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Black Holes and Galaxy MetamorphosisApr 26 2001Supermassive black holes can be seen as an agent of galaxy transformation. In particular, a supermassive black hole can cause a triaxial galaxy to evolve toward axisymmetry by inducing chaos in centrophilic orbit families. This is one way in which a single ... More

The Discovery Potential of Space-Based Gravitational Wave AstronomyApr 02 2019A space-based interferometer operating in the previously unexplored mHz gravitational band has tremendous discovery potential. If history is any guide, the opening of a new spectral band will lead to the discovery of entirely new sources and phenomena. ... More

Intermediate-Mass Black Holes in Extragalactic Globular ClustersMar 08 2019Intermediate-mass black holes (IMBHs) have masses of about 100 to 100,000 solar masses. They remain elusive. Observing IMBHs in present-day globular clusters (GCs) would validate a formation channel for seed black holes in the early universe and inform ... More

The unique potential of extreme mass-ratio inspirals for gravitational-wave astronomyMar 08 2019The inspiral of a stellar-mass compact object into a massive ($\sim 10^{4}$-$10^{7} M_{\odot}$) black hole produces an intricate gravitational-wave signal. Due to the extreme-mass ratios involved, these systems complete $\sim 10^{4}$-$10^{5}$ orbits, ... More

Balancing the Baryon Budget: The fraction of the IGM due to Galaxy MergersMar 17 2010Observations indicate that roughly 60% of the baryons may exist in a Warm-Hot Intergalactic Medium (WHIM) at low redshifts. Following up on previous results showing that gas is released through galaxy mergers, we use a semi-analytic technique to estimate ... More

Supermassive Black Hole Binary Evolution in Axisymmetric Galaxies: the final parsec problem is not a problemFeb 07 2013During a galaxy merger, the supermassive black hole (SMBH) in each galaxy is thought to sink to the center of the potential and form a supermassive black hole binary; this binary can eject stars via 3-body scattering, bringing the SMBHs ever closer. In ... More

Numerical Simulations of Hot Halo Gas in Galaxy MergersJan 23 2009Galaxy merger simulations have explored the behaviour of gas within the galactic disk, yet the dynamics of hot gas within the galaxy halo has been neglected. We report on the results of high-resolution hydrodynamic simulations of colliding galaxies with ... More

A Full Loss Cone For Triaxial GalaxiesJan 23 2006Stars and compact objects that plunge toward a black hole are either 1) captured, emitting gravitational waves as the orbit decays, 2) tidally disrupted, leaving a disc of baryonic material, 3) scattered to a large radius, where they may thereafter avoid ... More

A First Look at Galaxy Flyby Interactions: Characterizing the Frequency of Flybys in a Cosmological ContextJun 06 2013Hierarchical structure formation theory is based on the notion that mergers drive galaxy evolution, so a considerable framework of semi-analytic models and N-body simulations has been constructed to calculate how mergers transform a growing galaxy. However, ... More

A First Look at Galaxy Flyby Interactions. II. Do Flybys matter?May 29 2015In the second paper of this series, we present results from cosmological simulations on the demographics of flyby interactions to gauge their potential impact on galaxy evolution. In a previous paper, we demonstrated that flybys -- an interaction where ... More

A First Look at Galaxy Flyby Interactions: I. Characterizing the Frequency of Flybys in a Cosmological ContextMar 09 2011May 02 2012Hierarchical structure formation theory is based on the notion that mergers drive galaxy evolution, so a considerable framework of semi-analytic models and N-body simulations has been constructed to calculate how mergers transform a growing galaxy. However, ... More

Tests of General Relativity and Fundamental Physics with Space-based Gravitational Wave DetectorsMar 07 2019Low-frequency gravitational-wave astronomy can perform precision tests of general relativity and probe fundamental physics in a regime previously inaccessible. A space-based detector will be a formidable tool to explore gravity's role in the cosmos, potentially ... More

Bar Formation from Galaxy FlybysMay 22 2014Recently, both simulations and observations have revealed that flybys - fast, one-time interactions between two galaxy halos - are surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach ... More

Bar-Induced Evolution of Dark Matter CuspsJun 18 2003The evolution of a stellar bar transforms not only the galactic disk, but also the host dark matter halo. We present high resolution, fully self-consistent N-body simulations that clearly demonstrate that dark matter halo central density cusps flatten ... More

Black Hole Growth from Cosmological N-body SimulationsMay 20 2008(Abridged) We use high resolution cosmological N-body simulations to study the growth of intermediate to supermassive black holes from redshift 49 to zero. We track the growth of black holes from the seeds of population III stars to black holes in the ... More

Ultramassive Black Hole CoalescenceMay 25 2014Although supermassive black holes (SMBHs) correlate well with their host galaxies, there is an emerging view that outliers exist. Henize 2-10, NGC 4889, and NGC1277 are examples of SMBHs at least an order of magnitude more massive than their host galaxy ... More

Classification of Stellar Orbits in Axisymmetric GalaxiesDec 05 2014It is known that two supermassive black holes (SMBHs) cannot merge in a spherical galaxy within a Hubble time; an emerging picture is that galaxy geometry, rotation, and large potential perturbations may usher the SMBH binary through the critical three-body ... More

The Role of a Massive Central Singularity in Galactic Mergers on the Survival of the Core Fundamental PlaneAug 24 1999In order for the core Fundamental Plane (cFP) to endure, small ellipticals must not survive mergers with giant ellipticals, despite the fact the small secondary galaxy can be as much as a million times more dense than the primary. However, our previous ... More

Voronoi Tessellation and Non-parametric Halo ConcentrationApr 16 2015We present and test TesseRACt, a non-parametric technique for recovering the concentration of simulated dark matter halos using Voronoi tessellation. TesseRACt is tested on idealized N-body halos that are axisymmetric, triaxial, and contain substructure ... More

Galaxy Rotation and Rapid Supermassive Black Hole Binary CoalescenceMay 22 2015During a galaxy merger, the supermassive black hole (SMBH) in each galaxy is thought to sink to the center of the potential and form a supermassive black hole binary; this binary can eject stars via 3-body scattering, bringing the SMBHs ever closer. In ... More

The Survival of The Core Fundamental Plane Against Galactic MergersNov 14 1998We have developed an effective simulation method and applied it to the problem of the accretion of very dense secondary companions by tenuous primaries. We have studied the accretion of objects of varying luminosity ratios, with sizes and densities drawn ... More

Growing Massive Black Holes in a Local Group Environment: the Central Supermassive, Slowly Sinking, and Ejected PopulationsFeb 02 2011We explore the growth of < 10^7 Msun black holes that reside at the centers of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea II (VL-2) as a framework ... More

LISA Observations of Supermassive Black Hole GrowthAug 23 2006Sep 05 2006Based on a high resolution cosmological n-body simulation, we track the hierarchical growth of black holes in galaxy clusters from z=20 to z=0. We present a census of black holes as function of redshift and will determine their mass assembly history under ... More

Interpretation of the 115 Day Periodic Modulation in the X-ray Flux of NGC 5408 X-1Oct 25 2010We comment on the recent observation of a 115-day modulation in the X-ray flux of the ultraluminous X-ray source (ULX) NGC 5408 X-1, and in particular, the interpretation of this modulation as the orbital period. We suggest that this modulation may instead ... More

Multimessenger science opportunities with mHz gravitational wavesMar 11 2019LISA will open the mHz band of gravitational waves (GWs) to the astronomy community. The strong gravity which powers the variety of GW sources in this band is also crucial in a number of important astrophysical processes at the current frontiers of astronomy. ... More

Multi-Messenger Astrophysics: Harnessing the Data RevolutionJul 12 2018The past year has witnessed discovery of the first identified counterparts to a gravitational wave transient (GW 170817A) and a very high-energy neutrino (IceCube-170922A). These source identifications, and ensuing detailed studies, have realized longstanding ... More

The Origin of Neutral Hydrogen Clouds in Nearby Galaxy Groups: Exploring the Range Of Galaxy InteractionsAug 19 2011We combine high resolution N-body simulations with deep observations of neutral hydrogen (HI) in nearby galaxy groups in order to explore two well-known theories of HI cloud formation: HI stripping by galaxy interactions and dark matter minihalos with ... More

Early Growth in a Perturbed Universe: Exploring Dark Matter Halo Populations in 2LPT and ZA SimulationsDec 15 2014We study the structure and evolution of dark matter halos from z = 300 to z = 6 for two cosmological N-body simulation initialization techniques. While the second order Lagrangian perturbation theory (2LPT) and the Zel'dovich approximation (ZA) both produce ... More

The Stellar Orbital Structure in Axisymmetric Galaxy Models with Supermassive Black Hole BinariesMay 10 2018It has been well-established that particular centrophilic orbital families in non-spherical galaxies can, in principle, drive a black hole binary to shrink its orbit through three-body scattering until the black holes are close enough to strongly emit ... More

Event Rate for Extreme Mass Ratio Burst Signals in the LISA BandFeb 20 2006Sep 22 2006Stellar mass compact objects in short period orbits about a $10^{4.5}$--$10^{7.5}$ solar mass massive black hole (MBH) are thought to be a significant continuous-wave source of gravitational radiation for the ESA/NASA Laser Interferometer Space Antenna ... More

Gravitational Wave Signal from Assembling the Lightest Supermassive Black HolesFeb 17 2010We calculate the gravitational wave signal from the growth of 10 million solar mass supermassive black holes (SMBH) from the remnants of Population III stars. The assembly of these lower mass black holes is particularly important because observing SMBHs ... More

Gravitational Wave Recoil and the Retention of Intermediate Mass Black HolesJul 09 2007During the inspiral and merger of a binary black hole, gravitational radiation is emitted anisotropically due to asymmetries in the merger configuration. This anisotropic radiation leads to a gravitational wave kick, or recoil velocity, as large as ~ ... More

Models of Cuspy Triaxial GalaxiesNov 28 2000We construct numerical models of mildly triaxial elliptical galaxies with central density cusps. Using a technique we call ``adiabatic squeezing'', we begin with a spherical gamma=1 Hernquist model and apply a drag to the velocities of the particles along ... More

HI Clouds in the M81 Filament as Dark Matter Minihalos--A Phase-Space MismatchSep 28 2010Cosmological galaxy formation models predict the existence of dark matter minihalos surrounding galaxies and in filaments connecting groups of galaxies. The more massive of these minihalos are predicted to host HI gas that should be detectable by current ... More

The Contribution of Halo White Dwarf Binaries to the LISA SignalDec 05 2007Oct 15 2008Galactic double white dwarfs were postulated as a source of confusion limited noise for LISA, the future space-based gravitational wave observatory. Until very recently, the Galactic population consisted of a relatively well studied disk population, a ... More

Expansion Techniques for Collisionless Stellar Dynamical SimulationsJun 17 2014We present GPU implementations of two fast force calculation methods, based on series expansions of the Poisson equation. One is the Self-Consistent Field (SCF) method, which is a Fourier-like expansion of the density field in some basis set; the other ... More

Supermassive Black Hole Growth and Merger Rates from Cosmological N-body SimulationsMar 20 2007Understanding how seed black holes grow into intermediate and supermassive black holes (IMBHs and SMBHs, respectively) has important implications for the duty-cycle of active galactic nuclei (AGN), galaxy evolution, and gravitational wave astronomy. Most ... More

Kickstarting Reionization with the First Black Holes: the effects of second-order perturbation theory in pre-reionization volumesNov 06 2012We explore structure formation in the dark ages ($z\sim 30-6$) using two well-known methods for initializing cosmological $N$-body simulations. Overall, both the Zel'dovich approximation (\za) and second order Lagrangian perturbation theory (\lpt) are ... More

Cyberinfrastructure Requirements to Enhance Multi-messenger AstrophysicsMar 11 2019The identification of the electromagnetic counterpart of the gravitational wave event, GW170817, and discovery of neutrinos and gamma-rays from TXS 0506+056 heralded the new era of multi-messenger astrophysics. As the number of multi-messenger events ... More

The HI environment of the M101 groupOct 31 2012Nov 27 2012We present a wide (8.5x6.7 degree, 1050x825 kpc), deep (sigma(N_HI)=10^(16.8-17.5) cm^-2) neutral hydrogen (HI) map of the M101 galaxy group. We identify two new HI sources in the group environment, one an extremely low surface brightness (and hitherto ... More

Search for Diffuse Neutral Hydrogen and HI Clouds in the NGC 2403 GroupMay 06 2009We have observed the NGC 2403 group of galaxies using the Robert C. Byrd Green Bank Telescope (GBT) in a search for faint, extended neutral hydrogen clouds similar to the clouds found around the M81/M82 group, which is located approximately 250 kpc from ... More

On the possibility of detecting ultra-short period exoplanets with LISAAug 21 2018Nov 05 2018Cunha et al. (2018) recently reexamined the possibility of detecting gravitational waves from exoplanets, claiming that three ultra-short period systems would be observable by LISA. We revisit their analysis and conclude that the currently known exoplanetary ... More

The Secondary Spin Bias of Dark Matter HaloesDec 05 2018We investigate the role of angular momentum in the clustering of dark matter haloes. We make use of data from two high-resolution N-body simulations spanning over four orders of magnitude in halo mass, from $10^{9.8}$ to $10^{14}\ h^{-1}\ \text{M}_\odot$. ... More

Relativistic Effects in Extreme Mass Ratio Gravitational Wave BurstsApr 19 2007Nov 08 2007Extreme mass ratio bursts (EMRBs) have been proposed as a possible source for future space-borne gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA). These events are characterized by long-period, nearly-radial orbits of ... More

Can a Satellite Galaxy Merger Explain the Active Past of the Galactic Center?Jul 14 2011Feb 06 2013Observations of the Galactic Center (GC) have accumulated a multitude of "forensic" evidence indicating that several million years ago the center of the Milky Way galaxy was teaming with starforming and accretion-powered activity -- this paints a rather ... More

Hypervelocity intracluster stars ejected by supermassive black hole binariesDec 13 2005Hypervelocity stars have been recently discovered in the outskirts of galaxies, such as the unbound star in the Milky Way halo, or the three anomalously fast intracluster planetary nebulae (ICPNe) in the Virgo Cluster. These may have been ejected by close ... More

Sowing black hole seeds: Direct collapse black hole formation with realistic Lyman-Werner radiation in cosmological simulationsMar 02 2018Jun 11 2018We study the birth of supermassive black holes from the direct collapse process and characterize the sites where these black hole seeds form. In the pre-reionization epoch, molecular hydrogen (H$_2$) is an efficient coolant, causing gas to fragment and ... More

Massive Black Hole Science with eLISAOct 10 2014Jan 09 2015The evolving Laser Interferometer Space Antenna (eLISA) will revolutionize our understanding of the formation and evolution of massive black holes along cosmic history by probing massive black hole binaries in the $10^3-10^7$ solar mass range out to redshift ... More

Astro2020 Decadal Science White Paper: The state of gravitational-wave astrophysics in 2020Mar 11 2019While still in its infancy, the budding field of gravitational-wave astronomy has so far exceeded most expectations, and the achievements that have already been made bode well for the decade to come. While the discoveries made possible by LIGO have captured ... More

Chandra and XMM-Newton Observations of the Abell 3391/Abell 3395 Intercluster FilamentFeb 23 2018We present Chandra and XMM-Newton X-ray observations of the Abell 3391/Abell 3395 intercluster filament. It has been suggested that the galaxy clusters Abell 3395, Abell 3391, and the galaxy group ESO-161 located between the two clusters, are in alignment ... More

The Evolution of Cuspy Triaxial Galaxies Harboring Central Black HolesNov 01 2001We use numerical simulations to study the evolution of triaxial elliptical galaxies with central black holes. In contrast to earlier numerical studies which used galaxy models with central density ``cores,'' our galaxies have steep central cusps, like ... More

Consequences of Disk Scale Height on LISA Confusion Noise from Close White Dwarf BinariesApr 06 2005Mar 04 2006Gravitational radiation from the Galactic population of close white dwarf binaries (CWDBs) is expected to produce a confusion-limited signal at the lower end of the sensitivity band of the Laser Interferometer Space Antenna (LISA). The canonical scale ... More

The Discovery Potential of Space-Based Gravitational Wave AstronomyApr 02 2019Apr 03 2019A space-based interferometer operating in the previously unexplored mHz gravitational band has tremendous discovery potential. If history is any guide, the opening of a new spectral band will lead to the discovery of entirely new sources and phenomena. ... More

Dancing in the Dark: Uncertainty in ultra-faint dwarf galaxy predictions from cosmological simulationsOct 29 2018Feb 08 2019The existence of ultra-faint dwarf (UFD) galaxies highlights the need to push our theoretical understanding of galaxies to extremely low mass. We examine the formation of UFDs by twice running a fully cosmological simulations of dwarf galaxies, but varying ... More

Effects of Inclination on Measuring Velocity Dispersion and Implications for Black HolesMay 01 2014Sep 23 2014The relation of central black hole mass and stellar spheroid velocity dispersion (the M-$\sigma$ relation) is one of the best-known and tightest correlations linking black holes and their host galaxies. There has been much scrutiny concerning the difficulty ... More

The Lives of High Redshift MergersApr 27 2012Jul 24 2012We present a comparative study of recent works on merger-timescales with dynamical friction and find a strong contrast between idealized/isolated mergers (Boylan-Kolchin et al. 2008) and mergers from a cosmological volume (Jiang et al. 2008). Our study ... More

Galaxy Rotation and Supermassive Black Hole Binary EvolutionApr 11 2017May 19 2017Supermassive black hole (SMBH) binaries residing at the core of merging galaxies are recently found to be strongly affected by the rotation of their host galaxies. The highly eccentric orbits that form when the host is counterrotating emit strong bursts ... More

Where are the Intermediate Mass Black Holes?Mar 19 2019Observational evidence has been mounting for the existence of intermediate mass black holes (IMBHs, 10^2-10^5 Msun), but observing them at all, much less constraining their masses, is very challenging. In one theorized formation channel, IMBHs are the ... More

Cosmological Hydrodynamic Simulations of Preferential Accretion in the SMBH of Milky Way Size GalaxiesOct 04 2016Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the ... More

Astro2020 Decadal Science White Paper: Gravitational Wave Survey of Galactic Ultra Compact BinariesMar 13 2019Ultra-compact binaries (UCBs) are systems containing compact or degenerate stars with orbital periods less than one hour. Tens of millions of UCBs are predicted to exist within theGalaxy emitting gravitational waves (GWs) at mHz frequencies. Combining ... More

Cosmological Hydrodynamic Simulations of Preferential Accretion in the SMBH of Milky Way Size GalaxiesOct 04 2016Jun 05 2018Using a new, high-resolution cosmological hydrodynamic simulation of a Milky Way-type (MW-type) galaxy, we explore how a merger-rich assembly history affects the mass budget of the central supermassive black hole (SMBH). We examine a MW-mass halo at the ... More

Astro2020 Science White Paper: Cosmology with a Space-Based Gravitational Wave ObservatoryMar 11 2019There are two big questions cosmologists would like to answer -- How does the Universe work, and what are its origin and destiny? A long wavelength gravitational wave detector -- with million km interferometer arms, achievable only from space -- gives ... More

Laser Interferometer Space AntennaFeb 02 2017Feb 23 2017Following the selection of The Gravitational Universe by ESA, and the successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year mission in response to ESA's call for missions for L3. The observatory will be based on three arms with ... More

Hypervelocity Star Candidates in the SEGUE G & K Dwarf SampleAug 15 2013Jan 03 2014We present 20 candidate hypervelocity stars from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) G and K dwarf samples. Previous searches for hypervelocity stars have only focused on large radial velocities; in this study we also ... More

Where are the Intermediate Mass Black Holes?Mar 19 2019Mar 22 2019Observational evidence has been mounting for the existence of intermediate mass black holes (IMBHs, 10^2-10^5 Msun), but observing them at all, much less constraining their masses, is very challenging. In one theorized formation channel, IMBHs are the ... More

Identifying High Metallicity M Giants at Intragroup Distances with SDSSFeb 09 2012Tidal stripping and three-body interactions with the central supermassive black hole may eject stars from the Milky Way. These stars would comprise a set of `intragroup' stars that trace the past history of interactions in our galactic neighborhood. Using ... More

Extraordinary transmission through a narrow slitDec 17 2018Dec 18 2018We revisit the problem of extraordinary transmission of acoustic (electromagnetic) waves through a slit in a rigid (perfectly conducting) wall. We use matched asymptotic expansions to study the pertinent limit where the slit width is small compared to ... More

Astro2020 science white paper: The gravitational wave view of massive black holesMar 16 2019Coalescing, massive black-hole (MBH) binaries are the most powerful sources of gravitational waves (GWs) in the Universe, which makes MBH science a prime focus for ongoing and upcoming GW observatories. The Laser Interferometer Space Antenna (LISA) -- ... More

Disentangling nature from nurture: tracing the origin of seed black holesApr 19 2019The origin and properties of black hole seeds that grow to produce the detected population of supermassive black holes are unconstrained at present. Despite the existence of several potentially feasible channels for the production of initial seeds in ... More

Probing Galactic Structure with the Spatial Correlation Function of SEGUE G-dwarf StarsJul 06 2015We measure the two-point correlation function of G-dwarf stars within 1-3 kpc of the Sun in multiple lines-of-sight using the Schlesinger et al. G-dwarf sample from the SDSS SEGUE survey. The shapes of the correlation functions along individual SEGUE ... More

What we can learn from multi-band observations of black hole binariesMar 10 2019The LIGO/Virgo gravitational-wave (GW) interferometers have to-date detected ten merging black hole (BH) binaries, some with masses considerably larger than had been anticipated. Stellar-mass BH binaries at the high end of the observed mass range (with ... More

Continuum Results for Light Hadronic Quantities using Domain Wall Fermions with the Iwasaki and DSDR Gauge ActionsJan 03 2012We present preliminary continuum results for light hadronic quantities obtained by the RBC/UKQCD collaboration using domain wall fermions with both the Iwasaki and the novel Dislocation Suppressing Determinant Ratio (DSDR) gauge actions. The DSDR action ... More

Measurements of $t\bar{t}$ spin correlations in CMSNov 26 2014We present an overview of the measurements of $t\bar{t}$ spin correlations in the CMS Collaboration. We present two analyses both in the dilepton channel using proton-proton collisions at $\sqrt{s}\, =\, 7$ TeV based on an integrated luminosity of 5.0 ... More

Groupoid identities common to four abelian group operationsJun 24 2009Jun 24 2009We exhibit a finite basis M for a certain variety $\mathbf{V}$ of medial groupoids. The set M consists of the medial law (xy)(zt)=(xz)(yt) and five other identities involving four variables. The variety $\mathbf{V}$ is generated by the four groupoids ... More

Vanishing of negative $K$-theory in positive characteristicDec 21 2011Dec 16 2013We show how a theorem of Gabber on alterations can be used to apply work of Cisinski, Suslin, Voevodsky, and Weibel to prove that $K_n(X)[1/p] = 0$ for $n < - \dim X$ where $X$ is a quasi-excellent noetherian scheme, $p$ is a prime that is nilpotent on ... More

Triangulated categories of motives in positive characteristicMay 23 2013Dec 05 2013This thesis presents a way to apply this theorem of Gabber to a large portion of Voevodsky's work in order to lift the assumption that resolution of singularities holds. This gives unconditional versions of many of his and others' theorems provided we ... More

Arbitrary Orientations Of Hamilton Cycles In Oriented GraphsJul 20 2009Aug 06 2009We use a randomised embedding method to prove that for all \alpha>0 any sufficiently large oriented graph G with minimum in-degree and out-degree \delta^+(G),\delta^-(G)\geq (3/8+\alpha)|G| contains every possible orientation of a Hamilton cycle. This ... More

Upper bound on the rate of adaptation in an asexual populationAug 01 2011Jul 23 2013We consider a model of asexually reproducing individuals. The birth and death rates of the individuals are affected by a fitness parameter. The rate of mutations that cause the fitnesses to change is proportional to the population size, N. The mutations ... More

Degeneracy and decomposability in abelian crossed productsSep 08 2008May 17 2010In this paper we study the relationship between degeneracy and decomposability in abelian crossed products. In particular we construct an indecomposable abelian crossed product division algebra of exponent $p$ and index $p^2$ for $p$ an odd prime. The ... More

Essential Dimension of Generic Symbols in Characteristic pMay 03 2017In this article the $p$-essential dimension of generic symbols over fields of characteristic $p$ is studied. In particular, the $p$-essential dimension of the length $\ell$ generic $p$-symbol of degree $n+1$ is bounded below by $n+\ell$ when the base ... More

Lower Bound on the Rate of Adaptation in an Asexual PopulationAug 18 2015We consider a model of asexually reproducing individuals with random mutations and selection. The rate of mutations is proportional to the population size, $N$. The mutations may be either beneficial or deleterious. In a paper by Yu, Etheridge and Cuthbertson ... More

Projective Model Structures for Exact CategoriesMar 21 2016In this article we provide sufficient conditions on weakly idempotent complete exact categories $E$ which admit an abelian embedding, such that various categories of chain complexes in $E$ are equipped with projective model structures. In particular we ... More

The PHENIX measurement of Heavy Flavor via Single Electrons in pp, d-Au, and Au-Au collisions at sqrt(s_NN)=200 GeVMar 30 2004The PHENIX experiment at RHIC has measured single electron spectra in proton-proton, deuteron-gold and gold-gold collisions at sqrt(s_NN)=200 GeV. The photonic contribution (photon conversions and Daltiz decays) is subtracted from the inclusive spectra ... More

Mean Field Theory of Thermal Energy Transport in Molecular JunctionsJan 23 2019Mean field theory is applied to nonequilibrium thermal energy transport in a model molecular junction. An approximation to the total time-dependent heat current in the junction is constructed using an ensemble of Ehrenfest trajectories, and the average ... More

The Projective Line as a MeridianMay 12 2017The purpose of the present article is to examine the essence of what has commonlybeen described as a "projective line", but which is here named a "meridian". This shall be done in several papers: this first paper devoted to the meridian itself, the second ... More

Indecomposable p-algebras and Galois subfields in generic abelian crossed productsMay 25 2007Let F be a Henselian valued field with char(F) = p and D a semi-ramified, "not strongly degenerate" p-algebra. We show that all Galois subfields of D are inertial. Using this as a tool we study generic abelian crossed product p-algebras, proving among ... More

A better comparison of cdh- and ldh-cohomologiesJun 30 2018In order to work with non-Nagata rings which are Nagata "up-to-completely-decomposed-universal-homeomorphism", specifically finite rank hensel valuation rings, we introduce the notions of pseudo-integral closure and pseudo-normalisation. We use this notion ... More

Differentiating Matrix FunctionsApr 02 2011May 19 2012Multivariable, real-valued functions induce matrix-valued functions defined on the space of d-tuples of n-times-n pairwise-commuting self-adjoint matrices. We examine the geometry of this space of matrices and conclude that the best notion of differentiation ... More

A Hierarchical Probability Model of Colon CancerMay 19 2010Dec 27 2010We consider a model of fixed size $N = 2^l$ in which there are $l$ generations of daughter cells and a stem cell. In each generation $i$ there are $2^{i-1}$ daughter cells. At each integral time unit the cells split so that the stem cell splits into a ... More

Rough path recursions and diffusion approximationsFeb 13 2014Jan 12 2016In this article, we consider diffusion approximations for a general class of stochastic recursions. Such recursions arise as models for population growth, genetics, financial securities, multiplicative time series, numerical schemes and MCMC algorithms. ... More

Crystal graphs, Tokuyama's theorem, and the Gindikin--Karpelevic formula for G_2Feb 03 2014We conjecture a deformation of the Weyl character formula for type G_2 in the spirit of Tokuyama's formula for type A. Using our conjecture we prove a combinatorial version of the Gindikin--Karpelevic formula for G_2, in the spirit of Bump--Nakasuji's ... More

Fundamental Agler DecompositionsJun 01 2012Aug 24 2012We use shift-invariant subspaces of the Hardy space on the bidisk to provide an elementary proof of the Agler Decomposition Theorem. We observe that these shift-invariant subspaces are specific cases of Hilbert spaces that can be defined from Agler decompositions ... More

Top-Quark Properties at the LHCMay 18 2016A review of recent measurements of top-quark properties is presented. Inclusive and differential top-quark pair charge asymmetry measurements using the full Run I dataset are found to be in agreement with the standard model (SM) predictions. Results of ... More

Un isomorphisme de SuslinJul 22 2014In this note we observe that we can remove the hypothesis of resolution of singularities from the isomorphism constructed by Suslin between the \'etale cohomology with compact support and Bloch's higher Chow groups over an algebraically closed field. ... More

Some observations about motivic tensor triangulated geometry over a finite fieldAug 09 2016We give a brief introduction to tensor triangulated geometry, a brief introduction to various motivic categories, and then make some observations about the conjectural structure of the tensor triangulated spectrum of the Morel-Voevodsky stable homotopy ... More

Positivity of cotangent bundlesMar 05 2008Jul 24 2008In this paper we prove a generalization of a theorem of Schneider, which gives a criterion for a projective surface over the complex numbers to have an ample cotangent bundle. After reviewing different notions of positivity, we introduce a slightly weaker ... More

A Variation on Selberg's Approximation ProblemJan 05 2014Jan 07 2014Let $\alpha\in\mathbb{C}$ in the upper half-plane and let $I$ be an interval. We construct an analogue of Selberg's majorant of the characteristic function of $I$ that vanishes at the point $\alpha$. The construction is based on the solution to an extremal ... More

Prime to p extensions of the generic abelian crossed productFeb 20 2007We prove that the noncyclic generic abelian crossed product p-algebras constructed by Amitsur and Saltman remain noncyclic after tensoring by any prime to p extension.

Astro2020 Science White Paper: The Local Relics of of Supermassive Black Hole SeedsMar 20 2019We have compelling evidence for stellar-mass black holes (BHs) of ~5-80 M_sun that form through the death of massive stars. We also have compelling evidence for so-called supermassive BHs (10^5-10^10 M_sun) that are predominantly found in the centers ... More

Multi-Messenger Astrophysics with Pulsar Timing ArraysMar 18 2019Pulsar timing arrays (PTAs) are on the verge of detecting low-frequency gravitational waves (GWs) from supermassive black hole binaries (SMBHBs). With continued observations of a large sample of millisecond pulsars, PTAs will reach this major milestone ... More