Results for "Harvey B. Richer"

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The Double Cluster G185 in M31Feb 11 1995We have identified a small globular cluster in M31 located approximately 4 arcseconds northwest of the M31 globular cluster G185. While several multiple globular clusters have been observed in the Magellanic Clouds none have been found in the Galaxy or ... More
The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)Jun 11 2003Oct 03 2003We continue our study of rich Galactic clusters by presenting deep CCD observations of both NGC 2168 (M35) and NGC 2323 (M50). Both clusters are found to be rich (NGC 2168 contains at least 1000 stars brighter than V = 22 and NGC 2323 contains approximately ... More
Star clusters as laboratories for stellar and dynamical evolutionNov 04 2009Open and globular star clusters have served as benchmarks for the study of stellar evolution due to their supposed nature as simple stellar populations of the same age and metallicity. After a brief review of some of the pioneering work that established ... More
The Initial Mass Function: Now and ThenNov 22 1996We examine whether existing data in clusters, both old and young, and in the field of the Galactic disk and halo is consistent with a universal slope for the initial mass function (IMF). The most reasonable statement that can be made at the current time ... More
A new method for suppressing excited-state contaminations on the nucleon form factorsNov 08 2018One of the most challenging tasks in lattice calculations of baryon form factors is the analysis and control of excited-state contaminations. Taking the isovector axial form factors of the nucleon as an example, both a dispersive representation and a ... More
Lattice calculation of the pion transition form factor $π^0 \to γ^* γ^*$Jul 27 2016Dec 15 2016We calculate the $\pi^0\to \gamma^*\gamma^*$ transition form factor ${\cal F}_{\pi^0\gamma^*\gamma^*}(q_1^2,q_2^2)$ in lattice QCD with two flavors of quarks. Our main motivation is to provide the input to calculate the $\pi^0$-pole contribution to hadronic ... More
Non-perturbative renormalization and O$(a)$-improvement of the non-singlet vector current with $N_{\mathrm{f}}=2+1$ Wilson fermions and tree-level Symanzik improved gauge actionNov 20 2018Feb 19 2019In calculating hadronic contributions to precision observables for tests of the Standard Model in lattice QCD, the electromagnetic current plays a central role. Using a Wilson action with O($a$) improvement in QCD with $N_{\mathrm{f}}$ flavors, a counterterm ... More
Lattice calculation of the pion transition form factor $π^0 \to γ^* γ^*$Nov 07 2016Dec 06 2016We calculate the pion transition form factor ${\cal F}_{\pi^0\gamma^*\gamma^*}(q_1^2,q_2^2)$, which describe the interaction of an on-shell pion with two off-shell photons, using lattice QCD simulations with two degenerate flavors of dynamical quarks. ... More
Lattice calculation of the pion transition form factor with $N_f=2+1$ Wilson quarksMar 22 2019We present a lattice QCD calculation of the double-virtual neutral pion transition form factor, with the goal to cover the kinematic range relevant to hadronic light-by-light scattering in the muon $g-2$. Several improvements have been made compared to ... More
A Glimpse into the Past: The Recent Evolution of Globular ClustersJun 30 2008We present the serendipitous discovery of 195 extragalactic globular clusters (GCs) in one of the deepest optical images ever obtained, a 126 orbit HST/ACS imaging study of the nearby Galactic GC NGC 6397. The distant GCs are all found surrounding a bright ... More
Counting Pairs of Faint GalaxiesJun 07 1995The number of close pairs of galaxies observed to faint magnitude limits, when compared to nearby samples, determines the interaction or merger rate as a function of redshift. The prevalence of mergers at intermediate redshifts is fundamental to understanding ... More
Deep HST V- and I-Band Observations of Two Globular Clusters in the Halo of M31Aug 25 1997We present deep (V ~= 27) V- and I-band stellar photometry of G302 and G312, two globular star clusters in the halo of M31. These data were obtained using the Hubble Space Telescope's Wide Field/Planetary Camera 2. We find iron abundances of [Fe/H] = ... More
The Pulsar-White Dwarf-Planet System in Messier 4: Improved AstrometrySep 17 2003A young and undermassive white dwarf has been identified as the possible companion to the millisecond pulsar PSR B1620-26 in Messier 4. This association is important as it then helps constrain the mass of the third body in the system to be of order a ... More
The White Dwarf Cooling Age of M67Jun 12 1998Jul 22 1998A deep imaging survey covering the entire $23\arcmin$ diameter of the old open cluster M67 to $V = 25$ has been carried out using the mosaic imager (UHCam) on the Canada-France-Hawaii Telescope. The cluster color-magnitude diagram (CMD) can be traced ... More
Deep HST V- and I-Band Observations of the Halo of M31: Evidence for Multiple Stellar PopulationsJun 13 1996We present deep V & I WFPC2 photometry in two fields in the M31 halo 32' and 50' from the center of M31 along the SE minor axis at the locations of the M31 GCs G302 and G312 respectively. The M31 halo LFs are not consistent with a single high-metallicity ... More
The white dwarf cooling sequence in the old open cluster NGC 188Jun 12 2002We develop the white dwarf luminosity function (LF) of the old open cluster NGC 188 in order to determine a lower limit to the age of the cluster by using the faint end of the cooling sequence. To produce an extensive sequence of the cooling white dwarfs ... More
Exploratory studies for the position-space approach to hadronic light-by-light scattering in the muon $g-2$Nov 07 2017The well-known discrepancy in the muon $g-2$ between experiment and theory demands further theory investigations in view of the upcoming new experiments. One of the leading uncertainties lies in the hadronic light-by-light scattering contribution (HLbL), ... More
Hadronic light-by-light scattering in the anomalous magnetic moment of the muonNov 20 2018Hadronic light-by-light scattering in the anomalous magnetic moment of the muon $a_\mu$ is one of two hadronic effects limiting the precision of the Standard Model prediction for this precision observable, and hence the new-physics discovery potential ... More
The leading hadronic contribution to the running of the Weinberg angle using covariant coordinate-space methodsNov 21 2018We present a preliminary study of the leading hadronic contribution to the running of the Weinberg angle $\theta_{\mathrm{W}}$. The running is extracted from the correlation function of the electromagnetic current with the vector part of the weak neutral ... More
Globular Clusters in NGC 1275May 07 1996We present the results of a deep photometric study of the outer halo of NGC 1275, the highly active cD galaxy at the center of the Perseus cluster. We find a modest excess of faint ($R > 22.5$) starlike objects in its halo, indicating a population of ... More
A Measurement of Diffusion in 47 TucanaeFeb 06 2015Feb 20 2015Using images from the Hubble Space Telescope Wide-Field Camera 3, we measure the rate of diffusion of stars through the core of the globular cluster 47 Tucanae using a sample of young white dwarfs identified in these observations. This is the first direct ... More
The Spectral Types of White Dwarfs in Messier 4Sep 11 2009We present the spectra of 24 white dwarfs in the direction of the globular cluster Messier 4 obtained with the Keck/LRIS and Gemini/GMOS spectrographs. Determining the spectral types of the stars in this sample, we find 24 type DA and 0 type DB (i.e., ... More
When do stars in 47 Tucanae lose their mass?Feb 25 2015Aug 05 2015By examining the diffusion of young white dwarfs through the core of the globular cluster 47 Tucanae, we estimate the time when the progenitor star lost the bulk of its mass to become a white dwarf. According to stellar evolution models of the white-dwarf ... More
A Young White Dwarf Companion to Pulsar 1620-26: Evidence for Early Planet FormationJul 18 2003The pulsar B1620-26 has two companions, one of stellar mass and one of planetary mass. We detected the stellar companion using Hubble Space Telescope observations. The color and magnitude of the stellar companion indicate that it is an undermassive white ... More
A Massive Magnetic Helium Atmosphere White Dwarf Binary in a Young Star ClusterJun 11 2019We have searched the Gaia DR2 catalogue for previously unknown hot white dwarfs in the direction of young open star clusters. The aim of this experiment was to try and extend the initial-final mass relation (IFMR) to somewhat higher masses, potentially ... More
The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 ClustersAug 16 2010Aug 27 2010We present new measurements of the centers for 65 Milky Way globular clusters. Centers were determined by fitting ellipses to the density distribution within the inner $2\arcmin$ of the cluster center, and averaging the centers of these ellipses. The ... More
The Dearth of Massive, Helium-Rich White Dwarfs in Young Open Star ClustersSep 07 2004Dec 07 2004Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster's total WD population. The mean derived mass of the sample is 0.8 Msun - ... More
Isochrones and Luminosity Functions for Old White DwarfsAug 31 1999Using a new grid of models of cooling white dwarfs, we calculate isochrones and luminosity functions in the Johnson-Kron/Cousins and HST filter sets for systems containing old white dwarfs. These new models incorporate a non-grey atmosphere which is necessary ... More
The Dynamical Effects of White Dwarf Birth Kicks in Globular Star ClustersFeb 06 2009Mar 02 2009Recent observations of the white dwarf (WD) populations in the Galactic globular cluster NGC 6397 suggest that WDs receive a kick of a few km/s shortly before they are born. Using our Monte Carlo cluster evolution code, which includes accurate treatments ... More
Faint, moving objects in the Hubble Deep Field: components of the dark halo?Aug 24 1999The deepest optical image of the sky, the Hubble Deep Field (HDF), obtained with the Hubble Space Telescope (HST) in December 1995, has been compared to a similar image taken in December 1997. Two very faint, blue, isolated and unresolved objects are ... More
Orbifold finiteness under geometric and spectral constraintsJan 03 2014May 12 2015The class of Riemannian orbifolds of dimension n defined by a lower bound on the sectional curvature and the volume and an upper bound on the diameter has only finitely many members up to orbifold homeomorphism. Furthermore, any class of isospectral Riemannian ... More
Measuring the Gain of a Micro-Channel Plate/Phosphor Assembly Using a Convolutional Neural NetworkJun 13 2019This paper presents a technique to measure the gain of a single-plate micro-channel plate (MCP)/phosphor assembly by using a convolutional neural network to analyse images of the phosphor screen, recorded by a charge coupled device. The neural network ... More
The JCMT Gould Belt Survey: A First Look at the Auriga-California Molecular Cloud with SCUBA-2Jan 24 2018We present 850 and 450 micron observations of the dense regions within the Auriga-California molecular cloud using SCUBA-2 as part of the JCMT Gould Belt Legacy Survey to identify candidate protostellar objects, measure the masses of their circumstellar ... More
Hadronic light-by-light scattering amplitudes from lattice QCD versus dispersive sum rulesDec 01 2017The hadronic contribution to the eight forward amplitudes of light-by-light scattering ($\gamma^*\gamma^*\to \gamma^*\gamma^*$) is computed in lattice QCD. Via dispersive sum rules, the amplitudes are compared to a model of the $\gamma^*\gamma^*\to {\rm ... More
Light-by-light forward scattering amplitudes in Lattice QCDOct 25 2017We present our preliminary results on the calculation of hadronic light-by-light forward scattering amplitudes using vector four-point correlation functions computed on the lattice. Using a dispersive approach, forward scattering amplitudes can be described ... More
Quantifying mass segregation and new core radii for 54 milky way globular clustersAug 16 2013We present core radii for 54 Milky Way globular clusters determined by fitting King-Michie models to cumulative projected star count distributions. We find that fitting star counts rather than surface brightness profiles produces results that differ significantly ... More
The Initial-Final Mass Relation: Direct Constraints at the Low Mass EndJun 27 2007Oct 16 2007The initial-final mass relation represents a mapping between the mass of a white dwarf remnant and the mass that the hydrogen burning main-sequence star that created it once had. The relation thus far has been constrained using a sample of ~40 stars in ... More
On the Radial Distribution of White Dwarfs in the Globular Cluster NGC 6397Sep 26 2007We have examined the radial distribution of white dwarfs over a single HST/ACS field in the nearby globular cluster NGC 6397. In relaxed populations, such as in a globular cluster, stellar velocity dispersion, and hence radial distribution, is directly ... More
Proper Motions and Internal Dynamics in the Core of the Globular Cluster M71Mar 23 2012We have used Gemini North together with the NIRI-ALTAIR adaptive optics imager in the H and K bands to explore the core of the Galactic globular cluster M71 (NGC 6838). We obtained proper motions for 217 stars and have resolved its internal proper motion ... More
The CFHT Open Star Cluster Survey. III. The White Dwarf Cooling Age of the Rich Open Star Cluster NGC 2099 (M37)Sep 21 2001We present deep CCD photometry of the very rich, intermediate aged (similar to the Hyades) open star cluster NGC 2099 (M37). The V, B-V color-magnitude diagram (CMD) for the cluster shows an extremely well populated and very tightly constrained main-sequence ... More
The Masses of Population II White DwarfsSep 11 2009Globular star clusters are among the first stellar populations to have formed in the Milky Way, and thus only a small sliver of their initial spectrum of stellar types are still burning hydrogen on the main-sequence today. Almost all of the stars born ... More
Hadronic light-by-light scattering contribution to the muon g-2 on the latticeJan 12 2018We briefly review several activities at Mainz related to hadronic light-by-light scattering (HLbL) using lattice QCD. First we present a position-space approach to the HLbL contribution in the muon g-2, where we focus on exploratory studies of the pion-pole ... More
Temperatures of dust and gas in S~140Apr 20 2015In dense parts of interstellar clouds (> 10^5 cm^-3), dust & gas are expected to be in thermal equilibrium, being coupled via collisions. However, previous studies have shown that the temperatures of the dust & gas may remain decoupled even at higher ... More
The leading hadronic contribution to $(g-2)_μ$ from lattice QCD with $N_{\rm f}=2+1$ flavours of O($a$) improved Wilson quarksApr 05 2019The comparison of the theoretical and experimental determinations of the anomalous magnetic moment of the muon $(g-2)_\mu$ constitutes one of the strongest tests of the Standard Model at low energies. In this article, we compute the leading hadronic contribution ... More
The properties of SCUBA cores in the Perseus molecular cloud: the bias of clump-finding algorithmsOct 21 2009We present a new analysis of the properties of star-forming cores in the Perseus molecular cloud, identified in SCUBA 850 micron data. Our goal is to determine which core properties can be robustly identified and which depend on the extraction technique. ... More
The chemical composition of planetary nebulae and HII regions in NGC 3109Sep 27 2007Oct 09 2007We present deep spectrophotometry for a sample of 8 PNe and 12 HII regions in the irregular galaxy NGC 3109, to analyze the chemical composition of both types of nebulae. We present line intensities and the physical conditions and the abundances of He, ... More
Alternative Visual Units for an Optimized Phoneme-Based Lipreading SystemSep 16 2019Lipreading is understanding speech from observed lip movements. An observed series of lip motions is an ordered sequence of visual lip gestures. These gestures are commonly known, but as yet are not formally defined, as `visemes'. In this article, we ... More
The White Dwarf Cooling Sequence of the Globular Cluster Messier 4May 06 2002We present the white dwarf sequence of the globular cluster M4, based on a 123 orbit Hubble Space Telescope exposure, with limiting magnitude V = 30, I = 28. The white dwarf luminosity function rises sharply for I >25.5, consistent with the behaviour ... More
HST Photometry of the Globular Cluster M4May 14 1998This paper presents a detailed description of the acquisition and processing of a large body of imaging data for three fields in the globular cluster M4 taken with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. Analysis with ... More
A Deep HST Study of the Globular Cluster NGC 6397: Reduction MethodsMar 05 2008We describe here the reduction methods that we developed to study the faintest red dwarfs and white dwarfs in an outer field of NGC6397, which was observed by \hst for 126 orbits in 2005. The particular challenge of this data set is that the faintest ... More
Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low Mass White DwarfsMay 07 2007Oct 04 2007We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H] ~ 0.4) open clusters in our Galaxy, ... More
Formation and Evolution of Blue Stragglers in 47 TucanaeSep 07 2016Blue stragglers (BSS) are stars whose position in the Color-Magnitude Diagram (CMD) places them above the main sequence turn-off (TO) point of a star cluster. Using data from the core of 47 Tuc in the ultraviolet (UV), we have identified various stellar ... More
Dynamical estimate of post main sequence stellar masses in 47 TucanaeMay 18 2016We use the effects of mass segregation on the radial distribution of different stellar populations in the core of 47 Tucanae to find estimates for the masses of stars at different post main sequence evolutionary stages. We take samples of main sequence ... More
Distances to the globular clusters 47 Tucanae and NGC 362 using Gaia DR2 parallaxesJul 18 2018Sep 10 2018Using parallaxes from Gaia DR2, we estimate the distance to the globular clusters 47 Tuc and NGC 362, taking advantage of the background stars in the Small Magellanic Cloud and quasars to account for various parallax systematics. We found the parallax ... More
Globular cluster absolute ages from cooling brown dwarfsFeb 01 2017Globular clusters are the oldest conglomerates of stars in our Galaxy and can be useful laboratories to test theories from stellar evolution to cosmology. In this paper, we present a new method to estimate the absolute age of a globular cluster from observations ... More
The CFHT Open Star Cluster Survey II -- Deep CCD Photometry of the Old Open Star Cluster NGC 6819Apr 10 2001Jul 19 2001We present analysis of deep CCD photometry for the very rich, old open star cluster NGC 6819. These CFH12K data results represent the first of nineteen open star clusters which were imaged as a part of the CFHT Open Star Cluster Survey. We find a tight, ... More
Comparing the White Dwarf Cooling Sequences in 47 Tuc and NGC 6397Oct 01 2013Using deep Hubble Space Telescope imaging, color-magnitude diagrams are constructed for the globular clusters 47 Tuc and NGC 6397. As expected, because of its lower metal abundance, the main sequence of NGC 6397 lies well to the blue of that of 47 Tuc. ... More
Ultra-Deep Hubble Space Telescope Imaging of the Small Magellanic Cloud: The Initial Mass Function of Stars with M <~ 1 MsunDec 05 2012Dec 31 2012We present a new measurement of the stellar initial mass function (IMF) based on ultra-deep, high-resolution photometry of >5,000 stars in the outskirts of the Small Magellanic Cloud (SMC) galaxy. The Hubble Space Telescope (HST) Advanced Camera for Surveys ... More
A Dynamical Signature of Multiple Stellar Populations in 47 TucanaeJun 05 2013Based on the width of its main sequence, and an actual observed split when viewed through particular filters, it is widely accepted that 47 Tucanae contains multiple stellar populations. In this contribution, we divide the main-sequence of 47 Tuc into ... More
The CFHT Open Star Cluster Survey I -- Cluster Selection and Data ReductionApr 10 2001Jul 19 2001We present this paper in conjuction with the following as the first results in the CFHT Open Star Cluster Survey. This survey is a large BVR imaging data set of 19 open star clusters in our Galaxy. This data set was taken with the CFH12K mosaic CCD (42' ... More
The Initial-Final Mass Relationship: Spectroscopy of White Dwarfs in NGC 2099 (M37)Sep 07 2004Dec 07 2004We present new observations of very faint white dwarfs (WDs) in the rich open star cluster NGC 2099 (M37). Following deep, wide field imaging of the cluster using CFHT, we have now obtained spectroscopic observations of candidate WDs using both GMOS on ... More
JEDI-net: a jet identification algorithm based on interaction networksAug 14 2019Sep 10 2019We investigate the performance of a jet identification algorithm based on interaction networks (JEDI-net) to identify all-hadronic decays of high-momentum heavy particles produced at the LHC and distinguish them from ordinary jets originating from the ... More
Anomaly Inflow for Gauge DefectsOct 06 1993Topological defects constructed out of scalar fields and possessing chiral fermion zero modes are known to exhibit an anomaly inflow mechanism which cancels the anomaly in the effective theory of the zero modes through an inflow of current from the space ... More
Recurrent Transition Networks for Character LocomotionOct 04 2018Jan 17 2019Manually authoring transition animations for a complete locomotion system can be a tedious and time-consuming task, especially for large games that allow complex and constrained locomotion movements, where the number of transitions grows exponentially ... More
Chemical Mapping of the Milky Way With The Canada-France Imaging Survey: A Non-parametric Metallicity-Distance Decomposition of the GalaxyAug 21 2017We present the chemical distribution of the Milky Way, based on 2,900$\, {\rm deg^2}$ of $u$-band photometry taken as part of the Canada-France Imaging Survey. When complete, this survey will cover 10,000$\, {\rm deg^2}$ of the Northern sky. By combing ... More
Solving the measurement problem: de Broglie-Bohm loses out to EverettMar 12 2004The quantum theory of de Broglie and Bohm solves the measurement problem, but the hypothetical corpuscles play no role in the argument. The solution finds a more natural home in the Everett interpretation.
Computing Hasse-Witt matrices of hyperelliptic curves in average polynomial timeFeb 13 2014We present an efficient algorithm to compute the Hasse-Witt matrix of a hyperelliptic curve C/Q modulo all primes of good reduction up to a given bound N, based on the average polynomial-time algorithm recently introduced by Harvey. An implementation ... More
Computing Hasse-Witt matrices of hyperelliptic curves in average polynomial time, IIOct 20 2014We present an algorithm that computes the Hasse-Witt matrix of given hyperelliptic curve over Q at all primes of good reduction up to a given bound N. It is simpler and faster than the previous algorithm developed by the authors.
The Lower Main Sequence and Mass Function of the Globular Cluster Messier 4May 06 2002Jul 11 2002The deepest optical image ever in a globular star cluster, a Hubble Space Telescope (HST) 123 orbit exposure in a single field of Messier 4, was obtained in 2 filters (F606W, F814W) over a 10 week period in early 2001. A somewhat shallower image obtained ... More
Probing the Faintest Stars in a Globular Star ClusterFeb 07 2007NGC 6397 is the second closest globular star cluster to the Sun. Using 5 days of time on the Hubble Space Telescope, we have constructed the deepest ever color-magnitude diagram for this cluster. We see a clear truncation in each of its two major stellar ... More
Ages for Globular Clusters in the Outer Galactic Halo: The Second Parameter Clusters Palomar~3, Palomar~4 and EridanusSep 14 1998We have used the WFPC2 camera on the Hubble Space Telescope to obtain photometry of the outer-halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the "second parameter" anomaly because of their red horizontal-branch ... More
The White Dwarf Cooling Sequence of NGC6397Jan 25 2007Feb 20 2007We present the results of a deep Hubble Space Telescope (HST) exposure of the nearby globular cluster NGC6397, focussing attention on the cluster's white dwarf cooling sequence. This sequence is shown to extend over 5 magnitudes in depth, with an apparent ... More
The Galactic Inner Halo: Searching for White Dwarfs and Measuring the Fundamental Galactic Constant, Vo/RoApr 01 2003Oct 03 2003We establish an extragalactic, zero-motion frame of reference within the deepest optical image of a globular star cluster, an HST 123-orbit exposure of M4 (GO 8679, cycle 9). The line of sight beyond M4 (l,b (deg) = 351,16) intersects the inner halo (spheroid) ... More
The errant life of a heavy quark in the quark-gluon plasmaDec 01 2010Feb 27 2011In the high-temperature phase of QCD, the heavy quark momentum diffusion constant determines, via a fluctuation-dissipation relation, how fast a heavy quark kinetically equilibrates. This transport coefficient can be extracted from thermal correlators ... More
Moments of GPDs and transverse-momentum dependent PDFs from the latticeAug 06 2010I review lattice-QCD calculations of the electromagnetic and generalized form factors (GFFs), which determine the transverse structure of the nucleon, and briefly comment on recent calculations related to transverse-momentum dependent parton distribution ... More
A calculation of the bulk viscosity in SU(3) gluodynamicsOct 19 2007We perform a lattice Monte-Carlo calculation of the trace-anomaly two-point function at finite temperature in the SU(3) gauge theory. We obtain the long-distance properties of the correlator in the continuum limit and extract the bulk viscosity zeta via ... More
Lattice QCD and the two-photon decay of the neutral pionMar 01 2013Two-photon decays probe the structure of mesons and represent an important contribution to hadronic light-by-light scattering. For the neutral pion, the decay amplitude tests the effects of the chiral anomaly; for a heavy quarkonium state, it measures ... More
Age Gradient and the Second Parameter Problem in the Galactic HaloJan 12 1996We establish a framework for determing absolute ages of Galactic globular clusters and then use these ages to investigate the age-metallicity and age-Galactocentric distance relations for the 36 clusters with the most reliable age data. The clusters span ... More
Hubble Space Telescope Observations of White Dwarfs in the Globular Cluster M4Jul 26 1995With the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope, we have discovered in M4 (NGC 6121, C 1620-264) the first extensive sequence of cooling white dwarfs seen in a globular cluster. Adopting a distance modulus of (m-M)_V = 12.65 ... More
White Dwarfs in Globular Clusters: HST Observations of M4Feb 19 1997Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258 white dwarfs (WDs) in the Galactic globular cluster M4. Fields at three radial distances from the cluster center were observed and sizeable WD populations were found in all three. ... More
A Deep, Wide-Field, and Panchromatic View of 47 Tuc and the SMC with HST: Observations and Data Analysis MethodsDec 06 2011In HST Cycle 17, we imaged the well known globular star cluster 47 Tucanae for 121 orbits using ACS and both the UVIS and IR channels of WFC3 (GO-11677, PI - H. Richer). This unique data set was obtained to address many scientific questions that demand ... More
Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD PerspectiveApr 19 2011Jun 09 2011Transport properties of a thermal medium determine how its conserved charge densities (for instance the electric charge, energy or momentum) evolve as a function of time and eventually relax back to their equilibrium values. Here the transport properties ... More
High-Precision Thermodynamics and Hagedorn Density of StatesMay 26 2009We compute the entropy density of the confined phase of QCD without quarks on the lattice to very high accuracy. The results are compared to the entropy density of free glueballs, where we include all the known glueball states below the two-particle threshold. ... More
Finite Temperature Sum Rules in Lattice Gauge TheoryNov 05 2007We derive non-perturbative sum rules in SU($N$) lattice gauge theory at finite temperature. They relate the susceptibilities of the trace anomaly and energy-momentum tensor to temperature derivatives of the thermodynamic potentials. Two of them have been ... More
Glueball Regge TrajectoriesAug 02 2005We investigate the spectrum of glueballs in 3D and 4D SU(N) gauge theories. Our motivation is to determine whether the states lie on straight Regge trajectories. To this end we develop new lattice techniques to reliably determine the states carrying higher ... More
Locality and Statistical Error Reduction on Correlation FunctionsSep 20 2002Feb 26 2003We propose a multilevel Monte-Carlo scheme, applicable to local actions, which is expected to reduce statistical errors on correlation functions. We give general arguments to show how the efficiency and parameters of the algorithm are determined by the ... More
QCD at non-zero temperature from the latticeDec 21 2015I review the status of lattice QCD calculations at non-zero temperature. After summarizing what is known about the equilibrium properties of strongly interacting matter, I discuss in more detail recent results concerning the quark-mass dependence of the ... More
Lattice QCD and the Timelike Pion Form FactorMay 10 2011Apr 03 2012We present a formula that allows one to calculate the pion form factor in the timelike region 2mpi <= sqrt{s} <= 4mpi in lattice QCD. The form factor quantifies the contribution of two-pion states to the vacuum polarization. It must be known very accurately ... More
The spectrum of SU(N) gauge theories in finite volumeDec 13 2004Apr 26 2005We compute the spatial-volume dependence of the spectrum of 4D SU(3 <= N <= 6) gauge theories by lattice Monte-Carlo techniques. Setting the scale with the string tension, the spatial volume is L^3 with 0.78fm <= L <= 2.3fm. The Euclidean `time' direction ... More
Lorentz-covariant coordinate-space representation of the leading hadronic contribution to the anomalous magnetic moment of the muonJun 04 2017We present a Lorentz-covariant, Euclidean coordinate-space expression for the hadronic vacuum polarisation, the Adler function and the leading hadronic contribution to the anomalous magnetic moment of the muon. The representation offers a lot of flexibility ... More
Hadron Structure on the LatticeJun 16 2011A few chosen nucleon properties are described from a lattice QCD perspective: the nucleon sigma term and the scalar strangeness in the nucleon; the vector form factors in the nucleon, including the vector strangeness contribution, as well as parity breaking ... More
The transverse structure of the QCD stringAug 06 2010The characterization of the transverse structure of the QCD string is discussed. We formulate a conjecture as to how the stress-energy tensor of the underlying gauge theory couples to the string degrees of freedom. A consequence of the conjecture is that ... More
Density, short-range order and the quark-gluon plasmaAug 14 2008We study the thermal part of the energy density spatial correlator in the quark-gluon plasma. We describe its qualitative form at high temperatures. We then calculate it out to distances approx. 1.5/T in SU(3) gauge theory lattice simulations for the ... More
Energy-momentum tensor correlators and spectral functionsJun 24 2008We calculate the thermal Euclidean correlators and the spectral functions of the energy-momentum tensor for pure gauge theories, including at non-zero spatial momentum, at leading order in perturbation theory. Our goal is to improve the extraction of ... More
Glueballs and the Pomeron -- a Lattice StudyOct 04 2005We perform lattice calculations of the lightest J=0,2,4,6 glueball masses in the D=3+1 SU(3) gauge theory and extrapolate to the continuum limit. Assuming that these masses lie on linear Regge trajectories we find a leading glueball trajectory alpha(t) ... More
Vortices on the worldsheet of the QCD stringJun 03 2005We investigate the properties of the QCD string in the Euclidean SU(N) pure gauge theory when the space-time dimensions transverse to it are periodic. From the point of view of an effective string theory, the string tension $\sigma$ and the low-energy ... More
The Spectral Energy Distributions of White Dwarfs in 47 Tucanae: The Distance to the ClusterDec 06 2011We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs to pure hydrogen atmosphere white dwarf models. Our photometric dataset is obtained from a 121 orbit Hubble ... More
Lattice Gauge Theory Sum Rule for the Shear ChannelMay 15 2010An exact expression is derived for the $(\omega,p)=0$ thermal correlator of shear stress in SU($N_c$) lattice gauge theory. I remove a logarithmic divergence by taking a suitable linear combination of the shear correlator and the correlator of the energy ... More
Finite Volume Effects in Thermal Field TheoryMay 11 2009We analyze the effect of a finite volume on the thermodynamic potentials of a relativistic quantum field theory defined on a hypertorus at vanishing chemical potential. Using the symmetries of the Euclidean partition function, we interpret the thermodynamic ... More
Glueball matrix elements: a lattice calculation and applicationsAug 22 2008We compute the matrix elements of the energy-momentum tensor between glueball states and the vacuum in SU(3) lattice gauge theory and extrapolate them to the continuum. These matrix elements may play an important phenomenological role in identifying glue-rich ... More