December 1998 arXiv papers — page 17

R. D. Oudmaijer, M. A. T. Groenewegen, H. Schrijver

We investigate the properties of K0V stars with Hipparcos parallaxes and spectral types taken from the Michigan Spectral Survey. The sample of 200 objects allows the empirical investigation of the magnitude selection (Malmquist) bias, which appears clearly present. By selecting those objects that are not affected by bias, we find a mean absolute magnitude of

Tom Theuns, Anthony Leonard, Joop Schaye, George Efstathiou

We have performed high-resolution hydrodynamic simulations of the Lyman-alpha forest in a variety of popular cold dark matter dominated cosmologies, including a low density and a vacuum-dominated model. The fluctuation amplitude of these models is chosen to match the observed abundance of galaxy clusters at low redshift. We assume that the intergalactic medi

M. Vivekanand, B. C. Joshi

The pair of drifting subpulses of the radio pulsar PSR B0031-07 appear to be well separated from each other on the average, overlapping at less than one thirtieth of the peak energy. Strictly, the integrated profile of the pair (after removing the drift) does not show more than two subpulses; however this result is likely to be modified with the availability

Ryoichi Nishi, Hajime Susa, Hideya Uehara, Masako Yamada

We investigate the thermal and dynamical evolution of primordial gas clouds in the universe after decoupling. Comparing the time-scale of dynamical evolution with that of fragmentation, we can estimate the typical fragmentation scale. We propose the following scenario of the formation process of first luminous objects consisting of large number stars. First,

Abhas Mitra

If the cores of Galaxies and AGNs comprise Supermassive Stars (SMSs) (Hoyle and Fowler 1963), nuclear energy generation may not be ignited for masses $M > 6\times 10^4 M_\odot$, and highly supermassive stars are likely to generate their luminosity, $L_{KH}$ slow gravitational contraction. We show that for such massive Newtonian SMSs, both the value of $L_{KH

T. Di Matteo, A. Esin, A. C. Fabian, R. Narayan

Several models for the hard X-ray Background (XRB) suggest that it is due to the emission from heavily obscured AGN. Recent studies have revealed the presence of a new population of hard X-ray sources which must contribute significantly to the XRB. However, whether the majority of these sources are obscured AGN or some other type of object at present remains

S. Perlmutter, G. Aldering, G. Goldhaber, R. A. Knop

We report measurements of the mass density, Omega_M, and cosmological-constant energy density, Omega_Lambda, of the universe based on the analysis of 42 Type Ia supernovae discovered by the Supernova Cosmology Project. The magnitude-redshift data for these SNe, at redshifts between 0.18 and 0.83, are fit jointly with a set of SNe from the Calan/Tololo Supern

J. P. Beaulieu, H. J. G. L. M. Lamers, W. J. de Wit

We will review some results based on the EROS and the on going EROS-2 microlensing surveys to search for dark matter in the Galactic halo via microlensing effects on LMC/SMC stars. Microlensing surveys provide systematic observations for millions of stars over a long period in both Magellanic Clouds and give birth to very powerful database. We will quickly r

B. Kaulakys, T. Meskauskas

The noise of signals or currents consisting from a sequence of pulses, elementary events or moving discrete objects (particles) is analyzed. A simple analytically solvable model is investigated in detail both analytically and numerically. It is shown that 1/f noise may result from the statistics of the pulses transit times with random increments of the time

Ernest Ma, Subir Sarkar, Utpal Sarkar

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an $SU(2)_R$ gauge symmetry. We study the equilibrating effects of the resulting additional right-handed

Marcos Marino, Gregory Moore, Grigor Peradze

The correlation functions of supersymmetric gauge theories on a four-manifold X can sometimes be expressed in terms of topological invariants of X. We show how the existence of superconformal fixed points in the gauge theory can provide nontrivial information about four-manifold topology. In particular, in the example of gauge group SU(2) with one doublet hy

V. Barger, K. Whisnant

We determine the three-neutrino mixing and mass parameters that are allowed by the solar and atmospheric neutrino data when vacuum oscillations are responsible for both phenomena. The global fit does not appreciably change the allowed regions for the parameters obtained from effective two-neutrino fits. We discuss how measurements of the solar electron energ

K-I. Ishikawa, T. Onogi, N. Yamada

We present the perturbative matching coefficient to $O(aα_s)$ which relates the $ΔB$=2 operator in the continuum to that of the lattice static theory, which is important in the accurate extraction of the continuum value of the $B_B$ from lattice simulations. The coefficients are obtained by the one-loop calculations in both of the continuum and lattice theor

Toshio Nakatsu, Naoto Yokoi

As a toy model to search for Hamiltonian formalism of the $AdS/CFT$ correspondence, we examine a Hamiltonian formulation of the $AdS_2/CFT_1$ correspondence emphasizing unitary representation theory of the symmetry. In the course of a canonical quantization of the bulk scalars, a particular isomorphism between the unitary irreducible representations in the b

A. Mobius, C. Frenzel, R. Thielsch, R. Rosenbaum

We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x films. The sets were prepared by different, electron-beam-evaporation-based technologies: evaporation of the alloy, and gradient deposition from separate Ni and Si crucibles. The characterization included electron and scanning tunneling microscopy, glow discharge optical emission s

Jose Gaite, Alvaro Dominguez, Juan Perez-Mercader

There is an ongoing debate in cosmology about the value of the length scale at which ``homogeneity'' in the matter distribution is reached or even if such a scale exists. In the wake of this debate, we intend in this letter to clarify the meaning of the statement transition to homogeneity and of the concept of correlation length. We show that there a

Luis N. Epele, Silvia Mollerach, Esteban Roulet

We discuss in detail the possibility of observing pairs of simultaneous parallel air showers produced by the fragments of cosmic ray nuclei which disintegrated in collisions with solar photons. We consider scenarios with different cosmic ray compositions, exploring the predicted rates for existing and planned detectors and looking for methods to extract info

Nikolas Provatas, Nigel Goldenfeld, Jonathan Dantzig, Jeffrey C. LaCombe

We examine scaling in two-dimensional simulations of dendritic growth at low undercooling, as well as in three-dimensional pivalic acid dendrites grown on NASA's USMP-4 Isothermal Dendritic Growth Experiment. We report new results on self-similar evolution in both the experiments and simulations. We find that the time dependent scaling of our low underco

B. I. Ermolaev, F. I. Olness, A. G. Shuvaev

We compute the deeply virtual Compton scattering (DVCS) amplitude for forward and backward scattering in the asymptotic limit. Since this calculation does not assume ordering of the transverse momenta, it includes important logarithmic contributions that are beyond those summed by the DGLAP evolution. These contributions lead to a power-like behavior for the

A. Meiksin, Martin White

We find statistically significant correlations in the cosmological matter power spectrum over the full range of observable scales. While the correlations between individual modes are weak, the band-averaged power spectrum shows strong non-trivial correlations. The correlations are significant when the modes in either one or both bands are in the non-linear r

Margarita Garcia Perez, Owe Philipsen, Ion Olimpiu Stamatescu

We develop a cooling method controlled by a physical cooling radius that defines a scale below which fluctuations are smoothed out while leaving physics unchanged at all larger scales. We apply this method to study topological properties of lattice gauge theories, in particular the behaviour of instantons, dislocations and instanton--anti-instanton pairs. Mo

T. Feldmann, P. Kroll, B. Stech

We present further tests and applications of the new eta-eta' mixing scheme recently proposed by us. The particle states are decomposed into orthonormal basis vectors in a light-cone Fock representation. Because of flavor symmetry breaking the mixing of the decay constants can be identical to the mixing of particle states at most for a specific choice of

Robert D. Klauber

This paper is a brief overview of a more extensive article recently published in Found. Phys. Lett. [2]. Apparent disagreement with experiment as well as internal inconsistencies found in the traditional analysis of relativistically rotating frames/disks are summarized. As one example, a point p at 0 degrees on the circumference of a rotating disk does not,

Louise M Griffiths, Domingos Barbosa, Andrew R Liddle

We use a compilation of cosmic microwave anisotropy data to constrain the epoch of reionization in the Universe, as a function of cosmological parameters. We consider spatially-flat cosmologies, varying the matter density $Ω_0$ (the flatness being restored by a cosmological constant), the Hubble parameter $h$ and the spectral index $n$ of the primordial powe

Ricardo Amorim, Nelson R. F. Braga

An interesting tool for investigating the quantum features of a field theory is the introduction of compensating fields. For instance, the anomalous divergence of the chiral current can be calculated in the field-antifield formalism from an extended form of QCD with compensating fields. The interpretation of this procedure from the bosonized point of view, i

Frederik Denef

We study the attractor mechanism in low energy effective D=4, N=2 Yang-Mills theory weakly coupled to gravity, obtained from the effective action of type IIB string theory compactified on a Calabi-Yau manifold. Using special Kähler geometry, the general form of the leading gravitational correction is derived, and from this the attractor equations in the weak

Michael B. Mensky

Decoherence of a quantum system (which then starts to display classical features) results from the interaction of the system with the environment, and is well described in the framework of the theory of continuous quantum measurements (CQM). Reviewed are the various approaches to the CQM theory, and the approach based on the effective complex Hamiltonians is

Domenico Giulini, Donald Marolf

The Dirac quantization `procedure' for constrained systems is well known to have many subtleties and ambiguities. Within this ill-defined framework, we explore the generality of a particular interpretation of the Dirac procedure known as refined algebraic quantization. We find technical conditions under which refined algebraic quantization can reproduce

P. M. Chadwick, K. Lyons, T. J. L. McComb, S. McQueen

This paper has been withdrawn by the authors.

Sergey N. Solodukhin

The existence of black hole horizon is considered as a boundary condition to be imposed on the fluctuating metrics. The coordinate invariant form of the condition for class of spherically symmetric metrics is formulated. The diffeomorphisms preserving this condition act in (arbitrary small) vicinity of the horizon and form the group of conformal transformati

A. Lipowski, D. Johnston

Using Monte Carlo simulations we show that the three-dimensional Ising model with four-spin (plaquette) interactions has some characteristic glassy features. The model dynamically generates diverging energy barriers, which give rise to slow dynamics at low temperature. Moreover, in a certain temperature range the model possesses a metastable (supercooled liq

D. S. Berman

The D-3 brane is examined from the point of view of the wrapped M-theory five brane on a torus. In particular, the S-dual versions of the 3-brane are identified as coming from different gauge choices of the auxiliary field that is introduced in the PST description of the five brane world volume theory.

M. Reinecke, W. Hillebrandt, J. C. Niemeyer

First results of simulations are presented which compute the dynamical evolution of a Chandrasekhar-mass white dwarf, consisting of equal amounts of carbon and oxygen, from the onset of violent thermonuclear burning, by means of a new two-dimensional numerical code. Since in the interior of such a massive white dwarf nuclear burning progresses on microscopic

T. -H. Gimm, S. -S. Lee, S. -P. Hong, S. -H. Suck Salk

A possibility of holon (boson) pair condensation is explored for hole doped high T_c cuprates, by using the U(1) slave-boson representation of the t-J Hamiltonian with the inclusion of hole-hole repulsion. A phase diagram of the hole doped high T_c cuprates is deduced by allowing both the holon pairing and spinon pairing. It is shown that the spin gap size r

M. Reinecke, W. Hillebrandt, J. C. Niemeyer, R. Klein

We present a new way of modeling deflagration fronts in reactive fluids, the main emphasis being on turbulent thermonuclear deflagration fronts in white dwarfs undergoing a Type Ia supernova explosion. Our approach is based on a level set method which treats the front as a mathematical discontinuity and allows full coupling between the front geometry and the

Rafael Brada, Mordehai Milgrom

We have recently discovered that the modified dynamics (MOND) implies some universal upper bound on the acceleration that can be contributed by a `dark halo'--assumed in a Newtonian analysis to account for the effects of MOND. Not surprisingly, the limit is of the order of the acceleration constant of the theory. This can be contrasted directly with the

Wynn C. G. Ho, Dong Lai

In a coalescing neutron star-neutron star (NS-NS) or neutron star-black hole (NS-BH) binary, oscillation modes of the NS can be resonantly excited by the companion during the final minutes of the inspiral. The resonant energy transfer between the orbit and NS speeds up or slows down the inspiral and induces a phase change in the emitted gravitational waves f

A. W. Thomas, C. Boros

We point out that the $\Delta\pi$ component of the nucleon wave function is vital to the interpretation of the recent H1 data for leading baryon production. While the $n/p$ ratio is equal to two with the $N\pi$ component alone, the inclusion of the $\Delta\pi$ component brings this ratio very near to unity, as observed in the experiment. This result demonstr

O. Babelon, M. Talon

We consider dynamical systems associated to Lax pairs depending rationnally on a spectral parameter. We show that we can express the symplectic form in terms of algebro--geometric data provided that the symplectic structure on L is of Kirillov type. In particular, in this case the dynamical system is integrable.

D. Bruss, C. Macchiavello

We establish a connection between optimal quantum cloning and optimal state estimation for d-dimensional quantum systems. In this way we derive an upper limit on the fidelity of state estimation for d-dimensional pure quantum states and, furthermore, for generalized inputs supported on the symmetric subspace.

H. Nikolic

The standard definition of the Poisson brackets is generalized to the non-equal-time Poisson brackets. Their relationship to the equal-time Poisson brackets, as well as to the equal- and non-equal-time commutators, is discussed.

G. Morigi, J. Eschner, J. I. Cirac, P. Zoller

We study laser cooling of two ions that are trapped in a harmonic potential and interact by Coulomb repulsion. Sideband cooling in the Lamb-Dicke regime is shown to work analogously to sideband cooling of a single ion. Outside the Lamb-Dicke regime, the incommensurable frequencies of the two vibrational modes result in a quasi-continuous energy spectrum that

Paul B. Slater

Among the monotone metrics on the (n^{2} - 1)-dimensional convex set of n x n density matrices, as Petz and Sudar have recently elaborated, there are a minimal (Bures) and a maximal one. We examine the proposition that it is physically meaningful to treat the volume elements of these metrics as densities-of-states for thermodynamic purposes. In the n = 2 (sp

Erasmo Recami

Some recent experiments, performed at Berkeley, Cologne, Florence and Vienna led to the claim that something seems to travel with a speed larger than the speed c of light in vacuum. Various other experimental results seem to point in the same direction: For instance, localized wavelet-type solutions of Maxwell equations have been found, both theoretically an

Richard Kreckel

This paper shortly describes some important changes to the pvegas-code since its first publication. It proceeds with a report on the scaling-behavior that was found on a wide range of current parallel hardware and discusses some issues of optimization that may be thrown up.

R. Marani, E. J. Robinson

Via a non-perturbative method we study the population dynamics and photoelectron spectra of Cs atoms subject to intense chirped laser pulses, with gaussian beams. We include above threshold ionization spectral peaks. The frequency of the laser is near resonance with the 6s-7p transition. Dominant couplings are included exactly, weaker ones accounted for pert

A. Strachan, C. O. Dorso

We study fragmentation of small atomistic clusters via molecular dynamics. We calculate the time scales related to fragment formation and emission. We also show that some degree of thermalization is achieved during the expansion process, which allows the determination of a local temperature. In this way we can calculate the break-up temperature as a function

A. Strachan, C. O. Dorso

We study phase transitions of small two dimensional Lennard Jones drops via microcanonical molecular dynamics in a broad energy range. We found that the caloric curve can be extended to high energies to comprehend high evaporation rates and highly non-equilibrium phenomena such as multifragmentation. Multifragmentation appears as a constant temperature regio

David Borthwick, Alejandro Uribe

Given an integral symplectic manifold, we construct a family of "coherent state" maps into complex projective space. The maps are built from sections of the tensor powers of a hermitian line bundle whose curvature is a multiple of the symplectic form. We show that this family is an almost-complex version of the Kodiara embedding. That is, the maps ar

Xiao-Song Lin, Zhenghan Wang

A model of random walk on knot diagrams is used to study the Alexander polynomial and the colored Jones polynomial of knots. In this context, the inverse of the Alexander polynomial of a knot plays the role of an Ihara-Selberg zeta function of a directed weighted graph, counting with weights cycles of random walk on a 1-string link whose closure is the knot

Julian Dontchev, Maximilian Ganster, Alev Kanibir

A topological space $(X,τ)$ is called a locally LC-space if every point of $X$ has a neighborhood $U$ such that every Lindelöf subset of $(U,τ|U)$ is a closed subset of $(U,τ|U)$. The aim of this paper is to continue the study of locally LC-spaces.

Julian Dontchev, Maximilian Ganster, Laszlo Zsilinszky

The aim of this paper is introduce and initiate the study of extremally $T_1$-spaces, i.e., the spaces where all hereditarily compact $C_2$-subspaces are closed. A $C_2$-space is a space whose nowhere dense sets are finite.

David Blanc

We define inductively a sequence of purely algebraic invariants - namely, classes in the Quillen cohomology of the Pi-algebra π_* X - for distinguishing between different homotopy types of spaces. Another sequence of such cohomology classes allows one to decide whether a given abstract Pi-algebra can be realized as the homotopy Pi-algebra of a space in the f

Boris Shoikhet

We prove a direct analogue of the classical Duflo formula in the case of $L_\infty$-algebras. We conjecture an analogous formula in the case of an arbitrary Q-manifold. When $G$ is a compact connected Lie group, the Duflo theorem for the Q-manifold $(ΠTG,d_{DR})$ is exactly the Duflo theorem for the Lie algebra $g = Lie G$. The corresponding theorem for the

David G. Wagner

Let k be a field of characteristic zero. We consider graded subalgebras A of k[x_1,...,x_m]/(x_1^2,...,x_m^2) generated by d linearly independant linear forms. Representations of matroids over k provide a natural description of the structure of these algebras. In return, the numerical properties of the Hilbert function of A yield some information about the T

Christos Epameinonda Kokorelis

We discuss aspects of the heterotic string effective field theories in orbifold constructions of the heterotic string. We calculate the moduli dependence of threshold corrections to gauge couplings in (2,2) symmetric orbifold compactifications. We perform the calculation of the threshold corrections for a particular class of abelian (2,2) symmetric non-decom

M. Bordag, K. Kirsten

We develop a formalism for the calculation of the ground state energy of a spinor field in the background of a cylindrically symmetric magnetic field. The energy is expressed in terms of the Jost function of the associated scattering problem. Uniform asymptotic expansions needed are obtained from the Lippmann-Schwinger equation. The general results derived a

G. Lambiase, V. V. Nesterenko, M. Bordag

A simple method is proposed to construct the spectral zeta functions required for calculating the electromagnetic vacuum energy with boundary conditions given on a sphere or on an infinite cylinder. When calculating the Casimir energy in this approach no exact divergencies appear and no renormalization is needed. The starting point of the consideration is th

A. Duviryak

Abelian potentials of pointlike moving sources are obtained from the nonstandard theory of Yang--Mills field. They are used for the construction of the time-symmetric and time-asymmetric Fokker-type action integrals describing the dynamics of two-particle system with confinement interaction. The time-asymmetric model is reformulated in the framework of the H

O. I. Zavialov, A. M. Malokostov

A generalization of the Wigner function for the case of a free particle with the ``relativistic'' Hamiltonian $\sqrt{{\bf p}^2+m^2}$ is given.

Tao Han, Andre S. Turcot, Ren-Jie Zhang

We study the observability of a Standard Model-like Higgs boson at an upgraded Fermilab Tevatron via the mode $h \to W^*W^*$. We concentrate on the main channel $gg \to h \to W^*W^* \to l νl ν$. We also find the mode $q\bar q'\to W h \to W W^*W^* \to l^\pm νl^\pm νjj$ useful. We perform detector level simulations by making use of a Monte Carlo program SH

J. H. Munoz, A. A. Rojas, G. Lopez Castro

The Cabibbo-suppressed non-leptonic decays of B (and D) mesons to final states involving tensor mesons are computed using the non-relativistic quark model of Isgur-Scora-Grinstein-Wise with the factorization hypothesis. We find that some of these B decay modes, as B --> (K^*, D^*)D^*_2, can have branching ratios as large as 6 x 10^{-5} which seems to be at t

T. M. Aliev, M. Savci

We investigate the exclusive B -> pi e^+ e^- and B -> rho e^+ e^- decays in framework of the general two Higgs doublet model (model III), in which an extra phase angle in the charged--Higgs fermion coupling, i.e., a new source for CP violation exists. The CP violation for both decays are calculated and it is observed that the CP violating asymmetry in model

Fredrick I. Olness

We provide a brief overview of some current experimental and theoretical issues of heavy quark production.

Jose F. Nieves, Palash B. Pal

In the linearized theory of gravity coupled to the electromagnetic field, we calculate the cross sections of two processes in which both the gravitational and electromagnetic interactions play a role. Those processes, in which a graviton is produced in the final state, are: (a) the photoproduction of gravitons off electrons and (b) the production of a photon

A. Ali, G. Hiller

We present a theoretical reappraisal of the branching ratios and CP asymmetries for the decays $ B \to X_q \ell^+ \ell^-$, with $q=d,s$, taking into account current theoretical uncertainties in the description of the inclusive decay amplitudes from the long-distance contributions, an improved treatment of the renormalization scale dependence, and other param

N. N. Nikolaev, W. Schäfer, A. Szczurek, J. Speth

We revisit the evaluation of the pionic mechanism of the $\bar{u}-\bar{d}$-asymmetry in the proton structure function. Our analysis is based on the extended AGK unitarity relation between contributions of different mechanisms to the inclusive particle production and the total photoabsorption cross-section (i.e. the proton structure function). We reanalyze th

M. Wakamatsu

We carry out a systematic investigation of twist-two spin dependent structure functions of the nucleon within the framework of the chiral quark soliton model (CQSM) by paying special attention to the role of chiral symmetry of QCD. We observe a substantial difference between the predictions of the longitudinally polarized distribution functions and the trans

L. A. Fernandez, V. Martin-Mayor

We study the critical properties of the monopole-percolation transition in U(1) lattice gauge theory coupled to scalars at infinite ($β=0$) gauge coupling. We find strong scaling corrections in the critical exponents that must be considered by means of an infinite-volume extrapolation. After the extrapolation, our results are as precise as the obtained for t

B. Abbott

We present a measurement of the Drell-Yan cross section at high dielectron invariant mass using 120/pb of data collected in pbar-p collisions at sqrt(s) = 1.8 TeV by the D0 collaboration during 1992-96. No deviation from standard model expectations is observed. We use the data to set limits on the energy scale of quark-electron compositeness with common cons

Kamiokande Collaboration, Y. Fukuda, T. Hayakawa, E. Ichihara

A search for day-night variations in the solar neutrino flux resulting from neutrino oscillations has been carried out using the 504 day sample of solar neutrino data obtained at Super-Kamiokande. The absence of a significant day-night variation has set an absolute flux independent exclusion region in the two neutrino oscillation parameter space.

Alexander Vilenkin

I review the tunneling, Hartle-Hawking and Linde proposals for the wave function of the universe and comment on the recent work on quantum creation of open universes.

L. Herrera, Filipe M. Paiva, N. O. Santos

Circular and radial geodesics are studied in the spacetime described by the $γ$ metric. Their behaviour is compared with the spherically symmetric situation, bringing out the sensitivity of the trajectories to deviations from spherical symmetry.

Susan M. Scott, Geoffery Ericksson

In 1985 Goode and Wainwright devised the concept of an isotropic singularity. Since that time, numerous authors have explored the interesting consequences, in mathematical cosmology, of assuming the existence of this type of singularity. In this paper, we collate all examples of cosmological models which are known to admit an isotropic singularity, and make

Massimo Giovannini

We present a class of exact cosmological solutions of the low energy string effective action in the presence of a homogeneous magnetic fields. We discuss the physical properties of the obtained (fully anisotropic) cosmologies paying particular attention to their vacuum limit and to the possible isotropization mechanisms. We argue that quadratic curvature cor

Suncica Elezovic-Hadzic, Natasa Vasiljevic

We study the problem of critical adsorption of piecewise directed random walks on a boundary of fractal lattices that belong to the Sierpinski gasket family. By applying the exact real space renormalization group method, we calculate the crossover exponent $ϕ$, associated with the number of adsorbed steps, for the complete fractal family. We demonstrate that

H. Saleur

These are lectures presented at the Les Houches Summer School ``Topology and Geometry in Physics'', July 1998. They provide a simple introduction to non perturbative methods of field theory in 1+1 dimensions, and their application to the study of strongly correlated condensed matter problems - in particular quantum impurity problems. The level is mod

Christophe Josserand

We discuss the problem of an explosion in the cubic-quintic superfluid model, in relation to some experimental observations. We show numerically that an explosion in such a model might induce a cavitation bubble for large enough energy. This gives a consistent view for rebound bubbles in superfluid and we indentify the loss of energy between the successive r

A. de Candia, V. Cataudella, A. Coniglio

We study the properties of the q-state frustrated bond percolation model by a Monte Carlo "bond flip" dynamics, using an algorithm originally devised by Sweeny and suitably modified to treat the presence of frustration. We analyze the percolation transition of the model, and find that it falls in the universality class of the q/2-state ferromagnetic

G. Falci, G. Giaquinta, U. Weiss

We introduce the Quantum Dissipative Villain (QDV) model as a prototype model to study tunneling in dissipative quantum mechanics. Dissipation is provided by a coupled linear environment. In the QDV model, the discrete character of a tunneling degree of freedom coupled to an environment is explicit, leading to a rich dual structure. We derive general exact m

A. Werner, F. Schmid, M. Mueller

By means of extensive Monte Carlo simulations of the bond fluctuation model, we study the effect of adding AB diblock copolymers on the properties of an interface between demixed homopolymer phases. The parameters are chosen such that the homopolymers are strongly segregated, and the whole range of copolymer concentrations in the two phase coexistence region

Holger Frahm, Claus Rödenbeck

We study the phase diagram of coupled spin-1/2 chains with bilinear and (chiral) three-spin exchange interactions in a magnetic field. The model is soluble on a one-parametric line in the space of coupling constants connecting the limiting cases of a single and two decoupled Heisenberg chains with nearest neighbour exchange only. We give a complete classific

J. Schiøtz, T. Vegge, K. W. Jacobsen

Nanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be model

G. Falci, U. Weiss

We study exact self duality in the model of a Brownian particle in a washboard (WB) potential which describes a Josephson Junction (JJ) coupled to an environment, for arbitrary temperature and arbitrary form of the spectral density of the environment. To this end we introduce the Quantum Dissipative Villain Model (QDVM), which models tunneling of a degree of

Pierre-Antoine Bares, Mauro Mobilia

We investigate three different methods to tackle the problem of diffusion-limited reactions (annihilation) of hard-core classical particles in one dimension. We first extend an approach devised by Lushnikov and calculate for a single species the asymptotic long-time and/or large distance behavior of the two-point correlation function. Based on a work by Gryn

A. N. Das, Biplab Chattopadhyay

We consider an extended version of the pair tunneling model including interlayer single particle hopping (ISPH) as a complementary process to pair tunneling. The normal state gap, as found in cuprates, is taken to suppress the effective ISPH in conformity with the experimental observations, and this in turn enhances the pair tunneling process. The effective

Ronald Blaak

We derive an exact, analytic expression for the fourth virial coefficient of a system of polydisperse spheres under the constraint that the smallest sphere has a radius smaller than a given function of the radii of the three remaining particles.

Walter Kob, Jurgen Horbach, Kurt Binder

Using a large scale molecular dynamics computer simulation we investigate the dynamics of a supercooled melt of SiO_2. We find that with increasing temperature the temperature dependence of the diffusion constants crosses over from an Arrhenius-law, with activation energies close to the experimental values, to a power-law dependence. We show that this crosso

Wen-ge Wang

A generalization of Brillouin-Wigner perturbation theory is applied numerically to the Wigner Band Random Matrix model. The perturbation theory tells that a perturbed energy eigenstate can be divided into a perturbative part and a non-perturbative part with the perturbative part expressed as a perturbation expansion. Numerically it is found that such a divis

D. V. Khveshchenko

We consider the fractional drag in a double layer system of two-dimensional electrons in the half-filled lowest Landau level. At sufficiently large inter-layer separations the drag is dominated by exchange of acoustic phonons and exhibits novel temperature and inter-layer distance dependences. At low temperatures the phonon mediated drag is strongly enhanced

H. M. Ronnow

This paper has been withdrawn by the author due to an error in the data-analysis.

N. Gov, E. Akkermans

A new description is presented for the roton part of the energy spectrum of supe rfluid ${^4}$He. It is based on the assumption that in addition to the Feynman density excitations, there exist localized modes which describe vortex-core elements. The energy spectrum which results from the hybridization of these two kinds of excitations is compared to the expe

Tahir Yaqoob

A recent X-ray observation of the cluster 1E0657-56 (z=0.296) with ASCA implied an unusually high temperature of ~17 keV. Such a high temperature would make it the hottest known cluster and severely constrain cosmological since, in a Universe with critical density Omega=1 the probability of observing such a cluster is only 4e-5. Here we test the robustness o

B. Stelzer, J. Wilms, R. Staubert, D. Gruber

We report on a pre-eclipse dip of the X-ray binary Her X-1 observed by the Rossi X-ray Timing Explorer (RXTE) in July 1996. We present the evolution of the spectral parameters in the 3-18 keV range with a temporal resolution of 16 s and show that the varying flux of the spectrum can be interpreted solely by a time varying column density. We also find that th

C. Surace, P. Heraudeau, D. Lemke, S. Oliver

The European Large Area ISO Survey (ELAIS) will provide Infrared observations of 4 regions in the sky with ISO. Around 2000 Infrared sources have been detected at 7 and 15 microns (with ISOCAM), 90 and 175 microns (with ISOPHOT)) over 13 square degrees of the sky. We present the source extraction pipeline of the 90 microns ISOPHOT observations, describe and

D. Villani, S. di Serego Alighieri

We have performed deep imaging in the IR J- and K-bands for three sub-samples of radio sources extracted from the Westerbork Northern Sky Survey, a large low-frequency radio survey containing Ultra Steep Spectrum (USS), Gigahertz Peaked Spectrum (GPS) and Flat Spectrum (FS) sources. We present the results of these IR observations, carried out with the ARcetr

Luigi Stella, Mario Vietri

We consider the interpretation of a pair of kHz Quasi Periodic Oscillations (QPOs) in the Fourier spectra of two Low Mass X-Ray Binaries, Sco X-1 and 4U1608-52, hosting an old accreting neutron star. The observed frequency difference of these QPOs decreaseas as their frequency increases, contrary to simple beat frequency models, which predict a constant freq

P. M. Chadwick, K. Lyons, T. J. L. McComb, S. McQueen

The close X-ray selected BL Lac PKS 2155--304 has been observed using the University of Durham Mark 6 very high energy (VHE) gamma ray telescope during 1996 September/October/November and 1997 October/November. VHE gamma rays with energy > 300 GeV were detected with a time-averaged integral flux of (4.2 +/- 0.7 (stat) +/- 2.0 (sys)) x 10^-11 cm^-2 s^-1. Ther

A. V. Zasov, A. V. Moiseev

A comlex structure of nuclear disks of normal spiral galaxies was illustrated on the example of five galaxies, observed at 6m telescope. A problem of gravitational stability of nuclear disks is shortly discussed.

L. Ciotti

The properties of the analitycal phase--space distribution function of two-component spherical self-consistent galaxy models, where one density distribution follows the Hernquist profile, and the other a gamma=0 model, with different total masses and core radii (H0 models), presented in Ciotti (1998), are here summarized. A variable amount of radial Osipkov-