August 1996 arXiv papers — page 5

James E. Hetrick

A progress report on experiences with a gauge fixing method proposed in LATTICE 94 is presented. In this algorithm, an SU(N) operator is diagonalized at each site, followed by gauge fixing the diagonal (Cartan) part of the links to Coulomb gauge using the residual abelian freedom. The Cartan sector of the link field is separated into the physical gauge field

Mark W. Bailey

We present measurements of charmonium and bottomonium production using a data sample collected by CDF during the 1992-93 p-pbar collider run at the Fermilab Tevatron.

M. L. Bedran, M. O. Calvao, I. Damiao Soares, F. M. Paiva

The gravitational properties of the {\em only} static plane-symmetric vacuum solution of Einstein's field equations without cosmological term (Taub's solution, for brevity) are presented: some already known properties (geodesics, weak field limit and pertainment to the Schwarzschild family of spacetimes) are reviewed in a physically much more transpa

Robin W Tucker, C Wang

Recent developments in theories of non-Riemannian gravitational interactions are outlined. The question of the motion of a fluid in the presence of torsion and metric gradient fields is approached in terms of the divergence of the Einstein tensor associated with a general connection. In the absence of matter the variational equations associated with a broad

Y. -C. Kao, D. -H. Lee

The manifestation of the bulk quantum Hall effect on edge is the chiral anomaly. The chiral anomaly {\it is} the underlying principle of the ``edge approach'' of quantum Hall effect. In that approach, $\sxy$ should not be taken as the conductance derived from the space-local current-current correlation function of the pure one-dimensional edge proble

T. Hassenkam, S. Pedersen, K. Baklanov, A. Kristensen

We investigate experimentally and theoretically the spin-orbit effects on the weak localization in a (110) GaAs 2-dimensional electron gas (2DEG). We analyze the role of two different terms in the spin splitting of the conduction band: the Dresselhaus terms, which arise due to the lack of inversion center in the bulk GaAs, and the Rashba terms, which are cau

C. M. Varma

The anomalous part of the NMR relaxation rate of coppernuclei in the normal state of copper-oxide metals is calculated using the orbital magnetic parts of the fluctuations derived in a recent theory to explain the long wavelength transport anomalies. Oxygen and Yttrium reside on lattice sites at which the anomalous contribution is absent at all hole densitie

J. V. Selinger, R. L. B. Selinger

Polyisocyanates can be synthesized with chiral and achiral pendant groups distributed randomly along the chains. The overall chiral order, measured by optical activity, is strongly cooperative and depends sensitively on the concentration of chiral pendant groups. To explain this cooperative chiral order theoretically, we map the random copolymer onto the one

Olle Gunnarsson, Erik Koch, Richard M. Martin

The Mott-Hubbard transition is studied for a Hubbard model with orbital degeneracy N, using a diffusion Monte-Carlo method. Based on general arguments, we conjecture that the Mott-Hubbard transition takes place for U/W \propto \sqrt{N}, where U is the Coulomb interaction and W is the band width. This is supported by exact diagonalization and Monte-Carlo calc

V. N. Muthukumar, Claudius Gros, Wolfgang Wenzel, Roser Valenti

We present experimental data for the Raman intensity in the spin-Peierls compound CuGeO_3 and theoretical calculations from a one-dimensional frustrated spin model. The theory is based on (a) exact diagonalization and (b) a recently developed solitonic mean field theory. We find good agreement between the 1D-theory in the homogeneous phase and evidence for a

M. A. Moore

The sharp drops in the resistance and magnetization which are usually attributed to a phase transition from the vortex liquid state to a crystal state are explained instead as a crossover between three and two dimensional behavior, which occurs when the phase coherence length in the liquid becomes comparable to the sample thickness. Estimates of the width of

Reinhold Egger, Herbert Schoeller

The RKKY law and the Kondo screening cloud around a magnetic impurity are investigated for correlated electrons in 1D (Luttinger liquid). We find slow algebraic distance dependences, with a crossover between both types of behavior. Monte Carlo simulations have been developed to study this crossover. In the strong coupling regime, the Knight shift is shown to

Kwan-tai Leung, Joergen Vitting Andersen

A simple and robust spring-block model obeying threshold dynamics is introduced to study surface fracture of an overlayer subject to stress induced by adhesion to a substrate. We find a novel phase transition in the crack morphology and fragment-size statistics when the strain and the substrate coupling are varied. Across the transition, the cracks display i

Onur Sehitoglu, Cem Bozsahin

In this paper we outline a lexical organization for Turkish that makes use of lexical rules for inflections, derivations, and lexical category changes to control the proliferation of lexical entries. Lexical rules handle changes in grammatical roles, enforce type constraints, and control the mapping of subcategorization frames in valency-changing operations.

Ermanno F. Borra, Marc Ferrari, Luc Girard, Gilberto Moretto

We review the present status of liquid mirror telescopes. Interferometric tests of liquid mirrors (the largest one having a diameter of 2.5 meters ) show excellent optical qualities. The basic technology is now sufficiently reliable that it can be put to work. Indeed, a handful of liquid mirrors have now been built that are used for scientific work. A 3.7-m

Manuel Forestini, Corinne Charbonnel

The structural and nucleosynthetic evolution of 3, 4, 5, 6 and \mass{7} stars with two metallicities ($Z = 0.005$ and 0.02) has been computed in detail, from the early pre-main sequence phase up to the thermally pulsing (TP) AGB phase or the onset of off-center carbon burning. Typically 10 to 20 thermal pulses have been followed for each TP-AGB object. This

C. Lobo, A. Biviano, F. Durret, D. Gerbal

We have obtained a mosaic of CCD images of the Coma cluster in the V-band covering a region of approximately 0.4 degrees$^2$ around both central cluster galaxies NGC 4889 and NGC 4874. An additional frame of $\sim$ 90 arcmin$^2$ was taken of the south-west region around NGC 4839. We derived a catalogue of 7023 galaxies and 4096 stars containing positions, ce

R. Turolla

Accretion onto old, isolated neutron stars is reviewed. The detection of their X--ray emission with ROSAT is discussed and a summary of the current status of observations is presented.

Dan Edidin, William Graham

Let $X$ be a projective variety with a torus action, which for simplicity we assume to have dimension 1. If $X$ is a smooth complex variety, then the geometric invariant theory quotient $X//G$ can be identifed with the symplectic reduction $X_r$. Lerman introduced a construction (valid for symplectic manifolds) called symplectic cutting, which constructs a m

Daniel Schaerer

We review the properties of massive star evolution in different environments, where the major environmental factor is metallicity. Comparisons between evolutionary models and observations of massive OB, WR stars and related objects are presented. We also review several observations asking for future improvements of stellar models and theoretical developments

P. Shanta, S. Chaturvedi, V. Srinivasan

Eigenstates of the linear combinations $a^2+βa^{\dagger2}$ and $ab+βa^\dagger b^\dagger$ of two boson creation and annihilation operators are presented. The algebraic procedure given here is based on the work of Shanta et al. [Phys. Rev. Lett. {\bf 72}, 1447, 1994] for constructing eigenstates of generalized annihilation operators.

S. Chaturvedi, V. Srinivasan

An interpolation between the canonical partition functions of Bose, Fermi and Maxwell-Boltzmann statistics is proposed. This interpolation makes use of the properties of Jack polynomials and leads to a physically appealing interpolation between the statistical weights of the three statistics. This, in turn, can be used to define a new exclusion statistics in

S. V. Kravchenko, D. Simonian, M. P. Sarachik, Whitney Mason

The non-linear (electric field-dependent) resistivity of the 2D electron system in silicon exhibits scaling as a function of electric field and electron density in both the metallic and insulating phases, providing further evidence for a true metal-insulator transition in this 2D system at B=0. Comparison with the temperature scaling yields separate determin

Chanju Kim, V. P. Nair

We present a functional derivation of recursion rules for scattering amplitudes in a non-Abelian gauge theory in a form valid to arbitrary loop order. The tree-level and one-loop recursion rules are explicitly displayed.

Gautam Bhattacharyya

I review the bounds on the $R$-parity-violating supersymmetric Yukawa couplings from the considerations of proton stability, $n$--$\bar{n}$ oscillation, $ν_e$-Majorana mass, neutrino-less double $β$ decay, charged-current universality, $e$--$μ$--$τ$ universality, $ν_μ$--$e$ scattering, atomic parity violation, $ν_μ$ deep-inelastic scattering, $K^{+}$-decays,

V. A. Smirnov

Explicit formulae for asymptotic expansions of Feynman diagrams in typical limits of momenta and masses with external legs on the mass shell are presented.

Gabriel Lopes Cardoso, Gottfried Curio, Dieter Lust

We consider a class of four parameter D=4, N=2 string models, namely heterotic strings compactified on K3 times T2 together with their dual type II partners on Calabi-Yau three-folds. With the help of generalized modular forms (such as Siegel and Jacobi forms), we compute the perturbative prepotential and the perturbative Wilsonian gravitational coupling F1

Marek Zukowski, Ryszard Horodecki, Michal Horodecki, Pawel Horodecki

The structure of a local hidden variable model for experiments involving sequences of measurements rigorously is analyzed. Constraints imposed by local realism on the conditional probabilities of the outcomes of such measurement schemes are explicitly derived. The violation of local realism in the case of ``hidden nonlocality'' is illustrated by an o

Andrzej Czarnecki, Vladimir A. Smirnov

An asymptotic expansion of the two-loop two-point ``master'' diagram with two masses $m$ and $M$, on the mass shell $Q^2=M^2$, is presented. The treatment of the non-analytical terms arising in the expansion around the branching point is discussed. Some details of the calculation of a new class of two-loop integrals are given.

F. De Fazio

The matrix element of the kinetic energy operator between B meson states is computed by means of a QCD relativistic potential model, with the result: $μ_π^2=0.66 GeV^2$. A comparison with the outcome of other theoretical approaches and a discussion of the phenomenological implications of this result are carried out.

S. Kasuya, M. Kawasaki, T. Yanagida

We investigate two cosmological axion problems (isocurvature fluctuations and domain-wall formation) in chaotic inflationary universe. It is believed that these problems are solved if potential for the Peccei-Quinn scalar field is very flat. However, we find that too many domain walls are produced through parametric resonance decay of the Peccei-Quinn scalar

Maarten Golterman, Yigal Shamir

We present a lattice gauge-fixing action $S_{gf}$ with the following properties: (a) $S_{gf}$ is proportional to the trace of $(\sum_μ\partial_μA_μ)^2$, plus irrelevant terms of dimension six and higher; (b) $S_{gf}$ has a unique absolute minimum at $U_{x,μ}=I$. Noting that the gauge-fixed action is not BRST invariant on the lattice, we discuss some importan

HoSeong La

Dilatation, i.e. scale, symmetry in the presence of the dilaton in Minkowski space is derived from diffeomorphism symmetry in curved spacetime, incorporating the volume-preserving diffeomorphisms. The conditions for scale invariance are derived and their relation to conformal invariance is examined. In the presence of the dilaton scale invariance automatical

G. S. Agarwal, S. Chaturvedi

A new proof for the completeness of the coherent states $D(α)\mid f>$ for the Heisenberg Weyl group and the groups $SU(2)$ and $SU(1,1)$ is presented. Generalizations of these results and their consequences are disussed.

Erik Koelink

Lecture notes for an eight hour course on quantum groups and $q$-special functions at the fourth Summer School in Differential Equations and Related Areas, Universidad Nacional de Colombia and Universidad de los Andes, Bogotá, Colombia, July 22 -- August 2, 1996. The lecture notes contain an introduction to quantum groups, $q$-special functions and their int

O. A. Rumyantsev, M. H. Urin

A nonstandard method for calculating the nuclear $2νββ$ - decay amplitude is proposed. The method is based on the explicit use of those approximate symmetries of a nuclear hamiltonian, which correspond to the operators of allowed $β$ -- transitions. Within the framework of the proposed method the mentioned amplitude is calculated for a wide range of nuclei.

Ziwei Lin, Miklos Gyulassy

Opposite-sign lepton pairs ($ee$,$eμ$ and $μμ$) from open charm decay are proposed as a measure of nuclear shadowing effects. Via an approximate scaling the ratio of the dilepton spectra from $p+A$ to those from $pp$ reflects the shadowing function well. We show that the required measurements are feasible at the Relativistic Heavy ion Collider (RHIC) by cons

G. Jonkmans, S. Ahmad, D. S. Armstrong, G. Azuelos

The first measurement of the elementary process $\mu^- p \rightarrow \nu_{\mu} n \gamma$ is reported. A photon pair spectrometer was used to measure the partial branching ratio ($2.10 \pm 0.22) \times 10^{-8}$ for photons of k > 60 MeV. The value of the weak pseudoscalar coupling constant determined from the partial branching ratio is $g_p(q^{2}=-0.88m_{\mu}

C. Wei, Steven P. Lewis, E. J. Mele, Andrew M. Rappe

We present a method for calculating ab initio interatomic forces which scales quadratically with the size of the system and provides a physically transparent representation of the force in terms of the spatial variation of the electronic charge density. The method is based on a reciprocity theorem for evaluating an effective potential acting on a charged ion

Erich Poppitz, Lisa Randall

It has been argued that the superpotential can be renormalized in the presence of massless particles. Possible implications which have been considered include the restoration of supersymmetry at higher loops or a shift to a supersymmetric vacuum state. We argue that even in the presence of massless particles, there are no new contributions to the superpotent

D. C. Cabra, K. D. Rothe

We consider the QCD$_2$ partition function in the non-local, decoupled formulation and systematically establish which subset of the nilpotent Noether charges is required to vanish on the physical states. The implications for the Hilbert space structure are also examined.

H. C. Pauli, J. Merkel

The front form Hamiltonian for quantum chromodynamics, reduced to an effective Hamiltonian acting only in the $q\bar q$ space, is solved approximately. After coordinate transformation to usual momentum space and Fourier transformation to configuration space a second order differential equation is derived. This retarded Schrödinger equation is solved by varia

S. Chaturvedi, V. Srinivasan

A general formula for the grand canonical partition function for a para Fermi system of any order and of any number of levels is derived.

Clovis Wotzasek

We study the non-abelian extension of the soldering process of two chiral WZW models of opposite chiralities, resulting in a (non-chiral) WZW model living in a 2D space-time with non trivial Riemanian curvature.

S. Willenbrock

I review the status of the top quark, and look forward to three topics relevant to future top-quark physics; spin correlation, single-top-quark production, and unification.

Robert J. Oakes

The full order $α_s^4$ perturbative QCD calculation of the production of $B_c$ mesons at the Tevatron is compared with the fragmentation approximation. The non-fragmentation diagrams, in which two or more quarks and/or gluons can simultaneously be nearly on-shell, are important unless $P_T\gg M_{B_c}$.

Debajyoti Choudhury, Jan Kalinowski

We perform a detailed analysis of the processes $e^+e^- \rightarrow \barν νγ$ and $\barνν\bar{q}q$ at future linear $e^+e^-$ colliders and assess their sensitivity to anomalous gauge boson couplings. We consider center of mass energies $\sqrt{s}=$ 350, 500 and 800 GeV. We demonstrate that significant improvements can be obtained if the phase space informatio

M. Cacciari

The state of the art of the theoretical calculations for heavy quarks photoproduction is reviewed. The full next-to-leading order calculation and two possible resummations, the high energy one for total cross sections and the large $p_T$ one for differential cross sections, are described.

Sean Fleming, Oscar F. Hernandez, Ivan Maksymyk, Helene Nadeau

We present the non-relativistic QCD (NRQCD) prediction for the polarization of the J-Psi produced in b to J-Psi + X, as well as the helicity-summed production rate. We propose that these observables provide a means of measuring the three most important color-octet NRQCD matrix elements involved in J-Psi production. Anticipating the measurement of the polariz

S. Jadach, W. Placzek, B. F. L. Ward

We present O(alpha) YFS exponentiated results for wide angle Bhabha scattering at LEP/SLC energies using a new Monte Carlo event generator BHWIDE 1.xx. Our calculations include two options for the pure weak corrections, as presented in Beenakker et al. and in Bohm et al. From comparison with the results of Beenakker et al., Montagna et al. and Cacciari et al

W. J. Stirling

Some of the new experimental results and theoretical developments presented at the Workshop on Deep Inelastic Scattering and Related Phenomena (Rome, April 1996) are reviewed.

A. Rebhan

In hot gauge theories, perturbation theory at the scale of the Debye screening mass requires the resummation of the so-called hard thermal loops, which corresponds to using an effective action obtained by integrating out the modes with momentum of order of the temperature. As is well-known, quantities which are sensitive to the nonperturbative magnetic scree

A. V. Kotikov, G. Parente

We present a set of formulae to extract the longitudinal deep inelastic structure function $F_L$ from the transverse structure function $F_2$ and its derivative $dF_2/dlnQ^2$ at small $x$. Using $F_2$ HERA data we obtain $F_L$ in the range $10^{-4} \leq x \leq 10^{-2}$ at $Q^2=20$ GeV$^2$

M. Stratmann, W. Vogelsang

We study photoproduction of jets and heavy flavors in a polarized collider mode of HERA at $\sqrt{S}= 298$ GeV. We examine the sensitivity of the cross sections and their asymmetries to the proton's polarized gluon distribution and to the completely unknown parton distributions of longitudinally polarized photons.

Toshiaki Ito

The unitarity triangle on the first quadrant in the $ρ-η$ plane is discussed in the framework of the quark mass matrices in the NNI basis. If the quark mass matrices of the up-type is the Fritzsch one and the down-type is the one proposed by Branco et al., respectively, one gets the unitarity triangle with the vertex on the first quadrant. This simple model

M. Takizawa, Y. Nemoto, M. Oka

We study the \egg, \egm and \epg decays using an extended three-flavor Nambu-Jona-Lasinio model that includes the 't~Hooft instanton induced interaction. We find that the $η$-meson mass, the \egg, \egm and \epg decay widths are in good agreement with the experimental values when the $U_{A}(1)$ breaking is strong and the flavor $SU(3)$ singlet-octet mixin

Kei-Ichi Kondo

We discuss how to define and obtain the running coupling of a gauge theory in the approach of the Schwinger-Dyson equation, in order to perform a non-perturbative study of the theory. For this purpose, we introduce the nonlocally generalized gauge fixing into the SD equation, which is used to define the running coupling constant (this method is applicable on

Y. Iwasaki, K. Kanaya, S. Kaya, S. Sakai

We investigate and elucidate the phase structure of QCD for general number of flavors $N_F$ with Wilson quarks, varying $N_F$ from 2 up to 300. Based on numerical results combined with the result of the perturbation theory we propose the following picture: When $N_F \ge 17$, there is only a trivial fixed point and therefore the theory in the continuum limit

Jeffrey E. Mandula, Michael C. Ogilvie

We discuss the renormalization of the lattice formulation of the Heavy Quark Effective Theory (LHQET). In addition to wave function and composite operator renormalizations, on the lattice the classical velocity is also renormalized. The origin of this renormalization is the reduction of Lorentz (or O(4)) invariance to (hyper)cubic invariance. We present resu

G. Boyd, B. Allés, M. D'Elia, A. Di Giacomo

We investigate the performance of the hybrid Monte Carlo algorithm in updating non-trivial global topological structures. We find that the hybrid Monte Carlo algorithm has serious problems decorrelating the global topological charge. This represents a warning which must be seriously considered when simulating full QCD, regardless of the number and type of fe

F. Csikor, Z. Fodor, J. Hein, J. Heitger

The finite temperature phase transition in the SU(2)-Higgs model at a Higgs boson mass $M_H \simeq 35$ GeV is studied in numerical simulations on four dimensional lattices with time-like extensions up to $L_t=5$. $T_c/M_H$ is extrapolated to the continuum limit and a comparison with the perturbative prediction is made. A one-loop calculation to the coupling

U. Kerres

A procedure is proposed to study QFT at zero or at finite temperature by a sequence of real space renormalization group (RG) or blockspin transformations. They transform to effective theories on coarser and coarser lattices.The ultimate aim is to compute constraint effective potentials, i.e. the free energy as a function of suitable order parameters.From the

M. E. Berbenni-Bitsch, A. P. Gottlob, S. Meyer, M. Puetz

The Hybrid Monte Carlo algorithm for the simulation of QCD with dynamical staggered fermions is compared with Kramers equation algorithm. We find substantially different autocorrelation times for local and nonlocal observables. The calculations have been performed on the parallel computer CRAY T3D.

Jun Nishimura

Inspired by a possible relation between large $N$ gauge theory and string theory, we search for nontrivial fixed points in large $N$ gauge theory in more than four dimensions. We study large $N$ gauge theory through Monte Carlo simulation of the twisted Eguchi-Kawai model in six dimensions as well as in four dimensions. The phase diagram of the system with t

B. Alles, C. Christou, A. Feo, H. Panagopoulos

Using the background field technique, we calculate the 3-loop beta function of lattice $SU(N)$ gauge theories. In the pure gluonic case, we present our results, comparing to those recently obtained by Luescher and Weisz. We also provide a progress report in the case of QCD with Wilson fermions.

Yigal Shamir

The lattice formulation of gauge theories in a renormalizable gauge is discussed. The formulation invokes a new phase diagram, and it may allow for a lattice definition of Chiral Gauge Theories.

S. Aoki, M. Doui, T. Hatsuda, Y. Kuramashi

First results of lattice QCD simulation on the nucleon tensor-charge $δq$ are presented. From the quenched QCD simulations with the Wilson quark action at $β= 5.7$ on a 16$^3\times$ 20 lattice and on a $12^3\times 20$ lattice, we find (i) the connected part $δq_{con.}$ is determined with small statistical error, (ii) the disconnected part $δq_{dis.}$, which

Shun-ichi Kitahara, Shinji Ejiri, Tsuneo Suzuki, Koji Yasuta

The critical properties of the abelian Polyakov loop and the Polyakov loop in terms of Dirac string are studied in finite temperature abelian projected $SU(2)$ QCD. The critical point and the critical exponents are determined from each Polyakov loop in the maximally abelian gauge using the finite-size scaling analyses. Those critical points and exponents are

M. G. Alford, T. R. Klassen, G. P. Lepage

We describe two ideas useful in the construction of highly improved quark actions for simulations on coarse lattices: (1) Field transformations to solve the doubler problem without destroying tree-level improvement for on- or off-shell quantities. (2) Anisotropic lattices with smaller temporal than spatial lattice spacing. We present first simulation results

Carmen Chicone, Bahram Mashhoon, David Retzloff

The long term nonlinear dynamics of a Keplerian binary system under the combined influences of gravitational radiation damping and external tidal perturbations is analyzed. Gravitational radiation reaction leads the binary system towards eventual collapse, while the external periodic perturbations could lead to the ionization of the system via Arnold diffusi

Raphael Bousso

The Reissner-Nordstrom-de Sitter black holes of standard Einstein-Maxwell theory with a cosmological constant have no analogue in dilatonic theories with a Liouville potential. The only exception are the solutions of maximal mass, the Charged Nariai solutions. We show that the structure of the solution space of the Dilatonic Charged Nariai black holes is qui

William M. Pezzaglia

The automorphism invariant theory of Crawford[J. Math. Phys. 35, 2701 (1994)] has show great promise, however its application is limited by the paradigm to the domain of spin space. Our conjecture is that there is a broader principle at work which applies even to classical physics. Specifically, the laws of physics should be invariant under polydimensional t

Svante Janson, Donald E. Knuth

A perturbation technique can be used to simplify and sharpen A. C. Yao's theorems about the behavior of shellsort with increments $(h,g,1)$. In particular, when $h=Θ(n^{7/15})$ and $g=Θ(h^{1/5})$, the average running time is $O(n^{23/15})$. The proof involves interesting properties of the inversions in random permutations that have been $h$-sorted and $g

H. -J. Mikeska, U. Neugebauer, U. Schollwoeck

We investigate antiferromagnetic spin ladders with nonmagnetic impurities by variational and numerical (Lanczos and DMRG) methods. The interaction between the two unpaired spins opposite to the impurities is described by an effective exchange interaction $J_{eff}$, the magnitude of which depends on the impurity distance. The magnitude of $J_{eff}$ is differe

Michael Lassig, Harald Kinzelbach

The strong-coupling regime of Kardar-Parisi-Zhang surface growth driven by short-ranged noise has an upper critical dimension d_> less or equal to four (where the dynamic exponent z takes the value z (d_>) = 2). To derive this, we use the mapping onto directed polymers with quenched disorder. Two such polymers coupled by a small contact attraction are shown

Frank K. Wilhelm, Andrei D. Zaikin, Gerd Schoen

Recent experiments on the proximity induced supercurrent in mesoscopic normal wires revealed a surprising temperature dependence. They suggest clean-limit behavior although the wires are strongly disordered. We demonstrate that this unexpected scaling is actually contained in the conventional description of diffusive superconductors and find excellent agreem

B. Elattari, V. Kagalovsky, H. A. Weidenmueller

The passage of light or of electrons through a disordered medium is modified in the presence of resonances. We describe a simple model for this problem, and present first results.

R. Hilfer, F. M. Haas

Continuum Monte-Carlo simulations at constant pressure are performed on short chain molecules at surfaces. The rodlike chains, consisting of seven effective monomers, are attached at one end to a flat twodimensional substrate. It is found that the model exhibits phases similar to the liquid condensed and liquid expanded phases of Langmuir monolayers. The mod

L. J. Storrie-Lombardi, R. G. McMahon, M. J. Irwin

Though observationally rare, damped Lya absorption systems dominate the mass density of neutral gas in the Universe. Eleven high redshift damped Lya systems covering 2.8<z<4.4 were discovered in 26 QSOs from the APM z>4 QSO Survey, extending these absorption system surveys to the highest redshifts currently possible. Combining our new data set with previous

L. J. Storrie-Lombardi, M. J. Irwin, R. G. McMahon

Eleven candidate damped Lya absorption systems were identified in 27 spectra of the quasars from the APM z>4 survey covering the redshift range 2.8<z(abs)<4.4 (8 with z(abs)>3.5). High resolution echelle spectra (0.8A FWHM) have been obtained for three quasars, including 2 of the highest redshift objects in the survey. Two damped systems have confirmed HI co

Christopher W. Mauche

Properties of the quasi-coherent oscillations in the extreme ultraviolet (EUV) flux of the dwarf nova SS Cygni are described, with emphasis on (1) the scaling between the period of the oscillation and the EUV flux and (2) the mean power spectra and waveforms. In addition, a quasi-coherent oscillation at ν= 0.012 +/- 0.002 Hz (FWZI) is discovered and proposed

L. Morales-Rueda, M. D. Still, P. Roche

We present time-resolved spectrophotometry of GK Per taken on the rise to outburst maximum, in which we detect 5000 s QPOs in the optical emission lines. We use this opportunity to provide a kinematically-resolved analysis of the phenomenon. Observations are consistent with reprocessing off blobs of gas orbiting within the inner accretion disc, and evidence

Laerte Sodré, Héctor Cuevas

We have investigated some statistical properties of integrated spectra of galaxies with principal component analysis. The projection of the spectra onto the plane defined by the first two principal components shows that normal galaxies are in a quasi-linear sequence that we call spectral sequence and is closely related to the Hubble morphological sequence. W

C. M. Baugh, J. P. Gardner, C. S. Frenk, R. M. Sharples

We present the first measurement of the angular correlation function in a $K$-selected galaxy survey, from two fields covering almost 10 square degrees. The angular correlation function at small angles is well described by a $θ^{-0.8}$ power law, as for optically selected samples. The clustering amplitude is reduced by a factor of $\sim 4$ between galaxies w

B. Leibundgut

The singular way of scheduling at major observatories has favored certain types of astronomy. This has led to the discrimination of certain types of observations which could not be accommodated. It is the goal of future operations to open possibilities for some additional types of observational astronomy. Together with improved observatory operations the new

B. Leibundgut, J. Spyromilio

Distant supernovae can now be detected routinely. To date 34 supernovae at $z > 0.1$ have been discovered. Among them are 12 Type~Ia supernovae confirmed spectroscopically and suited to measure the cosmic deceleration when appropriately employed as standard candles. However, peak magnitudes have been determined for only two objects so far and a determination

Man Hoi Lee, Arif Babul, Lev Kofman, Nick Kaiser

In Paper I we studied the theory of gravitational microlensing for a planar distribution of point masses. In this second paper, we extend the analysis to a three-dimensional lens distribution. First we study the lensing properties of three-dimensional lens distributions by considering in detail the critical curves, the caustics, the illumination patterns, an

Lev Kofman, Nick Kaiser, Man Hoi Lee, Arif Babul

(Abridged) In this paper we refine the theory of microlensing for a planar distribution of point masses. We derive the macroimage magnification distribution P(A) at high magnification (A-1 >> tau^2) for a low optical depth (tau << 1) lens distribution by modeling the illumination pattern as a superposition of the patterns due to individual ``point mass plus

Ralph Kaufmann

We prove a general formula for the intersection form of two arbitrary monomials in boundary divisors. Furthermore we present a tree basis of the cohomology of $\overline {M}_{0,n}$. With the help of the intersection form we determine the Gram matrix for this basis and give a formula for its inverse. This enables us to calculate the tensor product of the high

Lucia Caporaso, Joe Harris

We obtain a recursive formula answering the following question: How many irreducible, plane curves of degree d and (geometric) genus g pass through 3d-1+g general points in the plane? The formula is proved by studying suitable degenerations of plane curves.

Lucia Caporaso, Joe Harris

We answer some enumerative questions about irreducible rational curves on Hirzebruch surfaces, by combining an idea of Kontsevich with the study of the geometry of certain natural parameter spaces. Our formulas generalize Kontsevich&#39;s formula for rational plane curves of given degree.

Lucia Caporaso, Joe Harris

A new, simple method to approach enumerative questions about rational curves on rational surfaces is described. Applications include a short proof of Kontsevich&#39;s formula for plane curves and a the solution of the analogous problem for the Hirzebruch surface F_3.

S. Majid

We show that the bicovariant first order differential calculi on a factorisable semisimple quantum group are in 1-1 correspondence with irreducible representations $V$ of the quantum group enveloping algebra. The corresponding calculus is constructed and has dimension $dim V^2$. The differential calculi on a finite group algebra $C G$ are also classified and

Scott A. Grossman, Ronald E. Taam

Double-diffusive convection refers to mixing where the effects of thermal and composition gradients compete to determine the stability of a fluid. In addition to the familiar fast convective instability, such fluids exhibit the slow, direct salt finger instability and the slow, overstable semiconvective instability. Previous approaches to this subject usuall

Yuri Shirman

We consider Dynamical Supersymmetry Breaking (DSB) in models with classical flat directions. We analyze a number of examples, and develop a systematic approach to determine if classical flat directions are stabilized in the full quantum theory, or lead to run-away behavior. In some cases pseudo-flat directions remain even at the quantum level before taking i

Trygve Johnsen

We study a connection between two topics: Decoding of Goppa codes arising from an algebraic curve, and rank two extensions of certain line bundles on the curve.

N. N. Scoccola, H. Weigel, B. Schwesinger

Static polarizabilities of the low--lying $1/2^+$ baryons are studied within the collective coordinate approach to the three flavor generalization of the Skyrme model; in particular, magnetic polarizabilities are considered. Predicted polarizabilities, which result from different treatments of the strange degrees of freedom in this model, are critically comp

N. N. Nikolaev, W. Schaefer, B. G. Zakharov, V. R. Zoller

We discuss the implications of a strong enhancement of diffraction for multiproduction in DIS off nuclear targets. The predicted effects are large and observable at HERA. We present the prediction of a large tensor structure function b_2(x) of the deuteron which does not vanish at small x.

Dae Sung Hwang, C. S. Kim, Wuk Namgung

We derive the virial theorem of the relativistic two-body system for the study of the B-meson physics. It is also shown that the solution of the variational equation always satisfies the virial theorem. From the virial theorem we also obtained $μ_π^2 \equiv -λ_1 \equiv < p^2> = 0.40\sim 0.58$ GeV$^2$, which is consistent with the result of the QCD sum rule c

P. Ko

I review recent developments in theoretical understandings of J/psi productions in various processes at Tevatron, B decay and J/psi photoproduction including the color-octet mechanism.