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High Resolution X-ray Spectroscopy of Galaxies and Clusters with AXAFOct 21 1998We review the high resolution X-ray spectroscopy capabilities of the AXAF observatory focusing on the High Energy Transmission Grating (HETG). As part of the Guaranteed Time Observation (GTO) program, the HETG science team will observe both elliptical ... More

X-ray Absorption Due to Cold Gas in Cluster Cooling CoresMar 09 1999We have calculated the emergent X-ray properties for models of cluster cooling flows including the effects of accumulated cooled material. The opacity of this cooled gas can reduce the overall X-ray luminosity of the cooling flow, and values of Mdot based ... More

X-Ray Spectral Properties of the Cluster Abell 2029Dec 03 1997We have analyzed ASCA and ROSAT PSPC spectra and images of the galaxy cluster Abell 2029. The ASCA spectra of the cluster indicate that the gas temperature declines with radius. The PSPC image shows that the cluster is very regular and smooth. Also, there ... More

The Insignificance of Global Reheating in the Abell 1068 Cluster: X-Ray AnalysisOct 01 2003We report on a Chandra observation of the massive, medium redshift (z=0.1386) cooling flow cluster Abell 1068. We detect a clear temperature gradient in the X-ray emitting gas from kT ~ 5 keV in the outer part of the cluster down to roughly 2 keV in the ... More

Calibrating AGN Feedback in ClustersOct 27 2009Whether caused by AGN jets, shocks, or mergers, the most definitive evidence for heating in cluster cores comes from X-ray spectroscopy. Unfortunately such spectra are essentially limited to studying the emission spectrum from the cluster as a whole. ... More

Probing The Ultraviolet Luminosity Function of the Earliest Galaxies with the Renaissance SimulationsMar 03 2015Jun 12 2015In this paper, we present the first results from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich AMR calculations of high redshift galaxy formation performed on the Blue Waters supercomputer. These simulations contain ... More

First Light: exploring the Spectra of High-Redshift Galaxies in the Renaissance SimulationsJan 10 2017Jun 19 2017We present synthetic observations for the first generations of galaxies in the Universe and make predictions for future deep field observations for redshifts greater than 6. Due to the strong impact of nebular emission lines and the relatively compact ... More

Late Pop III Star Formation During the Epoch of Reionization: Results from the Renaissance SimulationsApr 12 2016We present results on the formation of Pop III stars at redshift 7.6 from the Renaissance Simulations, a suite of extremely high-resolution and physics-rich radiation transport hydrodynamics cosmological adaptive-mesh refinement simulations of high redshift ... More

Interaction of Cygnus A with its environmentFeb 17 2015Cygnus A, the nearest truly powerful radio galaxy, resides at the centre of a massive galaxy cluster. Chandra X-ray observations reveal its cocoon shocks, radio lobe cavities and an X-ray jet, which are discussed here. It is argued that X-ray emission ... More

On theories of enhanced CP violation in B_s,d meson mixingSep 15 2010Nov 23 2010The DO collaboration has measured a deviation from the standard model (SM) prediction in the like sign dimuon asymmetry in semileptonic b decay with a significance of 3.2 sigma. We discuss how minimal flavour violating (MFV) models with multiple scalar ... More

Scaling Relations for Galaxies Prior to ReionizationAug 11 2014Sep 03 2014The first galaxies in the Universe are the building blocks of all observed galaxies. We present scaling relations for galaxies forming at redshifts $z \ge 15$ when reionization is just beginning. We utilize the ``Rarepeak' cosmological radiation hydrodynamics ... More

Light Scalars and the Generation of Density Perturbations During Preheating or Inflaton DecayDec 01 2004Jan 15 2005Reheating after inflation can occur through inflaton decay or efficient parametric resonant production of particles from the oscillation of the inflaton. If the particles produced interact with scalars that were light during inflation, then significant ... More

A Chandra study of the large-scale shock and cool filaments in Hydra A: Evidence for substantial gas dredge-up by the central outburstFeb 26 2011We present the results of a Chandra study of the Hydra A galaxy cluster, where a powerful AGN outburst created a large-scale cocoon shock. We investigated possible azimuthal variations in shock strength and shape, finding indications for a weak shock ... More

Cosmological Effects of Powerful AGN Outbursts in Galaxy Clusters: Insights from an XMM-Newton Observation of MS0735+7421Jan 12 2007We report on the results of an analysis of XMM-Newton observations of MS0735+7421, the galaxy cluster which hosts the most energetic AGN outburst currently known. The previous Chandra image shows twin giant X-ray cavities (~200 kpc diameter) filled with ... More

Galaxy Properties and UV Escape Fractions During Epoch of Reionization: Results from the Renaissance SimulationsApr 26 2016Oct 07 2016Cosmic reionization is thought to be primarily fueled by the first generations of galaxies. We examine their stellar and gaseous properties, focusing on the star formation rates and the escape of ionizing photons, as a function of halo mass, redshift, ... More

XMM-Newton view of MS0735+7421: the most energetic AGN outburst in a galaxy clusterNov 08 2006We discuss the possible cosmological effects of powerful AGN outbursts in galaxy clusters by starting from the results of an XMM-Newton observation of the supercavity cluster MS0735+7421.

Chandra Observation of the Radio Source / X-ray Gas Interaction in the Cooling Flow Cluster Abell 2052Jul 12 2001We present a Chandra observation of Abell 2052, a cooling flow cluster with a central cD that hosts the complex radio source 3C 317. The data reveal ``holes'' in the X-ray emission that are coincident with the radio lobes. The holes are surrounded by ... More

Chandra X-Ray Spectroscopy and Imaging of the Galaxy Cluster PKS 0745-191Oct 28 2002We present a detailed spectral and spatial analysis of the galaxy cluster PKS 0745-191, using recent observations from the Chandra X-ray Observatory. The data provide information on the temperature and metallicity of the intracluster medium, the distribution ... More

Heating the IGM by X-rays from Population III Binaries in High Redshift GalaxiesApr 25 2014Aug 05 2014Due to their long mean free path, X-rays are expected to have an important impact on cosmic reionization by heating and ionizing the IGM on large scales, especially after simulations have suggested that Population III stars may form in pairs at redshifts ... More

X-ray Background at High Redshifts from Pop III Remnants: Results from Pop III star formation rates in the Renaissance SimulationsJul 09 2016Oct 07 2016Due to their long mean free paths, X-rays are expected to have many significant impacts globally on the properties of the intergalactic medium (IGM) by their heating and ionizing processes on large scales. At high redshifts, X-rays from Population (Pop) ... More

On type I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasersDec 15 2009The output pulses of a commercial high-power femtosecond fiber laser or amplifier are typically around 300-500 fs with a wavelength around 1030 nm and 10s of $\mu$J pulse energy. Here we present a numerical study of cascaded quadratic soliton compression ... More

Derivation of Nonlinear Evolution Equations for Coupled and Single Fields in a Quadratic MediumApr 20 2006We derive coupled propagation equations for ultrashort pulses in a degenerate three-wave mixing process in quadratic media, using approximations consistent with the slowly evolving wave approximation [T. Brabec and F. Krausz, Phys. Rev. Lett. 78, 3282 ... More

Suppression of Superfluid Density and the Pseudogap State in the Cuprates by ImpuritiesJul 18 2016We use scanning tunneling microscopy (STM) to study magnetic Fe impurities intentionally doped into the high-temperature superconductor Bi$_{2}$Sr$_{2}$Ca$_{2}$CuO$_{8+\delta}$. Our spectroscopic measurements reveal that Fe impurities introduce low-lying ... More

First Light II: Emission Line Extinction, Population III Stars, and X-ray BinariesSep 13 2017Dec 08 2017We produce synthetic spectra and observations for metal-free stellar populations and high mass X-ray binaries in the Renaissance Simulations at a redshift of 15. We extend our methodology from the first paper in the series by modelling the production ... More

Formation of massive black holes in rapidly growing pre-galactic gas cloudsJan 22 2019The origin of supermassive black holes (SMBHs) that inhabit the centers of massive galaxies is largely unconstrained. Remnants from supermassive stars (SMSs) with masses around 10,000 solar masses provide the ideal seed candidates, known as direct collapse ... More

Evidence for a TDE origin of the radio transient Cygnus A-2Apr 12 2019In 2015, a radio transient named Cygnus A-2 was discovered in Cygnus A with the Very Large Array. Because of its radio brightness ($\nu F_{\nu} \approx 6 \times 10^{39}$ erg s$^{-1}$), this transient likely represents a secondary black hole in orbit around ... More

The Higgs Decay Width in Multi-Scalar Doublet ModelsSep 10 2007Nov 30 2007We show that there are regions of parameter space in multi-scalar doublet models where, in the first few hundred inverse femtobarns of data, the new charged and neutral scalars are not directly observable at the LHC and yet the Higgs decay rate to b bbar ... More

Constraining the Axion-Photon Coupling with Massive StarsOct 04 2012We point out that stars in the mass window ~ 8-12 Msun can serve as sensitive probes of the axion-photon interaction, g_{A\gamma\gamma}. Specifically, for these stars axion energy losses from the helium-burning core would shorten and eventually eliminate ... More

MESAFace, a graphical interface to analyze the MESA outputAug 29 2012MESA (Modules for Experiments in Stellar Astrophysics) has become very popular among astrophysicists as a powerful and reliable code to simulate stellar evolution. Analyzing the output data thoroughly may, however, present some challenges and be rather ... More

Comment on studying the corrections to factorization in B -> D(*) XMar 01 2001Mar 08 2001We propose studying the mechanism of factorization in exclusive decays of the form B->D(*)X by examining the differential decay rate as a function of the invariant mass of the light hadronic state X. If factorization works primarily due to the large N_c ... More

Filaments in the southern giant lobe of Centaurus A: constraints on nature and origin from modelling and GMRT observationsApr 09 2014May 23 2014We present results from imaging of the radio filaments in the southern giant lobe of Centaurus A using data from GMRT observations at 325 and 235 MHz, and outcomes from filament modelling. The observations reveal a rich filamentary structure, largely ... More

Scaling laws for soliton pulse compression by cascaded quadratic nonlinearitiesJun 11 2007Aug 20 2007We present a detailed study of soliton compression of ultra-short pulses based on phase-mismatched second-harmonic generation (\textit{i.e.}, the cascaded quadratic nonlinearity) in bulk quadratic nonlinear media. The single-cycle propagation equations ... More

Optical solitons in graded-index multimode fiberFeb 07 2013Solitons are non-dispersing localized waves that occur in diverse physical settings. A variety of optical solitons have been observed, but versions that involve both spatial and temporal degrees of freedom are rare. Optical fibers designed to support ... More

Color Breaking in the Early UniverseMar 05 2013Mar 27 2013We explore the possibility that color symmetry SU(3) was not an exact symmetry at all times in the early universe, using minimal extensions of the standard model that contain a color triplet scalar field and perhaps other fields. We show that, for a range ... More

Analyticity and the Isgur-Wise FunctionNov 06 1992We reconsider the recent derivation by de Rafael and Taron of bounds on the slope of the Isgur-Wise function. We argue that one must be careful to include cuts starting below the heavy meson pair production threshold, arising from heavy quark-antiquark ... More

The Rare Decays $\piee$, $\etaee$ and \etamumu$ in Chiral Perturbation TheoryJul 10 1992We calculate the decay rates for $\piee$, $\etaee$ and $\etamumu$ in chiral perturbation theory. The linear combination of counterterms necessary to render these amplitudes finite is fixed by the recently measured branching fraction for $\etamumu$. We ... More

Towards a High Energy Theory for the Higgs Phase of GravitySep 22 2005Sep 30 2005Spontaneous Lorentz violation due to a time-dependent expectation value for a massless scalar has been suggested as a method for dynamically generating dark energy. A natural candidate for the scalar is a Goldstone boson arising from the spontaneous breaking ... More

Simulations of the merging cluster of galaxies Cygnus ADec 13 2018The archetype FR-II galaxy Cygnus A lies in a moderately rich cluster about to undergo a major merger. We study the pre-merger Cygnus cluster environment using smoothed particle hydrodynamics simulations constrained by 2Ms of Chandra observations of the ... More

Scalar Representations and Minimal Flavor ViolationNov 11 2009Nov 18 2009We discuss the representations that new scalar degrees of freedom (beyond those in the minimal standard model) can have if they couple to quarks in a way that is consistent with minimal flavor violation. If the new scalars are singlets under the flavor ... More

Minimal Extension of the Standard Model Scalar SectorNov 01 2006The minimal extension of the scalar sector of the standard model contains an additional real scalar field with no gauge quantum numbers. Such a field does not couple to the quarks and leptons directly but rather through its mixing with the standard model ... More

Charm Mass Dependence of the $\CO(α_s^2 n_f)$ Correction to Inclusive $B\rightarrow X_c e\barν_e$ DecayOct 26 1994We compute the $\alpha_s^2 n_f$ perturbative QCD contribution to semileptonic B decay, including the finite mass of the charm quark. This result provides an estimate of the size of the two-loop correction, which is found to be about 50\% of the one-loop ... More

Population III Stars and Remnants in High Redshift GalaxiesMay 06 2013Jun 27 2013Recent simulations of Population III star formation have suggested that some fraction form in binary systems, in addition to having a characteristic mass of tens of solar masses. The deaths of metal-free stars result in the initial chemical enrichment ... More

Non-Gaussian Enhancements of Galactic Halo Correlations in Quasi-Single Field InflationNov 07 2017We consider a quasi-single field inflation model in which the inflaton interacts with a massive scalar field called the isocurvaton. Due to the breaking of time translational invariance by the inflaton background, these interactions induce kinetic mixing ... More

Fully Coupled Simulation of Cosmic Reionization. III. Stochastic Early Reionization by the Smallest GalaxiesApr 28 2017Sep 22 2018Previously we identified a new class of early galaxy that we estimate contributes up to 30\% of the ionizing photons responsible for reionization. These are low mass halos in the range $M_h =10^{6.5}-10^{8} M_{\odot}$ that have been chemically enriched ... More

Perturbative Strong Interaction Corrections to the Heavy Quark Semileptonic Decay RateSep 13 1994Oct 03 1994We calculate the part of the order $\alpha_s^2$ correction to the semileptonic heavy quark decay rate proportional to the number of light quark flavors, and use our result to set the scale for evaluating the strong coupling in the order $\alpha_s$ term ... More

The B -> X_s gamma Photon SpectrumMar 10 1999The photon energy spectrum in inclusive weak radiative B -> X_s gamma decay is computed to order alpha_s^2 beta_0. This result is used to extract a value for the HQET parameter $\bar\Lambda$ from the average <1-2E_\gamma/m_B>, and a value of the parameter ... More

Gauge Theory for Baryon and Lepton Numbers with LeptoquarksApr 02 2013May 16 2013Models where the baryon (B) and lepton (L) numbers are local gauge symmetries that are spontaneously broken at a low scale are revisited. We find new extensions of the Standard Model which predict the existence of fermions that carry both baryon and lepton ... More

Hadronic Event Shapes in $B$ DecayNov 18 1993We compute the differential momentum correlation function for hadrons produced in the decay of $B$-mesons. This measure of hadronic event shapes tests the free $b$-quark decay picture for nonleptonic and semileptonic decays of $B$-mesons. Our results ... More

Quasi Single Field Inflation in the non-perturbative regimeJun 29 2017Dec 18 2017In quasi single field inflation there are massive fields that interact with the inflaton field. If these other fields are not much heavier than the Hubble constant during inflation ($H$) these interactions can lead to important consequences for the cosmological ... More

Spontaneous Lorentz Violation and the Long-Range Gravitational Preferred-Frame EffectJan 28 2005Mar 23 2005Lorentz-violating operators involving Standard Model fields are tightly constrained by experimental data. However, bounds are more model-independent for Lorentz violation appearing in purely gravitational couplings. The spontaneous breaking of Lorentz ... More

The Hrushovski property for hypertournaments and profinite topologiesSep 17 2018We study the problem of extending partial isomorphisms for hypertournaments, which are relational structures generalizing tournaments. This is a generalized version of an old question of Herwig and Lascar. We show that the generalized problem has a negative ... More

Universal Three Dimensional Optical LogicJul 18 2014Modern integrated circuits are essentially two-dimensional (2D). Partial three-dimensional (3D) integration and 3D-transistor-level integrated circuits have long been anticipated as routes to improve the performance, cost and size of electronic computing ... More

The Flight Spectral Response of the ACIS InstrumentSep 09 2002Sep 24 2002We discuss the flight calibration of the spectral response of the Advanced CCD Imaging Spectrometer (ACIS) on-board the Chandra X-ray Observatory (CXO). The spectral resolution and sensitivity of the ACIS instrument have both been evolving over the course ... More

A right-handed isotropic medium with a negative refractive indexAug 23 2004The sign of the refractive index of any medium is soley determined by the requirement that the propagation of an electromagnetic wave obeys Einstein causality. Our analysis shows that this requirement predicts that the real part of the refractive index ... More

Stable Heavy Pentaquark StatesFeb 09 2004If the Theta^+(1540) is interpreted as a bound state of a $\bar s$ quark and two (ud) diquarks in a relative P-wave, then it is very likely that there exist pentaquark states with a heavy antiquark, $\bar b$ or $\bar c$, and two ``light'' diquarks in ... More

The Insignificance of Global Reheating in the Abell 1068 Cluster: Multiwavelength AnalysisOct 01 2003We present a detailed, multiwavelength study of the Abell 1068 galaxy cluster, and we use this data to test cooling and energy feedback models of galaxy clusters. Near ultraviolet and infrared images of the cluster show that the cD galaxy is experiencing ... More

Enhanced nonperturbative effects in jet distributionsDec 18 2002Mar 11 2003We consider the triple differential distribution d\Gamma/(dE_J)(dm_J^2)(d\Omega_J) for two-jet events at center of mass energy M, smeared over the endpoint region m_J^2 << M^2, |2 E_J -M| ~ \Delta, \lqcd << \Delta << M. The leading nonperturbative correction, ... More

High-power femtosecond pulses without a modelocked laserMay 10 2017Jul 20 2017We demonstrate a fiber system which amplifies and compresses pulses from a gain-switched diode. A Mamyshev regenerator shortens the pulses and improves their coherence, enabling subsequent amplification by parabolic pre-shaping. As a result, we are able ... More

Reverse Triangle Inequalities for Riesz Potentials and Connections with PolarizationJul 23 2013We study reverse triangle inequalities for Riesz potentials and their connection with polarization. This work generalizes inequalities for sup norms of products of polynomials, and reverse triangle inequalities for logarithmic potentials. The main tool ... More

Conformal Invariance for Non-Relativistic Field TheoryOct 04 1999Jan 29 2000Momentum space Ward identities are derived for the amputated n-point Green's functions in 3+1 dimensional non-relativistic conformal field theory. For n=4 and 6 the implications for scattering amplitudes (i.e. on-shell amputated Green's functions) are ... More

Wigner symmetry in the limit of large scattering lengthsFeb 16 1999Mar 01 1999We note that in the limit where the NN 1S0 and 3S1 scattering lengths, a^(1S0) and a^(3S1), go to infinity, the leading terms in the effective field theory for strong NN interactions are invariant under Wigner's SU(4) spin-isospin symmetry. This explains ... More

Ultrafast and octave-spanning optical nonlinearities from strongly phase-mismatched cascaded interactionsSep 20 2011Jul 12 2012Cascaded nonlinearities have attracted much interest, but ultrafast applications have been seriously hampered by the simultaneous requirements of being near phase-matching and having ultrafast femtosecond response times. Here we show that in strongly ... More

Light bullets in quadratic media with normal dispersion at the second harmonicFeb 14 2003Stable two- and three-dimensional spatiotemporal solitons (STSs) in second-harmonic-generating media are found in the case of normal dispersion at the second harmonic (SH). This result, surprising from the theoretical viewpoint, opens a way for experimental ... More

Nonlocal explanation of stationary and nonstationary regimes in cascaded soliton pulse compressionJun 13 2007Aug 19 2007We study soliton pulse compression in materials with cascaded quadratic nonlinearities, and show that the group-velocity mismatch creates two different temporally nonlocal regimes. They correspond to what is known as the stationary and nonstationary regimes. ... More

Compensation of nonlinear phase shifts with third-order dispersion: fiber stretchers can out-perform grating stretchers in short-pulse fiber amplifiersApr 07 2005We show that nonlinear phase shifts and third-order dispersion can compensate each other in short-pulse fiber amplifiers. In particular, we consider chirped-pulse fiber amplifiers at wavelengths for which the fiber dispersion is normal. The nonlinear ... More

Comment on $V_{ub}$ from Exclusive Semileptonic B and D DecaysNov 06 1997Mar 10 1998The prospects for determining $|V_{ub}|$ from exclusive B semileptonic decay are discussed. The double ratio of form factors $(f^{B\to\rho}/f^{B\to K^*})/ (f^{D\to\rho}/f^{D\to K^*})$ is calculated using chiral perturbation theory. Its deviation from ... More

Multi-megawatt, self-seeded Mamyshev oscillatorFeb 24 2018We demonstrate a fiber oscillator that achieves 3 MW peak power, is easily started and is environmentally stable. The Mamyshev oscillator delivers 190-nJ pulses that can be compressed externally to 35 fs duration. Accurate numerical modeling of the gain ... More

Limits to compression with cascaded quadratic soliton compressorsJan 04 2008We study cascaded quadratic soliton compressors and address the physical mechanisms that limit the compression. A nonlocal model is derived, and the nonlocal response is shown to have an additional oscillatory component in the nonstationary regime when ... More

Electronic states and optical properties of PbSe nanorods and nanowiresOct 28 2010A theory of the electronic structure and excitonic absorption spectra of PbS and PbSe nanowires and nanorods in the framework of a four-band effective mass model is presented. Calculations conducted for PbSe show that dielectric contrast dramatically ... More

Self-Similar Evolution of Parabolic Pulses in a LaserFeb 03 2004Apr 01 2004Self-similar propagation of ultrashort, parabolic pulses in a laser resonator is observed theoretically and experimentally. This constitutes a new type of pulse-shaping in modelocked lasers: in contrast to the well-known static (soliton-like) and breathing ... More

How Magnetic is the Dirac Neutrino?Apr 15 2005Dec 16 2005We derive model-independent, "naturalness" upper bounds on the magnetic moments \mu_\nu of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find ... More

Anthropic Distribution for Cosmological Constant and Primordial Density PerturbationsJul 21 2004Sep 29 2004The anthropic principle has been proposed as an explanation for the observed value of the cosmological constant. Here we revisit this proposal by allowing for variation between universes in the amplitude of the scale-invariant primordial cosmological ... More

An Alignment Effect in FR I Radio Galaxies: U-band Polarimetry of the Abell 2597 Cluster Central GalaxyOct 28 1998We have obtained U-band polarimetry of the spatially extended, blue optical continuum associated with the FR I radio source PKS 2322-122. PKS 2322-122 is located in the Abell 2597 cluster central galaxy. We find a three sigma upper limit to the degree ... More

The Birth of a Galaxy: Primordial Metal Enrichment and Stellar PopulationsNov 11 2010Nov 30 2011By definition, Population III stars are metal-free, and their protostellar collapse is driven by molecular hydrogen cooling in the gas-phase, leading to large characteristic masses. Population II stars with lower characteristic masses form when the star-forming ... More

Loop-Induced Stochastic Bias at Small WavevectorsDec 20 2017Primordial non-Gaussianities enhanced at small wavevectors can induce a power spectrum of the galaxy overdensity that differs greatly from that of the matter overdensity at large length scales. In previous work, it was shown that "squeezed" three-point ... More

LOFAR and HDF5: Toward a New Radio Data StandardDec 10 2010For decades now, scientific data volumes have experienced relentless, exponential growth. As a result, legacy astronomical data formats are straining under a burden not conceived when these formats were first introduced. With future astronomical projects ... More

Fully-Coupled Simulation of Cosmic Reionization. I: Numerical Methods and TestsJun 04 2013Dec 15 2014We describe an extension of the Enzo code to enable fully-coupled radiation hydrodynamical simulation of inhomogeneous reionization in large $\sim (100 Mpc)^3$ cosmological volumes with thousands to millions of point sources. We solve all dynamical, radiative ... More

Chandra Observation of the Cluster Environment of a WAT Radio Source in Abell 1446Jun 18 2007Nov 27 2007Wide-angle tail (WAT) radio sources are often found in the centers of galaxy clusters where intracluster medium (ICM) ram pressure may bend the lobes into their characteristic C-shape. We examine the low redshift (z=0.1035) cluster Abell 1446, host to ... More

The deformation theory of sheaves of commutative ringsJan 21 2011Jul 12 2011We define a sheaf of abelian groups whose cohomology is represented by the cotangent complex. We show how obstructions to some standard deformation problems arise as the classes of torsors under and gerbes banded by this sheaf.

A hyperelliptic Hodge integralJul 24 2008We calculate the hyperelliptic Hodge integral lambda_g lambda_{g-1} / (1 - psi) for use in arXiv:math/0702219. The proof uses the WDVV equations for the genus zero Gromov--Witten invariants of P(1,1,2).

The Birth of a Galaxy. II. The Role of Radiation PressureJun 05 2012Jul 26 2012Massive stars provide feedback that shapes the interstellar medium of galaxies at all redshifts and their resulting stellar populations. Here we present three adaptive mesh refinement radiation hydrodynamics simulations that illustrate the impact of momentum ... More

The First Population II Stars Formed in Externally Enriched Mini-halosApr 28 2015Jul 30 2015We present a simulation of the formation of the earliest Population II stars, starting from cosmological initial conditions and ending when metals created in the first supernovae are incorporated into a collapsing gas-cloud. This occurs after a supernova ... More

Heavy Quark Fragmentation to Baryons Containing Two Heavy QuarksMay 25 1993We discuss the fragmentation of a heavy quark to a baryon containing two heavy quarks of mass $m_Q\gg\Lambda_{\rm QCD}$. In this limit the heavy quarks first combine perturbatively into a compact diquark with a radius small compared to $1/\Lambda_{\rm ... More

Heavy Quark Fragmentation to Polarised QuarkoniumMay 12 1993May 13 1993We calculate the polarisation of $\psi$'s and $\Upsilon$'s produced by the fragmentation of heavy quarks. We find that fragmentation to transversely aligned quarkonium is slightly enhanced relative to longitudinally polarised. This net alignment corresponds ... More

Spatially Extended 21 cm Signal from Strongly Clustered UV and X-Ray Sources in the Early UniverseMay 08 2014Jan 27 2015We present our prediction for the local 21 cm differential brightness temperature ($\delta T_{b}$) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early Universe, by a numerical simulation of their formation ... More

Uniqueness of minimal morphisms of logarithmic schemesJan 12 2016We give a sufficient condition under which the moduli space of morphisms between logarithmic schemes is quasifinite under the moduli space of morphisms between the underlying schemes. This implies that the moduli space of stable maps from logarithmic ... More

Obstruction theories and virtual fundamental classesNov 17 2011We give a new definition of an obstruction theory for infinitesimal deformation theory and relate it to earlier definitions of Artin, Fantechi-Manetti, Li-Tian, and Behrend-Fantechi.

The deformation theory of sheaves of commutative rings IIFeb 14 2011We compare the obstruction classes defined in arXiv:1101.4069 to those defined by Illusie. We also give sheaf theoretic proofs of some of the standard properties of the cotangent complex.

Semileptonic B decays to excited charmed mesonsMay 30 1997Aug 07 1997Exclusive semileptonic B decays into excited charmed mesons are investigated at order $\Lambda_{QCD}/m_Q$ in the heavy quark effective theory. Differential decay rates for each helicity state of the four lightest excited $D$ mesons ($D_1$, $D_2^*$, $D_0^*$, ... More

The Growth of Black Holes and Bulges at the Cores of Cooling FlowsDec 11 2006Central cluster galaxies (cDs) in cooling flows are growing rapidly through gas accretion and star formation. At the same time, AGN outbursts fueled by accretion onto supermassive black holes are generating X-ray cavity systems and driving outflows that ... More

Ultrabroadband dispersive radiation by spatiotemporal oscillation of multimode wavesSep 07 2015Despite the abundance and importance of three-dimensional systems, relatively little progress has been made on spatiotemporal nonlinear optical waves compared to time-only or space-only systems. Here we study radiation emitted by three-dimensionally evolving ... More

A new chiral electro-optic effect: Sum-frequency generation from optically active liquids in the presence of a dc electric fieldJun 24 2003We report the observation of sum-frequency signals that depend linearly on an applied electrostatic field and that change sign with the handedness of an optically active solution. This recently predicted chiral electro-optic effect exists in the electric-dipole ... More

Criteria for the experimental observation of multi-dimensional optical solitons in saturable mediaSep 16 2004Criteria for experimental observation of multi-dimensional optical solitons in media with saturable refractive nonlinearities are developed. The criteria are applied to actual material parameters (characterizing the cubic self-focusing and quintic self-defocusing ... More

The Detectability of AGN Cavities in Cooling-Flow ClustersSep 02 2009Sep 04 2009Chandra X-ray Observatory has revealed X-ray cavities in many nearby cooling flow clusters. The cavities trace feedback from the central active galactic nulceus (AGN) on the intracluster medium (ICM), an important ingredient in stabilizing cooling flows ... More

Radio Properties of Cavities in the ICM: Imprints of AGN ActivityDec 14 2006We present new, high resolution radio images of sources associated with cD galaxies and X-ray cavity systems located in cluster cores. The cavity properties derived from archival Chandra observations give reliable estimates of the total jet power and ... More

Validating Semi-Analytic Models of High-Redshift Galaxy Formation using Radiation Hydrodynamical SimulationsOct 17 2017Mar 28 2018We use a cosmological hydrodynamic simulation calculated with Enzo and the semi-analytic galaxy formation model (SAM) GAMMA to address the chemical evolution of dwarf galaxies in the early universe. The long-term goal of the project is to better understand ... More

X-ray Cavities and Cooling FlowsNov 12 2003Recent data have radically altered the X-ray perspective on cooling flow clusters. X-ray spectra show that very little of the hot intracluster medium is cooler than about 1 keV, despite having short cooling times. In an increasing number of cooling flow ... More

New Perspectives on Cooling Flows and Cluster Radio SourcesDec 14 2000We discuss new results from the Chandra X-ray Observatory and XMM-Newton on cluster cooling flows, emphasizing early results from our Chandra programs. We find cooling rates reduced by factors of 5-10 compared to those from earlier missions. Nevertheless, ... More

Radiative Efficiency and Content of Extragalactic Radio Sources: Toward a Universal Scaling Relation Between Jet Power and Radio PowerJun 11 2008We present an analysis of the energetics and particle content of the lobes of 24 radio galaxies at the cores of cooling clusters. The radio lobes in these systems have created visible cavities in the surrounding hot, X-ray-emitting gas, which allow direct ... More

Optical Cherenkov radiation by cascaded nonlinear interaction: an efficient source of few-cycle energetic near- to mid-IR pulsesSep 02 2011When ultrafast noncritical cascaded second-harmonic generation of energetic femtosecond pulses occur in a bulk lithium niobate crystal optical Cherenkov waves are formed in the near- to mid-IR. Numerical simulations show that the few-cycle solitons radiate ... More