations on genus-zero Gromov-Witten invariants, ... More
Tail Invariant Measures of the Dyck ShiftJun 02 2004Nov 07 2007We show that the one-sided Dyck shift has a unique tail invariant topologically $\sigma$-finite measure (up to scaling). This invariant measure of the one sided Dyck turns out to be a shift-invariant probability. Furthermore, it is one of the two ergodic ... More
Explicit moduli spaces for congruences of elliptic curvesApr 26 2018We determine explicit birational models over Q for the modular surfaces parametrising pairs of N-congruent elliptic curves in all cases where this surface is an elliptic surface. In each case we also determine the rank of the Mordell-Weil lattice and ... More
The Euler characteristic of a category as the sum of a divergent seriesJul 05 2007The Euler characteristic of a cell complex is often thought of as the alternating sum of the number of cells of each dimension. When the complex is infinite, the sum diverges. Nevertheless, it can sometimes be evaluated; in particular, this is possible ... More
Perfect numbers and groupsApr 01 2001A number is perfect if it is the sum of its proper divisors; here we call a finite group `perfect' if its order is the sum of the orders of its proper normal subgroups. (This conflicts with standard terminology but confusion should not arise.) The notion ... More
Up-to-Homotopy MonoidsDec 10 1999Feb 22 2000Informally, a homotopy monoid is a monoid-like structure in which properties such as associativity only hold `up to homotopy' in some consistent way. This short paper comprises a rigorous definition of homotopy monoid and a brief analysis of some examples. ... More
A general theory of self-similarityOct 21 2010Nov 09 2010A little-known and highly economical characterization of the real interval [0, 1], essentially due to Freyd, states that the interval is homeomorphic to two copies of itself glued end to end, and, in a precise sense, is universal as such. Other familiar ... More
Higher Operads, Higher CategoriesMay 02 2003Higher-dimensional category theory is the study of n-categories, operads, braided monoidal categories, and other such exotic structures. It draws its inspiration from areas as diverse as topology, quantum algebra, mathematical physics, logic, and theoretical ... More
Structures in higher-dimensional category theorySep 04 2001This paper, written in 1998, aims to clarify various higher categorical structures, mostly through the theory of generalized operads and multicategories. Chapters I and II, which cover this theory and its application to give a definition of weak n-category, ... More
The triangle-free processJun 26 2008Consider the following stochastic graph process. We begin with the empty graph on n vertices and add edges one at a time, where each edge is chosen uniformly at random from the collection of potential edges that do not form triangles when added to the ... More
TASI Lectures on Holographic Space-Time, SUSY and Gravitational Effective Field TheoryJul 22 2010Sep 23 2010I argue that the conventional field theoretic notion of vacuum state is not valid in quantum gravity. The arguments use gravitational effective field theory, as well as results from string theory, particularly the AdS/CFT correspondence. Different solutions ... More
M Theory and CosmologyNov 10 1999This is a series of lectures on M Theory for cosmologists. After summarizing some of the main properties of M Theory and its dualities I show how it can be used to address various fundamental and phenomenological issues in cosmology.
Quantum Hair on D-branes and Black Hole Information in String TheoryJun 05 1996Jun 07 1996We introduce a notion of quantum hair which completely characterizes the state of a D-brane in perturbative string theory. The hair manifests itself as a phase (more generally a unitary matrix in subspaces of degenerate string eigenstates) in the scattering ... More
Numerical simulations of quasar absorbersJul 25 2005The physical state of the intergalactic medium can be probed in great detail with the intervening absorption systems seen in quasar spectra. The properties of the Hydrogen absorbers depend on many cosmological parameters, such as the matter-power spectrum, ... More
Numerical study of energy diffusion in King modelsNov 07 1995The energy diffusion coefficients D_n(E) (n=1,2) for a system of equal mass particles moving self-consistently in an N-body realisation of a King model are computed from the probability per unit time, P(E, Delta E), that a star with initial energy E will ... More
Majority Rule at Low Temperatures on the Square and Triangular LatticesMay 16 1996We consider the majority rule renormalization group transformation applied to nearest neighbor Ising models. For the square lattice with 2 by 2 blocks we prove that if the temperature is sufficiently low, then the transformation is not defined. We use ... More
Conformal Invariance and Stochastic Loewner Evolution Predictions for the 2D Self-Avoiding Walk - Monte Carlo TestsJul 25 2002Feb 05 2003Simulations of the self-avoiding walk (SAW) are performed in a half-plane and a cut-plane (the complex plane with the positive real axis removed) using the pivot algorithm. We test the conjecture of Lawler, Schramm and Werner that the scaling limit of ... More
Getting more flavour out of one-flavour QCDDec 02 2013We argue that no notion of flavour is necessary when performing amplitude calculations in perturbative QCD with massless quarks. We show this explicitly at tree-level, using a flavour recursion relation to obtain multi-flavoured QCD from one-flavour QCD. ... More
Cartesian closed 2-categories and permutation equivalence in higher-order rewritingJul 24 2013Sep 20 2013We propose a semantics for permutation equivalence in higher-order rewriting. This semantics takes place in cartesian closed 2-categories, and is proved sound and complete.
Natural coordinate descent algorithm for L1-penalised regression in generalised linear modelsMay 16 2014Aug 25 2015The problem of finding the maximum likelihood estimates for the regression coefficients in generalised linear models with an L1 sparsity penalty is shown to be equivalent to minimising the unpenalised maximum log-likelihood function over a box with boundary ... More
Full abstraction for fair testing in CCSMay 27 2013In previous work with Pous, we defined a semantics for CCS which may both be viewed as an innocent presheaf semantics and as a concurrent game semantics. It is here proved that a behavioural equivalence induced by this semantics on CCS processes is fully ... More
Full abstraction for fair testing in CCS (expanded version)Sep 29 2014Nov 02 2014In previous work with Pous, we defined a semantics for CCS which may both be viewed as an innocent form of presheaf semantics and as a concurrent form of game semantics. We define in this setting an analogue of fair testing equivalence, which we prove ... More
Proof of a new colour decomposition for QCD amplitudesSep 10 2015Nov 15 2015Recently, Johansson and Ochirov conjectured the form of a new colour decomposition for QCD tree-level amplitudes. This note provides a proof of that conjecture. The proof is based on "Mario World" Feynman diagrams, which exhibit the hierarchical Dyck ... More
On the Possibility of Large Axion Moduli SpacesSep 19 2014May 23 2015We study the diameters of axion moduli spaces, focusing primarily on type IIB compactifications on Calabi-Yau three-folds. In this case, we derive a stringent bound on the diameter in the large volume region of parameter space for Calabi-Yaus with simplicial ... More
A stability result for the union-closed size problemNov 10 2013A family of sets is called union-closed if whenever $A$ and $B$ are sets of the family, so is $A\cup B$. The long-standing union-closed conjecture states that if a family of subsets of $[n]$ is union-closed, some element appears in at least half the sets ... More
H3+ and UKIRT: a saga of discoveryApr 24 2009This paper relates the history of attempts to detect H3+ in the dense interstellar medium, from the early 1980's to the successful detection in 1996.
Affine Grassmannians in A^1-algebraic topologyJan 25 2018Let k be a field. Denote by Spc(k)_* the unstable, pointed motivic homotopy category and by Omega_Gm: Spc(k)_* \to Spc(k)_* the Gm-loops functor. For a k-group G, denote by Gr_G the affine Grassmannian of G. If k is infinite and G is split reductive, ... More
Riemann-Hilbert problems from Donaldson-Thomas theoryNov 11 2016We study a class of Riemann-Hilbert problems arising naturally in Donaldson-Thomas theory. In certain special cases we show that these problems have unique solutions which can be written explicitly as products of gamma functions. We briefly explain connections ... More
Note on a Paper by Ooguri and VafaNov 28 2016Nov 30 2016In a recent paper, Ooguri and Vafa [arXiv:1610.04564] argued that a mild extension of the Weak Gravity conjecture\cite{weakgrav} led to the conclusion that the only models of quantum gravity in AdS space with "radius large compared to the string scale" ... More
Kähler structures on spaces of framed curvesJan 11 2017We consider the space $\mathcal{M}$ of Euclidean similarity classes of framed loops in $\mathbb{R}^3$. Framed loop space is shown to be an infinite-dimensional K\"{a}hler manifold by identifying it with a complex Grassmannian. We show that the space of ... More