Results for "R. Adam"

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Tensile Strength and the Mining of Black HolesJul 13 2012There are a number of important thought experiments that involve raising and lowering boxes full of radiation in the vicinity of black hole horizons. This paper looks at the limitations placed on these thought experiments by the null energy condition, ... More
Brane tunneling and virtual brane-antibrane pairsSep 24 2007Sep 24 2017We survey barrier penetration by quantum tunneling for four cases: nonrelativistic point particles, scalar fields, relativistic point particles, and DBI branes. We examine two novel features that arise for DBI brane tunneling: the rate can sometimes increase ... More
Algorithmic Randomness For Amenable GroupsFeb 11 2018Mar 21 2018We develop the theory of algorithmic randomness for the space $A^G$ where $A$ is a finite alphabet and $G$ is a computable amenable group. We give an effective version of the Shannon-McMillan-Breiman theorem in this setting. We also extend a result of ... More
The Irreducible Subgroups of Exceptional Algebraic GroupsAug 17 2016Dec 20 2017This paper is a contribution to the study of the subgroup structure of exceptional algebraic groups over algebraically closed fields of arbitrary characteristic. Following Serre, a closed subgroup of a semisimple algebraic group $G$ is called irreducible ... More
Schwinger pair production at nonzero temperatures or in compact directionsDec 17 2015Electric fields may decay by quantum tunneling: as calculated by Schwinger, an electron-positron pair may be summoned from the vacuum. In this paper I calculate the pair-production rate at nonzero temperatures. I find that at high temperatures the decay ... More
A Holographic Dual of the Quantum InequalitiesMay 18 2016In this note, we establish the 2-D Quantum Inequalities - first proved by Flanagan - for all CFTs with a causal holographic dual. Following the treatment of Kelly \& Wall, we establish that the Boundary Causality Condition in an asymptotic AdS spacetime ... More
Liberation of specific angular momentum through radiation and scattering in relativistic black-hole accretion discsFeb 26 2015Jul 16 2015A key component of explaining the array of galaxies observed in the Universe is the feedback of active galactic nuclei, each powered by a massive black hole's accretion disc. For accretion to occur, angular momentum must be lost by that which is accreted. ... More
The decay of hot KK spaceAug 25 2014Apr 30 2015The non-perturbative instabilities of hot Kaluza-Klein spacetime are investigated. In addition to the known instability of hot space (the nucleation of 4D black holes) and the known instability of KK space (the nucleation of bubbles of nothing by quantum ... More
Boom and Bust Inflation: a Graceful Exit via Compact Extra DimensionsJul 03 2008A model of inflation is proposed in which compact extra dimensions allow a graceful exit without recourse to flat potentials or super-Planckian field values. Though bubbles of true vacuum are too sparse to uniformly reheat the Universe by colliding with ... More
Schwinger pair production at nonzero temperatures or in compact directionsDec 17 2015Jan 27 2019Electric fields may decay by quantum tunneling: as calculated by Schwinger, an electron-positron pair may be summoned from the vacuum. In this paper I calculate the pair-production rate at nonzero temperatures. I find that at high temperatures the decay ... More
The Irreducible Subgroups of Exceptional Algebraic GroupsAug 17 2016This paper is a contribution to the study of the subgroup structure of exceptional algebraic groups over algebraically closed fields of arbitrary characteristic. Following Serre, a closed subgroup of a semisimple algebraic group $G$ is called irreducible ... More
Cosmology Beyond EinsteinAug 25 2015The accelerating expansion of the Universe poses a major challenge to our understanding of fundamental physics. One promising avenue is to modify general relativity and obtain a new description of the gravitational force. Because gravitation dominates ... More
On The Strength of Two Recurrence TheoremsMay 24 2013This paper uses the framework of reverse mathematics to investigate the strength of two recurrence theorems of topological dynamics. It establishes that one of these theorems, the existence of an almost periodic point, lies strictly between WKL and ACA ... More
HyperinflationMay 08 2017Jan 01 2019A model of cosmological inflation is proposed in which field space is a hyperbolic plane. The inflaton never slow-rolls, and instead orbits the bottom of the potential, buoyed by a centrifugal force. Though initial velocities redshift away during inflation, ... More
The Thin-Wall Approximation in Vacuum Decay: a LemmaNov 21 2017Nov 26 2018The 'thin-wall approximation' gives a simple estimate of the decay rate of an unstable quantum field. Unfortunately, the approximation is uncontrolled. In this paper I show that there are actually two different thin-wall approximations and that they bracket ... More
Causality and radiatively induced CPT violationMay 03 2001May 31 2001We consider quantum electrodynamics with an additional Lorentz- and CPT-violating axial-vector term in the fermionic sector and discuss the possibility that radiative corrections induce a Lorentz- and CPT-violating Chern-Simons-like term for the gauge ... More
Singular operators with antisymmetric kernels, related capacities, and Wolff potentialsDec 13 2010We consider a generalization of the Riesz operator in $R^d$ and obtain estimates for its norm and for related capacities via the modified Wolff potential. These estimates are based on the certain version of $T1$ theorem for Calder\'on-Zygmund operators ... More
On 'Nothing'Nov 01 2011May 16 2012Nothing---the absence of spacetime---can be either an endpoint of tunneling, as in the bubble of nothing, or a starting point for tunneling, as in the quantum creation of a universe. We argue that these two tunnelings can be treated within a unified framework, ... More
Bubbles of Nothing and the Fastest Decay in the LandscapeOct 25 2010Sep 23 2011The rate and manner of vacuum decay are calculated in an explicit flux compactification, including all thick-wall and gravitational effects. For landscapes built of many units of a single flux, the fastest decay is usually to discharge just one unit. ... More
Baryogenesis in Lorentz-violating gravity theoriesMay 30 2017Lorentz-violating theories of gravity typically contain constrained vector fields. We show that the lowest-order coupling of such vectors to $\mathrm{U}(1)$-symmetric scalars can naturally give rise to baryogenesis in a manner akin to the Affleck-Dine ... More
Density-functional study of oxygen adsorption on Mo(112)Nov 15 2004Atomic oxygen adsorption on the Mo(112) surface has been investigated by means of first-principles total energy calculations. Among the variety of possible adsorption sites it was found that the bridge sites between two Mo atoms of the topmost row are ... More
Risk models for breast cancer and their validationJul 05 2019Strategies to prevent cancer and diagnose it early when it is most treatable are needed to reduce the public health burden from rising disease incidence. Risk assessment is playing an increasingly important role in targeting individuals in need of such ... More
Fe IX Calculations for the Solar Dynamics ObservatoryJul 03 2011Sep 20 2011New calculations of the energy levels, radiative transition rates and collisional excitation rates of \ion{Fe}{ix} have been carried out using the Flexible Atomic Code, paying close attention to experimentally identified levels and extending existing ... More
The Case of the Disappearing InstantonJun 02 2011Instantons are tunneling solutions that connect two vacua, and under a small change in the potential, instantons sometimes disappear. We classify these disappearances as smooth (decay rate goes to 0 at disappearance) or abrupt (decay rate not equal to ... More
Giant Leaps and Minimal Branes in Multi-Dimensional Flux LandscapesOct 25 2010Sep 14 2011There is a standard story about decay in multi-dimensional flux landscapes: that from any state, the fastest decay is to take a small step, discharging one flux unit at a time; that fluxes with the same coupling constant are interchangeable; and that ... More
The Second Law of Quantum ComplexityJan 04 2017Dec 05 2018We give arguments for the existence of a thermodynamics of quantum complexity that includes a "Second Law of Complexity". To guide us, we derive a correspondence between the computational (circuit) complexity of a quantum system of $K$ qubits, and the ... More
Singularities of Nonlinear Elliptic SystemsMay 09 2012May 07 2013Through Morrey's spaces (plus Zorko's spaces) and their potentials/capacities as well as Hausdorff contents/dimensions, this paper estimates the singular sets of nonlinear elliptic systems of the even-ordered Meyers-Elcrat type and a class of quadratic ... More
Constraints on Small-Scale Structures of Dark Matter from Flux Anomalies in Quasar Gravitational LensesJul 09 2010Sep 27 2011We investigate the statistics of flux anomalies in gravitationally lensed QSOs as a function of dark matter halo properties such as substructure content and halo ellipticity. We do this by creating a very large number of simulated lenses with finite source ... More
Wavelet-Based Scalar-on-Function Finite Mixture Regression ModelsDec 02 2013Classical finite mixture regression is useful for modeling the relationship between scalar predictors and scalar responses arising from subpopulations defined by the differing associations between those predictors and responses. Here we extend the classical ... More
The Effects of Correlations on Neutrino Opacities in Nuclear MatterJan 11 1998Including nucleon-nucleon correlations due to both Fermi statistics and nuclear forces, we have developed a general formalism for calculating the neutral-current neutrino-nucleon opacities in nuclear matter. We derive corrections to the dynamic structure ... More
Stability and Spectrum of Compactifications on Product ManifoldsOct 23 2013Dec 23 2014We study the spectrum and perturbative stability of Freund-Rubin compactifications on $M_p \times M_{Nq}$, where $M_{Nq}$ is itself a product of $N$ $q$-dimensional Einstein manifolds. The higher-dimensional action has a cosmological term $\Lambda$ and ... More
Populating the Whole LandscapeJul 31 2011Feb 19 2012Every de Sitter vacuum can transition to every other de Sitter vacuum despite any obstacle, despite intervening anti-de Sitter sinks, despite not being connected by an instanton. Eternal inflation populates the whole landscape.
Independence, Relative Randomness, and PA DegreesJul 11 2012We study pairs of reals that are mutually Martin-L\"{o}f random with respect to a common, not necessarily computable probability measure. We show that a generalized version of van Lambalgen's Theorem holds for non-computable probability measures, too. ... More
The Complexity Geometry of a Single QubitMar 29 2019The computational complexity of a quantum state quantifies how hard it is to make. `Complexity geometry', first proposed by Nielsen, is an approach to defining computational complexity using the tools of differential geometry. Here we demonstrate many ... More
Increasing the Capability of Neural Networks for Surface Reconstruction from Noisy Point CloudsNov 29 2018Dec 03 2018This paper builds upon the current methods to increase their capability and automation for 3D surface construction from noisy and potentially sparse point clouds. It presents an analysis of an artificial neural network surface regression and mapping method, ... More
Risk models for breast cancer and their validationJul 05 2019Jul 09 2019Strategies to prevent cancer and diagnose it early when it is most treatable are needed to reduce the public health burden from rising disease incidence. Risk assessment is playing an increasingly important role in targeting individuals in need of such ... More
Comment on "Vacuum Photon Splitting in Lorentz-Violating Quantum Electrodynamics"Dec 11 2003It has been argued in hep-ph/0212382 that there may be observable effects from photon triple splitting in an extended version of quantum electrodynamics with Lorentz violation in the fermion sector. The argument is based on an analogy with photon splitting ... More
An \emph{ab initio} study on split silicon-vacancy defect in diamond: electronic structure and related propertiesOct 08 2013Oct 14 2013The split silicon-vacancy defect (SiV) in diamond is an electrically and optically active color center. Recently, it has been shown that this color center is bright and can be detected at the single defect level. In addition, the SiV defect shows a non-zero ... More
Small Steps and Giant Leaps in the LandscapeApr 22 2010Oct 21 2010For landscapes of field theory vacua, we identify an effect that can greatly enhance the decay rates to wildly distant minima--so much so that such transitions may dominate over transitions to near neighbors. We exhibit these 'giant leaps' in both a toy ... More
Toward Attribute Efficient Learning AlgorithmsNov 27 2003We make progress on two important problems regarding attribute efficient learnability. First, we give an algorithm for learning decision lists of length $k$ over $n$ variables using $2^{\tilde{O}(k^{1/3})} \log n$ examples and time $n^{\tilde{O}(k^{1/3})}$. ... More
Using Kepler Candidates to Examine the Properties of Habitable Zone ExoplanetsMay 23 2016Jun 03 2016An analysis of the currently known exoplanets in the habitable zones (HZs) of their host stars is of interest in both the wake of the NASA Kepler mission and with prospects for expanding the known planet population through future ground- and space-based ... More
Superfluids and the Cosmological Constant ProblemMay 15 2018We introduce a novel method to circumvent Weinberg's no-go theorem for self-tuning the cosmological vacuum energy: a Lorentz-violating finite-temperature superfluid can counter the effects of an arbitrarily large cosmological constant. Fluctuations of ... More
Physical drivers of galaxies' cold-gas content: exploring environmental and evolutionary effects with DARK SAGEJun 22 2017Aug 16 2017We combine the latest spectrally stacked data of 21-cm emission from the ALFALFA survey with an updated version of the Dark Sage semi-analytic model to investigate the relative contributions of secular and environmental astrophysical processes on shaping ... More
The universal emergence of self-affine roughness from deformationJan 10 2019Most natural and man-made surfaces appear to be rough on many length scales. There is presently no unifying theory of the origin of roughness or the self-affine nature of surface topography. One likely contributor to the formation of roughness is deformation, ... More
The Jacobson--Morozov theorem and complete reducibility of Lie subalgebrasJul 22 2015Oct 02 2017In this paper we determine the precise extent to which the classical sl_2-theory of complex semisimple finite-dimensional Lie algebras due to Jacobson--Morozov and Kostant can be extended to positive characteristic. This builds on work of Pommerening ... More
Tack energy and switchable adhesion of liquid crystal elastomersAug 11 2012The mechanical properties of liquid crystal elastomers (LCEs) make them suitable candidates for pressure-sensitive adhesives (PSAs). Using the nematic dumbbell constitutive model, and the block model of PSAs, we study their tack energy and the debonding ... More
Hierarchical Attentive Recurrent TrackingJun 28 2017Sep 05 2017Class-agnostic object tracking is particularly difficult in cluttered environments as target specific discriminative models cannot be learned a priori. Inspired by how the human visual cortex employs spatial attention and separate "where" and "what" processing ... More
A Small-gap Effective-Temperature Model of Transient Shear Band Formation During FlowFeb 04 2015Sep 12 2016Recent Couette-cell shear experiments of carbopol gels have revealed the formation of a transient shear band before reaching the steady state, which is characterized by homogeneous flow. This shear band is observed in the small-gap limit where the shear ... More
Liquid-Fed Pulsed Plasma Thruster for Propelling NanosatellitesJun 29 2019This paper presents a novel micropropulsion system for nanosatellite applications - a liquid fed pulsed-plasma thruster (LF-PPT) comprised of a Lorentz-force pulsed plasma accelerator (PPA) and a low-energy surface flashover (LESF) igniter. A 3 {\mu}F ... More
Forward Modeling Transient Brightenings and Microflares around an Active Region Observed with Hi-CAug 22 2014Small scale flare-like brightenings around active regions are among the smallest and most fundamental of energetic transient events in the corona, providing a testbed for models of heating and active region dynamics. In a previous study, we modeled a ... More
Flux Compactifications on $(S_2)^N$Jan 28 2014We investigate a simple extra-dimensional model and its four-dimensional vacua. This model has a two-form flux and a positive cosmological constant, and the extra dimensions are compactified as the product of $N$ two-spheres. The theory is an interesting ... More
Compactifying de Sitter Naturally Selects a Small Cosmological ConstantNov 11 2013Nov 29 2014We study compactifications of $D$-dimensional de Sitter space with a $q$-form flux down to $D-Nq$ dimensions. We show that for $(N-1)(q-1)\geq 2$ there are double-exponentially or even infinitely many compact de Sitter vacua, and that their effective ... More
Sums of entire functions having only real zerosAug 12 2006Aug 05 2007We show that certain sums of products of Hermite-Biehler entire functions have only real zeros, extending results of Cardon. As applications of this theorem we construct sums of exponential functions having only real zeros, we construct polynomials having ... More
Cupping with random setsJun 07 2012We prove that a set is K-trivial if and only if it is not weakly ML-cuppable. Further, we show that a set below zero jump is K-trivial if and only if it is not ML-cuppable. These results settle a question of Ku\v{c}era, who introduced both cuppability ... More
Density, forcing, and the covering problemApr 09 2013We present a notion of forcing that can be used, in conjunction with other results, to show that there is a Martin-L\"of random set X such that X does not compute 0' and X computes every K-trivial set.
Complete Reducibility in Good CharacteristicMay 05 2015Sep 30 2016Let $G$ be a simple algebraic group of exceptional type, over an algebraically closed field of characteristic $p \ge 0$. A closed subgroup $H$ of $G$ is called $G$-completely reducible ($G$-cr) if whenever $H$ is contained in a parabolic subgroup $P$ ... More
Low temperature thermal conductivity in a d-wave superconductor with coexisting charge order: Effect of self-consistent disorder and vertex correctionsNov 01 2008Given the experimental evidence of charge order in the underdoped cuprate superconductors, we consider the effect of coexisting charge order on low-temperature thermal transport in a d-wave superconductor. Using a phenomenological Hamiltonian that describes ... More
Evolutionary Models of Super-Earths and Mini-Neptunes Incorporating Cooling and Mass LossMay 11 2015Jun 29 2015We construct models of the structural evolution of super-Earth- and mini-Neptune-type exoplanets with hydrogen-helium envelopes, incorporating radiative cooling and XUV-driven mass loss. We conduct a parameter study of these models, focusing on initial ... More
Preserving Randomness for Adaptive AlgorithmsNov 02 2016We introduce the concept of a randomness steward, a tool for saving random bits when executing a randomized estimation algorithm $\mathsf{Est}$ on many adaptively chosen inputs. For each execution, the chosen input to $\mathsf{Est}$ remains hidden from ... More
Radiation reaction at 3.5 post-Newtonian order in effective field theoryMay 17 2012We derive the radiation reaction forces on a compact binary inspiral through 3.5 order in the post-Newtonian expansion using the effective field theory approach. We utilize a recent formulation of Hamilton's variational principle that rigorously extends ... More
Structure-preserving second-order integration of relativistic charged particle trajectories in electromagnetic fieldsJan 19 2017Time-centered, hence second-order, methods for integrating the relativistic momentum of charged particles in an electromagnetic field are derived. A new method is found by averaging the momentum before use in the magnetic rotation term, and an implementation ... More
Jump operations for Borel graphsApr 08 2016We investigate the class of bipartite Borel graphs organized by the order of Borel homomorphism. We show that this class is unbounded by finding a jump operator for Borel graphs analogous to a jump operator of Louveau for Borel equivalence relations. ... More
Isomorphisms of Lattices of Bures-Closed Bimodules over Cartan MASAsMar 05 2013For i=1,2, let (M_i,D_i) be pairs consisting of a Cartan MASA D_i in a von Neumann algebra M_i, let atom(D_i) be the set of atoms of D_i, and let S_i be the lattice of Bures-closed D_i bimodules in M_i. We show that when M_i have separable preduals, there ... More
Liquid-Fed Pulsed Plasma Thruster for Propelling NanosatellitesJun 29 2019Sep 03 2019This paper presents a novel micropropulsion system for nanosatellite applications - a liquid fed pulsed-plasma thruster (LF-PPT) comprised of a Lorentz-force pulsed plasma accelerator (PPA) and a low-energy surface flashover (LESF) igniter. A 3 {\mu}F ... More
Potential Games are Necessary to Ensure Pure Nash Equilibria in Cost Sharing GamesFeb 14 2014We consider the problem of designing distribution rules to share "welfare" (cost or revenue) among individually strategic agents. There are many known distribution rules that guarantee the existence of a (pure) Nash equilibrium in this setting, e.g., ... More
Theoretical Transit Spectra for GJ 1214b and Other "Super-Earths"Mar 08 2012Aug 29 2012We present new calculations of transit spectra of super-Earths that allow for atmospheres with arbitrary proportions of common molecular species and haze. We test this method with generic spectra, reproducing the expected systematics and absorption features, ... More
The Jacobson--Morozov theorem and complete reducibility of Lie subalgebrasJul 22 2015Jun 05 2016In this paper we determine the precise extent to which the classical sl_2-theory of complex semisimple finite-dimensional Lie algebras due to Jacobson--Morozov and Kostant can be extended to positive characteristic. This builds on work of Pommerening ... More
Massive mimetic cosmologyFeb 21 2019We study the first cosmological implications of the mimetic theory of massive gravity recently proposed by Chamseddine and Mukhanov. This is a novel theory of ghost-free massive gravity which additionally contains a mimetic dark matter component. In an ... More
Discriminating between a Stochastic Gravitational Wave Background and Instrument NoiseFeb 05 2010The detection of a stochastic background of gravitational waves could significantly impact our understanding of the physical processes that shaped the early Universe. The challenge lies in separating the cosmological signal from other stochastic processes ... More
Darboux Coordinates on Coadjoint Orbits of Lie AlgebrasMar 05 1996The method of constructing spectral Darboux coordinates on finite dimensional coadjoint orbits in duals of loop algebras is applied to the one pole case, where the orbit is identified with a coadjoint orbit in the dual of a finite dimensional Lie algebra. ... More
From Bi-immunity to Absolute UndecidabilityOct 17 2012Mar 20 2013An infinite binary sequence A is absolutely undecidable if it is impossible to compute A on a set of positions of positive upper density. Absolute undecidability is a weakening of bi-immunity. Downey, Jockusch and Schupp asked whether, unlike the case ... More
Massive mimetic cosmologyFeb 21 2019May 29 2019We study the first cosmological implications of the mimetic theory of massive gravity recently proposed by Chamseddine and Mukhanov. This is a novel theory of ghost-free massive gravity which additionally contains a mimetic dark matter component. In an ... More
Global cycle properties in locally isometric graphsJun 10 2015Jan 07 2016A graph G is locally isometric if the subgraph induced by the neighbourhood of every vertex is an isometric subgraph of G. It is shown that the hamilton cycle problem for locally isometric graphs with maximum degree at most 8 is NP-complete. Structural ... More
Reducible subgroups of exceptional algebraic groupsJan 28 2018Sep 12 2018Let $G$ be a simple algebraic group over an algebraically closed field. A closed subgroup $H$ of $G$ is called $G$-completely reducible ($G$-cr) if, whenever $H$ is contained in a parabolic subgroup $P$ of $G$, it is contained in a Levi factor of $P$. ... More
Smooth Particle LensingApr 17 2006We present a numerical technique to compute the gravitational lensing induced by simulated haloes. It relies on a 2D-Tree domain decomposition in the lens plane combined with a description of N-Body particles as extended clouds with a non-singular density. ... More
Effect of coexisting order of various form and wave vector on low-temperature thermal conductivity in d-wave superconductorsAug 21 2009In light of recent experimental evidence of density wave order in the cuprates, we consider a phenomenological model of a d-wave superconductor with coexisting charge, spin or pair density wave order of various form and wave vector. We study the evolution ... More
Reducible subgroups of exceptional algebraic groupsJan 28 2018Let $G$ be a simple algebraic group over an algebraically closed field. A closed subgroup $H$ of $G$ is called $G$-completely reducible ($G$-cr) if, whenever $H$ is contained in a parabolic subgroup $P$ of $G$, it is contained in a Levi factor of $P$. ... More
Inflationary Instabilities of Einstein-Aether CosmologySep 18 2013Nov 22 2013We examine the consequences of Lorentz violation during slow-roll inflation. We consider a canonical scalar inflaton coupled, through its potential, to the divergence of a fixed-norm timelike vector field, or "aether." The vector is described by Einstein-aether ... More
Effects of Collisions with Rocky Planets on the Properties of Hot JupitersJun 25 2012Observed Hot Jupiters exhibit a wide range of physical properties. For a given mass, many planets have inflated radii, while others are surprisingly compact and may harbor large central cores. Motivated by the observational sample, this paper considers ... More
Numerical Calibration of the HCN$-$Star Formation CorrelationJan 30 2018Sep 11 2018HCN(1$-$0) emission traces dense gas and correlates very strongly with star formation rates (SFRs) on scales from small Milky Way clouds to whole galaxies. The observed correlation offers strong constraints on the efficiency of star formation in dense ... More
First detection of a virial shock with SZ data: implication for the mass accretion rate of Abell 2319Dec 15 2017Shocks produced by the accretion of infalling gas in the outskirt of galaxy clusters are expected in the hierarchical structure formation scenario, as found in cosmological hydrodynamical simulations. Here, we report the detection of a shock front at ... More
Limits to joining with generics and randomsSep 14 2012Posner and Robinson (1981) proved that if $S \subseteq \omega$ is non-computable, then there exists a $G \subseteq \omega$ such that $S \oplus G \geq_T G'$. Shore and Slaman (1999) extended this result to all $n \in \omega$, by showing that if $S \nleq_T ... More
Thermal derivation of the Coleman-De Luccia tunneling prescriptionJun 12 2007Sep 01 2007We derive the rate for transitions between de Sitter vacua by treating the field theory on the static patch as a thermal system. This reproduces the Coleman-De Luccia formalism for calculating the rate, but leads to a modified interpretation of the bounce ... More
Quantum Complexity and Negative CurvatureAug 08 2016As time passes, once simple quantum states tend to become more complex. For strongly coupled k-local Hamiltonians, this growth of computational complexity has been conjectured to follow a distinctive and universal pattern. In this paper we show that the ... More
Global cycle properties in graphs with large minimum clustering coefficientJun 11 2015Jan 07 2016The clustering coefficient of a vertex in a graph is the proportion of neighbours of the vertex that are adjacent. The minimum clustering coefficient of a graph is the smallest clustering coefficient taken over all vertices. A complete structural characterization ... More
Finite subgroups of simple algebraic groups with irreducible centralizersJun 09 2016We determine all finite subgroups of simple algebraic groups that have irreducible centralizers - that is, centralizers whose connected component does not lie in a parabolic subgroup.
On the involution fixity of exceptional groups of Lie typeJul 12 2017Mar 03 2018The involution fixity ${\rm ifix}(G)$ of a permutation group $G$ of degree $n$ is the maximum number of fixed points of an involution. In this paper we study the involution fixity of primitive almost simple exceptional groups of Lie type. We show that ... More
The static structure factor of amorphous silicon and vitreous silicaSep 14 2009Liquids are in thermal equilibrium and have a non-zero static structure factor S(Q->0) = [<N^2>-<N>^2]/<N> = rho*k_B*T*Chi_T where rho is the number density, T is the temperature, Q is the scattering vector and Chi_T is the isothermal compressibility. ... More
Linear growth of structure in massive bigravityApr 15 2014Oct 02 2014The ghost-free theory of massive gravity with two dynamical metrics has been shown to produce viable cosmological expansion, where the late-time acceleration of the Universe is due to the finite range of the gravitational interaction rather than a nonzero ... More
The nature of spacetime in bigravity: two metrics or none?Mar 31 2014Aug 13 2014The possibility of matter coupling to two metrics at once is considered. This appears natural in the most general ghost-free, bimetric theory of gravity, where it unlocks an additional symmetry with respect to the exchange of the metrics. This double ... More
A vacuum-adapted approach to quantum Feynman-Kac formulaeFeb 23 2012The vacuum-adapted formulation of quantum stochastic calculus is employed to perturb expectation semigroups via a Feynman-Kac formula. This gives an alternative perspective on the perturbation theory for quantum stochastic flows that has recently been ... More
The typical Turing degreeNov 04 2011The Turing degree of a real measures the computational difficulty of producing its binary expansion. Since Turing degrees are tailsets, it follows from Kolmogorov's 0-1 law that for any property which may or may not be satisfied by any given Turing degree, ... More
A Rate-Compatible Sphere-Packing Analysis of Feedback Coding with Limited RetransmissionsFeb 07 2012May 21 2012Recent work by Polyanskiy et al. and Chen et al. has excited new interest in using feedback to approach capacity with low latency. Polyanskiy showed that feedback identifying the first symbol at which decoding is successful allows capacity to be approached ... More
Numerical Studies of the Compressible Ising Spin GlassSep 12 2005We study a two-dimensional compressible Ising spin glass at constant volume. The spin interactions are coupled to the distance between neighboring particles in the Edwards-Anderson model with +/- J interactions. We find that the energy of a given spin ... More
A Wrinkle in Coleman - De LucciaJun 04 2007Jun 19 2007Stringy effects on vacuum transitions are shown to include surprisingly large decay rates through very high potential barriers. This simple, yet counter-intuitive result will drastically modify the measure on the landscape of string vacua.
Cooling of relativistic electron beams in chirped laser pulsesMay 18 2015The next few years will see next-generation high-power laser facilities (such as the Extreme Light Infrastructure) become operational, for which it is important to understand how interaction with intense laser pulses affects the bulk properties of a relativistic ... More
Sequential Attend, Infer, Repeat: Generative Modelling of Moving ObjectsJun 05 2018Nov 21 2018We present Sequential Attend, Infer, Repeat (SQAIR), an interpretable deep generative model for videos of moving objects. It can reliably discover and track objects throughout the sequence of frames, and can also generate future frames conditioning on ... More
Using Learned Predictions as Feedback to Improve Control and Communication with an Artificial Limb: Preliminary FindingsAug 08 2014Many people suffer from the loss of a limb. Learning to get by without an arm or hand can be very challenging, and existing prostheses do not yet fulfil the needs of individuals with amputations. One promising solution is to provide greater communication ... More
Fast localization of coalescing binaries with a heterogeneous network of advanced gravitational wave detectorsMay 07 2019We present the expected performance regarding fast sky localization of coalescing binaries with a network of three gravitational wave detectors having heterogeneous sensitivities, such as the LIGO-Virgo network. A hierarchical approach can be used in ... More