September 1999 arXiv papers — page 25

A. Bialas, W. Czyz

The coincidence method of measuring the entropy of a system, proposed some time ago by Ma, is generalized to include systems out of equilibrium. It is suggested that the method can be adapted to analyze multiparticle states produced in high-energy collisions.

G. K. Leontaris, J. Rizos

In this paper, we present solutions to the fermion mass hierarchy problem in the context of the minimal supersymmetric standard theory augmented by an anomalous family-dependent U(1)_X symmetry. The latter is spontaneously broken by non-zero vevs of a pair of singlet fields whose magnitude is determined through the D- and F-flatness conditions of the superpo

S. J. Brodsky

Exclusive and semi-exclusive processes, the diffractive dissociation of hadrons into jets, and hard diffractive processes such as vector meson leptoproduction provide new testing grounds for QCD and essential information on the structure of light-cone wavefunctions of hadrons, particularly the pion distribution amplitude. I review the basic features of the l

E. V. Bugaev, B. V. Mangazeev

The total photoabsorption cross section on the nucleon is studied using nondiagonal GVDM. Vector meson-nucleon scattering amplitudes are calculated in two-gluon exchange approximation of QCD. The off-diagonal transitions of diffraction dissociation type between different vector mesons and their contributions to the expression for the total photoabsorption cr

Shailesh Chandrasekharan

Cluster algorithms have been recently used to eliminate sign problems that plague Monte-Carlo methods in a variety of systems. In particular such algorithms can also be used to solve sign problems associated with the permutation of fermion world lines. This solution leads to the possibility of designing fermion cluster algorithms in certain cases. Using the

Frithjof Karsch

We review recent results on QCD at finite temperature and non-vanishing baryon number density. We focus on observables which are of immediate interest to experimental searches for the Quark Gluon Plasma, i.e. the phase transition temperature, the equation of state in two and three flavour QCD and thermal effects on hadron masses. Some new developments in fin

C. Alexandrou, Ph. de Forcrand, M. D'Elia

Center vortices are unambiguously identified after Laplacian Center Gauge fixing and their influence on confinement and chiral symmetry breaking is investigated on a sample of SU(2) configurations at zero and finite temperature.

C. Alexandrou, Ph. de Forcrand, M. D'Elia, H. Panagopoulos

We compare the performance of an UV-filtered Multiboson algorithm, including a global quasi-heatbath update, to the standard Hybrid Monte Carlo algorithm in full QCD with two flavours of Wilson fermions.

Roberto Frezzotti, Pietro Antonio Grassi, Stefan Sint, Peter Weisz

The problem of unphysical zero modes in lattice QCD with Wilson fermions can be solved in a clean way by including a mass term proportional to $i \psibar γ_5 τ^3 ψ$ in the standard lattice theory with Nf=2 mass degenerate Wilson quarks. We argue that up to cutoff effects, this lattice theory is equivalent to standard lattice QCD, for suitable choices of the

R. Bertle, M. Faber, J. Greensite, S. Olejnik

We investigate the structure of center projected vortices of SU(2) lattice gauge theory at zero and finite temperature. At zero temperature we find, in agreement with the area law behaviour of Wilson loops, that most of the P-vortex plaquettes are parts of a single huge vortex. This vortex is an unorientable surface and has a very irregular structure with ma

M. N. Chernodub, E. -M. Ilgenfritz, A. Schiller

Local correlations of Z-vortex operators with gauge and Higgs fields (lattice quantum vortex profiles) as well as vortex two-point functions are studied in the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs model. The vortex profiles resemble certain features of the classical vortex solutions in the continuum. The vortex-vortex inter

Maneesh Wadhwa

LEP offers an excellent opportunity to measure two photon processes over a large kinematical range and thus study the complex nature of the photon. This article reviews the experimental status of ``Two Photon Physics'' at LEP. The recent results on resonances, multi-hadron production and photon structure functions are discussed

A. Garat, R. H. Price

The ``close limit,'' a method based on perturbations of Schwarzschild spacetime, has proved to be a very useful tool for finding approximate solutions to models of black hole collisions. Calculations carried out with second order perturbation theory have been shown to give the limits of applicability of the method without the need for comparison with

Marshall Bern, David Eppstein, Pankaj K. Agarwal, Nina Amenta

Here we present the results of the NSF-funded Workshop on Computational Topology, which met on June 11 and 12 in Miami Beach, Florida. This report identifies important problems involving both computation and topology.

Pablo G. Bolcatto, Cesar R. Proetto

The combined effect of finite potential barriers and dielectric mismatch between dot and matrix on excitonic properties of semiconductor quantum dots has been studied. To avoid the unphysical divergence in the self-polarization energy which arises for the simplest and profusely adopted step-like model of the dielectric interface, we proposed a realistic (fin

Alain Karma, Youngyih H. Lee, Mathis Plapp

We investigate the three-dimensional morphology of the dendrite tip using the phase-field method. We find that, for low undercoolings, this morphology is ostensibly independent of anisotropy strength except for a localized shape distortion near the tip that only affects the value of the tip radius $ρ$ (which is crudely approximated by $ρ\approx (1-α)ρ_{Iv}$

G. Jackeli, V. Yu. Yushankhai

Based on the t-J model and the self-consistent Born approximation, the damping of quasiparticle hole states near the Fermi surface is calculated in a low doping regime. Renormalization of spin-wave excitations due to hole doping is taken into account. The damping is shown to be described by a familiar form $\text{Im}Σ({\bf k}^{\prime},ε)\propto (ε^{2}/ ε_{F}

G. Jackeli, N. M. Plakida

Dynamic spin susceptibility is calculated for the t-J model in the paramagnetic phase by applying the memory function method in terms of the Hubbard operators. A self-consistent system of equations for the memory function is obtained within the mode coupling approximation. Both itinerant hole excitations and localized spin fluctuations give contributions to

R. Crook, C. G. Smith, M. Y. Simmons, D. A. Ritchie

We have used the scanning charged tip of an Atomic Force Microscope (AFM) to produce images of the conductance variation of a quantised 1D ballistic channel. The channel was formed using electron beam defined 700 nm wide split gate surface electrodes over a high mobility GaAs/AlGaAs heterostructure with a two dimensional electron gas (2DEG) 98 nm beneath the

Peter D. Olmsted

The possible ``phase diagrams'' for shear-induced phase transitions between two phases are collected. We consider shear-thickening and shear-thinning fluids, under conditions of both common strain rate and common stress in the two phases, and present the four fundamental shear stress vs. strain-rate curves and discuss their concentration dependence.

G. Sierra, J. Dukelsky, G. G. Dussel, Jan von Delft

The reduced BCS model that is commonly used for ultrasmall superconducting grains has an exact solution worked out long ago by Richardson in the context of nuclear physics. We use it to check the quality of previous treatments of this model, and to investigate the effect of level statistics on pairing correlations. We find that the ground state energies are

M. Crescimanno, C. G. Koay, R. Peterson

We find a limit cycle in a quasi-equilibrium model of evaporative cooling of a two-component fermion gas. The existence of such a limit cycle represents an obstruction to reaching the quantum ground state evaporatively. We show that evaporatively the βμ~ 1. We speculate that one may be able to cool an atomic fermi gas further by photoassociating dimers near

A. Marco Saitta, Michael L. Klein

The mechanical resistance of a polyethylene strand subject to tension and the way its properties are affected by the presence of a knot is studied using first-principles molecular dynamics calculations. The distribution of strain energy for the knotted chains has a well-defined shape that is very different from the one found in the linear case. The presence

Proshun Sinha-Ray, Henrik Jeldtoft Jensen

We turn the stochastic critical forest-fire model introduced by Drossel and Schwabl (PRL 69, 1629, 1992) into a deterministic threshold model. This new model has many features in common with sandpile and earthquake models of Self-Organized Criticality. Nevertheless our deterministic forest-fire model exhibits in detail the same macroscopic statistical proper

Deepak Dhar

This is a somewhat expanded version of the notes of a series of lectures given at Lausanne and Stellenbosch in 1998-99. They are intended to provide a pedagogical introduction to the abelian sandpile model of self-organized criticality, and its related models : the q=0 state Potts model, Takayasu aggregation model, the voter model, spanning trees, Eulerian w

C. Groeber, R. Eder

We present a Quantum Monte Carlo study of the temperature dependent dynamics of the two-dimensional Kondo insulator. Working at the so-called symmetrical point allows to perform minus-sign free QMC simulations. Study of the temperature dependence of the single-particle Green's function and the dynamical spin correlation function provides evidence for two

S. Brosig, K. Ensslin, R. J. Warburton, C. Nguyen

We present magnetotransport experiments on high-quality InAs-AlSb quantum wells that show a perfectly clean single-period Shubnikov-de Haas oscillation down to very low magnetic fields. In contrast to theoretical expectations based on an asymmetry induced zero-field spin splitting, no beating effect is observed. The carrier density has been changed by the pe

I. Ya. Korenblit, Amnon Aharony, O. Entin-Wohlman

The combined effects of hole doping and magnetic dilution on a lamellar Heisenberg antiferromagnet are studied in the framework of the frustration model. Magnetic vacancies are argued to remove some of the frustrating bonds generated by the holes, thus explaining the increase in the temperature and concentration ranges exhibiting three dimensional long range

K. Y. Michael Wong, S. Li, Y. W. Tong

Using the cavity method and diagrammatic methods, we model the dynamics of batch learning of restricted sets of examples, widely applicable to general learning cost functions, and fully taking into account the temporal correlations introduced by the recycling of the examples.

Igor Zutic, S. Das Sarma

We show that spin-polarized electron transmission across semiconductor/superconductor (Sm/S) hybrid structures depends sensitively on the degree of spin polarization as well as the strengths of potential and spin-flip scattering at the interface. We demonstrate that increasing the Fermi velocity mismatch in the Sm and S regions can lead to enhanced junction

S. A. Vitkalov, H. Zheng, K. M. Mertes, M. P. Sarachik

This paper has been withdrawn by the authors. Measurements at many different angles spanning a broad range of electron densities indicate that the observed doubling of the period of Shubnikov-de Haas oscillations, which we had attributed to a transition to a new spin-ordered phase, is also consistent with an alternative explanation. A full interpretation of

Shiro Kawabata

We study the magneto-transport in Aharonov-Bohm (AB) billiards forming doubly connected structures. In these systems, non-averaged conductance oscillates as a function of magnetic flux with period h/e. We derive formulas of the correlation function C of the magneto-conductance for chaotic and regular AB billiards by use of the semiclassical theory. The diffe

Krzysztof Sacha, Jakub Zakrzewski, Dominique Delande

The dynamics of Rydberg states of atomic hydrogen perturbed simultaneously by a static electric field and a resonant microwave field of elliptical polarization is analysed in the quantum perturbative limit of small amplitudes. For some configurations, the secular motion (i.e. evolution in time of the elliptical electronic trajectory) may be classically predo

David Arnett

The role of hydrodynamic mixing in astrophysics is reviewed, emphasizing connections with laser physics experiments and inertial confinement fusion (ICF). Computer technology now allows two dimensional (2D) simulations, with complex microphysics, of stellar hydrodynamics and evolutionary sequences, and holds the promise for 3D. Careful validation of astrophy

M. Joffre, P. Fischer, J. Frieman, D. Johnston

We describe first results of a project to create weak lensing mass maps for a complete, X-ray luminosity-limited sample of 19 nearby (z < 0.1) southern galaxy clusters scheduled for Sunyaev-Zel&#39;dovich observations by the Viper Telescope at the South Pole. We have collected data on 1/3 of the sample and present motivation for the project as well as projec

Geraint F. Lewis, Russell M. Robb, Rodrigo A. Ibata

We report on one year of photometric monitoring of the ultraluminous BAL quasar APM 08279+5255. The temporal sampling reveals that this gravitationally lensed system has brightened by ~0.2 mag in 100 days. Two potential causes present themselves; either the variability is intrinsic to the quasar, or it is the result of microlensing by stars in a foreground s

D. Q. Lamb, Francisco J. Castander, Daniel E. Reichart

We find that the local galactic extinction towards the field of gamma-ray burst GRB970228 is $A_V=1.09^{+0.10}_{-0.20}$, which implies a substantial dimming and change in the spectral slope of the intrinsic GRB970228 afterglow. We measure a color $(V_{606}-I_{814})_{ST} = -0.18^{+0.51}_{-0.61}$ for the extended source coincident with the afterglow. Taking in

D. Q. Lamb

I review some of the highlights of the Rome Workshop on Gamma-Ray Bursts, and discuss some of the questions these results pose about the nature and origin of gamma-ray bursts.

C. Graziani, D. Q. Lamb, G. H. Marion

We use a rigorous method, based on Bayesian inference, for calculating the odds favoring the hypothesis that any particular class of astronomical transients produce gamma-ray bursts over the hypothesis that they do not. We then apply this method to a sample of 83 Type Ia supernovae and a sample of 20 Type Ib-Ic supernovae. We find overwhelming odds against t

J. Robert Buchler, Zoltan Kollath

We give a status report of convective Cepheid and RR Lyrae model pulsations. Some striking successes can be reported, despite the use of a rather simple treatment of turbulent convection with a 1D time-dependent diffusion equation for the turbulent energy. It is now possible to obtain stable double-mode (beat) pulsations in both Cepheid and RR Lyrae models w

Wei Cui, Wan Chen, S. N. Zhang

We report the first detection of a pair of correlated emission lines in the X-ray spectrum of black hole candidate 4U 1630-47 during its 1996 outburst, based on RXTE observations of the source. At the peak plateau of the outburst, the emission lines are detected, centered mostly at $\sim$5.7 keV and $\sim$7.7 keV, respectively, while the line energies exhibi

Stirling A. Colgate, J. Robert Buchler

The mechanism for efficient and coherent angular momentum transport remains one of the unsolved puzzles in astrophysics despite the enormous efforts that have been made. We suggest that important new insight could be gained in this problem through an experimental and theoretical study of a laboratory device (Ranque-Hilsch tube) that displays a similar enhanc

R. Ramaty, S. T. Scully, R. E. Lingenfelter, B. Kozlovsky

Using cosmic-ray energetics as a discriminator, we investigate evolutionary models of LiBeB. We employ a Monte Carlo code which incorporates the delayed mixing into the ISM both of the synthesized Fe, due to its incorporation into high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the transport of the cosmic rays. We normalize the LiBeB

E. Waxman, B. T. Draine

The prompt optical flash recently detected accompanying GRB990123 suggests that, for at least some GRBs, gamma-ray emission is accompanied by prompt optical-UV emission with luminosity L(1-7.5eV)=10^{49}(ΔΩ/4π)erg/s, where ΔΩis the solid angle into which gamma-ray and optical-UV emission is beamed. Such an optical-UV flash can destroy dust in the beam by sub

G. A. Mamon

A galaxy system must have a minimum velocity dispersion for its mass to be greater than the sum of the masses of its galaxies. Nearly half of the nearby Hickson compact groups (HCGs) have too low a velocity dispersion in comparison with the rotational velocities of their spiral galaxies and internal velocity dispersions of their early types. A detailed study

Roger Haynes, David Lee, Jeremy Allington-Smith, Robert Content

We describe a new system for multiple object spectroscopy and integral field spectroscopy at near-infrared wavelengths using optical fibers. Both modes of the SMIRFS instrument have been tested at the UK Infrared Telescope with the CGS4 infrared spectrograph. The modular system includes a common optical system to image the fiber slit onto the cold slit insid

F. Combes

The study of high-redshift objects is rapidly developing, allowing to build the star formation history of the Universe. Since most of the flux from starbursts comes out in the FIR region, the submm and mm are privileged domains for the exploration at high z. I review the recent work on galaxies at high redshift in this wavelength region, for the continuum as

Brian Chaboyer, P. Demarque, D. B. Guenther

A grid of stellar evolution models for Procyon A has been calculated. These models include the best physics available to us (including the latest opacities and equation of state) and are based on the revised astrometric mass of Girard et al (1996). Models were calculated with helium diffusion and with the combined effects of helium and heavy element diffusio

Pawan Kumar, Tsvi Piran

Gamma-ray bursts are believed to be some catastrophic event in which material is ejected at a relativistic velocity, and internal collisions within this ejecta produce the observed $γ$-ray flash. The angular size of a causally connected region within a relativistic flow is of the order the angular width of the relativistic beaming, $γ^{-1}$. Thus, different

John Gribbin

Spreading of life-bearing spores across the Galaxy (panspermia) may be easier than is usually acknowledged.

Stefan Gottloeber, Anatoly Klypin, Andrey V. Kravtsov

We discuss the impact of the cosmological environment on the evolution of dark matter halos using a high-resolution simulation within a spatially flat LCDM cosmology.

M. Vigotti, L. Gregorini, U. Klein, K. -H. Mack

We present total flux densities of 1049 radio sources in the frequency range from 151 MHz to 10.6 GHz. These sources belong to the B3-VLA sample, which is complete down to 100 mJy at 408 MHz. The data constitute a homogeneous spectral database for a large sample of radio sources, 50 times fainter than the 3C catalogue, and will be used to perform a spectral

Alfred Gautschy

To answer the topical question we survey synoptically the recent literature in pulsation theory. We restrict the topics to research on roAp stars, EC 14026 variables, strange modes, luminous blue variables, pulsation-rotation coupling, and pulsations in compact objects seen from the classical, as well as the relativistic viewpoint.

J. H. Knapen, I. Shlosman, C. H. Heller, R. J. Rand

We present high angular and velocity resolution two-dimensional kinematic observations in the spectral lines of H alpha and CO J=1-0 of the circumnuclear starburst region in the barred spiral galaxy M100, and compare them with kinematics derived from our previously published numerical modeling. The H alpha data, fully sampled and at sub-arcsecond resolution,

K. Takahashi, H. M. Lee

We study the evolution of globular clusters with mass spectra under the influence of the steady Galactic tidal field, including the effects of velocity anisotropy. Similar to single-mass models, velocity anisotropy develops as the cluster evolves, but the degree of anisotropy is much smaller than isolated clusters. Except for very early epochs of the cluster

Naoyuki Tamura, Hiroyuki Hirashita

In this paper, we examine whether tidal forces exerted by the Galaxy or M31 have an influence on the Local Group dwarf spheroidal galaxies (dSphs) which are their companions. We focus on the surface brightness profiles of the dSphs, especially their core radii because it is suggested based on the numerical simulations that tidal disturbance can make core rad

Jeffrey A. Willick

I describe a Tully-Fisher (TF) survey of galaxies in 15 Abell Clusters distributed around the sky in the redshift range 9000-13,000 km/sec. The observations were done between 1992 and 1995 at the Las Campanas (LCO) and Palomar Observatories. The program is known as the LP10K survey. The basic data set consists of R band CCD magnitudes and H-alpha rotation cu

Jeffrey A. Willick

The closely related issues of (1) reconstructing density and velocity fields from redshift survey and distance indicator data and (2) determining cosmological parameters from such data sets are discussed. I focus on possible explanations for the discrepant values of $β\equivΩ^{0.6}/b$ resulting from analyses that employ various reconstruction methods. Althou

Andrew W. Stephens, Jay A. Frogel, Sergio Ortolani, Roger Davies

This paper presents color transformations for HST NICMOS camera 2 observations to the ground-based CIT/CTIO photometric system, using observations of nineteen moderately bright, red stars in Baade&#39;s window in the color range 0.7 < (J-K) < 1.6. We estimate an extension of the transformation to 0.4 < (J-K) < 3.0 with five standards observed by STScI. Convo

B. Paczynski, A. Udalski, M. Szymanski, M. Kubiak

We present UBVI photometry for 8530 stars in Baade&#39;s Window obtained during the OGLE-II microlensing survey. Among these are over one thousand red clump giants. 1391 of them have photometry with errors smaller than 0.04, 0.06, 0.12, and 0.20 mag in the I, V, B and U-band, respectively. We constructed a map of interstellar reddening. The corrected colors

I. A. Lubashevsky, V. V. Gafiychuk

The equivalence of two optimality principles leading to Murray&#39;s law has been discussed. The first approach is based on minimization of biological work needed for maintaining the blood flow through the vessels at required level. The second one is the principle of minimal drag and lumen volume. Characteristic features of these principles are considered. A