October 1998 arXiv papers — page 23

Rainer Walke, Klaus Morawetz

Using a pseudo-particle technique we simulate large-amplitude isoscalar giant octupole excitations in a finite nuclear system. Dependent on the initial conditions we observe either clear octupole modes or over-damped octupole modes which decay immediately into quadrupole ones. This shows clearly a behavior beyond linear response. We propose that octupole mod

J. J. Blanco-Pillado, Ken D. Olum

We classify the possible shapes of cosmic string cusps and how they transform under Lorentz boosts. A generic cusp can be brought into a form in which the motion of the cusp tip lies in the plane of the cusp. The cusp whose motion is perpendicular to this plane, considered by some authors, is a special case and not the generic situation. We redo the calculat

Michael D. Hildreth

Knowledge of the beam energy at LEP2 is of primary importance to set the absolute energy scale for the measurement of the W-boson mass. The beam energy above 80 GeV is derived from continuous measurements of the magnetic bending field by 16 NMR probes situated in a number of the LEP dipoles. The relationship between the fields measured by the probes and the

Ting-Wai Chiu

The response of the Neuberger-Dirac fermion operator $D=\Id + V$ in the topologically nontrivial background gauge field depends on the negative mass parameter $m_0$ in the Wilson-Dirac fermion operator $D_w$ which enters $D$ through the unitary operator $V = D_w (D_w^{\dagger} D_w)^{-1/2}$. We classify the topological phases of $D$ by comparing its index to

Petr M. Lavrov, Jorge Ananias Neto, Wilson Oliveira

The aim of this paper is to consider a possibility of constructing for arbitrary dynamical systems with first-class constraints a generalized canonical quantization method based on the osp(1,2) supersymmetry principle. This proposal can be considered as a counterpart to the osp(1,2)-covariant Lagrangian quantization method introduced recently by Geyer, Lavro

Lawrence Ein, Robert Lazarsfeld

We present in this paper a geometric theorem which clarifies and extends in several directions work of Brownawell, Kollar and others on the effective Nullstellensatz. To begin with, we work on an arbitrary smooth complex projective variety X, with previous results corresponding to the case when X is projective space. In this setting we prove a local effectiv

Takeshi Chiba

We point out that the singular instanton of Hawking-Turok type, in which the singularity occurs due to the divergence of a massless scalar field, can be generated by Euclideanized regular $p$-brane solutions in string (or M-) theory upon compactification to four dimensions.

Evgeny Ivanov, Galliano Valent

We present details of the harmonic space construction of a quaternionic extension of the four-dimensional Taub-NUT metric. As the main merit of the harmonic space approach, the metric is obtained in an explicit form following a generic set of rules. It exhibits $SU(2)\times U(1)$ isometry group and depends on two parameters, Taub-NUT `mass' and the cosmo

Yoshihisa Kitazawa, Hiroyuki Takata

We consider two Dirichlet p-branes with lower dimensional brane charges and their scattering. We first calculate the cylinder amplitude of open string with suitable boundary conditions. We compare this result with that in the IIB matrix model. We find the agreement between them in the long distance, low velocity, or large field limit. We also find a way to i

Kazuya Koyama, Jiro Soda

We propose a primeval baryon isocurvature model in the context of the Affleck-Dine (AD) baryogenesis mechanism. Quantum fluctuations of the AD field during inflation produce fluctuations in the baryon number. We obtain a model which gives both the appropriate baryon to entropy ratio of the order $10^{-11}$ and the gaussian baryon isocurvature perturbation of

A. Donnachie, H. G. Dosch, Michael Rueter

Cross sections for the reactions gamma^(*) gamma^(*) --> hadrons and gamma^(*) gamma^(*) --> 2 vector mesons are calculated as functions of energy (sqrt(s) > 20 GeV) and photon virtualities. Good agreement with experiment is obtained for the total hadronic cross section and, after allowing for a valence-quark contribution from the hadronic part of the photon

The WA102 Collaboration, D. Barberis et al

A study of the f1(1285) and f1(1420) produced in central pp interactions has been performed. For the first time in a single experiment the branching fractions of both mesons in all major decay modes have been determined. Both the f1(1285) and f1(1420) are consistent with being produced by double Pomeron exchange.

Takaaki Kajita

New atmospheric neutrino results from Super-Kamiokande are presented. Results from Kamiokande on upward going muons are also presented. All these data, together with the Kamiokande atmospheric neutrino data give evidence for neutrino oscillations. Two flavor nu_mu <-> nu_tau oscillations, with large sin^2(2theta) and Delta-m^2 in the region of 10^-3 to 10^-2

A. Zabrodin

We prove that the tau-function of the integrable discrete sine-Gordon model apart from the &#34;standard&#34; bilinar identities obeys a number of &#34;non-standard&#34; ones. They can be combined into a bivector 3-dimensional difference equation which is shown to contain Hirota&#39;s difference analogue of the sine-Gordon equation and both auxiliary linear

D. Arnaudon, Z. Maassarani

The XXC models are multistate generalizations of the well known spin 1/2 XXZ model. These integrable models share a common underlying su(2) structure. We derive integrable open boundary conditions for the hierarchy of conserved quantities of the XXC models . Due to lack of crossing unitarity of the R-matrix, we develop specific methods to prove integrability

Samuel L. Braunstein, H. J. Kimble

The article by Bouwmeester et al. on experimental quantum teleportation constitutes an important advance in the burgeoning field of quantum information. The experiment was motivated by the proposal of Bennett et al. in which an unknown quantum state is `teleported&#39; by Alice to Bob. As illustrated in Fig. 1, in the implementation of this procedure, by Bou

Abdelaziz M. Hamza

The fundamental problem of Farley-Buneman turbulence in the auroral $E$-region has been discussed and debated extensively in the past two decades. In the present paper we intend to clarify the different steps that the auroral $E$-region plasma has to undergo before reaching a steady state. The mode-coupling calculation, for Farley-Buneman turbulence, is deve

Abdelaziz M. Hamza

The conventional theory of resonance broadening for a two-species plasma in a magnetic field is revised, and applied to an ionospheric turbulence case. The assumptions made in the conventional theory of resonance broadening have, in the past, led to replacing the frequency $ω$ by $ω+ik_{\perp}^{2}D^{*}$ in the resonant part of the linear dielectric function

J. Sztucki, M. Daoud, M. Kibler

The parity-allowed two-photon transitions between the ground state 3A2(T2) of the configuration 3d8 in cubical symmetry and the excited states of the same configuration are obtained via a simple model. This model is developed in a symmetry adapted framework by using second-order mechanisms and ionic wave-functions. It is applied to the recent experimental re

Tom Ostoma, Mike Trushyk

A new approach to Quantum Gravity is proposed that is manifestly compatible with Cellular Automata (CA) theory, and is based on a new quantum theory of inertia where Newtonian Inertia results from the electromagnetic forces between the (electrically) charged elementary particles of an accelerated mass and the surrounding (electrically) charged virtual partic

Hermann Riecke

A number of mechanisms that lead to the confinement of patterns to a small part of a translationally symmetric pattern-forming system are reviewed: nonadiabatic locking of fronts, global coupling and conservation laws, dispersion, and coupling to additional slow modes $via$ gradients. Various connections with experimental results are made.

D. Lacroix, Ph. Chomaz

We present a general discussion of the mean field dynamics of finite nuclei prepared under extreme conditions of temperature and pressure. We compare the prediction of semi-classical approximation with complete quantum simulations. Many features of the dynamics are carefully studied such as the collective expansion, the evaporation process, the different tim

Klaus Strobel, Fridolin Weber, Manfred K. Weigel

The properties of warm symmetric and asymmetric nuclear matter are investigated in the frame of the Thomas-Fermi approximation using a recent modern parametrization of the effective nucleon-nucleon interaction of Myers and Swiatecki. Special attention is paid to the liquid-gas phase transition, which is of special interest in modern nuclear physics. We have

L. Alvarez-Ruso, E. Oset, E. Hernandez

We have developed a model for the N N --> N N pi pi reaction and evaluated cross sections for the different charged channels. The low energy part of those channels where the pions can be in an isospin zero state is dominated by N* excitation, driven by an isoscalar source followed by the decay N* --> N (pi pi, T=0, s-wave). At higher energies, and in channel

A. Yu. Korchin, D. Van Neck, M. Waroquier, O. Scholten

The process p+d \leftrightarrow 3He + γ* at intermediate energies is described using a covariant and gauge-invariant model, and a realistic pd3He vertex. Both photodisintegration of 3He and proton-deuteron capture with production of e+e- pairs are studied, and results for cross sections and response functions are presented. The effect of time-like formfactor

Daniel Ferenc

We report on a possible application of the HBT phenomenon in testing the existence of two hypothetical phenomena. First, it is argued that the existence of a rapidly developing parton cascade in the earliest stages of a high energy nuclear collision process can be tested by studying two-photon HBT correlations over a wide longitudinal momentum scale - corres

O. Tirel, G. Auger, R. Nebauer, J. Aichelin

Recently it has been argued that the linear relation between the transverse energy and the apparent probability to emit a fragment proves that the total system is in thermal equilibrium. It is shown, for a specific reaction Xe+Sn at 50 A.MeV, that the same behavior is obtained in the context of Quantum Molecular Dynamical without invoking the idea of equilib

Javier Casahorrán

We analyse the behaviour of the Dirac equation in $d=1+1$ with Lorentz scalar potential. As the system is known to provide a physical realization of supersymmetric quantum mechanics, we take advantage of the factorization method in order to enlarge the restricted class of solvable problems. To be precise, it suffices to integrate a Ricatti equation to constr

Woodford W. Zachary, Vladimir M. Shtelen

A concept of asymptotic symmetry is introduced which is based on a definition of symmetry as a reducibility property relative to a corresponding invariant ansatz. It is shown that the nonlocal Lorentz invariance of the free-particle Schrödinger equation, discovered by Fushchych and Segeda in 1977, can be extended to Galilei-invariant equations for free parti

Boris A. Kupershmidt

telegrapher&#39;s equations and some random walks of Poisson type are shown to fit into the framework of the Hamiltonian formalism after an appropriate time-dependent rescaling of the basic variables has been made.

Ahmet Satir

Differential constraints compatible with the linearized equations of partial differential equations are examined. Recursion operators are obtained by integrating the differential constraints.

Alexander A. Borghardt, Darya Ya. Karpenko

The characteristic representation, or Goursat problem, for the Klein-Fock-Gordon equation with Volkov interaction [1] is regarded. It is shown that in this representation the explicit form of the Volkov propagator can be obtained. Using the characteristic representation technique, the Schwinger integral [2] in the Volkov problem can be calculated.

Sudhir Paul, A. Roy Chowdhury

N-fold Bäcklund transformation for the Davey-Stewartson equation is constructed by using the analytic structure of the Lax eigenfunction in the complex eigenvalue plane. Explicit formulae can be obtained for a specified value of N. Lastly it is shown how generalized soliton solutions are generated from the trivial ones.

Peter E. Hydon

This paper describes a new algorithm for determining all discrete contact symmetries of any differential equation whose Lie contact symmetries are known. The method is constructive and is easy to use. It is based upon the observation that the adjoint action of any contact symmetry is an automorphism of the Lie algebra of generators of Lie contact symmetries.

Alexander Braverman, Alexander Polishchuk

In this paper we investigate the representations of reductive groups over a finite field, introduced in 1987 by D.Kazhdan and G.Laumon. We show that generically these representations are irreducible and that their character is equal to the function obtained by traces of Frobenius morphism on the stalks of the corresponding Lusztig&#39;s character sheaf. This

C. D&#39;Antoni, R. Longo, F. Radulescu

We consider conformal nets on $S^1$ of von Neumann algebras, acting on the full Fock space, arising in free probability. These models are twisted local, but non-local. We extend to the non-local case the general analysis of the modular structure. The local algebras turn out to be $III_1$-factors associated with free groups. We use our set up to show examples

Jonathan Fine

This paper defines for each object $X$ that can be constructed out of a finite number of vertices and cells a vector $fX$ lying in a finite dimensional vector space. This is the flag vector of $X$. It is hoped that the quantum topological invariants of a manifold $M$ can be expressed as linear functions of the flag vector of the $i$-graph that arises from an

Viacheslav V. Nikulin

We present a variant of the Theory of Lorentzian (i. e. with a hyperbolic generalized Cartan matrix) Kac-Moody algebras recently developed by V. A. Gritsenko and the author. It is closely related with and strongly uses results of R. Borcherds. This theory should generalize well-known Theories of finite Kac-Moody algebras (i. e. classical semisimple Lie algeb

J. F. Gomes, F. E. Mendonça da Silveira, G. M. Sotkov, A. H. Zimerman

The problem of the classification of the extensions of the Virasoro algebra is discussed. It is shown that all $H$-reduced $\hat{\cal G}_{r}$-current algebras belong to one of the following basic algebraic structures: local quadratic $W$-algebras, rational $U$-algebras, nonlocal $V$-algebras, nonlocal quadratic $WV$-algebras and rational nonlocal $UV$-algebr

Ivan G. Avramidi, Giampiero Esposito

Invariance principles determine many key properties in quantum field theory, including, in particular, the appropriate form of the boundary conditions. A crucial consistency check is the proof that the resulting boundary-value problem is strongly elliptic. In Euclidean quantum gravity, the appropriate principle seems to be the invariance of boundary conditio

Shin&#39;ichi Nojiri, Sergei D. Odintsov

Trace anomaly for dilaton coupled conformal theories on curved background with non-zero dilaton is found from supergravity side as an IR effect using AdS/CFT correspondence. For $d=2$ it coincides with the conformal anomaly for dilaton coupled scalar (up to total derivative term which is known to be ambiguous). In four-dimensional case we get conformal anoma

G. Takacs, G. M. T. Watts

There has been some debate about the validity of quantum affine Toda field theory at imaginary coupling, owing to the non-unitarity of the action, and consequently of its usefulness as a model of perturbed conformal field theory. Drawing on our recent work, we investigate the two simplest affine Toda theories for which this is an issue - a2(1) and a2(2). By

Christofer Cronstrom

I consider the problem of generalising the Abelian Coulomb gauge condition to the non-Abelian Yang-Mills theory, with an arbitrary compact and semi-simple gauge group. It is shown that a straightforward generalisation exists, which reduces the Gauss law into a form involving the gauge potentials only, but not their time derivatives. The existence and uniquen

B. Geyer, D. M. Gitman, P. M. Lavrov

A modified version of triplectic quantization, first introduce by Batalin and Martnelius, is proposed which makes use of two independent master equations, one for the action and one for the gauge functional such that the initial classical action also obeys that master equation.

Oliver Haschke, Werner Ruehl

We develop a constructive method to derive exactly solvable quantum mechanical models of rational (Calogero) and trigonometric (Sutherland) type. This method starts from a linear algebra problem: finding eigenvectors of triangular finite matrices. These eigenvectors are transcribed into eigenfunctions of a selfadjoint Schrödinger operator. We prove the feasi

Carlos Castro

The construction of a $covariant$ Loop Wave functional equation in a 4D spacetime is attained by introducing a generalized $eleven$ dimensional categorical {\bf C}-space comprised of $8\times 8$ antisymmetric matrices. The latter matrices encode the generalized coordinates of the histories of points, loops and surfaces $combined$. Spacetime Topology change a

Peter Arnold

[Talk given at &#34;Continuous Advances in QCD &#39;98.&#34;] I give a simple physical picture of why the rate $Γ$ per unit volume of non-perturbative processes in hot non-Abelian plasmas (such as electroweak baryon number violation in the very early universe) depends on coupling as $Γ\sim α^5 T^4 \ln(1/α)$. The logarithmic dependence was recently discovered

Peter Arnold, Dam T. Son, Laurence G. Yaffe

Bodeker has recently argued that non-perturbative processes in very high temperature non-Abelian plasmas (such as electroweak baryon number violation in the very hot early Universe) are logarithmically enhanced over previous estimates and take place at a rate per unit volume of order $\alpha^5 T^4 \ln(1/\alpha)$ for small coupling. We give a simple physical

G. Moultaka

I report on two papers, hep-ph/9806279 and hep-ph/9807336, where complementary strategies are proposed for the determination of the chargino/neutralino sector parameters, $M_1, M_2, μ$ and $\tan β$, from the knowledge of some physical observables. This determination and the occurrence of possible ambiguities are studied as far as possible analytically within

Gordon P. Ramsey

We have used QCD and polarized deep-inelastic scattering data to construct x-dependent polarized parton distributions. These flavor dependent distributions evolve under the NLO DGLAP equations, satisfy positivity constraints and agree well with the data. We perform all of the analysis in x-space, avoiding difficulties with moments, and use these distribution

O. M. Juraev, T. Z. Nasyrov, Kh. Ablakulov, B. N. Kuranov

The relativistic quark potential model (QPM) is developed for describingvector mesons and their leptonic decays. The new representation Salpeter equation for vector mesons is proposed. Studying the $τ\toρν$ decay theexpression for $ρ$-meson leptonic decay constant $f_ρ$ isobtained. It is shown that quark model describes on a satisfactory level both theconsta

Apostolos Pilaftsis

We review the scenario of baryogenesis through leptogenesis induced by the out-of-equilibrium decays of heavy neutrinos. We pay special attention to the resonant phenomenon of CP violation through mixing of two nearly degenerate heavy Majorana neutrinos and show how unitarity and CPT invariance is maintained within the resummation approach. An important cons

B. A. Arbuzov

The problem of possible deviations from the Standard Model is considered in the framework of a variant of dynamical electroweak symmetry breaking. The parameters of the theory are obtained, which describe deviations from SM in $Z\to \bar b b$ decay, are also consistent with leptonic left-right asymertry (SLAC data) and with the existence of a nontrivial solu

D. Boyanovsky, H. J. de Vega, R. Holman, S. Prem Kumar

The real time evolution of field condensates is solved for small and large field amplitudes in scalar theories.For small amplitudes,the quantum equations of motion for the condensate can be linearized and solved by Laplace transform. The late time evolution turns to be determined by the singularities in the complex plane (one-particle poles, two- and multi-

Leif Lonnblad

This document describes the strategies for the development of the Pythia7 program. Both the internal and external structure of the program is discussed. Some comments on relationship to other software is given as well as some comments on coding conventions and other technical details.

Bodo Lampe

The complete density matrix for all polarization configurations in the process B--> t tbar, where B is an off--shell Z or photon and t is the top quark, is calculated numerically including oneloop QCD corrections, i.e. virtual and real gluon contributions in O(alphas). The analysis is done in the framework of the helicity formalism. The results are particula

K. J. Abraham, Bodo Lampe

We point out that the so--called &#39;radiative return&#39; events at LEP2 are suited to the study of nonstandard physics, particularly if the vector bosons are emitted into the central detector region. An effective vertex is constructed which contains the most general gauge invariant eeZGamma interaction and its phenomenological consequences are examined. L

Masako Bando, Koichi Yoshioka

The recent results of neutrino experiments indicate the existence of the right-handed neutrinos with masses around intermediate scale, which affects the prediction of the bottom-tau mass ratio. In the minimal supersymmetric standard model, this effect largely depends on the right-handed neutrino mass scale and then may severely limit its lower bound. In this

P. Rehberg

Chiral symmetry is known to be decisive for an understanding of the low energy sector of strong interactions. It is thus important for a model of relativistic heavy ion collisions to incorporate the dynamical breaking and restoration of chiral symmetry. Thus we study an expansion scenario for a quark-meson plasma using the Nambu--Jona-Lasinio (NJL) model in

A. E. Kaloshin

We show that the off-shell contributions in Compton scattering by pion may exist only in the single exchange diagrams. These contributions are canceled completely in the total gauge-invariant amplitude as it confirmed by one-loop calculations. It explains, in particular, some results of the chiral pertubation theory in the order $p^4$ but this cancelation ha

Jusak Tandean, G. Valencia

We study the decays Omega^- -> Cascade+pion using heavy-baryon chiral perturbation theory to quantify the |Delta I|=1/2 rule in these decay modes. The ratio of |Delta I|=3/2 to |Delta I|=1/2 amplitudes is somewhat larger in these decays than it is in other hyperon decays. At leading order there are two operators responsible for the |Delta I|=3/2 parts of the

Dong Chen, Ping Chen, Norman H. Christ, Robert G. Edwards

We describe the completed 8,192-node, 0.4Tflops machine at Columbia as well as the 12,288-node, 0.6Tflops machine assembled at the RIKEN Brookhaven Research Center. Present performance as well as our experience in commissioning these large machines is presented. We outline our on-going physics program and explain how the configuration of the machine is varie

Robert G. Edwards, Urs M. Heller, Rajamani Narayanan

We investigate the spectral flows of the hermitian Wilson-Dirac operator in the fundamental and adjoint representations on two ensembles of pure SU(2) gauge field configurations at the same physical volume. We find several background gauge field configurations where the index of the hermitian Wilson-Dirac operator in the adjoint representation is not four ti

A. Tsapalis

We demonstrate how correlation functions for non-diagonal operators can be measured with the loop-cluster algorithm for quantum spin models. We introduce the U(1) quantum link model and present the construction of a cluster algorithm for the model. We further show how an improved estimator for Wilson loops can be realized with the flux-cluster algorithm.

BNL E871 Collaboration, D. Ambrose, C. Arroyo, M. Bachman

In an experiment designed to search for and study very rare two-body decay modes of the K-long, we have observed four examples of the decay K-long -> e+ e-, where the expected background is 0.17+-0.10 events. This observation translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12}, consistent with recent theoretical predictions. This result repr

H. T. Diehl

Direct measurements of vector boson pair production processes and trilinear gauge boson couplings have been conducted by the CDF and DO Collaborations. Preliminary results from searches for anomalous WW/WZ->muon-neutrino-jet-jet and WZ->e-e-e-neutrino production are presented. 95% CL anomalous coupling limits from previously published DO results are -0.20 <

H. Avakian

The performance of the electromagnetic calorimeter of the HERMES experiment is described. The calorimeter consists of 840 radiation resistant F101 lead-glass counters. The response to positrons up to 27.5 GeV, the comparison between the measured energy and the momentum reconstructed from tracking, long-term stability, hadron rejection and neutral meson invar

The OPAL Collaboration, G. Abbiendi et al

The fraction of Z to bbbar events in hadronic Z decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The Z to bbbar decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging t

Alicia M. Sintes, Bernard F. Schutz

We describe a new technique for removing troublesome interference from external coherent signals present in the gravitational wave spectrum. The method works when the interference is present in many harmonics, as long as they remain coherent with one another. The method can remove interference even when the frequency changes. We apply the method to the data

J. D. Brown, S. R. Lau, J. W. York

Consider the definition E of quasilocal energy stemming from the Hamilton-Jacobi method as applied to the canonical form of the gravitational action. We examine E in the standard &#34;small-sphere limit,&#34; first considered by Horowitz and Schmidt in their examination of Hawking&#39;s quasilocal mass. By the term &#34;small sphere&#34; we mean a cut S(r),

Megan Govender, Roy Maartens, Sunil Maharaj

Relaxational effects in stellar heat transport can in many cases be significant. Relativistic Fourier-Eckart theory is inherently quasi-stationary, and cannot incorporate these effects. The effects are naturally accounted for in causal relativistic thermodynamics, which provides an improved approximation to kinetic theory. Recent results, based on perturbati

Lunjin Lu, John G. Cleary

This paper answers open questions about the correctness and the completeness of Dart-Zobel algorithm for testing the inclusion relation between two regular types. We show that the algorithm is incorrect for regular types. We also prove that the algorithm is complete for regular types as well as correct for tuple distributive regular types. Also presented is

Valery I. Rupasov

Using the Bethe ansatz method, we study the ground state properties of a $U\to\infty$ Anderson impurity in a ``gapless&#39;&#39; host, where a density of band states vanishes at the Fermi level $ε_F$ as $|ε-ε_F|$. As in metals, the impurity spin is proven to be screened at arbitrary parameters of the system. However, the impurity occupancy as a function of t

G. Bruun, Y. Castin, R. Dum, K. Burnett

We develop an extension of the well-known BCS-theory to systems with trapped fermions. The theory fully includes the quantized energy levels in the trap. The key ingredient is to model the attractive interaction between two atoms by a pseudo-potential which leads to a well defined scattering problem and consequently a BCS-theory free of divergences. We prese

Franco Bagnoli

An introduction to cellular automata (both deterministic and probabilistic) with examples. Definition of deterministic automata, dynamical properties, damage spreading and Lyapunov exponents; probabilistic automata and Markov processes, nonequilibrium phase transitions, directed percolation, diffusion; simulation techniques, mean field. Investigation themes:

Till Kamppeter, Franz G. Mertens, Angel Sanchez, A. R. Bishop

We study the effects of finite temperature on the dynamics of non-planar vortices in the classical, two-dimensional anisotropic Heisenberg model with XY- or easy-plane symmetry. To this end, we analyze a generalized Landau-Lifshitz equation including additive white noise and Gilbert damping. Using a collective variable theory with no adjustable parameters we

R. Torsten Clay, Anders W. Sandvik, David K. Campbell

We investigate numerically the ground state phase diagram of the one-dimensional extended Hubbard model, including an on--site interaction U and a nearest--neighbor interaction V. We focus on the ground state phases of the model in the V >> U region, where previous studies have suggested the possibility of dominant superconducting pairing fluctuations before

Stefan Luding, Sean McNamara

The inelastic hard sphere model of granular material is simple, easily accessible to theory and simulation, and captures much of the physics of granular media. It has three drawbacks, all related to the approximation that collisions are instantaneous: 1) The number of collisions per unit time can diverge, i.e. the ``inelastic collapse&#39;&#39; can occur. 2)

Remi Monasson, Riccardo Zecchina

The (2+p)-Satisfiability (SAT) problem interpolates between different classes of complexity theory and is believed to be of basic interest in understanding the onset of typical case complexity in random combinatorics. In this paper, a tricritical point in the phase diagram of the random $2+p$-SAT problem is analytically computed using the replica approach an

S. Schinzer, M. Sokolowski, M. Biehl, W. Kinzel

Using kinetic Monte-Carlo simulations of a Solid-on-Solid model we investigate the influence of step edge diffusion (SED) and evaporation on Molecular Beam Epitaxy (MBE). Based on these investigations we propose two strategies to optimize MBE-growth. The strategies are applicable in different growth regimes: during layer-by-layer growth one can reduce the de

G. L. Bendazzoli, S. Evangelisti, G. Fano, F. Ortolani

We apply the DMRG method to the Pariser-Parr-Pople hamiltonian and investigate the onset of dimerization. We deduce the parameters of the hopping term and the contribution of the sigma bonds from ab initio calculations on ethylene. Denoting by R_{ij} the C-C distances, we perform a variational optimization of the dimerization delta= (R_{i,i+1} - R_{i-1,i})/2

Giampaolo Mistura, Francesco Ancilotto, Lorenzo Bruschi, Flavio Toigo

We have studied the wetting transition of Ar adsorbed on solid CO2 by means of high-precision adsorption isotherms measured with a quartz microbalance. We observe triple-point wetting. At variance with many theoretical studies based on a model adsorption potential, which predict for this system a genuine prewetting transition around 100K we find that a detai

M. K. Aliev, G. R. Alimov, I. Kholbaev, L. I. Leonyuk

The microwave absorption R in the Y-Ba-Cu-O single crystals was investigated near {T_c \approx 92 K} and in the external magnetic field {0<H \leq 9 kOe}. A modified ESR spectrometer was used in the experiment. The method of temperature modulation, along with the usual method of magnetic-field modulation, was first applied in studying of the microwave respons

Z. F. Ezawa

An improved composite-boson theory of quantum Hall ferromagnets is formulated both for the monolayer and bilayer systems. In this scheme the field operator describes solely the physical degrees of freedom representing the deviation from the ground state. Skyrmions are charged excitations confined to the lowest Landau level. By evaluating the excitation energ

C. H. Mak, R. Egger, H. Weber-Gottschick

A general algorithm toward the solution of the fermion sign problem in finite-temperature quantum Monte Carlo simulations has been formulated for discretized fermion path integrals with nearest-neighbor interactions in the Trotter direction. This multilevel approach systematically implements a simple blocking strategy in a recursive manner to synthesize the

Tokuzo Shimada

We revisit the globally coupled map lattice (GCML) and also propose a new extended globally coupled map lattice (EGCML) with an inverse power law interaction. In GCML we clarify the mechanism of the basic posi-nega switch in the two-cluster regime. We show that there is a natural mechanism in GCML which guarantees no mixing of maps across their mean field in

A. Refregier, S. T. Brown, M. Kamionkowski, D. J. Helfand

The coherent image distortions induced by weak gravitational lensing can be used to measure the power spectrum of density inhomogeneities in the universe. We present our on-going effort to detect this effect with the FIRST radio survey, which currently contains about 400,000 sources over 4,200 square degrees, and thus provides a unique resource for this purp

J. D. Monnier, P. G. Tuthill, B. Lopez, P. Cruzalebes

We present new observations of the red supergiant VY CMa at 1.25 micron, 1.65 micron, 2.26 micron, 3.08 micron and 4.8 micron. Two complementary observational techniques were utilized: non-redundant aperture masking on the 10-m Keck-I telescope yielding images of the innermost regions at unprecedented resolution, and adaptive optics imaging on the ESO 3.6-m

Ch. Theis, R. Spurzem

A database on shape evolution of direct N-body models formed out of cold, dissipationless collapse is generated using GRAPE and HARP special purpose computers. Such models are important to understand the formation of elliptical galaxies. Three dynamically distinct phases of shape evolution were found, first a fast dynamical collapse which gives rise to the r

Yi, Lee, Woo, Demarque

We show that the UV flux of old stellar systems can tell us about their ages. Two independent populations synthesis groups that have had wildly different views have here worked together and generated two solutions that can be easily tested using space telescopes. Proposed tests will constrain the ages of giant Es, that are often considered the oldest populat

C. Mendes de Oliveira, U. Hopp, R. Bender, N. Drory

We describe our preliminary results on a search for high-redshift ($z >$ 0.5) galaxy clusters using near-infrared photometry obtained with the Omega camera at the 3.5m telescope at Calar Alto.

Michael A. Strauss, Michael Blanton

We review the use of peculiar velocities of galaxies as a probe of cosmological models. We put particular emphasis on comparison of the peculiar velocity and density fields, focussing on the discrepancies between various recent analyses. We discuss the limitations of the commonly used linear bias model, which may lie at the heart of some of the current contr

Jochen Greiner, Rosanne DiStefano

In a recent ROSAT observation, taken during its optical low state, we found that the VY Scl star V751 Cyg was a highly luminous source of soft X-rays. The ROSAT HRI count rate of V751 Cyg was a factor of 10-20 higher than upper limits obtained with ROSAT during previous observations, during which V751 Cyg happened to be in the optical high state. Analysis of

C. S. Reynolds

Any cold, optically-thick matter in the vicinity of an accreting black hole, such as the accretion disk, can intercept and reprocess some fraction of the hard X-ray continuum emission, thereby imprinting atomic features into the observed spectrum. This process of `X-ray reflection&#39; primarily gives rise to a broad reflection `hump&#39; peaking at 30keV an

Livia Origlia, Jeffrey D. Goldader, Claus Leitherer, Daniel Schaerer

We present evolutionary synthesis models applied to near--infrared spectral features observed in the spectra of young Magellanic Cloud clusters and starburst galaxies. The temporal evolution of the first and second overtones of CO at 2.29 micron (2-0 bandhead) and 1.62 micron (6-3 bandhead) and of the (U-B), (B-V) and (J-K) colors are investigated. We find t

Patrizia A. Caraveo, Roberto Mignani, Giovanni F. Bignami

SNR0540-69 is a supernova remnant in the LMC, harbouring a young (~1600 yrs) radio/optical/X-ray pulsar (P=50 ms). Ground based Halpha imaging of the region has shown a unique spiral-like structure centered around the pulsar. In narrow band HST imaging, the feature seems resolved in a ring-like structure, probably ejected by the progenitor star in a pre-supe

Mario Mateo, Edward W. Olszewski, Heather L. Morrison

We have obtained deep photometric data in 24 fields along the southeast extension of the major axis of the Sagittarius dwarf spheroidal (Sgr dSph) galaxy, and in four fields along the northwest extension. Using star counts at the expected position of the Sgr upper main-sequence within the resulting color-magnitude diagrams (CMDs), we unambiguously detect Sgr

C. Terquem, J. Papaloizou, R. Nelson

We review results on the dynamics of warped gaseous discs. We consider tidal perturbation of a Keplerian disc by a companion star orbiting in a plane inclined to the disc. The perturbation induces the precession of the disc, and thus of any jet it could drive. In some conditions the precession rate is uniform, and as a result the disc settles into a warp mod

A. M. Read, W. Pietsch

We report here the results of spectral imaging observations with the ROSAT PSPC of the field surrounding the very nearby (D=3.38 Mpc) Sculptor galaxy, NGC7793. Many point sources are detected within the field, several of them showing evidence for variability. Seven sources are seen to lie within the optical confines of the system, the brightest (Lx ~ 9x10e38

I. Marquez, F. Durret, P. Petitjean

We have observed a sample of 15 and 8 quasars with redshifts between 0.11 and 0.87 (mean value 0.38) in the J and K&#39; bands respectively. Eleven of the quasars were previously known to be associated with extended emission line regions. After deconvolution of the image, substraction of the PSF when possible, and identification of companions with the help o