January 2000 arXiv papers — page 17

Ch. Preis, Ch. Helm, K. Schmalzl, Ch. Walter

A microscopic theory for the coupling of intrinsic Josephson oscillations and dispersive phonon branches in layered superconductors is developed. Thereby the effect of phonons on the electronic c-axis transport enters through an effective longitudinal dielectric function. This coupling provides an explanation of recently observed subgap resonances in the $I_

M. M. Mola, J. T. King, C. P. McRaven, S. Hill

A cavity perturbation technique is used to study the microwave response of the organic superconductor k-(BEDT-TTF)2Cu(NCS)2. Observation of a Josephson plasma resonance, below Tc (approx. 10 K), enables investigation of the vortex structure within the mixed state of this highly anisotropic, type-II, superconductor. Contrary to previous assumptions, frequency

Jun-ichiro Watanabe, Tatsuya Nakajima

We report on numerical studies of the energy spectrum and the localization properties in the double-layer quantum Hall system at $ν= 1$. The Coulomb interaction is treated by the Hartree-Fock approximation, and the localization properties in the presence of disorder are studied by evaluating participation ratios for the Hartree-Fock eigenfunctions. We show t

Mark Srednicki

Matsumoto and Yoshimura [hep-ph/9910393] have argued that there are loop corrections to the number density of heavy particles (in thermal equilibrium with a gas of light particles) that are not Boltzmann suppressed by a factor of e^(-M/T) at temperatures T well below the mass M of the heavy particle. We argue, however, that their definition of the number den

Renata Kallosh, Andrei Linde

We investigate the possibility of gravity localization on the brane in the context of supersymmetric theories. To realize this scenario one needs to find a theory with the supersymmetric flow stable in IR at two critical points, one with positive and the other with negative values of the superpotential. We perform a general study of the supersymmetric flow e

Pawel Horodecki, Maciej Lewenstein

We introduce the definition of generic bound entanglement for the case of continuous variables. We provide some examples of bound entangled states for that case, and discuss their physical sense in the context of quantum optics. We rise the question of whether the entanglement of these states is generic. As a byproduct we obtain a new many parameter family o

Rafael Angel Araya-Gochez

We show that an MHD-instability driven dynamo (IDD) operating in a hot accretion disk is capable of generating energetically adequate magnetic flux deposition rates above and below a mildly advective accretion disk structure. The dynamo is driven by the magnetorotational instability (MRI) of a toroidal field in a shear flow and is limited by the buoyancy of

Vyacheslav S Krushkal, Frank Quinn

We present a new, more elementary proof of the Freedman-Teichner result that the geometric classification techniques (surgery, s-cobordism, and pseudoisotopy) hold for topological 4-manifolds with groups of subexponential growth. In an appendix Freedman and Teichner give a correction to their original proof, and reformulate the growth estimates in terms of c

T. Hambye, G. O. Koehler, E. A. Paschos, P. H. Soldan

We present a recent analysis of epsilon'/epsilon in the 1/N_c expansion. We show that the 1/N_c corrections to the matrix element of Q_6 are large and positive, indicating a Delta I=1/2 enhancement similar to the one of Q_1 and Q_2 which dominate the CP conserving amplitude. This enhances the CP ratio and can bring the standard model prediction close to

F. Csikor, Z. Fodor, P. Hegedus, A. Jakovac

Recent lattice results have shown that there is no Standard Model (SM) electroweak phase transition (EWPT) for Higgs boson masses above \approx 72 GeV, which is below the present experimental limit. According to perturbation theory and 3-dimensional (3d) lattice simulations there could be an EWPT in the Minimal Supersymmetric Standard Model (MSSM) that is st

Sergei M. Kuzenko, Stefan Theisen

We derive N = 1, 2 superfield equations as the conditions for a (nonlinear) theory of one abelian N = 1 or N = 2 vector multiplet to be duality invariant. The N = 1 super Born-Infeld action is a particular solution of the corresponding equation. A family of duality invariant nonlinear N = 1 supersymmetric theories is described. We present the solution of the

Mikhail S. Plyushchay, Michel Rausch de Traubenberg

We construct new relativistic linear differential equation in $d$ dimensions generalizing Dirac equation by employing the Clifford algebra of the cubic polynomial associated to Klein-Gordon operator multiplied by the mass parameter. Unlike the Dirac case where the spin content is unique and Lorentz covariance is manifest, here the spin as well as Lorentz cov

Sunil Mukhi, Nemani V. Suryanarayana, David Tong

In type II string theories, we examine intersecting brane constructions containing brane-antibrane pairs suspended between 5-branes, and more general non-BPS constructions. The tree-level spectra are obtained in each case. We identify various models with distinct physics: parallel brane-antibrane pairs, adjacent pairs, non-adjacent pairs, and configurations

N. N. Nikolaev, V. R. Zoller

In 1994 Zakharov and the present authors argued that in color dipole (CD) BFKL approach to DIS excitation of open charm at moderately large Q2 is dominated by hard BFKL exchange. In view of the rapid accumulation of the experimental data on small-x charm structure function of the proton F2cc from HERA, we subject the issue of dominance of the rightmost hard

S. Choi, Y. Japha, K. Burnett

We develop a general theory of adiabatic output coupling from trapped atomic Bose-Einstein Condensates at finite temperatures. For weak coupling, the output rate from the condensate, and the excited levels in the trap, settles in a time proportional to the inverse of the spectral width of the coupling to the output modes. We discuss the properties of the out

Akishi Kato, Yuji Satoh

We discuss the modular invariance of the SL(2,R) WZW model. In particular, we discuss in detail the modular invariants using the \hat{sl}(2,R) characters based on the discrete unitary series of the SL(2,R) representations. The explicit forms of the corresponding characters are known when no singular vectors appear. We show, for example, that from such charac

R. Voituriez, S. Nechaev

Multifractal properties of the distribution of topological invariants for a model of trajectories randomly entangled with a nonsymmetric lattice of obstacles are investigated. Using the equivalence of the model to random walks on a locally nonsymmetric tree, statistical properties of topological invariants, such as drift and return probabilities, have been s

Martin Weigt, Alexander K. Hartmann

In this letter we study the NP-complete vertex cover problem on finite connectivity random graphs. When the allowed size of the cover set is decreased, a discontinuous transition in solvability and typical-case complexity occurs. This transition is characterized by means of exact numerical simulations as well as by analytical replica calculations. The replic

Alaka Das, Ujjal Ghosal, Krishna Kumar

Possibility of asymmetric square convection is investigated numerically using a few mode Lorenz-like model for thermal convection in Boussinesq fluids confined between two stress free and conducting flat boundaries. For relatively large value of Rayleigh number, the stationary rolls become unstable and asymmetric squares appear as standing waves at the onset

P. Astone, S. D'Antonio, G. Pizzella

Using simulated signals and measured noise with the EXPLORER and NAUTILUS detectors we find the efficiency of signal detection and the signal arrival time dispersion versus the signal-to-noise ratio.

G. Aldazabal, L. E. Ibanez, F. Quevedo

The success of SU(5)-like gauge coupling unification boundary conditions $g_3^2=g_2^2=5/3 g_1^2$ has biased most attempts to embed the SM interactions into a unified structure. After discussing the limitations of the orthodox approach, we propose an alternative that appears to be quite naturally implied by recent developments based on D-brane physics. In thi

R. R. Rodriguez-Guzman, J. L. Egido, L. M. Robledo

Properties of the ground and several collective excited states of the light nuclei ^{30,32,34}Mg are described in the framework of the angular momentum projected Generator Coordinate Method using the quadrupole moment as collective coordinate and the Gogny force as the effective interaction. The calculated excitation energies and B(E2) transition probabiliti

Takeshi Chiba

We derive the low-energy effective action of four-dimensional gravity in the Randall-Sundrum scenario in which two 3-branes of opposite tension reside in a five-dimensional spacetime. The dimensional reduction with the Ansatz for the radion field by Charmousis et al., which solves five-dimensional linearized field equations, results in a class of scalar-tens

R. Horvat

The dispersion relation in matter of ultrahigh-energy neutrinos above the pole of the $W$ resonance ($E_ν \gsim {\rm 10}^{7} {\rm GeV} $), is studied. We perform our calculation using the real-time formulation of Thermal Field Theory in which the massless limit for the $W$ boson is taken. The range of active-to-sterile neutrino oscillation parameters for whi

R. Stubner, R. Winkler, O. Pankratov

We extend standard k.p theory to take into account periodic perturbations which are rapidly oscillating with a wavelength of a few lattice constants. Our general formalism allows us to explicitly consider the Bragg reflections due to the perturbation-induced periodicity. As an example we calculate the effective masses in the lowest two conduction bands of sp

Nahomi Kan, Kiyoshi Shiraishi

Many efforts have been devoted to the studies of the phenomenology in particle physics with extra dimensions. We propose the degenerate fermion star in the five dimensions, and study what effects caused by the geometry of extra dimensions should appear in its structure. We note that Kaluza-Klein excited modes have effects for the larger scale of extra dimens

Brien C. Nolan

The gravitational strength of the central singularity in spherically symmetric space-times is investigated. Necessary conditions for the singularity to be gravitationally weak are derived and it is shown that these are violated in a wide variety of circumstances. These conditions allow conclusions to be drawn about the nature of the singularity without havin

Kenji Suzuki

We consider a $(3+1)$-dimensional QCD model using a dual supergravity description with a non-extremal $D0$-$D4$ brane background. We calculate the spectrum of glueball masses and Wilson loops in the background. The mass spectrum is shown to coincide with one in non-extremal $D4$-brane systems, and an area low of spatial Wilson loops is established. We show t

J. Acacio de Barros, P. Suppes

In this article we show that the three-particle GHZ theorem can be reformulated in terms of inequalities, allowing imperfect correlations due to detector inefficiencies. We show quantitatively that taking into accout those inefficiencies, the published results of the Innsbruck experiment support the nonexistence of local hidden variables that explain the exp

Detlef Duerr, Sheldon Goldstein, Stefan Teufel, Nino Zanghi

We sketch a derivation of abstract scattering theory from the microscopic first principles defined by Bohmian mechanics. We emphasize the importance of the flux-across-surfaces theorem for the derivation, and of randomness in the impact parameter of the initial wave function---even for an, inevitably inadequate, orthodox derivation.

Qiong-gui Lin

Neutral fermions of spin $\frac 12$ with magnetic moment can interact with electromagnetic fields through nonminimal coupling. The Dirac--Pauli equation for such a fermion coupled to a spherically symmetric or central electric field can be reduced to two simultaneous ordinary differential equations by separation of variables in spherical coordinates. For a w

Jose L. Cereceda

By selecting a certain subensemble of joint detection events in a two-particle interferometer arrangement, a formal nonlocality contradiction of the Hardy type is derived for an ensemble of particle pairs configured in the maximally entangled state. It is argued, however, that the class of experiments exhibiting this kind of contradiction does not rule out t

P. K. Biswas, Sadhan K. Adhikari

The low-energy scattering of ortho positronium (Ps) by H, He, Ne, and Ar atoms has been investigated in the coupled-channel framework by using a recently proposed time-reversal-symmetric nonlocal electron-exchange model potential with a single parameter $C$. For H and He we use a three-Ps-state coupled-channel model and for Ar and Ne we use a static-exchange

G. D. van Albada, E. Coccia, V. Fafone, H. van der Graaf

We present measurements of mechanical vibrations induced by 0.6 GeV electrons impinging on cylindrical and spherical aluminium resonators. To monitor the amplitude of the resonator's vibrational modes we used piezoelectric ceramic sensors, calibrated by standard accelerometers. Calculations using the thermo-acoustic conversion model, agree well with the

Shadow J. Q. Robinson, L. Zamick, Y. Y. Sharon

This paper has been withdrawn by the authors as we await a larger model space calculation.

D. Gourio, INDRA collaboration

Proton and deuteron correlation functions have been investigated with both impact parameter and emission source selections. The correlations of the system (129Xe + natSn) at 50 AMeV have been measured with the 4 pi INDRA which provides a complete kinematical description of each event. The emission time scale analyzed with a quantum model reveals the time seq

Juergen Vollmer, Tamas Tel, Laszlo Matyas

A generalized multibaker map with periodic boundary conditions is shown to model boundary-driven transport, when the driving is applied by a ``perturbation'' of the dynamics localised in a macroscopically small region. In this case there are sustained density gradients in the steady state. A non-uniform stationary temperature profile can be maintaine

M. Krbalek, P. Seba

We analyze statistical properties of the city bus transport in Cuernavaca (Mexico) and show that the bus arrivals display probability distributions conforming those given by the Unitary Ensemble of random matrices.

David Ruelle

A quantum spin system is discussed, where a heat flow between infinite reservoirs takes place in a finite region. A time dependent force may also be acting. Our analysis is based on a simple technical assumption concerning the time evolution of infinite quantum spin systems. This assumption, physically natural but currently proved for few specific systems on

E. Musso, L. Nicolodi

We study an analogue of the classical Bianchi-Darboux transformation for L-isothermic surfaces in Laguerre geometry, the Bianchi-Darboux transformation. We show how to construct the Bianchi-Darboux transforms of an L-isothermic surface by solving an integrable linear differential system. We then establish a permutability theorem for iterated Bianchi-Darboux

Uwe Semmelmann, Gregor Weingart

We discuss a peculiar interplay between the representation theory of the holonomy group of a Riemannian manifold, the Weitzenboeck formula for the Hodge-Laplace operator on forms and the Lichnerowicz formula for twisted Dirac operators. For quaternionic Kaehler manifolds this leads to simple proofs of eigenvalue estimates for Dirac and Laplace operators. Mor

Alessandro Arsie

Having fixed a Kaehler class and the unique corresponding hyperkaehler metric, we prove that all special Lagrangian submanifolds of an irreducible symplectic 4-fold X are bi-Lagrangian and that they are obtained by complex submanifolds via a sort of "hyperkaehler rotation trick"; thus they retain part of the rigidity of complex submanifolds: indeed a

Paolo Piccinni, Izu Vaisman

We consider manifolds equipped with a foliation $\cal F$ of codimension $4q$, and an almost quaternionic structure $Q$ on the transversal bundle of ${\cal F}$. After discussing conditions of projectability and integrability of $Q$, we study the transversal twistor space $Z{\cal F}$ which, by definition, consists of the $Q$-compatible almost complex structure

Shicheng Wang, Qing Zhou

In this paper, we proved that any closed orientable 3-manifold 1-dominates at most finitely many geometric 3-manifolds.

Peter G. Doyle, J. Laurie Snell

A popular account of the connection between random walks and electric networks.

V. P. Gusynin

Non-perturbative effect of the formation of a chiral symmetry breaking condensate <\barψψ> and of a dynamically generated fermion mass in QED in the presence of an external magnetic field is considered. The dynamical mass of a fermion (energy gap in the fermion spectrum) is shown to depend essentially nonanalytically on the renormalized coupling constant αin

Eric Bergshoeff, Rein Halbersma

We investigate domain-wall/quantum field theory correspondences in various dimensions. We give particular emphasis to the special case of the quantum mechanics of 0--branes.

Everton M. C. Abreu

Recently it was shown how to regularize the Batalin-Vilkovisky (BV) field-antifield formalism of quantization of gauge theories with the non-local regularization (NLR) method. The objective of this work is to make an analysis of the behaviour of this NLR formalism, connected to the BV framework, using two different regulators: a simple second order different

Christos Kokorelis

We discuss the appearance of modular functions at the one-loop gauge and gravitational couplings in (0,2) non-decomposable N=1 four dimensional orbifold compactifications of the heterotic string. We define the limits for the existence of states causing singularities in the moduli space in the perturbative regime for a generic vacuum of the heterotic string.

Alfio Bonanno

A new approach to study the scaling behavior of the scalar theory near the Gaussian fixed point in $d$-dimensions is presented. For a class of initial data an explicit use of the Green&#39;s function of the evolution equation is made. It is thus discussed under which conditions non-polynomial relevant interactions can be generated by the renormalization grou

K. B. Korotchenko

The basic principles of the quantum mechanics in the K-field formalism (see author&#39;s papers) are stated in the paper. K-field formalism arises from geometric generalization of de Broglie postulate. So, the quantum theory equations (including well-known Schrodinger, Klein-Gordon and quadratic Dirac equations) are obtained as the free wave equations on a m

Jaroslaw Piskorski

This paper presents the operator form of the effective potential V governing the time evolution in 2 and 3 and n dimensional subspace of states. The general formula for the n dimensional case is considered the starting point for the calculation of the explicit formulae for 2 and 3 dimensional degenerate and non-degenerate cases. We relate the 2 and 3 dimensi

J. Khoury, H. Verlinde

It was recently shown, using the AdS/CFT correspondence, that the low energy effective action of a large $N$ open string theory satisfies a holographic RG flow equation closely related to the Hamilton-Jacobi equation of 5-d supergravity. In this paper we re-obtain the same flow equation in the dual regime of small &#39;t Hooft coupling $λ\ll 1$. Our derivati

Y. N. Srivastava, A. Widom

The Kinoshita-Lee-Nauenberg (KLN) theorem describes the fact that inclusive electromagnetic and weak production processes in the vacuum do not contain singularities in the ultra-relativistic limit of zero mass. When these production processes occur in condensed matter, the KLN theorem fails. One consequence of this failure is that precision lifetime determin

Jens O. Andersen

In this talk, I review recent developments in equilibrium thermal field theory. Screened perturbation theory and hard-thermal-loop perturbation theory are discussed. A self-consistent $Φ$-derivable approach is also briefly reviewed.

H. Baer, F. E. Paige, S. D. Protopopescu, X. Tata

ISAJET is a Monte Carlo program which simulates $pp$, $\bar pp$ and $e^+e^-$ interactions at high energies. This document summarizes the physics underlying the program and describes how to use it. Version~7.48 includes several new features. Anomaly Mediated SUSY Breaking (AMSB) models and right-handed sneutrinos have been added; the latter play a role, e.g.,

Sibaji Raha

One of the confident predictions of QCD is that at sufficiently high temperature and/or density, hadronic matter should undergo a thermodynamic phase transition to a colour deconfined state of matter - popularly called the Quark-Gluon Plasma (QGP). In low energy effective theories of Quantum Chromodynamics (QCD), one usually talks of the chiral transition fo

S. V. Chekanov, A. De Roeck, E. A. De Wolf

We show that the most popular method to simulate Bose-Einstein (BE) interference effects predicts negligible correlations between identical pions originating from the hadronic decay of different W&#39;s produced in e+e- -> W+W- -> 4 jets at typical linear collider energies.

E. Gotsman, E. Levin, U. Maor, E. Naftali

We extend our previous treatment of $γ^*p$ cross section based on Gribov&#39;s hypothesis to the case of photon-photon scattering. With the aid of two parameters, determined from experimental data, we separate the interactions into two categories corresponding to short (&#34;soft&#34;) and long (&#34;hard&#34;) distance processes. The photon-photon cross sec

S. Tsujikawa

We study parametric amplification of Kaluza-Klein (KK) modes in a higher $D$-dimensional generalized Kaluza-Klein theory, which was originally considered by Mukohyama in the narrow resonance case. It was suggested that KK modes can be enhanced by an oscillation of a scale of compactification by the $d$-dimensional sphere $S^d~(d=D-4)$ and by the direct produ

M. Miyama

We discuss the Drell-Yan proton-deuteron (p-d) asymmetry R_{pd}, which is defined by the proton-proton and proton-deuteron cross-section ratio Δ_{(T)}σ^{pd}/2Δ_{(T)}σ^{pp}, and its relation to the polarized light-antiquark flavor asymmetry. Using a formalism of the polarized {\it pd} Drell-Yan process, we show that the R_{pd} especially in the large-x_F regi

Kaushik Bhattacharya, Palash B. Pal

We show that neutrino cross sections are direction dependent in a background magnetic field.

S. Kumano

We discuss the possibility of finding polarized antiquark flavor asymmetry in Drell-Yan processes. We find that the difference between polarized proton-proton and proton-deuteron Drell-Yan cross sections should provide valuable information on the polarized flavor asymmetry. Numerical results indicate that the asymmetry effects are conspicuous especially in t

Kurt Langfeld, Hugo Reinhardt

We investigate the high temperature limit of SU(2) and SO(3) lattice gauge theory, respectively. In particular, we study the Stefan-Boltzmann constant in both cases. As is well known, the Stefan-Boltzmann constant extracted from SU(2) lattice gauge theory by incorporating finite size effects is smaller than the continuum value which assumes three gluon degre

P. Hernandez, K. Jansen, L. Lellouch

We describe in some detail our numerical treatment of Neuberger&#39;s lattice Dirac operator as implemented in a practical application. We discuss the improvements we have found to accelerate the numerical computations and give an estimate of the expense when using this operator in practice.

D. B. Leinweber, A. W. Thomas, S. V. Wright

As a direct source of information on chiral symmetry breaking within QCD, the sigma commutator is of considerable importance. With recent advances in the calculation of hadron masses within full QCD it is of interest to see whether the sigma commutator can be calculated directly from the dependence of the nucleon mass on the input quark mass. We show that pr

Martin L. Perl, Valerie Halyo, Peter C. Kim, Eric R. Lee

We describe our ongoing work on, and future plans for, searches in bulk matter for fractional charge elementary particles and very massive elementary particles. Our primary interest is in searching for such particles that may have been produced in the early universe and may be found in the more primeval matter available in the solar system: meteorites, mater

W. Molzon

I review recent results from experiments on rare decays of kaons, concentrating on searches for lepton flavor violation (LFV) and on measurements of quark mixing (CKM) matrix elements. The LFV results are the culmination of 15 years of experimentation at Brookhaven National Laboratory and are unlikely to be improved upon soon. The CKM studies derive from mea

S. Bethke

Selected topics on precision tests of the Standard Model of the Electroweak and the Strong Interaction at the LEP $e^+e^-$ collider are presented, including an update of the world summary of measurements of $α_s$, representing the state of knowledge of summer 1999. This write-up of lecture notes consists of a reproduction of slides, pictures and tables, supp

Paul Newman

Selected recent data from collider experiments pertaining to the understanding of QCD at low Bjorken-x are reviewed. The status of QCD and Regge factorisation in hard diffractive interactions is discussed in terms of data from HERA and the Tevatron. The possibility of anomalous behaviour in the $γγ$ total cross section is confronted with the most recent meas

Alec Maassen van den Brink

We study the Regge-Wheeler and Zerilli equations (RWE and ZE) at the `algebraically special frequency&#39; $Ω$, where these equations admit an exact solution (elaborated here), generating the SUSY relationship between them. The physical significance of the SUSY generator and of the solutions at $Ω$ in general is elucidated as follows. The RWE has no (quasino

J. R. Morris

It is shown that, in contrast to the case of extreme 4d dilatonic black holes, 4d neutral dilatonic black holes with horizon singularities can not be interpreted as nonsingular nondilatonic black p-branes in (4+p) dimensions, regardless of the number of extra dimensions p. That is, extra dimensions do not remove naked singularities of 4d neutral dilatonic bl

Yoshitaka Degura, Kiyoshi Shiraishi

We treat the model which describes &#34;extreme black holes&#34; moving slowly. We derive an effective lagrangian in the low energy for this model and then investigate a statistical behavior of &#34;extreme black holes&#34; in the finite temperature.

Alan G. Wiseman

The finite part of the self-force on a static scalar test-charge outside a Schwarzschild black hole is zero. By direct construction of Hadamard&#39;s elementary solution, we obtain a closed-form expression for the minimally coupled scalar field produced by a test-charge held fixed in Schwarzschild spacetime. Using the closed-form expression, we compute the n

Rebecca Menes, Philip Pincus, Bean Stein

We generalize the predictions for attractions between over-all neutral surfaces induced by charge fluctuations/correlations to non-uniform systems that include dielectric discontinuities, as is the case for mixed charged lipid membranes in an aqueous solution. We show that the induced interactions depend in a non-trivial way on the dielectric constants of me

D. C. Johnston, M. Troyer, S. Miyahara, D. Lidsky

A comprehensive theoretical and experimental study is presented of the magnetic susceptibility versus temperature χ(T) of spin S = 1/2 two- and three-leg Heisenberg ladders and ladder oxide compounds. Extensive quantum Monte Carlo simulations of χ(T) were carried out for both isolated and coupled two-leg ladders with spatially anisotropic intraladder exchang

J. R. Anglin, W. H. Zurek

This is a less technical presentation of the ideas in quant-ph/9804035 [Phys Rev Lett 83 (1999), 1707-1710]. A second order phase transition induced by a rapid quench can lock out topological defects with densities far exceeding their equilibrium expectation values. This phenomenon is a generic prediction of nonequilibrium statistical mechanics, and can appe

K. E. Khor, S. Das Sarma

We use Monte-Carlo simulations to study island formation in the growth of thin semiconducting films deposited on lattice-mismatched substrates. It is known that islands nucleate with critical nuclei of about one atom and grow two dimensionally until they reach a critical size s$_c$, when it is favorable for the islands to become three dimensional. We investi

Yi-Hang Nie, Yan-Hong Jin, J. -Q. Liang, H. J. W. Müller-Kirsten

The tunnel splitting in biaxial antiferromagnetic particles is studied with a magnetic field applied along the hard anisotropy axis. We observe the oscillation of tunnel splitting as a function of the magnetic field due to the quantum phase interference of two tunneling paths of opposite windings. The oscillation is similar to the recent experimental result

D. B. Haviland, K. Andersson, P. Agren

Experiments on one-dimensional small capacitance Josephson Junction arrays are described. The arrays have a junction capacitance that is much larger than the stray capacitance of the electrodes, which we argue is important for observation of Coulomb blockade. The Josephson energy can be tuned in situ and an evolution from Josephson-like to Coulomb blockade b

J. -Q. Liang, H. J. W. Müller-Kirsten, D. K. Park, F. -C. Pu

The point-particle-like Hamiltonian of a biaxial spin particle with external magnetic field along the hard axis is obtained in terms of the potential field description of spin systems with exact spin-coordinate correspondence. The Zeeman energy term turns out to be an effective gauge potential which leads to a nonintegrable pha se of the Euclidean Feynman pr

R. Schiller, W. Mueller, W. Nolting

We present a model calculation for the temperature dependent behaviour of surface states on a ferromagnetic local-moment film. The film is described within the s-f model featuring local magnetic moments being exchange coupled to the itinerant conduction electrons. The surface states are generated by modifying the hopping in the vicinity of the surface of the

T. A. Vilgis, A. Johner, J. -F. Joanny

Polyelectrolytes in poor solvents show a necklace structure where collapsed polymer pearls are linked to stretched strings. In the present paper the elasticity of such chains is studied in detail. Different deformation regimes are addressed. The first is the continuous regime, where many pearls are present. A continuous force extension relation ship is calcu

D. Loison

We study the phase transition in generalized chiral or Stiefel&#39;s models using Monte Carlo simulations. These models are characterized by a breakdown of symmetry O(N)/O(N-P). We show that the phase transition is clearly first order for N >= 3 when P=N and P=N-1, contrary to predictions based on the Renormalization Group in 4-εexpansion but in agreement wi

D. Loison, K. D. Schotte

Starting from the hypothesis of a second order transition we have studied modifications of the original Heisenberg antiferromagnet on a stacked triangular lattice (STA-model) by the Monte Carlo technique. The change is a local constraint restricting the spins at the corners of selected triangles to add up to zero without stopping them from moving freely (STA

D. Loison, K. D. Schotte

The nature of the phase transition for the XY stacked triangular antiferromagnet (STA) is a controversial subject at present. The field theoretical renormalization group (RG) in three dimensions predicts a first order transition. This prediction disagrees with Monte Carlo (MC) simulations which favor a new universality class or a tricritical transition. We s

N. Breda, R. A. Broglia, G. Colo`, G. Onida

The electron--phonon coupling in fullerene C28 has been calculated from first principles. The value of the associated coupling constant lambda/N(0) is found to be a factor three larger than that associated with C60. Assuming similar values of the density of levels at the Fermi surface N(0) and of the Coulomb pseudopotential for C28-based solids as those asso

L. Siurakshina, D. Ihle, R. Hayn

A spin-rotation-invariant Green&#39;s-function theory of long-range and short-range order (SRO) in the $S=1/2$ antiferromagnetic Heisenberg model with spatially anisotropic couplings on a simple cubic lattice is presented. The staggered magnetization, the two-spin correlation functions, the correlation leng spin-rotation-invariant Green&#39;s-function theory

Mahesh Chandran

Magnetic relaxation in a type-II superconductor is simulated for a range of temperatures (T) in a simple model of 2D Josephson junction array (JJA) with finite screening. The high-T phase, that is characterised by a single time scale τ_α, crosses over to an intermediate phase at a lower temperature T_{cr} wherein a second time scale τ_β<<τ_α emerges. The rel

A. K. Geim, S. V. Dubonos, J. J. Palacios

Each time a vortex enters or exits a small superconductor, a different fluxoid state develops. We have observed splitting and sharp kinks on magnetization curves of such individual states. The features are the manifestation of first and second order transitions, respectively, and reveal the existence of distinct vortex phases within a superconducting state w

Jae Dong Noh

We investigate phase transitions in a solid-on-solid model where double-height steps as well as single-height steps are allowed. Without the double-height steps, repulsive interactions between up-up or down-down step pairs give rise to a disordered flat phase. When the double-height steps are allowed, two single-height steps can merge into a double-height st

K. Hukushima, H. Kawamura

Extensive equilibrium Monte Carlo simulations are performed for a three-dimensional Heisenberg spin glass with the nearest-neighbor Gaussian coupling to investigate its spin-glass and chiral-glass orderings. The occurrence of a finite-temperature chiral-glass transition without the conventional spin-glass order is established. Critical exponents characterizi

H. Kawamura, K. Hukushima

Spin-glass and chiral-glass orderings of a three-dimensional isotropic Heisenberg spin glass are studied both by equilibrium and off-equilibrium Monte Carlo simulations with emphasis on their dynamical aspects. The model is found to exhibit a finite-temperature chiral-glass transition without the conventional spin-glass order. Although chirality is an Ising-

D. Rigopoulou, A. Franceschini, R. Genzel, P. van der Werf

A new population of faint galaxies characterized by an extremely high rate of evolution with redshift up to z~1.5 has recently been discovered by ISO. These sources are likely to contribute significantly to the cosmic far-IR extragalactic background. We have carried out near-infrared VLT-ISAAC spectroscopy of a sample of ISOCAM galaxies from the Hubble Deep

Rafael Angel Araya-Gochez

Recent evidence of the phenomenal energetics involved in gamma ray burst events strongly suggests that the progenitor must efficiently convert gravitational binding energy into a moderately collimated outflow, possibly in the form of a Poynting jet. We show that an MHD-instability driven dynamo (IDD) operating in a hot accretion disk is capable of generating

T. M. Tauris, T. Sennels

We have investigated the formation of the binary radio pulsars PSR B2303+46 and PSR J1141-6545 via Monte Carlo simulations of a large number of interacting stars in binary systems. PSR B2303+46 has recently been shown (van Kerkwijk & Kulkarni 1999) to be the first neutron star - white dwarf binary system observed, in which the neutron star was born after the

P. A. M. van Hoof, P. G. Martin, G. J. Ferland

This paper describes the most important differences between Cloudy 90 and Cloudy 94, the most recent upgrade of the code which has now been posted on the WWW. It also describes the upgrade of the grain model in Cloudy which is currently underway.

C. J. Conselice, M. A. Bershady, J. S. Gallagher

We present a method of determining the likely triggering mechanisms for luminous, nearby starbursts based on their optical asymmetry and (B-V) color -- what we term as indices of `physical morphology.&#39; By comparing the starbursts&#39; locations in a color-asymmetry diagram to an independent, nearby galaxy sample, we identify which starbursts are likely t

A. J. Burgasser, J. D. Kirkpatrick, R. M. Cutri, H. McCallon

We report the discovery of a widely separated (258$\farcs3\pm0\farcs$4) T dwarf companion to the Gl 570ABC system. This new component, Gl 570D, was initially identified from the Two Micron All Sky Survey (2MASS). Its near-infrared spectrum shows the 1.6 and 2.2 $\micron$ CH$_4$ absorption bands characteristic of T dwarfs, while its common proper motion with

Andrew Gould, Cheongho Han

We investigate whether the &#34;close/wide&#34; class of degeneracies in caustic-crossing binary microlensing events can be broken astrometrically. Dominik showed that these degeneracies are particularly severe because they arise from a degeneracy in the lens equation itself rather than a mere &#34;accidental&#34; mimicking of one light curve by another. A m