September 2000 arXiv papers — page 14

Peter Zahn, Ingrid Mertig

The influence of a c(2x2) ordered interface alloy of 3d transition metals at the ferromagnet/nonmagnet interface on interlayer exchange coupling (IXC), the formation of quantum well states (QWS) and the phenomenon of Giant MagnetoResistance is investigated. We obtained a strong dependence of IXC on interface alloy formation. The GMR ratio is also strongly in

S. B. Popov, M. Colpi, M. E. Prokhorov, A. Treves

We model populations of isolated neutron stars in the Galaxy following their orbital and magneto-rotational evolution. It is shown that accretors become more abundant than coolers at fluxes below $\sim 10^{-13}$ erg cm$^{-2}$ s$^{-1},$ and one can predict that about one accreting neutron star per square degree should be observed at the {\it Chandra} and {\it

Mathieu Dutour

We extend a classical result by Rankin. We consider the following question: given $n$ vectors $v_i$ in the ball of radius $R$ of an infinite dimensional Banach space ${\cal B}$ with $d(v_i,v_j)\geq 1$, can we bound the number $n$?

Masayasu Harada, Koichi Yamawaki

We propose a novel way of matching effective field theory with the underlying QCD in the sense of a Wilsonian renormalization group equation (RGE). We derive Wilsonian matching conditions between current correlators obtained by the operator product expansion in QCD and those by the hidden local symmetry (HLS) model. This determines without much ambiguity the

Mircea Neagu

The paper studies the harmonic maps on a direction between a Riemannian space and a generalized Lagrange space. Also, it is proved there that the solutions of C^2 class of certain ODEs or PDEs are harmonic maps, in the sense of this paper.

Kazuo Hosomichi, Kazumi Okuyama, Yuji Satoh

We discuss the correlation functions of the SL(2,C)/SU(2) WZW model, or the CFT on the Euclidean AdS_3. We argue that their calculation is reduced to that of a free theory by taking into account the renormalization and integrating out a certain zero-mode, which is an analog of the zero-mode integration in Liouville theory. Based on the resultant free field p

Burkhard Eden, Anastasios Petkou, Christian Schubert, Emery Sokatchev

We show that, although the correlator of four stress-tensor multiplets in N=4 SYM is known to have radiative corrections, certain linear combinations of its components are protected from perturbative renormalisation and remain at their free-field values. This result is valid for weak as well as for strong coupling and for any gauge group. Our argument uses I

M. N. Achasov, K. I. Beloborodov, A. V. Berdyugin, A. G. Bogdanchikov

The cross sections of the processes $e^+e^- \to K^+K^-$, $e^+e^- \to K_SK_L$ and $e^+e^- \to π^+π^-π^0$ were measured in the SND experiment at the VEPP-2M collider in the energy region near the $ϕ(1020)$ meson. These measurements were based on about $10^6$ $K^+K^-$, $0.5 \times 10^6$ $K_SK_L$ and $0.4 \times 10^6$ $π^+π^-π^0$ selected events. Themeasured cro

Per Bak, Kan Chen, Maya Paczuski

Fires in the one-dimensional Bak-Chen-Tang forest fire model propagate as solitons, resembling shocks in Burgers turbulence. The branching of solitons, creating new fires, is balanced by the pair-wise annihilation of oppositely moving solitons. Two distinct, diverging length scales appear in the limit where the growth rate of trees, $p$, vanishes. The width

Hiroyuki Hata, Shun'ichi Shinohara

Tachyon condensation on a bosonic D-brane was recently demonstrated numerically in Witten's open string field theory with level truncation approximation. This non-perturbative vacuum, which is obtained by solving the equation of motion, has to satisfy furthermore the requirement of BRST invariance. This is indispensable in order for the theory around the

Joel Giedt

Inequivalent standard-like observable sector embeddings in $Z_3$ orbifolds with two discrete Wilson lines, as determined by Casas, Mondragon and Muñoz, are completed by examining all possible ways of embedding the hidden sector. The hidden sector embeddings are relevant to twisted matter in nontrivial representations of the Standard Model and to scenarios wh

Cong Xu, Carol J. Lonsdale, David L. Shupe, JoAnn O'Linger

Empirical 'backward' galaxy evolution models for IR-bright galaxies are constrained using multiband IR surveys. A new Monte-Carlo algorithm is developed for this task. It exploits a large library of realistic Spectral Energy Distributions (SEDs) of 837 local IR galaxies (IRAS 25$μm$ selected) from the UV (1000Å) to the radio (20cm), including ISO-mea

Brian C. Hall

This set of lecture notes gives an introduction to holomorphic function spaces as used in mathematical physics. The emphasis is on the Segal-Bargmann space and the canonical commutation relations. Later sections describe more advanced topics such as the Segal-Bargmann transform for compact Lie groups and the infinite-dimensional theory.

Carlton M. Caves, Christopher A. Fuchs, Pranaw Rungta

We consider entanglement for quantum states defined in vector spaces over the real numbers. Such real entanglement is different from entanglement in standard quantum mechanics over the complex numbers. The differences provide insight into the nature of entanglement in standard quantum theory. Wootters [Phys. Rev. Lett. 80, 2245 (1998)] has given an explicit

Markus Michler, Harald Weinfurter, Marek Zukowski

We present two experiments testing the hypothesis of noncontextual hidden variables (NCHV's). The first one is based on observation of two-photon pseudo-Greenberger-Horne-Zeilinger correlations, with two of the originally three particles mimicked by the polarization degree of freedom and the spatial degree of freedom of a single photon. The second one, a

Nguyen Tuan Anh

Based on the principle of causality, I advance a new principle of variation and try to use it as the most general principle for research into laws of nature.

E. S. Choi, J. S. Brooks, J. S. Qualls, Y. S. Song

We describe an AC method for the measurement of the longitudinal (Sxx) and transverse (Sxy, i.e. Nernst) thermopower of mm-size single crystal samples at low temperatures (T<1 K) and high magnetic fields (B>30 T). A low-frequency (33 mHz) heating method is used to increase the resolution, and to determine the temperature gradient reliably in high magnetic fi

Gustavo R. Gonzalez-Martin

Geometric relativistc interactions in a new geometric unified theory are classified using the dynamic holonomy groups of the connection. Physical meaning may be given to these interactions if the frame excitations represent particles. These excitations have algebraic and topological quantum numbers. The proton, electron and neutrino may be associated to the

Gustavo R. Gonzalez-Martin

The value of the alpha constant, known to be equal to an algebraic expression in terms of pi and entire numbers related to certain group volumes, is derived from the relativistic structure group of a geometric unified theory, its subgroups and corresponding symmetric space quotients.

N. M. Zubarev

The formation of singularities on a free surface of a conducting ideal fluid in a strong electric field is considered. It is found that the nonlinear equations of two-dimensional fluid motion can be solved in the small-angle approximation. This enables us to show that for almost arbitrary initial conditions the surface curvature becomes infinite in a finite

Vladislav A. Bogoyavlenskiy

This paper theoretically analyzes the hydrodynamic shape stability problem for sonoluminescing bubbles. We present a semianalytical approach to describe the evolution of shape perturbations in the strongly nonlinear regime of violent collapse. The proposed approximation estimating the damping rate produced by liquid viscosity is used to elucidate the influen

C. M. Ko

Strange particles such as the kaon and lambda are useful in probing the properties of dense matter formed in heavy ion collisions. We review in this talk the theoretical understandings of their properties in nuclear medium based on both the effective chiral Lagrangian and the phenomenological hadronic model. We further review the effects due to changes in th

P. N. Shen, Q. B. Li, Z. Y. Zhang, Y. W. Yu

In the framework of the SU(3) chiral quark model, the $S-$wave baryon-baryon bound states are investigated. It is found that according to the symmetry character of the system and the contributions from chiral fields, there are three types of bound states. The states of the first type, such as $[ΩΩ]_{(0,0)}$ and $[Ξ^{*}Ω]_{(0,1/2)}$ are deeply bound dibaryon

Q. B. Li, P. N. Shen, Z. Y. Zhang, Y. W. Yu

The possible candidates of $S-$wave dibaryons with various strange numbers are studied under the chiral SU(3) quark model. It is shown that there are three types of baryon-baryon bound states. The states of the first type are called deuteron-like states. If chiral fields can provide enough attraction between interacting baryons, these systems, such as $[ΞΩ-

P. J. Forrester, N. S. Witte

Random matrix ensembles with orthogonal and unitary symmetry correspond to the cases of real symmetric and Hermitian random matrices respectively. We show that the probability density function for the corresponding spacings between consecutive eigenvalues can be written exactly in the Wigner surmise type form $a(s) e^{-b(s)}$ for $a$ simply related to a Pain

N. S. Witte, P. J. Forrester

The probabilities for gaps in the eigenvalue spectrum of finite $ N\times N $ random unitary ensembles on the unit circle with a singular weight, and the related hermitian ensembles on the line with Cauchy weight, are found exactly. The finite cases for exclusion from single and double intervals are given in terms of second order second degree ODEs which are

Mireille Boutin

We show that the maximal orbit dimension of a simultaneous Lie group action on n copies of a manifold does not pseudo-stabilize when n increases. We also show that if a Lie group action is (locally) effective on subsets of a manifold, then the induced Cartesian action is locally free on an open subset of a sufficiently big (but finite) number of copies of th

Paolo Cascini

For any odd $n$, we describe a smooth minimal (i.e. obtained by adding an irreducible hypersurface) compactification $\tilde S_n$ of the quasi-projective homogeneous variety $S_{n}=PGL(n+1)/SL(2)$ that parameterizes the rational normal curves in $P^n$. We show that $\tilde S_{n}$ is isomorphic to a component of the Maruyama scheme of the semi-stable sheaves

Laura Felicia Matusevich

The holonomic rank of the A-hypergeometric system H_A(β) is shown to depend on the parameter vector βwhen the underlying toric ideal I_A is a non Cohen Macaulay codimension 2 toric ideal. The set of exceptional parameters is usually infinite.

E. J. Dubuc, C. Sanchez de la Vega

In this paper we deal with Grothendieck&#39;s interpretation of Artin&#39;s interpretation of Galois&#39;s Galois Theory (and its natural relation with the fundamental group and the theory of coverings) as he developed it in Expose V, section 4, ``Conditions axiomatiques d&#39;une theorie de Galois&#39;&#39; in the SGA1 1960/61. This is a beautiful piece of

Tom M. W. Nye, Michael A. Singer

An expression is found for the $L^2$-index of a Dirac operator coupled to a connection on a $U_n$ vector bundle over $S^1\times{\mathbb R}^3$. Boundary conditions for the connection are given which ensure the coupled Dirac operator is Fredholm. Callias&#39; index theorem is used to calculate the index when the connection is independent of the coordinate on $

G. Militaru

The study of the pentagon (fusion) equation leds to the Structure and the Classification theorem for finite dimenasional Hopf algebras: there exists a one to one correspondence between the set of types of n-dimensional Hopf algebtras and the set of the orbits of the resticted Jordan action $GL_n(k) \times M_n(k)\otimes M_n(k) \to M_n(k) \otimes M_nk$ $(u, R)

Constantin Udriste, Mircea Neagu

We proved that the solutions of $C^2$ class of certain ODEs or PDEs belong to a class of harmonic maps between two convenient generalized Lagrange spaces.

Mircea Neagu

In this paper are studied the harmonic maps between two generalized Lagrange spaces. At the same time, it is proved that the solutions of $C^2$ class of certain ODEs or PDEs are harmonic maps between certain convenient generalized Lagrange spaces.

Evans M. Harrell

The Blaschke-Lebesgue Theorem states that among all planar convex domains of given constant width B the Reuleaux triangle has minimal area. It is the purpose of the present note to give a direct proof of this theorem by analyzing the underlying variational problem. The advantages of the proof are that it shows uniqueness (modulo rigid deformations such as ro

A. B. Goncharov

We discuss the following two problems: 1) The properties of the multiple zeta-values and their generalizations, multiple polylogarithms at N-th roots of unity; 2) The action of the absolute Galois group on the pro-l-completion of the fundamental group of the projective line without zero, infinity, and all N-th roots of unity; and a surprising connection of t

Jean-Francois Burnol

I associate to a global field K a Lax-Phillips scattering which has the property of causality if and only if the Riemann Hypothesis holds for all the abelian L-functions of K. As a Hilbert space closure problem this provides an adelic variation on a theme initiated by Nyman and Beurling. The adelic aspects are related to previous work by Tate, Iwasawa and Co

M. Chabab

In this talk, I report on a work done in collaboration with R. Markazi and E.H. Saidi [1].

A. A. Abrikosov

The explicit multi-instanton solutions by &#39;tHooft and Jackiw, Nohl & Rebbi are generalized to curvilinear coordinates. The idea is that a gauge transformation can notably simplify the expressions obtained after the change of variables. The gauge transform generates a compensating addition to the gauge potential of pseudoparticles. Singularities of the co

Tasneem Zehra Husain, Maxim Zabzine

We consider simple CFT models which contain massless bosons, or massless fermions or a supersymmetric combination of the two, on the strip. We study the deformations of these models by relevant boundary operators. In particular, we work out the details for a boundary operator with a quadratic dependence on the fields and argue that some of our results can be

Yaron Oz, Tony Pantev, Daniel Waldram

We propose a correspondence between brane-antibrane systems and stable triples (E_1,E_2,T), where E_1,E_2 are holomorphic vector bundles and the tachyon T is a map between them. We demonstrate that, under the assumption of holomorphicity, the brane-antibrane field equations reduce to a set of vortex equations, which are equivalent to the mathematical notion

Nicolas Boulanger, Thibault Damour, Leonardo Gualtieri, Marc Henneaux

We report a no-go theorem excluding consistent cross-couplings for a collection of massless, spin-2 fields described, in the free limit, by the sum of Pauli-Fierz actions (one for each field). We show that, in spacetime dimensions >2, there is no consistent coupling, with at most two derivatives of the fields, that can mix the various &#34;gravitons&#34;. Th

T. D. Palev, J. Van der Jeugt

Generalized quantum statistics will be presented in the context of representation theory of Lie (super)algebras. This approach provides a natural mathematical framework, as is illustrated by the relation between para-Bose and para-Fermi operators and Lie (super)algebras of type B. Inspired by this relation, A-statistics is introduced, arising from representa

Cosmas Zachos

A brief pedagogical survey of the star product is provided, through Groenewold&#39;s original construction based on the Weyl correspondence. It is then illustrated how simple Landau orbits in a constant magnetic field, through their Dirac Brackets, define a noncommutative structure since these brackets exponentiate to a star product---a circumstance rarely o

M. V. Altaisky

The $ϕ^4$ field model is generalized to the case when the field $ϕ(x)$ is defined on a Lie group: $S[ϕ]=\int_{x\in G} L[ϕ(x)] dμ(x)$, $dμ(x)$ is the left-invariant measure on a locally compact group $G$. For the particular case of the affine group $G:x&#39;=ax+b,a\in\R_+, x,b \in \R^n$ t he Feynman perturbation expansion for the Green functions is shown to h

Massimo Di Pierro, Estia Eichten

We studied the hadronic decays of excited states of heavy mesons (D, D_s, B and B_s) to lighter states by emission of pi, eta or K. Wavefunctions and energy levels of these excited states are determined using a Dirac equation for the light quark in the potential generated by the heavy quark (including first order corrections in the heavy quark expansion). Tr

William B. Kilgore, Walter T. Giele

I present results of a next-to-leading order calculation of three jet production at hadron colliders. This calculation will have many applications. In addition to computing three-jet observables (spectra, mass distributions), this calculation permits the first next-to-leading order studies (at hadron colliders) of jet and event shape variables.

T. Ferbel

We present a study of inclusive direct-photon and neutral pion production in hadronic interactions that focuses on a comparison of the ratio of photon and pion yields with expectations from next-to-leading order perturbative QCD (NLO pQCD).

Naoyuki Haba, Hitoshi Murayama

We advocate a new approach to study models of fermion masses and mixings, namely anarchy proposed in hep-ph/9911341. In this approach, we scan the O(1) coefficients randomly. We argue that this is the correct approach when the fundamental theory is sufficiently complicated. Assuming there is no physical distinction among three generations of neutrinos, the p

D. Boyanovsky, H. J. de Vega

Infrared divergences from the exchange of dynamically screened magnetic gluons (photons) lead to the breakdown of the Fermi liquid description of the {\em normal} state of cold and dense QCD and QED. We implement a resummation of these divergences via the renormalization group to obtain the spectral density, dispersion relation, widths and wave function reno

V. Rizov, I. Vitev

We propose a three-fold covering of the group ${U}(2)$ as a gauge group for the electroweak interactions for the purpose of describing fields with integer and fractional electric charges with respect to the residual electromagnetic gauge group after a spontaneous breaking of the gauge symmetry. In a more general scheme we construct a three-fold covering of $

A. Kirk

For the first time a complete data set of the two-body decays of the f0(1370), f0(1500) and f0(1710) into all pseudoscalar mesons is available. The implications of these data for the flavour content for these three f0 states is studied. We find that they are in accord with the hypothesis that the scalar glueball of lattice QCD mixes with the qqbar nonet that

V. A. Ilyin, M. Maltoni, V. A. Novikov, L. B. Okun

The existence of extra chiral generations with all fermions heavier than $M_Z$ is strongly disfavored by the precision electroweak data. The exclusion of one additional generation of heavy fermions in SUSY extension of Standard Model is less forbidden if chargino and neutralino have low degenerate masses with $Δm \simeq 1$ GeV. However the data are fitted ni

Krishnendu Mukherjee

We compute the cross-section of the hadronic jets arising from the quark antiquark pair which are produced from a hard photons (of 4-momentum $q$) in the plasma, predominantly consisting of thermalised quarks and gluons. The quark antiquark pair is hard and scattered off the heat bath to form jets, while the gluons being soft get thermalised in the heat bath

F. S. Navarra, O. V. Utyuzh, Z. Wlodarczyk, G. Wilk

We demonstrate that the apparently ad hoc parametrization of the particle production spectra discussed in the literature and used in description of cosmic ray data can be derived from the information theory approach to multiparticle production processes. In particular, the violation of the Feynman scaling law can be interpreted as a manifestation of nonexten

M. Rybczynski, Z. Wlodarczyk, G. Wilk

We discuss the possible imprints of strangelets (i.e., lumps of Strange Quark Matter) in Chacaltaya experimental data using model of propagation of such objects through the atmosphere developed by us recently.

R. R. Volkas

Reasonably large relic neutrino asymmetries can be generated by active-sterile neutrino oscillations. After briefly discussing possible applications, I describe the Quantum Kinetic Equation formalism used to compute the asymmetry growth curves. I then show how the basic features of these curves can be understood on the basis of the adiabatic limit approximat

Guy D. Moore

I begin by answering a different question, ``Do we know the sphaleron rate?&#39;&#39; and conclude that we do. Then I discuss a crude but purely analytic picture which provides an estimate of the sphaleron rate within the context of Bodeker&#39;s effective theory. The estimate, which comes surprisingly close to the numerically determined sphaleron rate, give

S. Arunagiri

We discuss (i) the evaluation of the expectation values of four-quark operators assuming that the heavy quark expansion for $b$ sector converges at the third order in $1/m_Q$, and (ii) the estimation of the duality breaking short distance nonperturbative corrections to the parton decay rate. We finally point out the implications of the result obtained for th

Stefano Capitani

Using overlap as well as Wilson fermions, we have computed the one-loop renormalization factors of ten non-singlet operators which measure the third moment of quark momentum and helicity distributions (the lowest two having been computed in a previous paper), as well as the lowest three moments of the $g_2$ structure function and the lowest two non-trivial m

R. Bertle, M. Faber, J. Greensite, S. Olejnik

We review lattice evidence showing that center-vortex condensation is a serious candidate for the mechanism of colour confinement in quantum chromodynamics.

P. Vranas

Applications of Domain Wall fermions to various vector-like lattice theories are reviewed with an emphasis on QCD thermodynamics. Methods for improving their chiral properties at strong coupling are discussed and results from implementing them are presented.

Greg Landsberg

One of the most stimulating recent ideas in particle physics involves a possibility that our universe has additional compactified spatial dimensions, perhaps as large as 1 mm. In this mini-review, we discuss the results of recent experimental searches for such large extra dimensions.

D. E. Jaffe, CLEO Collaboration

Using data collected with the CLEO II detector we have performed a search for direct CP violation in the $Ξ$ hyperon system. CP violation gives rise to an asymmetry, A, between the parity-violating angular distributions of the decay chains $Ξ^- \To Λpi^-$, $Λ\To p π^-$ and $\barΞ^+ \To \barΛ π^+$, $\barΛ \To \bar{p} π^+$. In the Standard Model, A is expected

The SLD Collaboration, K. Abe

We present a direct measurement of the parity-violation parameter $A_c$ in the coupling of the $Z^0$ to $c$-quarks with the SLD detector. The measurement is based on a sample of 530k hadronic $Z^0$ decays, produced with a mean electron-beam polarization of $|P_e| = 73 %$. The tagging of $c$-quark events is performed using two methods: the exclusive reconstru

D0 collaboration, B. Abbott

We present the first measurement of the electron angular distribution parameter alpha_2 in W to e nu events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the D0 detector during the 1994--1995 Fermilab Tevatron run. We compare our results with next-to-leading order pert

W. Kummer, D. V. Vassilevich

Using heat kernel techniques we show that the relation between Hawking temperature and radiation flux known from Einstein gravity in D dimensions can be reproduced from the spherically reduced action. A recent controversy regarding the D=2 anomaly for that case is discussed. The generalized effective Polyakov action in the presence of a dilaton field is pres

S. Liberati

In this thesis, we investigate quantum vacuum effects in the presence of gravitational fields. After discussing the general theory of vacuum effects in strong fields we apply it to the relevant issue of the interaction of the quantum vacuum with black hole geometries. In particular we consider the long-standing problem of the interpretation of gravitational

Istvan Racz

The almost perfect correspondence between certain laws of classical black hole mechanics and the ordinary laws of thermodynamics is spoiled by the failure of the conventional back hole analogue of the third law. Our aim here is to contribute to the associated discussion by flashing light on some simple facts of black hole physics. However, no attempt is made

A. Kuiroukidis, D. B. Papadopoulos

New exact inflationary solutions are presented in the scalar field theory, minimally coupled to gravity, with a potential term. No use is made of the slow rollover approximation. The scale factors are completely nonsingular and the transition to the deccelerating phase is smooth. Moreover, in one of these models, asymptotically one has transition to the matt

Robert Konik, Andreas W. W. Ludwig

Motivated by recent work of Lin, Balents, and Fisher (cond-mat/9801285), we compute correlation functions at zero temperature for weakly coupled two-leg Hubbard ladders and (N,N) armchair carbon nanotubes. Lin et al. argued that such systems renormalize towards the SO(8) Gross-Neveu model, an integrable theory. We exploit this integrability to perform the co

W. C. Barber, D. P. Belanger

Ising Monte Carlo simulations of the random-field Ising system Fe(0.80)Zn(0.20)F2 are presented for H=10T. The specific heat critical behavior is consistent with alpha approximately 0 and the staggered magnetization with beta approximately 0.25 +- 0.03.

Louis Colonna-Romano, Stephen W. Pierson, Mark Friesen

A numerical study of the neutral two-dimensional (2D) lattice Coulomb gas is performed to examine dynamic scaling, finite size effects, and the dynamic critical exponent $z$ of the Kosterlitz-Thouless-Berezinskii transition. By studying large system sizes ($L=100$), we show $z=2.0 \pm0.2$ using Fisher-Fisher-Huse (FFH) scaling. We also present evidence that

Peter Swain, David Andelman

We present a general linear response description of membrane adhesion at rough or chemically structured surfaces. Our method accounts for non-local Van der Waals effects and contains the more approximate (and local) Deryagin approach in a simple limit. Specializing to supported membranes we consider the effects of substrate structure on the membrane adhesion

Y. Chen, Z. Honda, A. Zheludev, C. Broholm

Field-induced commensurate transverse magnetic ordering is observed in the Haldane-gap compound \nd by means of neutron diffraction. Depending on the direction of applied field, the high-field phase is shown to be either a 3-dimensional ordered Néel state or a short-range ordered state with dominant 2-dimensional spin correlations. The structure of the high-

B. M. Roehner

During a stock market peak the price of a given stock ($ i $) jumps from an initial level $ p_1(i) $ to a peak level $ p_2(i) $ before falling back to a bottom level $ p_3(i) $. The ratios $ A(i) = p_2(i)/p_1(i) $ and $ B(i)= p_3(i)/p_1(i) $ are referred to as the peak- and bottom-amplitude respectively. The paper shows that for a sample of stocks there is a

Giovanni Jona-Lasinio

The renormalization group has played an important role in the physics of the second half of the twentieth century both as a conceptual and a calculational tool. In particular it provided the key ideas for the construction of a qualitative and quantitative theory of the critical point in phase transitions and started a new era in statistical mechanics. Probab

Y. Zolotaryuk, S. Flach, V. Fleurov

Discrete breathers (nonlinear localised modes) have been shown to exist in various nonlinear Hamiltonian lattice systems. In the present paper we study the dynamics of classical spins interacting via Heisenberg exchange on spatial $d$-dimensional lattices (with and without the presence of single-ion anisotropy). We show that discrete breathers exist for case

M. Marchioro, A. Acrivos

Using Stokesian dynamics simulations, we examine the flow of a monodisperse, neutrally buoyant, homogeneous suspension of non-Brownian solid spheres in simple shear, starting from a large number of independent hard-sphere distributions and ensemble averaging the results. We construct a novel method for computing the gradient diffusivity via simulations on a

Brian R. La Cour, William C. Schieve

Tsallis has suggested a nonextensive generalization of the Boltzmann-Gibbs entropy, the maximization of which gives a generalized canonical distribution under special constraints. In this brief report we show that the generalized canonical distribution so obtained may differ from that predicted by the law of large numbers when empirical samples are held to t

M. Acquarone, C. Noce

For a dimer with a non-degenerate orbital built from atomic wave functions of Gaussian shape we evaluate all the electron-phonon couplings derived from the one-body and two-body electronic interactions, considering both the adiabatic and extreme non-adiabatic limit. Not only the values of the coupling parameters in the two limits, but also the expressions of

T. Alarcon, A. Perez-Madrid, J. M. Rubi

We show a new mechanism to extract energy from non-equilibrium fluctuations typical of periodically driven non-Hermitian systems. The transduction of energy between the driving force and the system is revealed by an \emph{anomalous} behavior of the susceptibility, leading to a diminution of the dissipated power and consequently to an improvement of the trans

G. G. Sergeeva

It was discussed the possibility of determination of 2D XY ordering temperature (Berezinskii-Kosterlitz-Thouless temperature) in striped Cu-O planes for quasi-two dimensional HTS with the semiconducting behavior of out-of-plane resistivity in normal state. From the results of the resistivity measurements for samples of underdoped Bi-2212 the values of 2D XY

Per Bak, Dante R Chialvo

We describe a mechanism for biological learning and adaptation based on two simple principles: (I) Neuronal activity propagates only through the network&#39;s strongest synaptic connections (extremal dynamics), and (II) The strengths of active synapses are reduced if mistakes are made, otherwise no changes occur (negative feedback). The balancing of those tw

S. S. Murzin, A. G. M. Jansen

In a recent preprint cond-mat/9906450 (published in PRL 84, 3141 (2000)) Bodo Huckestein showed that at real experimental conditions it is not possible to observe the quantum Hall effect (QHE) at $ω_{c}τ<1$ predicted by Khmelnitskii ($ω_{c}=eB/m$ is the cyclotron frequency and $τ$ is the scattering time). We would like to point out here that in fact the situ

Boris A. Akimov, Vladislav A. Bogoyavlenskiy, Ludmila I. Ryabova, Vyacheslav N. Vasilkov

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on <111>-BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration,

H. Yoshioka, M. Tsuchiizu, Y. Suzumura

We examine effects of the next-nearest-neighbor repulsion on electronic states of a one-dimensional interacting electron system which consists of quarter-filled band and interactions of on-site and nearest-neighbor repulsion. We derive the effective Hamiltonian for the electrons around wave number $\pm \kf$ ($\kf$: Fermi wave number) and apply the renormaliz

F. M. Izrailev

Generic properties of the strength function (local density of states (LDOS)) and chaotic eigenstates are analyzed for isolated systems of interacting particles. Both random matrix models and dynamical systems are considered in the unique approach. Specific attention is paid to the quantum-classical correspondence for the form of the LDOS and eigenstates, and

Dingping Li, Baruch Rosenstein

We develop an optimized perturbation theory for the Ginzburg - Landau description of thermal fluctuations effects in the vortex liquids. Unlike the high temperature expansion which is asymptotic, the optimized expansion is convergent. Radius of convergence on the lowest Landau level is $a_{T}=-3$ in 2D and $a_{T}=-5$ in 3D. It allows a systematic calculation

S. Boldyrev, V. Gurarie

We reduce the problem of integer quantum Hall transition to a random rotation of an N-dimensional vector by an su(N) algebra, where only N specially selected generators of the algebra are nonzero. The group-theoretical structure revealed in this way allows us to obtain a new series of conservation laws for the equation describing the electron density evoluti

L. Vichi

We consider a Fermi gas confined by a harmonic trapping potential and we highlight the role of the Fermi-Dirac statistics by studying frequency and damping of collective oscillations of quadrupole type in the framework of the quantum Boltzmann equation, in which statistical corrections are taken into account in the collisional integral. We are able to descri

James M. Stone, James E. Pringle

We present the results of axisymmetric, time-dependent magnetohydrodynamic simulations of accretion flows around black holes. The calculations begin from a rotationally supported thick torus which contains a weak poloidal field. Accretion is produced by growth and saturation of the magnetorotational instability (MRI) provided the wavelength of the fastest gr

S. Boissier, A. Boselli, N. Prantzos, G. Gavazzi

We study the star formation history of normal spirals by using a large and homogeneous data sample of local galaxies. For our analysis we utilise detailed models of chemical and spectrophotometric galactic evolution, calibrated on the Milky Way disc. We find that star formation efficiency is independent of galactic mass, while massive discs have, on average,

F. Haardt, M. R. Galli, A. Treves, L. Chiappetti

We report on observations of the two persistent black hole candidates LMC X-3 and LMCX-1 performed with \BS in October 1997. The flux of LMC X-1 was possibly measured up to 60 keV, but there is a possible confusion with PSR 0540-69. Fits with an absorbed multicolor disk black body are not satisfactory, while the superposition of this model with a power law i

Carlos A. Valotto, Ben Moore, Diego G. Lambas

We analyze systematic effects in the determination of the galaxy luminosity function in clusters using a deep mock catalogue constructed from a numerical simulation of a hierarchical universe. The results indicate a strong tendency to derive a rising faint end ($α\lsim -1.5$) in clusters selected in two dimensions, using a galaxy catalogue constructed with a

Ichi Tanaka, Toru Yamada, Edwin L. Turner, Yasushi Suto

We report on a wide-area (48&#39; x 9&#39;) imaging survey of faint galaxies in R and I bands toward the 1338+27 field where an unusual concentration of five QSOs at z\sim1.1, embedded in a larger-scale clustering of 23 QSOs, is known to exist. Using a quite homogeneous galaxy catalog with a detection completeness limit of I~23.5, we detect a significant clu

M. B. Bogdanov

The problem of restoration of the source brightness distribution from an analysis of the stellar and AGNs microlensing light curves is investigated. In case of microlensing of stars by a point-mass lens as well as for caustic crossing events for binary lens the problem can be reduced to solution of the Fredholm integral equation of the 1st kind. Concrete for

F. Heitsch, M. -M. Mac Low, R. S. Klessen

Hydrodynamic supersonic turbulence can only prevent local gravitational collapse if the turbulence is driven on scales smaller than the local Jeans lengths in the densest regions, a very severe requirement (Paper I). Magnetic fields have been suggested to support molecular clouds either magnetostatically or via magnetohydrodynamic (MHD) waves. Whereas the fi

G. P. Mathlin, A. C. Baker, D. K. Churches, M. G. Edmunds

We construct a simple, robust model of the chemical evolution of galaxies from high to low redshift, and apply it to published observations of damped Lyman-alpha quasar absorption line systems (DLAs). The elementary model assumes quiescent star formation and isolated galaxies (no interactions, mergers or gas flows). We consider the influence of dust and chem

D. W. Fox, W. H. G. Lewin, R. E. Rutledge, E. H. Morgan

We have searched the rising portion of type I X-ray bursts observed from the Rapid Burster with the Rossi X-ray Timing Explorer for the presence of periodicities. The 95 per cent confidence upper limit on the average root-mean-square variation of near coherent pulsations with a width of <1 Hz (in 60--2048 Hz) during the first second of the bursts is <8.8 per