February 1998 arXiv papers — page 16

Julien Favand, Frederic Mila

In order to study the tunneling of electrons through an interacting, 1D, dimerized molecule connected to leads, we consider the persistent current in a ring embedding this molecule. We find numerically that, for spinless fermions, a molecule with a gap mostly due to interactions, i.e. a Mott-Hubbard gap, gives rise to a larger persistent current than a molec

Hiroya Nakao

It is well known that a random multiplicative process with weak additive noise generates a power-law probability distribution. It has recently been recognized that this process exhibits another type of power law: the moment of the stochastic variable scales as a function of the additive noise strength. We clarify the mechanism for this power-law behavior of

P. Millet, C. Satto, J. Bonvoisin, B. Normand

We present magnetic susceptibility measurements on MgV$_2$O$_5$, a compound in which the vanadium oxide planes have the same topology as in CaV$_2$O$_5$. The most striking property is that there is an energy gap of about 15 K, much smaller than in CaV$_2$O$_5$, where the values reported are of the order of 500 K. We show that this may be understood naturally

J. C. Bonvin, Ph. A. Martin, J. Piasecki, X. Zotos

We study at the microscopic level the dynamics of a one-dimensional gravitationally interacting sticky gas. Initially, N identical particles of mass m with uncorrelated, randomly distributed velocities fill homogeneously a finite region of space. It is proved that at a characteristic time a single macroscopic mass is formed with certainty, surrounded by a du

M. Kotrla, M. Predota, F. Slanina

Interplay between kinetic roughening and phase ordering is studied in a growth SOS model with two kinds of particles and Ising-like interaction by Monte Carlo simulations. We found that, for a sufficiently large coupling, growth is strongly affected by interaction between species. Surface roughness increases rapidly with coupling. Scaling exponents for kinet

V. N. Kotov, J. Oitmaa, O. Sushkov

We analyze the ground state properties of the two-dimensional quantum antiferromagnet with a S=1/2 Kondo impurity. Perturbation theory around the strong Kondo coupling limit is developed and the results compared with studies, based on exact diagonalization of small clusters. We find that at intermediate coupling the impurity is partially screened and the mag

Masanori Yumoto, Hidetoshi Fukuyama, Hiroshi Matsukawa

The spatial inhomogeneities are expected to affect nucleation process in an essential way. These effects are studied theoretically by considering the case of the depinning of the charge density wave as a typical example. The threshold field of the depinning of the one-dimensional commensurate charge density wave with one impurity has been examined classicall

Augusto Gonzalez, Aurora Perez

We study trapped systems of bosons at zero temperature in three and two dimensions. Conditions are fulfilled for the application of Gross-Pitaevskii theory with a positive scattering length. Series expansions for ground-state properties are obtained in both the noninteracting and the strong-coupling (Thomas-Fermi) limits. From these expansions, analytic esti

Guillaume Rousseau, Hugues Chaté, Raymond Kapral

We study the behavior of vortex filaments subject to a uniform density of phase twist in oscillatory media described by the complex Ginzburg-Landau equation. The first instability is a supercritical Hopf bifurcation to stable propagating helical vortices. The secondary instability, also a forward Hopf bifurcation, leads to quasiperiodic supercoiled filaments

Keith A. Arnaud, Richard F. Mushotzky

We have analyzed 0.35-7.5 keV X-ray spectra of the center of the Perseus cluster collected using the Broad Band X-Ray Telescope (BBXRT) on the Astro-1 mission. These spectra are particularly useful for examining the nature of the X-ray absorber in cooling flows because of BBXRT's sensitivity between 0.35 and 1.0 keV. We confirm that there is X-ray absorp

Richard J. Rand

Two long-slit spectra of the diffuse ionized gas in NGC 891 are presented. The first reveals variations parallel to the major axis in emission line ratios in the halo gas at z=700 pc. It is found that filaments of Halpha emission show lower values of [NII]/Halpha, [SII]/Halpha and [OI]/Halpha. Although this result is expected if the filaments represent the w

Alice K. Harding, Alexander G. Muslimov

The study of physical processes associated with particle acceleration in the open field line region above the polar cap (PC) of an isolated neutron star (NS) plays a fundamental role in our understanding and interpretation of high-energy emission from pulsars. The systematic study of particle acceleration and formation of electron-positron pair fronts above

M. Loewenstein, K. Hayashida, T. Toneri, D. S. Davis

We have obtained the first broad-band X-ray spectra of the nearby compact elliptical galaxy M32 by using the ASCA satellite. The extracted spectra and X-ray luminosity are consistent with the properties of the hard spectral component measured in giant elliptical galaxies believed to originate from X-ray binaries. Two ASCA observations were performed two week

Coel Hellier

The SW Sextantis stars are a group of cataclysmic variables with distinctive observational characteristics, including absorption features in the emission line cores at phases 0.2-0.6. Hellier and Robinson have proposed that these features are caused by the accretion stream flowing over the accretion disk. However, in a simple model the absorption occurred at

Coel Hellier, T. Naylor

Using the latest compilation of cataclysmic variable orbital periods by Ritter & Kolb we argue against Verbunt's conclusion that the period gap is not significant for nova-like variables. We also discuss the relation of the VY Scl stars to the dwarf novae.

Coel Hellier, Koji Mukai, J. P. Osborne

Following a recent report that AO Psc has broad iron Kalpha emission lines we have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find that half of the systems have Kalpha lines broadened by ~200 eV, while the remainder have narrow lines. We argue that the Doppler effect is insufficient to explain the finding and propose that the lines o

D. V. Bisikalo, A. A. Boyarchuk, O. A. Kuznetsov, V. M. Chechetkin

Results of numerical simulations of the impact of a common envelope on the matter flow pattern near the outflowing component in a semidetached binary system are presented. Three-dimensional modeling of the matter transfer gas dynamics in a low-mass X-ray binary X1822-371 enable investigation of the structure of flows in the vicinity of the inner Lagrange poi

Alice K. Harding, Alexander G. Muslimov

We model the thermal X-ray profiles of Geminga, Vela and PSR 0656+14, which have also been detected as gamma-ray pulsars, to constrain the phase space of obliquity and observer angles required to reproduce the observed X-ray pulsed fractions and pulse widths. These geometrical constraints derived from the X-ray light curves are explored for various assumptio

Jonathan P. Gardner

I review galaxy number count models and present ncmod, an extendable and general purpose model for comparing and interpreting the results of field galaxy survey data. I develop techniques and software for converting the results of a survey done in one filter into another filter, for direct comparison with other surveys. Comparison of the data from surveys wh

R. G. Abraham

The current evidence for morphologically peculiar galaxy populations at high-redshifts is outlined. After describing various techniques which can be used to quantify the importance of ``morphological K-corrections'', and to objectively classify galaxy morphology in the presence of these biases, it is concluded that observational biases are not suffic

S. Pellegrini, L. Ciotti

We present the results of a new set of hydrodynamical simulations of hot gas flows in model elliptical galaxies with the following characteristics: the spatial luminosity distribution approaches a power law form at small radii, in accordance with the results of recent ground based observations, and with the Hubble Space Telescope; the dark matter has a peake

R. P. Olling, M. R. Merrifield

The local stellar kinematics of the Milky Way offer a useful tool for studying the rotation curve of the Galaxy. These kinematics -- usually parameterized by the Oort constants A and B -- depend on the local gradient of the rotation curve as well as its absolute value (Theta_0), and the Sun's distance to the Galactic center (R_0). The density of interste

R. G. Abraham

Evolution in the merger rate as a function of redshift is in principle the key observable testing hierarchical models for the formation and evolution of galaxies. However, in practice, direct measurement of this quantity has proven difficult. In this opening review I outline the current best estimates for the merger rate as a function of cosmic epoch, focuss

M. Colpi, R. Turolla, S. Zane, A. Treves

Old neutron stars (ONSs) which have radiated away their internal and rotational energy may still shine if accreting the interstellar medium. Despite their large number, only two promising candidates have been detected so far and rather stringent limits on their observability follow from the analysis of ROSAT surveys. This contrasts with optimistic theoretica

J. P. Aufdenberg, P. H. Hauschildt, S. N. Shore, E. Baron

We use a spherical non-LTE fully line blanketed model atmosphere to fit the full multi-wavelength spectrum, including the extreme ultraviolet (EUV) continuum observed by the {\it Extreme Ultraviolet Explorer}, of the B2 II star \epscma. The available spectrophotometry of \epscma\ from 350 Å to 25 \micron\ is best fit with model parameters \Teff = 21750\,K, \

Geoffrey C. Bower, Donald C. Backer

We present 7 mm lambda VLBA observations of the compact nonthermal radio source in the Galactic Center, Sgr A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal plasma. The measured major axis of Sgr A* is 0.76 \pm 0.04 mas, consistent with the predicted sc

I. Marquez, C. Boisson, F. Durret, P. Petitjean

We present long slit spectroscopy for the [OIII] and H$α$ wavelength ranges along nine different position angles for the Sa Seyfert 1.9 galaxy NGC 2992. Double profiles are present in several regions, suggesting that the gas is not simply following galaxy rotation. A simple kinematical model, which takes into account circular rotation together with a constan

Henning Heiselberg, Morten Hnorth-Jensen

Phase transitions in neutron stars due to formation of quark matter, kaon condensates, etc. are discussed with particular attention to the order of these transitions. Observational consequences of phase transitions in pulsar angular velocities are examined.

R. Brent Tully

A recalibration of the luminosity-linewidth technique is discussed which introduces (i) new cluster calibration data, (ii) new corrections for reddening as a function of inclination, and (iii) a new zero-point calibration using 13 galaxies with distances determined via the cepheid period-luminosity method. It is found that H_0= 82 +/- 16 km/s/Mpc (95% confid

R. Brent Tully

The first section discusses a recalibration of the luminosity-linewidth technique and its use in a determination of H_0. The recalibration introduces (i) new cluster calibration data, (ii) new corrections for reddening as a function of inclination, and (iii) a new zero-point calibration using 13 galaxies with distances determined via the cepheid period-lumin

O. Semerak, F. de Felice, V. Karas

We propose a simple and unambiguous way to deduce the parameters of black holes which may reside in AGNs and some types of X-ray binaries. The black-hole mass and angular momentum are determined in physical units. The method is applicable to the sources with periodic components of variability, provided one can assume the following: (i) Variability is due to

Einan Gardi, Marek Karliner

We investigate the possibility that alpha_s freezes as function of N_f within perturbation theory. We use two approaches -- direct search for a zero in the effective-charge (ECH) beta function, and the Banks-Zaks (BZ) expansion. We emphasize the fundamental difference between quantities with space-like vs. those with time-like momentum. We show that within t

Hitoshi Nishino

We present an alternative formulation of duality-symmetric eleven-dimensional supergravity with both three-form and six-form gauge fields. Instead of the recently-proposed scalar auxiliary field, we use a simpler lagrangian with a non-propagating auxiliary multiplier tensor field with eight-indices. We also complete the superspace formulation in a duality-sy

H. Sharda, R. K. Bansal, Ashwani Kumar

Average effective two-body interaction matrix elements in the s-d shell have been extracted, from data on experimentally measured isospin centroids, by combining the recently derived new sum rules equations for pick-up reactions with similar known equations for stripping reactions performed on general multishell target states. Using this combination of strip

Attila Csoto, Karlheinz Langanke

The He3(He3,2p)He4 and H3(H3,2n)He4 reactions are studied in a microscopic cluster model. We search for resonances in the He3+He3 and He4+p+p channels using methods that treat the two- and three-body resonance asymptotics correctly. Our results show that the existence of a low-energy resonance or virtual state, which could influence the Be-7 and B-8 solar ne

S. M. Bilenky, C. Giunti

We have considered the results of solar and atmospheric neutrino oscillation experiments in the scheme of mixing of three neutrinos with a mass hierarchy. It is shown that the recent results of the CHOOZ experiment imply that |U_{e3}|^2<<1 (U is the neutrino mixing matrix), that the oscillations of solar neutrinos are described by the two-generation formalis

U. Zuelicke, A. H. MacDonald

We argue that, at any filling factor, correlated quantum-Hall systems possess a set of chiral boson excitations which are generated by electronically rigid deformations of the system&#39;s periphery. We submit that tunneling electrons can be accommodated, at low energies, in these systems only by periphery-deformation excitations. This property would explain

Attila Csoto, Karlheinz Langanke

We calculate several &#34;size-like&#34; B-8 observables within the microscopic three-cluster model and study their potential constraints on the zero-energy astrophysical S_{17}(0) factor of the Be7(p,gamma)B8 reaction. We find within our three-cluster model that a simultaneous reproduction of the experimental data for the B-8 radius and quadrupole moment an

A. Gorsky, A. Marshakov, A. Mironov, A. Morozov

The second derivatives of prepotential with respect to Whitham time-variables in the Seiberg-Witten theory are expressed in terms of Riemann theta-functions. These formulas give a direct transcendental generalization of algebraic ones for the Kontsevich matrix model. In particular case they provide an explicit derivation of the renormalization group (RG) equ

J. M. Carmona, U. Marini Bettolo Marconi, J. J. Ruiz-Lorenzo, A. Tarancon

The present paper focuses on the order-disorder transition of an Ising model on a self-similar lattice. We present a detailed numerical study, based on the Monte Carlo method in conjunction with the finite size scaling method, of the critical properties of the Ising model on some two dimensional deterministic fractal lattices with different Hausdorff dimensi

Valery Telnov

Linear colliders offer a unique possibility to study gamma gamma and gamma electron interactions at the energies 0.1--2 TeV. This option is now included in design reports of NLC, JLC and TESLA/SBLC. This paper includes: status of photon colliders, new possibilities in study of Higgs boson, ways to achieve high luminosities.

Y. P. Jing, G. Boerner

We report the measurement of the three-point correlation function (3PCF) of galaxies for the Las Campanas Redshift Survey (LCRS). We have not only measured the 3PCF in redshift space but also developed a method to measure the projected 3PCF which has simple relations to the real space 3PCF. Both quantities have been measured as a function of triangle size an

Hodaka Oda, Shigemitsu Tomizawa, Norisuke Sakai, Tadakatsu Sakai

Recently, a non-hyperelliptic curve describing the Coulomb branch of N=2 SUSY $SU(N_c)$ Yang-Mills theory with an antisymmetric tensor matter was proposed using a configuration of a single M theory five-brane. We study the singular surface in the moduli space of the curve to compare it with results from the ``integrating in&#39;&#39; method in field theory.

Masakazu Murakami, Hidetoshi Fukuyama

The results of the mean field studies on the effects of the backward scattering with large momentum transfer in a two-dimensional electron system are extended to the case with various types of the Fermi surface and coupling constants. It is found that the coexistent state of d-wave superconductivity, antiferromagnetism and $π$-triplet pair can be stabilized

Daniel Gottesman

Instead of a quantum computer where the fundamental units are 2-dimensional qubits, we can consider a quantum computer made up of d-dimensional systems. There is a straightforward generalization of the class of stabilizer codes to d-dimensional systems, and I will discuss the theory of fault-tolerant computation using such codes. I prove that universal fault

P. Busch

This paper addresses the question whether a variant of a modal interpretation is conceivable that could accommodate property ascriptions associated with nonorthogonal resolutions of the unity and nonorthogonal families of relative states as they occur in imperfect or genuinely unsharp measurements. I will review a recent formulation of the quantum measuremen

Ph. Blanchard, P. Garbaczewski

The Schrödinger problem of deducing the microscopic dynamics from the input-output statistics data is known to admit a solution in terms of Markov diffusions. The uniqueness of solution is found linked to the natural boundaries respected by the underlying random motion. By choosing a reference Smoluchowski diffusion process, we automatically fix the Feynman-

P. Garbaczewski

We discuss the so-called Schr{ö}dinger problem of deducing the microscopic (basically stochastic) evolution that is consistent with given positive boundary probability densities for a process covering a finite fixed time interval. The sought for dynamics may preserve the probability measure or induce its evolution, and is known to be uniquely reproducible, i

P. Garbaczewski

Probablistic solutions of the so called Schrödinger boundary data problem provide for a unique Markovian interpolation between any two strictly positive probability densities designed to form the input-output statistics data for a certain dynamical process taking place in a finite-time interval. The key problem is to select the jointly continuous in all vari

R. B. Palmer

Parameters are given of machines with center-of-mass (CoM) energies of 3 TeV and 400 GeV but, besides a comment on neutrino radiation, the paper concentrates on progress on the design of a machine to operate at a light Higgs mass, assumed, for this study, to be 100 GeV (CoM).

A. Ts. Amatuni, S. G. Arutunian, M. R. Mailian

Present paper is devoted to formulation of the system of the master equations of the problem and analytical considerations of the limiting cases, which have an exact solutions (transversal and longitudinal flat bunches, linear approxim- ation). Presented consideration gives some hints to the construction of proper algorithm for numerical calculations.

Juan C. Gallardo, Richard C. Fernow, Robert B. Palmer

We present a Hamiltonian formulation of muon dynamics in toroidal sector solenoids (bent solenoids)

Kapil M. S. Bajaj, Jun Liu, Brian Naberhuis, Guenter Ahlers

We present experimental results for Rayleigh-Benard convection with rotation about a vertical axis at dimensionless rotation rates in the range 0 to 250 and upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with predictions of linear stability analysis. For rotation rates greater than 70 and close to onset, the patterns are cellular w

Henning Heiselberg

The freeze-out of hot and dense hadronic matter formed in relativistic nuclear collisions is probed by HBT interferometry of identical pions, kaons, etc. Coulomb repulsion/attraction of positive/negative particles show up at small particle momenta and is also very sensitive to the freeze-out conditions. The source sizes and times freeze-out are extracted fro

Sergei A. Voloshin

Anisotropic flow of protons, $π^{\pm}$, $K^+$, deuterons, tritons, $^3$He, and $^4$He is analyzed as a function of transverse momentum for different centralities of the collision.

Bernhard Köck

Mapping a locally free module to its l-th tensor power gives rise to a natural map from the Grothendieck group of all locally free modules to the Grothendieck group of all locally free representations of the l-th symmetric group. In this paper, we prove some formulas of Riemann-Roch type for the behaviour of this tensor power operation with respect to the pu

Joseph Lipman

The purpose, mainly expository and speculative, of this paper---an outgrowth of a survey lecture at the September 1997 Obergurgl working week---is to indicate some (not all) of the efforts that have been made to interpret equisingularity, and connections among them; and to suggest directions for further exploration. Zariski defined equisingularity on an n-di

L. Chiantini, C. Ciliberto

The Severi variety V_{n,d} of a smooth projective surface S is defined as the subvariety of the linear system |O_S(n)|, which parametrizes curves with d nodes. We show that, for a general surface S of degree k in P^3 and for all n>k-1, d=0,...,dim(|O_S(n)|), there exists one component of V_{n,d} which is reduced, of the expected dimension dim(|O_S(n)|)-d. Co

J. Daniel Christensen, Neil P. Strickland

We study phantom maps and homology theories in a stable homotopy category S via a certain Abelian category A. We express the group P(X,Y) of phantom maps X -> Y as an Ext group in A, and give conditions on X or Y which guarantee that it vanishes. We also determine P(X,HB). We show that any composite of two phantom maps is zero, and use this to reduce Margoli

K. P. Hadeler, E. N. Selivanova

There are new integrable cases due to the construction from the previous version.

C. R. Hagen

The problem of understanding the role of large gauge transformations in thermal field theories has recently inspired a number of studies of a one dimensional field theory. Such work has led to the conclusion that gauge invariance is restored only when the entire perturbation expansion can be summed. A careful reexamination of that model is shown, h0owever, t

Gernot Münster

Some points concerning the relation of strings to interfaces in statistical systems are discussed.

Jan de Boer, Kentaro Hori, Hirosi Ooguri

We study membrane scattering in a curved space with non-zero M-momentum p_{11} transfer. In the low-energy short-distance region, the membrane dynamics is described by a three-dimensional N=4 supersymmetric gauge theory. We study an n-instanton process of the gauge theory, corresponding to the exchange of n units of p_{11}, and compare the result with the sc

Vladimir E. Korepin, Takeshi Oota

We consider the scaling Lee-Yang model. It corresponds to the unique perturbation of the minimal CFT model M(2,5). This is not a unitary model. We used known expression for form factors in order to obtain a closed expression for a correlation function of a trace of energy-momentum tensor. This expression is a determinant of an integral operator. Similar dete

Kingman Cheung

The muon-proton ($μp$) collider is an interesting option of the muon collider. Here we discuss the physics potential of the $μp$ collider; especially, leptoquarks and contact interactions. We calculate the sensitivity reach for the second generation leptoquarks and leptogluons, $R$-parity violating squarks, and $μq$ contact interactions for the $μp$ collider

T. E. Browder

We review recent experimental results from CLEO and LEP experiments on hadronic decays of hadrons containing $b$ quarks. We discuss charm counting and the semileptonic branching fraction in $B$ decays and the color suppressed amplitude in $B$ decay. (to appear in the Proceedings of 1997 Heavy Flavors Conference in Santa Barbara)

Christopher T. Hill

We describe a class of models of electroweak symmetry breaking that involves strong dynamics and top quark condensation. A new scheme based upon a seesaw mechanism appears particularly promising. Various implications for the first-stage muon collider are discussed.

Lynne H. Orr

In this talk we discuss gluon radiation in top production and decay. After reviewing results for hadron colliders we consider soft gluon radiation at lepton colliders and present gluon distributions that are potentially sensitive to production-decay interference effects.

M. Shifman

1. QCD Sum Rules: 20 Years After; 2. QCD Vacuum and Basics of the SVZ Method: 2.1 General ideas; 2.2. Getting started/Playing with toy models; 3. Vacuum Condensates; 4. Rho Meson in QCD; 5. Basic Theoretical Instrument -- Wilson&#39;s OPE; 6. Practical Version of OPE; 7. Low Energy Theorems; 8. Are All Hadrons Alike? 9. Ecological Niche; 10. New Developments

M. S. Berger

Accurate measurements of particles masses, couplings and widths are possible by measuring production cross sections near threshold. We discuss the prospects for performing such measurements at a high luminosity muon collider.

Stephen Godfrey

I give an overview of the ability of a high energy $μ^+μ^-$ collider to discover new particles and interactions. I start with heavy fermions which will be the most straightforward to produce and observe. I then discuss single leptoquark production which is produced via the quark content of the photon and the discovery potential for extra gauge bosons which w

F. Klingl, W. Weise

Based on an effective Lagrangian which combines chiral SU(3) dynamics with vector meson dominance, we have developed a model for the forward vector meson-nucleon scattering amplitudes. We use this as an input to calculate the low energy part of the current-current correlation function in nuclear matter. For the isovector channel we find a significant enhance

J. A. Casas

We study the conditions for successful Affleck-Dine baryogenesis in generic inflation and supergravity scenarios, finding powerful restrictions on them. String-based SUGRA models are especially interesting since they are surprisingly suitable for the implementation not only of AD baryogenesis but also inflation itself, presenting a nice solution to the $η$--

E. J. Chun, C. W. Kim, U. W. Lee

It is shown that the singular seesaw mechanism can simultaneously explain all the existing data supporting nonzero neutrino masses and mixing. The three mass-squared differences that are needed to accommodate the atmospheric neutrino data (through $ν_μ- ν_s$ oscillation), the solar neutrino data via MSW mechanism (through $ν_e - ν_τ$ oscillation), and the po

Palash B Pal

In this talk, I discuss the general theory of neutrino oscillation experiments, putting special emphasis on the momentum distribution of the incoming neutrino beam. Then I discuss recent neutrino oscillation experiments, viz., LSND, KARMEN and CHOOZ. Experiments foreseeable in the near future have also been discussed at the end.

Alexander L. Bondarev

The various ways to reduce number of vectors describing condition of particles for high energy physics problems are presented. In particular decomposition of any vector with respect to the basis, consisting of any four linearly independent vectors, including the orthonormal basis; construction of orthonormal bases from vectors of a problem; expression of one

Alexander L. Bondarev

The article deals with a number of the existings variants of direct calculation of amplitudes of processes with polarized Dirac particles. It is shown, that all of them are special cases of one and the same mathematical scheme. The advantages and disadvantages of this scheme are considered. A new variant of the method of calculation of amplitudes, keeping al

Stephane Willocq

We review recent electroweak and B physics results obtained in polarized e+e- interactions at the SLC by the SLD experiment. Unique and precise measurements of the electroweak parameters Ae, Ab, Ac, Rb and Rc provide powerful constraints on the Standard Model. The excellent 3-D vertexing capabilities of SLD are further exploited to extract precise B+ and B0

The OPAL Collaboration, K. Ackerstaff et al

A search is described to detect charged Higgs bosons via the process e^+e^- -> H^+H^-, using data collected by the OPAL detector at center-of-mass energies of 130-172 GeV with a total integrated luminosity of 25 pb^-1. The decay channels are assumed to be H^+ -> qq&#39;(bar) and H^+ -> τ^+ ν_τ. No evidence for charged Higgs boson production is observed. The

C. Kiefer, D. Polarski, A. A. Starobinsky

According to the inflationary scenario for the very early Universe, all inhomogeneities in the Universe are of genuine quantum origin. On the other hand, looking at these inhomogeneities and measuring them, clearly no specific quantum mechanical properties are observed. We show how the transition from their inherent quantum gravitational nature to classical

G. P. Berman, G. D. Doolen, R. Mainieri, J. Rehacek

We present the results of molecular dynamics modeling on the structural properties of grain boundaries (GB) in thin polycrystalline films. The transition from crystalline boundaries with low mismatch angle to amorphous boundaries is investigated. It is shown that the structures of the GBs satisfy a thermodynamical criterion. The potential energy of silicon a

F. Marsiglio, T. Startseva, J. P. Carbotte

We outline a procedure for obtaining the electron-phonon spectral density by inversion of optical conductivity data, a process very similar in spirit to the McMillan-Rowell inversion of tunelling data. We assume both electron-impurity (elastic) and electron-phonon (inelastic) scattering processes. This procedure has the advantage that it can be utilized in t

M. Calandra, S. Sorella

We describe in detail a simple and efficient Green Function Monte Carlo technique for computing both the ground state energy and the ground state properties by the ``forward walking&#39;&#39; scheme. The simplicity of our reconfiguration process, used to maintain the walker population constant, allows to control any source of systematic error in a rigorous a

S. Scandolo, F. Ancilotto, G. L. Chiarotti, G. Santoro

We present ab-initio electronic structure results on the surface of sqr3 adsorbates. In particular, we address the issue of metal-insulator instabilities, charge-density-waves (CDWs) or spin-density-waves (SDWs), driven by partly filled surface states and their 2D Fermi surface, and/or by the onset of magnetic instabilities. The focus is both on the newly di

D. A. Gorokhov, G. Blatter

We consider the problem of the depinning of a weakly driven ($F\ll F_{c}$) pancake vortex from a columnar defect in a Josephson-coupled superconductor, where $F$ denotes the force acting on the vortex ($F_{c}$ is the critical force). The dynamics of the vortex is supposed to be of the Hall type. The Euclidean action $S_{Eucl}(T)$ is calculated in the entire

D. A. Gorokhov, G. Blatter

We analyse the thermally activated depinning of an elastic string (line tension $ε$) governed by Hall dynamics from a columnar defect modelled as a cylindrical potential well of depth $V_{0}$ for the case of a small external force $F.$ An effective 1D field Hamiltonian is derived in order to describe the 2D string motion. At high temperatures the decay rate

G. Santoro, S. Sorella, F. Becca, S. Scandolo

Motivated by the recent experimental evidence of commensurate surface CDW in Pb/Ge(111) and Sn/Ge(111) $\sqrt{3}$-adlayer structures, as well as by the insulating states found on K/Si(111):B and SiC(0001), we have investigated the role of electron-electron interactions, and also of electron-phonon coupling, on the narrow surface state band originating from t

P. Garbaczewski, G. Kondrat, R. Olkiewicz

We analyze the unforced and deterministically forced Burgers equation in the framework of the (diffusive) interpolating dynamics that solves the so-called Schrödinger boundary data problem for the random matter transport. This entails an exploration of the consistency conditions that allow to interpret dispersion of passive contaminants in the Burgers flow a

S. Bellucci, J. Gonzalez

Renormalization group methods are used to study the low-energy behavior of the unscreened Coulomb interaction in a one-dimensional electron system. By applying a GW approximation, a strong wavefunction renormalization is found in the model, as well as renormalization of the Fermi velocity. This may have significant effects depending on the filling level of t

Sergio Albeverio, Shao-Ming Fei

A set of new exact ground states of the generalized Hubbard models in arbitrary dimensions with explicitly given parameter regions is presented. This is based on a simple method for constructing exact ground states for homogeneous quantum systems.

Kicheon Kang

We derive a formula for the current through an interacting quantum dot coupled to two supercouducting leads, using the non-equilibrium Green&#39;s function formalism. It is shown that the formula takes an especially simple form, when the Andreev reflections in the junctions are negligible because of large Coulomb repulsion in the dot. Our formalism provides

Andre Kempe

This paper describes the conversion of a Hidden Markov Model into a finite state transducer that closely approximates the behavior of the stochastic model. In some cases the transducer is equivalent to the HMM. This conversion is especially advantageous for part-of-speech tagging because the resulting transducer can be composed with other transducers that en

D. M. Palmer, T. L. Cline, N. Gehrels, K. Hurley

Visible afterglow counterparts have now been detected for two GRBs (970228 and 970508) but are absent, with $L_{opt}/L_γ$ ratios at least two orders of magnitude lower, for other GRBs, e.g., 970828. The causes of this variation are unknown. Any correspondence which could be discovered between the gamma-ray properties of a GRB and its $L_{opt}/L_γ$ would be u

Tod E. Strohmayer, Alaa Ibrahim

We report on new RXTE X-ray spectral analysis of bursts from SGR 1806-20, the most prolific SGR source known. Previous studies of bursts from this source revealed a remarkable lack of spectral variability both in single bursts as well as from burst to burst. We present here some of the first evidence for significant spectral evolution within SGR bursts. We f

Tod E. Strohmayer

We summarize new RXTE observations to search for millisecond X-ray variability from the bright Galactic bulge source GX 3+1. During a short 2 ksec observation we did not detect kilohertz (kHz) quasiperiodic oscillations (QPO). We place an upper limit of about 1 % (rms) on the amplitude of such oscillations.

Janna Levin, Evan Scannapieco, Joseph Silk

The global geometry of the universe is in principle as observable an attribute as local curvature. Previous studies have established that if the universe is wrapped into a flat hypertorus, the simplest compact space, then the fundamental domain must be at least 0.4 times the diameter of the observable universe. Despite a standard lore that the other five com

E. Battaner, J. Jimenez-Vicente

Assuming the magnetic hypothesis for the formation of warps, we deduce a very simple formula for the warp curve in an idealized scenario. According to this formula the warp rises as the third power of radius in the innermost warped region, reaches the maximum slope at intermediate radii and has an asymptotic slope coincident with the direction of the extraga

Matthew N. Carlson, Jon A. Holtzman, Alan M. Watson, Carl J. Grillmair

We present an analysis of compact star clusters in deep HST/WFPC2 images of NGC 1275. B and R band photometry of roughly 3000 clusters shows a bimodality in the B-R colors, suggesting that distinct old and young cluster populations are present. The small spread in the colors of the blue clusters is consistent with the hypothesis that they are a single age po

P. Giommi, P. Padovani, E. Perlman

The results of a series of five \sax observations of the TeV BL Lac object 1ES2344+514 are briefly presented. Large amplitude luminosity variability, associated to impressive spectral changes in the hard X-rays, have been found. The shape of the lightcurve depends on energy, with the flare starting and ending in the hard band, but with maximum intensity poss

Eric G. Blackman, Insu Yi

Cosmological gamma-ray bursts (GRBs) and their afterglows seem to result from dissipation of bulk energy in relativistic outflows, but their engine has not been unambiguously identified. The engine could be a young pulsar formed from accretion induced collapse with a dynamo amplified field. Elsewhere, we suggest that such a ``Usov type&#39;&#39; strong field