Results for "Michael McDonald"

total 35254took 0.14s
Optical Line Emission in Brightest Cluster Galaxies at 0 < z < 0.6: Evidence for a Lack of Strong Cool Cores 3.5 Gyr Ago?Oct 26 2011In recent years the number of known galaxy clusters beyond z > 0.2 has increased drastically, with the release of multiple catalogs containing >30,000 optically-detected galaxy clusters over the range 0 < z < 0.6. Combining these catalogs with the availability ... More
Stellar Populations and Radial Migrations in Virgo Disk GalaxiesJan 30 2012Aug 27 2012We present stellar age profiles for 64 Virgo cluster disk galaxies whose analysis poses a challenge for current galaxy formation models. Our results can be summarized as follows: first, and contrary to observations of field galaxies, these cluster galaxies ... More
Quantum Breathing Mode of Trapped Systems in One and Two DimensionsNov 21 2013We investigate the quantum breathing mode (monopole oscillation) of trapped fermionic particles with Coulomb and dipole interaction in one and two dimensions. This collective oscillation has been shown to reveal detailed information on the many-particle ... More
MMTF-Halpha and HST-FUV Imaging of the Filamentary Complex in Abell 1795Sep 08 2009Jan 27 2010We have obtained deep, high spatial resolution images of the central region of Abell 1795 at Halpha and [NII] (6583A) with the Maryland Magellan Tunable Filter (MMTF), and in the far-ultraviolet (FUV) with the Advanced Camera for Surveys Solar Blind Channel ... More
A Measurement of the Temperature-Density Relation in the Intergalactic Medium Using a New Lyman-alpha Absorption Line Fitting MethodMay 29 2000The evolution of the temperature in the intergalactic medium is related to the reionization of hydrogen and helium, and has important consequences for our understanding of the Lya forest and of galaxy formation in gravitational models of large-scale structure. ... More
Are State-of-the-art Visual Place Recognition Techniques any Good for Aerial Robotics?Apr 16 2019Visual Place Recognition (VPR) has seen significant advances at the frontiers of matching performance and computational superiority over the past few years. However, these evaluations are performed for ground-based mobile platforms and cannot be generalized ... More
Doubly slice odd pretzel knotsApr 29 2019We prove that an odd pretzel knot is doubly slice if it has $2n+1$ twist parameters consisting of $n+1$ copies of $a$ and $n$ copies of $-a$ for some odd integer $a$. Combined with the work of Issa and McCoy, it follows that these are the only doubly ... More
Band Number and the Double Slice GenusJan 22 2019We study the double slice genus of a knot, a natural generalization of slice genus. We define a notion called band number, a natural generalization of band unknotting number, and prove it is an upper bound on double slice genus. Our bound is based on ... More
Heat content determines planar trianglesJul 12 2016We prove that heat content determines planar triangles.
HEAT: Hyperbolic Embedding of Attributed NetworksMar 07 2019May 02 2019Finding a low dimensional representation of hierarchical, structured data described by a network remains a challenging problem in the machine learning community. An emerging approach is embedding these networks into hyperbolic space because it can naturally ... More
Cold Molecular Gas Along the Cooling X-ray Filament in Abell 1795Jul 16 2012We present the results of interferometric observations of the cool core of Abell 1795 at CO(1-0) using the Combined Array for Research in Millimeter-Wave Astronomy. In agreement with previous work, we detect a significant amount of cold molecular gas ... More
A census of cool core galaxy clusters in IllustrisTNGOct 23 2017Nov 21 2018The thermodynamic structure of hot gas in galaxy clusters is sensitive to astrophysical processes and typically difficult to model with galaxy formation simulations. We explore the fraction of cool-core (CC) clusters in a large sample of $370$ clusters ... More
Revised Mass-to-Light Ratios For Nearby Galaxy Groups and ClustersDec 29 2014We present a detailed investigation of the cluster stellar mass-to-light (M*/L) ratio and cumulative stellar masses, derived on a galaxy-by-galaxy basis, for 12 massive (M500 ~ 10^14 - 10^15 Msun), nearby clusters with available optical imaging data from ... More
Constraints on the optical depth of galaxy groups and clustersOct 25 2016May 01 2017Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal ... More
Bulge-Disk Decompositions and Structural Bimodality of Ursa Major Cluster Spiral GalaxiesOct 30 2008We present bulge and disk (B/D) decompositions of existing K'-band surface brightness profiles for 65 Ursa Major cluster spiral galaxies. This improves upon the disk-only fits of Tully et al. (1996). The 1996 disk fits were used by Tully & Verheijen (1997) ... More
List rankings and on-line list rankings of graphsJan 15 2014A $k$-ranking of a graph $G$ is a labeling of its vertices from $\{1,\ldots,k\}$ such that any nontrivial path whose endpoints have the same label contains a larger label. The least $k$ for which $G$ has a $k$-ranking is the ranking number of $G$, also ... More
The Effect of Environment on the Formation of Halpha Filaments and Cool Cores in Galaxy Groups and ClustersFeb 09 2011We present the results of a combined X-ray and Halpha study of 10 galaxy groups and 17 galaxy clusters using the Chandra X-ray Observatory and the Maryland Magellan Tunable Filter. We find no difference in the morphology or detection frequency of Halpha ... More
The Near-IR Luminosity Function and Bimodal Surface Brightness Distribution of Virgo Cluster GalaxiesJan 22 2009We have acquired deep, H-band, imaging for a sample of 286 Virgo cluster galaxies with B <= 16 mag and extracted surface photometry from optical g,r,i,z Sloan Digital Sky Survey images of 742 Virgo Cluster Catalog galaxies, including those with H-band ... More
The Vcirc-sigma0 Relation of GalaxiesSep 24 2007Courteau et al. (2007a) reported on the dependence of the ratio of a galaxy's maximum circular velocity, Vcirc, to its central velocity dispersion, sigma0, on morphology, or equivalently total light concentration. This Vcirc-sigma0 concentration relation, ... More
Constraints on the optical depth of galaxy groups and clustersOct 25 2016Future data from galaxy redshift surveys, combined with high-resolutions maps of the cosmic microwave background, will enable measurements of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) signal with unprecedented statistical significance. This signal ... More
Stripping of the Hot Gas Halos in Member Galaxies of Abell 1795Nov 07 2017Sep 20 2018The nearby cluster Abell 1795 is used as a testbed to examine whether hot gas in cluster galaxies is stripped by the ram pressure of the intracluster medium (ICM). The expected X-ray emission in and around Abell 1795 galaxies is likely dominated by the ... More
The Transverse Proximity Effect: A Probe to the Environment, Anisotropy, and Megayear Variability of QSOsJul 31 2003Mar 19 2004The transverse proximity effect is the expected decrease in the strength of the Lya forest absorption in a QSO spectrum when another QSO lying close to the line of sight enhances the photoionization rate above that due to the average cosmic ionizing background. ... More
Sommerfeld Enhancement from Multiple MediatorsMar 28 2012Mar 30 2013We study the Sommerfeld enhancement experienced by a scattering object that couples to a tower of mediators. This can occur in, e.g., models of secluded dark matter when the mediator scale is generated naturally by hidden-sector confinement. Specializing ... More
Comments on the Hierarchy Problem in Effective TheoriesApr 23 2014We discuss aspects of the hierarchy problem in effective theories with light scalars and a large, physical ultraviolet (UV) cutoff. We make two main points: (1) The (naive) fine-tuning observed in an effective theory does not automatically imply that ... More
Mean field convergence of a model of multiple TCP connections through a buffer implementing REDMar 14 2006RED (Random Early Detection) has been suggested when multiple TCP sessions are multiplexed through a bottleneck buffer. The idea is to detect congestion before the buffer overflows by dropping or marking packets with a probability that increases with ... More
A Survey of 286 Virgo Cluster Galaxies at Optical griz and Near-IR H-band: Surface Brightness Profiles and Bulge-Disk DecompositionsApr 29 2011Jun 14 2011We present griz and H-band surface brightness profiles and bulge-disk decompositions for a morphologically-broad sample of 286 Virgo cluster galaxies. The H-band data come from a variety of sources including our survey of 171 galaxies at the UH 2.2-m, ... More
On the Origin of the Extended Halpha Filaments in Cooling Flow ClustersAug 02 2010We present a high spatial resolution Halpha survey of 23 cooling flow clusters using the Maryland Magellan Tunable Filter (MMTF), covering 1-2 orders of magnitude in cooling rate, dM/dt, temperature and entropy. We find 8/23 (35%) of our clusters have ... More
The challenging task of determining star formation rates: the case of a massive stellar burst in the brightest cluster galaxy of Phoenix galaxy clusterNov 08 2016Jan 16 2017Star formation in galaxies at the center of cooling-flow galaxy clusters is an important phenomenon in the context of formation and evolution of massive galaxies in the Universe. Yet, star formation rates (SFRs) in such systems continue to be elusive. ... More
Matrix Roots of Eventually Positive MatricesOct 23 2013Eventually positive matrices are real matrices whose powers become and remain strictly positive. As such, eventually positive matrices are a fortiori matrix roots of positive matrices, which motivates us to study the matrix roots of primitive matrices. ... More
Resonant torsion magnetometry in anisotropic quantum materialsFeb 22 2018Unusual behavior of quantum materials commonly arises from their effective low-dimensional physics, which reflects the underlying anisotropy in the spin and charge degrees of freedom. Torque magnetometry is a highly sensitive technique to directly quantify ... More
Integrated Stellar Populations: Confronting Photometry with SpectroscopyJun 19 2010We investigate the ability of spectroscopic techniques to yield realistic star formation histories (SFHs) for the bulges of spiral galaxies based on a comparison with their observed broadband colors. Full spectrum fitting to optical spectra indicates ... More
A Deeper Look at Faint H$α$ Emission in Nearby Dwarf GalaxiesJan 02 2016We present deep H$\alpha$ imaging of three nearby dwarf galaxies, carefully selected to optimize observations with the Maryland-Magellan Tunable Filter (MMTF) on the Magellan 6.5m telescope. An effective bandpass of $\sim$13\AA\ is used, and the images ... More
Cool Core Bias in Sunyaev-Zel'dovich Galaxy Cluster SurveysJan 19 2015Sunyaev-Zeldovich (SZ) surveys find massive clusters of galaxies by measuring the inverse Compton scattering of cosmic microwave background off of intra-cluster gas. The cluster selection function from such surveys is expected to be nearly independent ... More
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 RelationOct 24 2006Nov 01 2006We explore the dependence of the ratio of a galaxy's circular velocity, Vcirc, to its central velocity dispersion, sigma_0, on morphology, or equivalently total light concentration. Such a dependence is expected if light traces the mass. Over the full ... More
The Formation and Evolution of Virgo Cluster Galaxies - I. Broadband Optical & Infrared ColoursApr 29 2011We use a combination of deep optical (gri) and near-infrared (H) photometry to study the radially-resolved colours of a broad sample of 300 Virgo cluster galaxies. For most galaxy types, we find that the median g-H colour gradient is either flat (gas-poor ... More
New Constraints on the Escape of Ionizing Photons From Starburst Galaxies Using Ionization-Parameter MappingNov 09 2013Nov 12 2013The fate of ionizing radiation in starburst galaxies is key to understanding cosmic reionization. However, the galactic parameters on which the escape fraction of ionizing radiation depend are not well understood. Ionization-parameter mapping provides ... More
Memorable Maps: A Framework for Re-defining Places in Visual Place RecognitionNov 08 2018Mar 21 2019This paper presents a cognition-inspired agnostic framework for building a map for Visual Place Recognition. This framework draws inspiration from human-memorability, utilizes the traditional image entropy concept and computes the static content in an ... More
HST-COS Spectroscopy of the Cooling Flow in Abell 1795 - Evidence for Inefficient Star Formation in Condensing Intracluster GasJul 16 2014We present far-UV spectroscopy from the Cosmic Origins Spectrograph on the Hubble Space Telescope of a cool, star-forming filament in the core of Abell 1795. These data, which span 1025A - 1700A, allow for the simultaneous modeling of the young stellar ... More
Neutrino Mass and $μ\rightarrow e + γ$ from a Mini-SeesawMay 03 2011Aug 02 2011The recently proposed "mini-seesaw mechanism" combines naturally suppressed Dirac and Majorana masses to achieve light Standard Model neutrinos via a low-scale seesaw. A key feature of this approach is the presence of multiple light (order GeV) sterile-neutrinos ... More
Using H$α$ Filaments to Probe AGN Feedback in Galaxy ClustersDec 13 2018Mar 19 2019Recent observations of giant ellipticals and brightest cluster galaxies (BCGs) provide tentative evidence for a correlation between the luminosity of the H$\alpha$ emitting gas filaments and the strength of feedback associated with the active galactic ... More
Galaxy Winds in the Age of Hyperdimensional AstrophysicsMar 13 2019The past decade began with the first light of ALMA and will end at the start of the new era of hyperdimensional astrophysics. Our community-wide movement toward highly multiwavelength and multidimensional datasets has enabled immense progress in each ... More
The challenging task of determining star formation rates: the case of a massive stellar burst in the brightest cluster galaxy of Phoenix galaxy clusterNov 08 2016Star formation in galaxies at the center of cooling-flow galaxy clusters is an important phenomenon in the context of formation and evolution of massive galaxies in the Universe. Yet, star formation rates (SFRs) in such systems continue to be elusive. ... More
Using H$α$ Filaments to Probe AGN Feedback in Galaxy ClustersDec 13 2018Recent observations of giant ellipticals and brightest cluster galaxies (BCGs) provide tentative evidence for a correlation between the luminosity of the H$\alpha$ emitting gas filaments and the strength of feedback associated with the active galactic ... More
The Formation and Evolution of Virgo Cluster Galaxies - II. Stellar PopulationsNov 15 2010Apr 29 2011We use a combination of deep optical and near-infrared light profiles for a morphologically diverse sample of Virgo cluster galaxies to study the radially-resolved stellar populations of cluster galaxies over a wide range of galaxy structure. We find ... More
Optical Spectroscopy of Halpha Filaments in Cool Core Clusters: Kinematics, Reddening, and Sources of IonizationOct 31 2011Nov 28 2011We have obtained deep, high spatial and spectral resolution, long-slit spectra of the Halpha nebulae in the cool cores of 9 galaxy clusters. This sample provides a wealth of information on the ionization state, kinematics, and reddening of the warm gas ... More
A Holistic Visual Place Recognition Approach using Lightweight CNNs for Severe ViewPoint and Appearance ChangesNov 07 2018Nov 14 2018This paper presents a lightweight visual place recognition approach, capable of achieving high performance with low computational cost, and feasible for mobile robotics under severe viewpoint and appearance changes. Results on several benchmark datasets ... More
The Spectroscopy and H-band Imaging of Virgo cluster galaxies (SHIVir) Survey: Scaling Relations and the Stellar-to-Total Mass RelationMay 30 2017We present here parameter distributions and fundamental scaling relations for 190 galaxies as part of the Spectroscopy and H-bang Imaging of Virgo cluster galaxies (SHIVir) survey. We find the distribution of galaxy velocities to be bimodal about $V_{\rm ... More
Elaborating Inductive Datatypes and Course-of-Values Pattern Matching to CedilleMar 19 2019In CDLE, a pure Curry-style type theory, it is possible to generically derive induction for {\lambda}-encoded data whose types are least fixed points of functors. From this comes fruitful research into the design-space for datatype systems: \cite{FDJS18_CoV-Ind} ... More
Large-scale Correlation of Mass and Galaxies with the Lyman-alpha Forest Transmitted FluxDec 20 2001We present predictions of the correlation between the Lyman-alpha forest absorption in quasar spectra and the mass within \sim 5 Mpc/h (comoving) of the line of sight, using fully hydrodynamic and hydro-PM numerical simulations of the cold dark matter ... More
Axion superradiance in rotating neutron starsApr 17 2019It is a well-known fact that compact gravitating objects admit bound state configurations for massive bosonic fields. In this work we describe a new class of superradiant instabilities of axion bound states in neutron star magnetospheres. The instability ... More
Low-Energy Probes of a Warped Extra DimensionFeb 17 2010Sep 21 2010We investigate a natural realization of a light Abelian hidden sector in an extended Randall-Sundrum (RS) model. In addition to the usual RS bulk we consider a second warped space containing a bulk U(1)_x gauge theory with a characteristic IR scale of ... More
Packing and covering directed trianglesJun 22 2018Mar 07 2019We prove that if a directed multigraph $D$ has at most $t$ pairwise arc-disjoint directed triangles, then there exists a set of less than $2t$ arcs in $D$ which meets all directed triangles in $D$, except in the trivial case $t=0$. This answers affirmatively ... More
Stellar Population Trends in S0 GalaxiesOct 06 2010We present stellar population age and metallicity trends for a sample of 59 S0 galaxies based on optical SDSS and NIR J & H photometry. When combined with optical g and r passband imaging data from the SDSS archive and stellar population models, we obtain ... More
Andromeda Optical and Infrared Disk Survey I. New Insights in Wide-Field Near-IR Surface PhotometryMar 25 2013We present wide-field near-infrared J and Ks images of the Andromeda Galaxy taken with WIRCam on the Canada-France-Hawaii Telescope (CFHT) as part of the Andromeda Optical and Infrared Disk Survey (ANDROIDS). This data set allows simultaneous observations ... More
Star Formation Efficiency in the Cool Cores of Galaxy ClustersApr 04 2011We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys Solar Blind Channel) and Halpha (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed ... More
An Investigation of Sloan Digital Sky Survey Imaging Data and Multi-Band Scaling Relations of Spiral Galaxies (with Dynamical Information)Nov 21 2011We have compiled a sample of 3041 spiral galaxies with multi-band gri imaging from the Sloan Digital Sky Survey (SDSS) Data Release 7 and available galaxy rotational velocities derived from HI line widths. We compare the data products provided through ... More
Levelling the Playing Field: A Comprehensive Comparison of Visual Place Recognition Approaches under Changing ConditionsMar 21 2019Apr 29 2019In recent years there has been significant improvement in the capability of Visual Place Recognition (VPR) methods, building on the success of both hand-crafted and learnt visual features, temporal filtering and usage of semantic scene information. The ... More
On the Assembly Bias of Cool Core Clusters Traced by H$α$ NebulaeMar 12 2019Do cool-core (CC) and noncool-core (NCC) clusters live in different environments? We make novel use of H$\alpha$ emission lines in the central galaxies of redMaPPer clusters as proxies to construct large (1,000's) samples of CC and NCC clusters, and measure ... More
First lensed quasar system(s) from the VST-ATLAS survey: one quad and three nearly identical pairsJul 25 2016We have analyzed images from the VST ATLAS survey to identify candidate gravitationally lensed quasar systems in a sample of WISE sources with W1 - W2 > 0.7. Results from followup spectroscopy with the Baade 6.5 m telescope are presented for seven systems. ... More
An HST/WFC3-UVIS View of the Starburst in the Cool Core of the Phoenix ClusterNov 29 2012Feb 10 2013We present Hubble Space Telescope Wide Field Camera 3 observations of the core of the Phoenix Cluster SPT-CLJ2344-4243 in five broadband filters spanning rest-frame 1000--5500A. These observations reveal complex, filamentary blue emission, extending for ... More
The Massive and Distant Clusters of WISE Survey VI: Stellar Mass Fractions of a Sample of High-Redshift Infrared-selected ClustersMar 26 2019We present measurements of the stellar mass fractions ($f_\star$) for a sample of high-redshift ($0.93 \le z \le 1.32$) infrared-selected galaxy clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) and compare them to the stellar mass ... More
The Dynamical Properties of Virgo Cluster Disk GalaxiesOct 28 2013By virtue of its proximity, the Virgo Cluster is an ideal laboratory for testing our understanding structure formation in the Universe. In this spirit, we present a dynamical study Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo ... More
First lensed quasar systems from the VST-ATLAS survey: one quad, two doubles and two pairs of lensless twinsJul 25 2016Mar 20 2017We have analyzed images from the VST ATLAS survey to identify candidate gravitationally lensed quasar systems in a sample of WISE sources with W1 - W2 > 0.7. Results from followup spectroscopy with the Baade 6.5 m telescope are presented for eight systems. ... More
Levelling the Playing Field: A Comprehensive Comparison of Visual Place Recognition Approaches under Changing ConditionsMar 21 2019In recent years there has been significant improvement in the capability of Visual Place Recognition (VPR) methods, building on the success of both hand-crafted and learnt visual features, temporal filtering and usage of semantic scene information. The ... More
An Ionization Cone in the Dwarf Starburst Galaxy NGC 5253Sep 28 2011There are few observational constraints on how the escape of ionizing photons from starburst galaxies depends on galactic parameters. Here, we report on the first major detection of an ionization cone in NGC 5253, a nearby starburst galaxy. This high-excitation ... More
Spatially modulated heavy-fermion superconductivity in CeIrIn5Jul 13 2018Sep 21 2018The ability to spatially modulate the electronic properties of solids has led to landmark discoveries in condensed matter physics as well as new electronic applications. Although crystals of strongly correlated metals exhibit a diverse set of electronic ... More
Searching for Cooling Signatures in Strong Lensing Galaxy Clusters: Evidence Against Baryons Shaping the Matter Distribution in Cluster CoresMay 17 2013The process by which the mass density profile of certain galaxy clusters becomes centrally concentrated enough to produce high strong lensing (SL) cross-sections is not well understood. It has been suggested that the baryonic condensation of the intra-cluster ... More
Debug Support, Calibration and Emulation for Multiple Processor and Powertrain Control SoCsOct 25 2007The introduction of complex SoCs with multiple processor cores presents new development challenges, such that development support is now a decisive factor when choosing a System-on-Chip (SoC). The presented developments support strategy addresses the ... More
Q-ball Evolution, B-ball Baryogenesis and the f_{B} ProblemDec 29 2000Feb 22 2001We consider some of the issues surrounding the formation and evolution of Q-balls in the MSSM and its extensions. The ratio of the baryon number packed into Q-balls to that outside, f_{B}, plays a fundamental role in determining the relationship of dark ... More
Comment on Vacuum Stability and Electroweak Baryogenesis in the MSSM with Light StopsJul 09 1997Sep 03 1997We show that, for all values of $Tan \beta$ and the light right-handed stop mass for which the electroweak phase transition is strong enough to avoid washout following electroweak baryogenesis, the electroweak vacuum is stable over the lifetime of the ... More
Signatures of Planck Corrections in a Spiralling Axion Inflation ModelDec 22 2014May 04 2015The minimal sub-Planckian axion inflation model accounts for a large scalar-to-tensor ratio via a spiralling trajectory in the field space of a complex field $\Phi$. Here we consider how the predictions of the model are modified by Planck scale-suppressed ... More
Simultaneous Generation of WIMP Miracle-like Densities of Baryons and Dark MatterAug 23 2011Mar 05 2015The observed density of dark matter is of the magnitude expected for a thermal relic weakly-interacting massive particle (WIMP). In addition, the observed baryon density is within an order of magnitude of the dark matter density. This suggests that the ... More
Unparticles: Interpretation and CosmologyMay 13 2008May 14 2008We discuss the physical interpretation of unparticles and review the constraints from cosmology. Unparticles may be understood in terms of confined states of a strongly-coupled scale-invariant theory, where scale-invariance implies that the confined states ... More
Positive Order H^2 Mass Corrections and Affleck-Dine BaryogenesisFeb 21 1999Mar 03 1999It is usually assumed that the order H^2 corrections to the SUSY-breaking mass squared terms in the early Universe must be negative in order to allow the Affleck-Dine mechanism to work. We reconsider this assumption in the context of D-term inflation ... More
DisplaceNet: Recognising Displaced People from Images by Exploiting Dominance LevelMay 03 2019Every year millions of men, women and children are forced to leave their homes and seek refuge from wars, human rights violations, persecution, and natural disasters. The number of forcibly displaced people came at a record rate of 44,400 every day throughout ... More
Non-Thermal Dark Matter, High Energy Cosmic Rays and Late-Decaying Particles From Inflationary Quantum FluctuationsNov 16 2000May 23 2001It has been suggested that the origin of cosmic rays above the GZK limit might be explained by the decay of particles, X, with mass of the order of 10^{12} GeV. Generation of heavy particles from inflationary quantum fluctuations is a prime candidate ... More
Dynamical Cosmological Constant from A Very Recent Phase TransitionJul 12 2000Nov 19 2000Observation indicates that the expansion of the Universe is accelerating and favours a dynamical cosmological constant, \Lambda(t). We consider the possibility that this is due to a scalar field which has undergone a very recent phase transition. We study ... More
Negative Running of the Spectral Index, Hemispherical Asymmetry and the Consistency of Planck with Large $r$Mar 26 2014Oct 24 2014Planck favours a negative running of the spectral index, with the likelihood being dominated by low multipoles $l \lesssim 50$ and no preference for running at higher $l$. A negative spectral index is also necessary for the 2-$\sigma$ Planck upper bound ... More
Baryomorphosis: Relating the Baryon Asymmetry to the "WIMP Miracle"Sep 16 2010Apr 06 2011We present a generic framework, "baryomorphosis", which modifies the baryon asymmetry to be naturally of the order of a typical thermal relic WIMP density. We consider a simple scalar-based model to show how this is possible. This model introduces a sector ... More
Enhanced Dark Matter Annihilation Rate for Positron and Electron Excesses from Q-ball DecayApr 06 2009Sep 25 2009We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross-section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC and PPB-BETS. For Affleck-Dine ... More
Cosmological Constraints on Unparticles as Continuous Mass ScalarsSep 14 2007Mar 13 2009We study the cosmological constraints on unparticle interactions and the temperature of the Universe for the case where unparticle states can be modelled as continuous mass particles with lifetime > 1s. By considering thermal background quark decay to ... More
Naturally Large Cosmological Neutrino Asymmetries in the MSSMAug 09 1999May 11 2000A large neutrino asymmetry is an interesting possibility for cosmology, which can have significant observable consequences for nucleosynthesis and the cosmic microwave background. However, although it is a possibility, there is no obvious reason to expect ... More
Spontaneous Discrete Symmetry Breaking During Inflation and the NMSSM Domain Wall ProblemSep 30 1997Apr 02 1998The Next to Minimal Supersymmetric Standard Model (NMSSM), proposed as a solution of the mu problem of the Minimal Supersymmetric Standard Model, has a discrete Z_{3} symmetry which is spontaneously broken at the electroweak phase transition, resulting ... More
Nucleosynthesis bounds on small Dirac neutrino masses due to chiral symmetry breakingOct 10 1996Nov 19 1996We consider nucleosynthesis constraints on models which use chiral symmetry breaking as a basis for understanding very small Dirac neutrino masses. We show that present big-bang nucleosynthesis constraints impose a well-defined upper bound of 0.1eV on ... More
Renormalization group computation of likelihood functions for cosmological data setsOct 19 2018I show how a renormalization group (RG) method can be used to incrementally integrate the information in cosmological large-scale structure data sets (including CMB, galaxy redshift surveys, etc.). I show numerical tests for Gaussian fields, where the ... More
On Galvin orientations of line graphs and list-edge-colouringAug 07 2015The notion of a Galvin orientation of a line graph is introduced, generalizing the idea used by Galvin in his landmark proof of the list-edge-colouring conjecture for bipartite graphs. If L(G) has a proper Galvin orientation with respect to k, then it ... More
Isocurvature and Curvaton Perturbations with Red Power Spectrum and Large Hemispherical AsymmetryMay 02 2013May 21 2013We calculate the power spectrum and hemispherical asymmetry of isocurvature and curvaton perturbations due to a complex field \Phi which is evolving along the tachyonic part of its potential. Using a semi-classical evolution of initially sub-horizon quantum ... More
Spectral Index of Curvaton Perturbations in Flat Potential Inflation ModelsAug 05 2003Aug 17 2003This paper has been withdrawn. Comments regarding D-term inflation will be incorporated in a forthcoming article.
B-ball Baryogenesis and D-term InflationJan 29 1999Feb 05 1999The MSSM has flat directions in its scalar potential, along which it is natural for Bose condensates of squarks to form in the early Universe. A baryon asymmetry can be induced in these condensates via Affleck-Dine baryogenesis. The condensates are unstable ... More
Sub-Planckian Two-Field Inflation Consistent with the Lyth BoundApr 17 2014Oct 24 2014The BICEP2 observation of a large tensor-to-scalar ratio, $r = 0.20^{+0.07}_{-0.05}$, implies that the inflaton $\phi$ in single-field inflation models must satisfy $\phi \sim 10M_{Pl}$ in order to produce sufficient inflation. This is a problem if interaction ... More
Hemispherical Power Asymmetry from a Space-Dependent Component of the Adiabatic Power SpectrumMar 09 2014Jun 17 2014The hemispherical power asymmetry observed by Planck and WMAP can be interpreted as due to a spatially-varying and scale-dependent component of the adiabatic power spectrum. We derive general constraints on the magnitude and scale-dependence of a component ... More
Hemispherical Power Asymmetry from Scale-Dependent Modulated ReheatingSep 04 2013Feb 20 2014We propose a new model for the hemispherical power asymmetry of the CMB based on modulated reheating. Non-Gaussianity from modulated reheating can be small enough to satisfy the bound from Planck if the dominant modulation of the inflaton decay rate is ... More
Baryon-to-Dark Matter Ratio from Random Angular FieldsNov 19 2012Jan 14 2013We consider the baryon-to-dark matter ratio in models where the dark matter and baryon densities depend on angular fields \theta_{d} and \theta_{b} according to \rho_{d} ~ \theta_{d}^{\alpha} and \rho_{b} ~ \theta_{b}^{\beta}, with all values of \theta_{d} ... More
Anthropically Selected Baryon Number and Isocurvature ConstraintsJul 09 2012Dec 23 2012The similarity of the observed baryon and dark matter densities suggests that they are physically related, either via a particle physics mechanism or anthropic selection. A pre-requisite for anthropic selection is the generation of superhorizon-sized ... More
Right-Handed Sneutrinos as CurvatonsFeb 25 2003Jul 29 2003We consider the possibility that a right-handed sneutrino can serve as the source of energy density perturbations leading to structure formation in cosmology. The cosmological evolution of a coherently oscillating condensate of right-handed sneutrinos ... More
Inflaton Condensate Fragmentation in Hybrid Inflation ModelsMay 22 2001Jul 09 2002Inflation ends with the formation of a Bose condensate of inflatons. We show that in hybrid inflation models this condensate is typically unstable with respect to spatial perturbations and can fragment to condensate lumps. The case of D-term inflation ... More
Congruence classes of large configurations in vector spaces over finite fieldsJan 28 2019Bennett, Hart, Iosevich, Pakianathan, and Rudnev found an exponent $s<d$ such that any set $E\subset \mathbb{F}_q^d$ with $|E|\gtrsim q^s$ determines $\gtrsim q^{\binom{k+1}{2}}$ congruence classes of $(k+1)$-point configurations for $k\leq d$. Because ... More
A list analog of Vizing's Theorem for simple graphs with triangles but no other odd cyclesJul 02 2014Aug 07 2015This paper has been withdrawn by the author. Peterson and Woodall previously proved that the list-edge-colouring conjecture holds for graphs without odd cycles of length 5 or longer. D. Peterson and D. R. Woodall, Edge-choosability in line-perfect multigraphs, ... More
A geometric view of quantum cellular automataAug 15 2012Nielsen, et al. [1, 2] proposed a view of quantum computation where determining optimal algorithms is equivalent to extremizing a geodesic length or cost functional. This view of optimization is highly suggestive of an action principle of the space of ... More
Explaining the Dark Energy, Baryon and Dark Matter Coincidence via Domain-Dependent Random DensitiesJan 17 2013May 15 2013The dark energy, dark matter and baryon densities in the Universe are observed to be similar, with a factor of no more than 20 between the largest and smallest densities. We show that this coincidence can be understood via superhorizon domains of randomly ... More