January 1997 arXiv papers — page 6

Stanislaw J. Szarek

For a (compact) subset $K$ of a metric space and $\varepsilon > 0$, the {\em covering number} $N(K , \varepsilon )$ is defined as the smallest number of balls of radius $\varepsilon$ whose union covers $K$. Knowledge of the {\em metric entropy}, i.e., the asymptotic behaviour of covering numbers for (families of) metric spaces is important in many areas of m

G. Kaniadakis, A. Lavagno, P. Quarati

We have studied the kinetics of $q$-deformed bosons and fermions, within a semiclassical approach. This investigation is realized by introducing a generalized exclusion-inclusion principle, intrinsically connected with the quantum $q$-algebra by means of the creation and annihilation operators matrix elements. In this framework, we have derived a non-linear

Christof Schmidhuber

This is a colloquium-style review lecture for physicists and non-physicists, as part of the requirements for ``Habilitation'' at the university of Bern: At a pressure of 220 atm. and a temperature of 374 Celsius there is a second-order phase transition between water and steam. Understanding it requires the concept of the renormalization group. Images

C. Emmrich, H. Roemer

It is known that in the WKB approximation of multicomponent systems like Dirac equation or Born-Oppenheimer approximation, an additional phase appears apart from the Berry phase. So far, this phase was only examined in special cases, or under certain restrictive assumptions, namely that the eigenspaces of the matrix or endomorphism valued symbol of the Hamil

W. Bernreuther, A. Brandenburg, M. Flesch

We compute the order $α_s$ QCD corrections to the density matrix for the decay of a neutral Higgs boson $ϕ$ with (in)definite CP parity into a quark antiquark pair, respectively the QED corrections for the decay into a pair of charged leptons. We classify and calculate single spin asymmetries and spin-spin correlations which are generated by the scalar and p

Damien M. Pierce

The prediction of the strong coupling constant in grand unified theories is reviewed, first in the standard model, then in the supersymmetric version. Various corrections are considered. The predictions in both supergravity-induced and gauge-mediated supersymmetry breaking models are discussed. In the region of parameter space without large fine tuning the s

S. Anderson

Using the CLEO detector at the Cornell $e^+e^-$ storage ring, CESR, we study the two-photon production of $Λ\barΛ$, making the first observation of $γγ\to Λ\barΛ$. We present the cross-section for $ γγ\to Λ\barΛ$ as a function of the $γγ$ center of mass energy and compare it to that predicted by the quark-diquark model.

T. Coan, CLEO Collaboration

We report a measurement of the magnitude of the tau neutrino helicity from tau-pair events taken with the CLEO detector at the CESR electron-positron storage ring. Events in which each tau undergoes the decay tau -> h nu, with h a charged pion or kaon, are analyzed for energy correlations between the daughter hadrons, yielding |xi| = 2*|h_nu| = 1.03 +/- 0.06

M. Rogalla, Th. Eich, N. Evans, R. Geppert

We estimate the hardness factors and the equivalent 1 MeV neutron fluences for hadrons fluences expected at the GaAs positions wheels in the ATLAS Inner Detector. On this basis the degradation of the GaAs particle detectors made from different substrates as a function of years LHC operation is predicted.

R. Schaflitzel

We determine the subfactors $N\subset R$ of the hyperfinite $II_1$-factor R with finite index for which the $C^*$-tensor category of the associated $(N,N)$-bimodules is equivalent to the $C^*$-tensor category $\C{U}_G$ of all unitary finite dimensional representations of a given finite group G.

R. Schaflitzel

The article contains a detailed description of the connection between finite depth inclusions of $II_1$-subfactors and finite $C^*$-tensor categories (i.e. $C^*$-tensor categories with dimension function for which the number of equivalence classes of irreducible objects is finite). The $(N,N)$-bimodules belonging to a $II_1$-subfactor $N\subset M$ with finit

R. Schaflitzel

A brief introduction into bimodules of $II_1$-factors is presented. Furthermore a version of the following result due to M. Pimsner and S. Popa is derived: Let $N=M_{-1}\subset M=M_0 \subset M_1 \subset M_2 \subset \ldots$ denote the Jones tower of a $II_1$-factor $N\subset M$ with finite index. Then the factor obtained by the basic construction from the pai

A. P. Kampf, T. P. Devereaux

We investigate the role of a finite potential range of a nonmagnetic impurity for the local density of states in a d_{x^2-y^2} superconductor. Impurity induced subgap resonances are modified by the appearance of further scattering channels beyond the $s$--wave scattering limit. The structure of the local density of states (DOS) in the vicinity of the impurit

Andrey V. Chubukov, Philippe Monthoux, Dirk K. Morr

We argue that recent calculations by Amin and Stamp (PRL 77, 301 (1996); cond-mat/9601086) overestimate the strength of the vertex corrections in the spin-fermion model for cuprates. We clarify the physical origin of the apparent discrepancy between their results and earlier calculations. We also comment on the relative sign of the vertex correction.

Patrick A. Lee, Naoto Nagaosa, Tai-Kai Ng, Xiao-Gang Wen

We develop a slave-boson theory for the t-J model at finite doping which respect a SU(2) symmetry -- a symmetry previously known to be important at half filling. The mean field phase diagram is found to be consistent with the phases observed in the cuprate superconductors, which contains d-wave superconductor, spin gap, strange metal, and Fermi liquid phases

Jae Woo Lee

We have solved the kinetics of random sequential adsorption of linear $k$-mers on a one-dimensional disordered substrate for the random sequential adsorption initial condition and for the random initial condition. The jamming limits $θ(\infty, k', k)$ at fixed length of linear $k$-mers have a minimum point at a particular density of the linear $k'$-m

Tânia Tomé, Mário J. de Oliveira

We apply the dinamically driven renormalization group to study the critical properties of the Domany-Kinzel probabilistic cellular automaton. To preserve the absorbing state clusters with at least one site occupied are renormalized into a one occupied site and clusters with all sites empty are renormalized into a one empty site. We have obtained the phase di

Shoji Takada, Peter G. Wolynes

The barriers between metastable states near the glass transition of a random heteropolymer are studied using replicas by describing inhomogeneous states. The instanton solution for a replica space free energy functional is found numerically to estimate the size of activation barriers and of the critical nuclei themselves between the dynamic and the static gl

Shoji Takada, Peter G. Wolynes

Protein folding is analyzed using a replica variational formalism to investigate some free energy landscape characteristics relevant for dynamics. A random contact interaction model that satisfies the minimum frustration principle is used to describe the coil-globule transition (characterized by T_CG), glass transitions (by T_A and T_K) and folding transitio

Robert Shrock, Shan-Ho Tsai

We derive rigorous upper and lower bounds for the ground state entropy of the $q$-state Potts antiferromagnet on the honeycomb and triangular lattices. These bounds are quite restrictive, especially for large $q$.

C. E. Pfister, Y. Velenik

We give a mathematical theory of the wetting phenomenon in the 2D Ising model using the formalism of Gibbs states. We treat the grand canonical and canonical ensembles.

G. Parisi, P. Ranieri

We evaluate the corrections to the mean field values of the $x$ and the $z$ exponents at the first order in the $ε$-expansion, for $T=T_c $. We find that both $x$ and $z$ are decreasing when the space dimension decreases.

Yasuhiro Hatsugai

The metal-insulator transition in one dimensional fermionic systems with long-range interaction is investigated. We have focused on an excitation spectrum by the exact diagonalization technique in sectors with different momentum quantum numbers. At rational fillings, we have demonstrated gap opening transitions from the Tomonaga-Luttinger liquid to the Mott

Per Bak, Stefan Boettcher

Many natural phenomena evolve intermittently, with periods of tranquillity interrupted by bursts of activity, rather than following a smooth gradual path. Examples include earthquakes, volcanic eruptions, solar flares, gamma-ray bursts, and biological evolution. Stephen Jay Gould and Niles Eldredge have coined the term "punctuated equilibria" for thi

I. Ichinose, T. Matsui, K. Sakakibara

We present a quantitative study of the charge-spin separation(CSS) phenomenon in a U(1) gauge theory of the t-J model of high-Tc superconductures. We calculate the critical temperature of confinement-deconfinement phase transition below which the CSS takes place.

Nancy Sandler, Dmitrii L. Maslov

Recent experiments have revealed that the temperature dependence of the conductance of quasi-ballistic quantum wires bears clear features of the Luttinger-liquid state. In this paper, the conductance of an N-channel quantum wire is calculated within the model of N coupled Luttinger liquids and under the assumption of weak disorder. It is shown that as the nu

Henning Schomerus, Martin Sieber

We derive uniform approximations for contributions to Gutzwiller's periodic-orbit sum for the spectral density which are valid close to bifurcations of periodic orbits in systems with mixed phase space. There, orbits lie close together and give collective contributions, while the individual contributions of Gutzwiller's type would diverge at the bifu

Luonan Chen, Kazuyuki Aihara

We propose a neural network model with transient chaos, or a transiently chaotic neural network (TCNN) as an approximation method for combinatorial optimization problem, by introducing transiently chaotic dynamics into neural networks. Unlike conventional neural networks only with point attractors, the proposed neural network has richer and more flexible dyn

Luonan Chen, Kazuyuki Aihara

This paper aims to theoretically prove by applying Marotto's Theorem that both transiently chaotic neural networks (TCNN) and discrete-time recurrent neural networks (DRNN) have chaotic structure. A significant property of TCNN and DRNN is that they have only one fixed point, when absolute values of the self-feedback connection weights in TCNN and the di

Christian Y. Cardall, George M. Fuller

We discuss general relativistic effects in the steady-state neutrino-driven ``wind'' which may arise from nascent neutron stars. In particular, we generalize previous analytic estimates of the entropy per baryon $S$, the mass outflow rate $\dot M$, and the dynamical expansion time scale $τ_{dyn}$. We show that $S$ increases and $τ_{dyn}$ decreases wi

B. C. Bromley, M. S. Warren, W. H. Zurek

We propose a method to determine the cosmic mass density Omega from redshift-space distortions induced by large-scale flows in the presence of nonlinear clustering. Nonlinear structures in redshift space such as fingers of God can contaminate distortions from linear flows on scales as large as several times the small-scale pairwise velocity dispersion sigma_

J. I. Katz

Sari and Piran have demonstrated that the time structure of gamma-ray bursts must reflect the time structure of their energy release. A model which satisfies this condition uses the electrodynamic emission of energy by the magnetized rotating ring of dense matter left by neutron star coalescence; GRB are essentially fast, high field, differentially rotating

M. A. Zwaan, F. H. Briggs, D. Sprayberry

Results from the Arecibo HI Strip Survey, an unbiased extragalactic HI survey, combined with optical and 21cm follow-up observations, determine the HI Mass Function and the cosmological mass density of HI at the present epoch. Both are consistent with earlier estimates, computed for the population of optically selected galaxies. This consistency occurs becau

H. V. Fagundes, M. A. M. Gonzalez

A numerical integration is made, starting with a Kantowski-Sachs (KS) model with an added initial perturbation at time one-tenth the age of the universe, and evolving up to the present. According to a prediction by Barrow (1989), the ratio between the fluctuations of the average matter density and those of the metric tensor varies with the inverse squared wa

Juan Garcia-Bellido, Andrei Linde

We propose an open hybrid inflation scenario that produces an open universe with a `tilted' n>1 spectrum of metric perturbations. The model contains a symmetry breaking field that tunnels to its true vacuum, producing a single bubble inside which hybrid inflation drives the universe to almost flatness. In order to obtain density perturbations with n > 1

Mateusz Ruszkowski, Ralph A. M. J. Wijers

Gamma-ray bursters emit a small fraction of their flux in X rays, and because X-ray detectors are often very sensitive they may probe the gamma-ray burst universe more deeply than the current best gamma-ray instruments. On the reasonable assumptions that spectra of bursts observed by BATSE may be used to predict the X-ray fluxes of gamma-ray bursts, and that

Boris Stern, Roland Svensson, Juri Poutanen

The average peak-aligned profile of all bursts detected by BATSE with sufficient data quality has a simple ``stretched'' exponential shape, F ~ exp[-(t/t_0)^{1/3}], where $t$ is the time measured from the time for the peak flux of the event, and $t_0$ is a time constant. We study the behaviour of $t_0$ of both the post-peak and the pre-peak slopes of

Claudio Gheller, Ornella Pantano, Lauro Moscardini

We present a hydrodynamical code for cosmological simulations which uses the Piecewise Parabolic Method (PPM) to follow the dynamics of gas component and an N-body Particle-Mesh algorithm for the evolution of collisionless component. The gravitational interaction between the two components is regulated by the Poisson equation which is solved by a standard FF

Felix Ryde, Juri Poutanen, Roland Svensson, Stefan Larsson

We present a combined, non-simultaneous, ASCA GIS and CGRO OSSE spectrum of the Seyfert 2 galaxy, NGC 7172, and make broad band spectral fits. The only Seyfert 2 galaxy previously studied over such a broad band is NGC 4945. We find that the most probable model for the data is a power law with an exponential cut-off being affected by a neutral absorber. The b

Juri Poutanen, Roland Svensson, Boris Stern

The predictions of the two-phase accretion disc-corona models for active galactic nuclei are compared with observations. We discuss the possibility to use X-ray spectral slopes, equivalent widths of the iron line, and the observed flux-spectral index correlation as diagnostics of the X/gamma-ray source compactness and geometry as well as of the cold disc tem

V. G. Kurt, B. V. Komberg, V. V. Sokolov, S. V. Zharykov

The data of BVR observations of the middle-aged radio pulsar PSR 0656+14 on January, 20/21 at the BTA (6-m) are presented. The brightness is determined in Cousins B filter B ~~25.1 with lambda_eff=4448A in adjacent for HST F130LP long-pass filter of a star-like object, coinsiding with the position of VLA radio source. Relatively large observed V and R fluxes

Rupert A. C. Croft, David H. Weinberg, Lars Hernquist, Neal Katz

In gravitational instability models, \lya absorption arises from a continuous fluctuating medium, so that spectra provide a non-linear one-dimensional ``map'' of the underlying density field. We characterise this continuous absorption using statistical measures applied to the distribution of absorbed flux. We describe two simple members of a family o

Roland Svensson

Various types of active galactic nuclei (AGN) are briefly discussed, with an emphasis on the theory of recent X-ray and $γ$-ray observations of the subclass, Seyfert 1 galaxies. The large radiation power from AGN is thought to originate from gravitational power released by matter accreting onto a supermassive black hole. The physical mechanisms responsible f

J. M. Hameury, J. P. Lasota, J. M. Hure

We present a model for the dwarf nova WZ Sge which does not require assuming unusually and unexplained low values of the viscosity alpha-parameter during exceptionally long quiescent states of this system. We propose that the inner parts of the accretion disc are disrupted by either a magnetic field or evaporation, so that the disc is stable (or very close t

Rupert A. C. Croft, Enrique Gaztanaga

One way of recovering information about the initial conditions of the Universe is by measuring features of the cosmological density field which are preserved during gravitational evolution and galaxy formation. In this paper we study the total number density of peaks in a (galaxy) point distribution smoothed with a filter, evaluating its usefulness as a mean

Martin J. Rees

Although they were discovered more than 25 years ago, gamma-ray bursts are still a mystery. Even their characteristic distance is highly uncertain. All that we can be confident about is that they involve compact objects and relativistic plasma. Current ideas and prospects are briefly reviewed. There are, fortunately, several feasible types of observation tha

Serguei B. Isakov, Stefan Mashkevich

Statistical mechanics and thermodynamics for ideal fractional exclusion statistics with mutual statistical interactions is studied systematically. We discuss properties of the single-state partition functions and derive the general form of the cluster expansion. Assuming a certain scaling of the single-particle partition functions, relevant to systems of non

A. C. Quillen, T. E. Pickering

Upper limits for the disk mass-to-light ratios for the low surface brightness galaxies UGC 6614 and F568-6 (Malin 2) are estimated by considering the minimum velocity perturbations in the HI velocity field that should result from the spiral structure observed in the R band images. The weak observed response in the $ϕ$ velocity component limits the mass-to-li

D. A. Dicus, B. Dutta, S. Nandi

In theories with gauge mediated supersymmetry breaking, the scalar tau, (${\tilde τ_1}$) is the lightest superpartner for a large range of the parameter space. At the large electron positron collider (LEP 2) this scenario can give rise to events with four $τ$ leptons and large missing energy. Two of the $τ$'s ( coming from the decays of ${\tilde τ_1}$&#3

Baruch Horovitz, Anatoly Golub

An effective free energy of a two dimensional (i.e. large area) Josephson Junctions is derived, allowing for thermal fluctuations, for random magnetic fields and for external currents. We show by using replica symmetry breaking methods, that the junction has four distinct phases: disordered, Josephson ordered, a glass phase and a coexisting Josephson order w

C. Destri, H. J. de Vega

The NLIE (the non-linear integral equation equivalent to the Bethe Ansatz equations for finite size) is generalized to excited states, that is states with holes and complex roots over the antiferromagnetic ground state. We consider the sine-Gordon/massive Thirring model (sG/mT) in a periodic box of length $L$ using the light-cone approach, in which the sG/mT

Sergey N. Solodukhin

The string-black hole correspondence is considered in the context of the correspondence principle proposed recently by Horowitz and Polchinski. We demonstrate that the entropy of string states and the entropy of a Schwarzschild black hole can be matched including the subleading terms which depend on mass logarithmically. We argue the necessity to include the

G. Cernicchiaro, T. Martin, K. Hasselbach, D. Mailly

New experiments are presented on the transmission of electron waves through a 2DEG (2 dimensional electron gas) ring with a gate on top of one of the branches. Magnetoconductance oscillations are observed, and the phase of the Aharanov-Bohm signal alternates between 0 and pi as the gate voltage is scanned. A Fourier transform of the data reveals a dominant p

Anton Deitmar

Geometric zeta functions of Ihara and Hashimoto are generalized to higher rank. The $p$-adic version of the Patterson conjecture is proven.

A. Djouadi, V. Driesen, W. Hollik, A. Kraft

We analyze the coupling of CP-even and CP-odd Higgs bosons to a photon and a Z boson in extensions of the Standard Model. In particular, we study in detail the effect of charged Higgs bosons in two-Higgs doublet models, and the contribution of SUSY particle loops in the minimal supersymmetric extension of the Standard Model. The Higgs-$γZ$ coupling can be me

A. Bartl, H. Eberl, S. Kraml, W. Majerotto

We discuss pair production and decays of stops, sbottoms, $τ$-sneutrinos, and staus in $e^+e^-$ annihilation in the energy range $\sqrt{s} = 500 GeV$ to 2 TeV. Numerical predictions within the Minimal Supersymmetric Standard Model (MSSM) for cross sections and decay rates are presented. We study the stop discovery potential for $\sqrt{s} = 500 GeV$ and $10 \

Masanori Yamanaka, Masaki Oshikawa, Ian Affleck

The Lieb-Schultz-Mattis theorem for spin chains is generalized to a wide range of models of interacting electrons and localized spins in one-dimensional lattice. The existence of a low-energy state is generally proved except for special commensurate fillings where a gap may occur. Moreover, the crystal momentum of the constructed low-energy state is $2k_F$,

Nobuyoshi Ohta, Takashi Shimizu

We investigate the possibility of extending non-extreme black hole solutions made of intersecting M-branes to those with two non-extreme deformation parameters, similar to Reissner-Nordstrøm solutions. General analysis of possible solutions is carried out to reduce the problem of solving field equations to a simple algebraic one for static spherically-symmet

Branislav Jurco, Peter Schupp

We give the construction of twisted quantum Lax equations associated with quantum groups. We solve these equations using factorization properties of the corresponding quantum groups. Our construction generalizes in many respects the Adler-Kostant-Symes construction for Lie groups and the construction of M. A. Semenov Tian-Shansky for the Lie-Poisson case.

Dennis Bonatsos, C. Daskaloyannis, P. Kolokotronis

The system of two $Q$-deformed oscillators coupled so that the total Hamiltonian has the su$_Q$(2) symmetry is proved to be equivalent, to lowest order approximation, to a system of two identical Morse oscillators coupled by the cross-anharmonicity usually used empirically in describing vibrational spectra of triatomic molecules. The symmetry also imposes a

P. P. Raychev, R. P. Roussev, P. A. Terziev, D. Bonatsos

A simplified boson realization of the $so_q(3)$ subalgebra of $u_q(3)$ is constructed. A simplified form of the corresponding $so_q(3)$ basis states is obtained. The reduced matrix elements of a special second-rank tensor operator (quadrupole operator) are calculated in the $so_q(3)$ basis.

Andrei A. Suvernev, David Z. Goodson

A very efficient large-order perturbation theory is formulated for the nuclear motion of a linear triatomic molecule. To demonstrate the method, all of the experimentally observed rotational energies, with values of $J$ almost up to 100, for the ground and first excited vibrational states of CO$_2$ and for the ground vibrational states of N$_2$O and of OCS a

A. Yu. Korchin, O. Scholten, F. de Jong

We show that lepton-pair production in Virtual Compton Scattering offers, through interference with the well-known Bethe-Heitler process, a sensitive probe to learn the longitudinal response of resonances and the electromagnetic nucleon form factors. This interference can be measured directly in terms of an asymmetry. The role of off-shell effects in the N-N

N. Minkov, S. Drenska, P. Raychev, R. Roussev

A collective vector-boson model with broken SU(3) symmetry is applied to several deformed even-even nuclei. The model description of ground and $γ$ bands together with the corresponding B(E2) transition probabilities is investigated within a broad range of SU(3) irreducible representations (irreps) $(λ,μ)$. The SU(3)-symmetry characteristics of rotational nu

Dennis Bonatsos, P. Kolokotronis, D. Lenis, C. Daskaloyannis

Recent progress in two different fronts is reported. First, the concept of bisection of a harmonic oscillator (HO) or hydrogen atom (HA), used in the past in establishing the connection between U(3) and O(4), is generalized into multisection (trisection, tetrasection, etc). It is then shown that all symmetries of the N-dim anisotropic HO with rational ratios

Dennis Bonatsos, C. Daskaloyannis, P. Kolokotronis, D. Lenis

The concept of bisection of a harmonic oscillator or hydrogen atom, used in the past in establishing the connection between U(3) and O(4), is generalized into multisection (trisection, tetrasection, etc). It is then shown that all symmetries of the N-dimensional anisotropic harmonic oscillator with rational ratios of frequencies (RHO), some of which are unde

H. M. Fried

Using a new technique for the extraction of leading-log energy dependence from the non-Abelian portion of quark-line interactions, hadronic scattering amplitudes may be represented in terms of functional integrals over gluonic material exchanged between scattering quarks. If that material is further represented by a condensed tube of gluonic flux (obtained b

C. R. Fernandez-Pousa, M. V. Gallas, T. J. Hollowood, J. L. Miramontes

The quantum integrability of a class of massive perturbations of the parafermionic conformal field theories associated to compact Lie groups is established by showing that they have quantum conserved densities of scale dimension 2 and 3. These theories are integrable for any value of a continuous vector coupling constant, and they generalize the perturbation

G. M. Cicuta

The study of the convergence of power series expansions of energy eigenvalues for anharmonic oscillators in quantum mechanics differs from general understanding, in the case of quasi-exactly solvable potentials. They provide examples of expansions with finite radius and suggest techniques useful to analyze more generic potentials.

Michael Engelhardt

The equation of state of a one-dimensional classical nonrelativistic Coulomb gas of particles in the adjoint representation of SU(2) is given. The problem is solved both with and without sources in the fundamental representation at either end of the system. The gas exhibits confining properties at low densities and temperatures and deconfinement in the limit

H. J. de Vega, J. F. J. Salgado

The quantum evolution equations for the field expectation value are analytically solved to cubic order in the field amplitude and to one-loop level in the lambda phi-fourth model. We adapt and use the renormalization group (RG) method for such non-linear and non-local equations. The time dependence of the field expectation value is explicitly derived integra

V. B. Petkova, J. -B. Zuber

We review a method of construction of exceptional graphs generalising the ADE Dynkin diagrams which encode the spectrum of conformal field theories described by conformal embeddings of $\widehat{sl}(n)_k$.

Won Tae Kim, Yong-Wan Kim, Mu-In Park, Young-Jai Park

We apply newly improved Batalin-Fradkin-Tyutin Hamiltonian method to the chiral Schwinger Model in the case of the regularization ambiguity $a>1$. We show that one can systematically construct the first class constraints by the BFT Hamiltonian method, and also show that the well-known Dirac brackets of the original phase space variables are exactly the Poiss

Bo-yu Hou, Wen-li Yang

In this paper,we derive a $\hbar$-deformation of the $W_{N}$ algebra and its quantum Miura tranformation. The vertex operators for this $\hbar$-deformed $W_{N}$ algebra and its commutation relations are also obtained.

Theodore J. Allen, M. G. Olsson, Sinisa Veseli, Ken Williams

Starting from Buchmüller's observation that a chromoelectric flux tube meson will exhibit only the Thomas type spin-orbit interaction, we show that a model built upon the related assumption that a quark feels only a constant radial chromoelectric field in its rest frame implies a complete relativistic effective Hamiltonian that can be written explicitly

N. Arteaga-Romero, C. Carimalo, A. Nicolaidis, O. Panella

Active Galactic Nuclei are considered as sources of neutrinos, with neutrino energies extending up to 10^{18} eV. It is expected that these highly energetic cosmic neutrinos will be detected by the neutrino telescopes, presently under construction. The detection process is very sensitive to the total muon neutrino cross-section. We examine how the total cros

D. Müller

Based on the non-local light-ray operator technique, we develop an algorithm for the computational calculation of evolution kernels for higher-twist operators in leading order of the perturbation theory. We compute the evolution kernel for the twist-3 operators in the flavour singlet channel. Our result confirms the local anomalous dimensions computed by Buk

Tapobrata Sarkar, Rahul Basu

In this paper we check the validity of the ideas of double scaling as given by Ball and Forte in a semi inclusive process like $J/ψ$ production at HERA, in different kinematical regions, for low values of the Bjorken variable $x$. In particular, we study $J/ψ$ production in the inelastic and diffractive (elastic) regimes using the double scaling form of the

K. Schertler, C. Greiner, M. H. Thoma

The properties of strange quark matter at zero temperature are investigated including medium effects. The quarks are considered as quasiparticles which acquire an effective mass generated by the interaction with the other quarks of the dense system. Within this approach we find that these medium effects reduce the binding energy of strange quark matter with

Dirk Graudenz

Fixed-target experiments permit the study of hadron production in the target fragmentation region. It is expected that the tagging of specific particles in the target fragments can be employed to introduce a bias in the hard scattering process towards a specific flavour content. The case of hadrons containing a heavy quark is particularly attractive because

CCFR Collaboration, K. S. McFarland

The CCFR collaboration reports a precise measurement of electroweak parameters derived from the ratio of neutral-current to charged-current cross-sections in neutrino-nucleon scattering at the Fermilab Tevatron. This ratio of cross-sections measures the neutral current couplings to quarks, which implies a determination of sin^2 theta_W (on-shell) = 0.2236 +/

George Lavrelashvili

We present a brief review of some recent results on non-abelian solitons and black holes in different theories. Lecture given at the Simi-96, Tbilisi, Georgia, September 22-28, 1996.

R. Brunetti, K. Fredenhagen

We present a perturbative construction of the $φ^4$ model on a smooth globally hyperbolic space-time. Our method relies on a adaptation of the Epstein and Glaser method of renormalization to curved space-times using techniques from microlocal analysis.

Tevian Dray

Tensor distributions and their derivatives are described without assuming the presence of a metric. This provides a natural framework for discussing tensor distributions on manifolds with degenerate metrics, including in particular metrics which change signature.

David Hartley, Robin W. Tucker, Philip A. Tuckey, Tevian Dray

Irregularities in the metric tensor of a signature-changing space-time suggest that field equations on such space-times might be regarded as distributional. We review the formalism of tensor distributions on differentiable manifolds, and examine to what extent rigorous meaning can be given to field equations in the presence of signature-change, in particular

Allan P. Donsig, Alan Hopenwasser, Timothy D. Hudson, Michael P. Lamoureux

We study the meet irreducible ideals in certain direct limit algebras, namely the strongly maximal triangular subalgebras of AF C*-algebras. These ideals have a description in terms of the coordinates, or spectrum, that is a natural extension of one description of meet irreducible ideals in the upper triangular matrices. Additional information is available i

R. Bulla, A. C. Hewson

We use the numerical renormalization group method to study the O(3)-symmetric version of the impurity Anderson model of Coleman and Schofield. This model is of general interest because it displays both Fermi liquid and non-Fermi liquid behaviour, and in the large $U$ limit can be related to the compactified two channel Kondo model of Coleman, Ioffe and Tsvel

Olle Gunnarsson, Erik Koch, Richard M. Martin

We study how the electron hopping reduces the Mott-Hubbard band gap in the limit of a large Coulomb interaction U and as a function of the orbital degeneracy N. The results support the conclusion that the hopping contribution grows as roughly \sqrt{N}W, where W is the one-particle band width, but in certain models a crossover to a \sim NW behavior is found f

D. Vollhardt, N. Blümer, K. Held, M. Kollar

The microscopic basis for the stability of itinerant ferromagnetism in correlated electron systems is examined. To this end several routes to ferromagnetism are explored, using both rigorous methods valid in arbitrary spatial dimensions, as well as Quantum Monte Carlo investigations in the limit of infinite dimensions (dynamical mean-field theory). In partic

M. Fabrizio, R. Mélin

A model of disordered spin-Peierls system is considered, where domain walls are randomly distributed as a telegraph noise. For this realization of the disorder in an XX spin chain, we calculate exactly the density of states as well as several thermodynamic quantities. The resulting physical behavior should be qualitatively unchanged even for an XXZ chain, up

Tomaso Aste

We studied the geometrical and topological rules underlying the dispositions and the size distribution of non-overlapping, polydisperse circle-packings. We found that the size distribution of circles that densely cover a plane follows the power law: $N(R) \propto R^{-α}$. We obtained an approximate expression which relates the exponent $α$ to the average coo

Takeo Kato, Masatoshi Imada

We study a current-biased 0-π-0 Josephson junction made by high-T_c superconductors, theoretically. When a length of the πjunction is large enough, this junction contains a vortex-antivortex pair at both ends of the πjunction. Magnetic flux carried by the vortices is calculated using the sine-Gordon equation. The result shows that the magnetic flux of the vo

Umberto Marini Bettolo Marconi, Andrea Crisanti, Giulia Iori

The kinetics of an initially undercooled solid-liquid melt is studied by means of a generalized Phase Field model, which describes the dynamics of an ordering non-conserved field phi (e.g. solid-liquid order parameter) coupled to a conserved field (e.g. thermal field). After obtaining the rules governing the evolution process, by means of analytical argument

O. Gunnarsson

The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated using the so-called GW approximation. The calculation is performed within a model which considers the t1u charge carrier plasmon at 0.5 eV and takes into account scattering of the electrons within the t1u band. A moderate reduction (35 %) of the t1u band width is obtained.

Dennis Bonatsos, C. Daskaloyannis

The algebra of observables of a system of two identical vortices in a superfluid thin film is described as a generalized deformed oscillator with a structure function containing a linear (harmonic oscillator) term and a quadratic term. In contrast to the deformed oscillators occuring in other physical systems (correlated fermion pairs in a single-$j$ nuclear

S. Das Sarma, Subir Sachdev, Lian Zheng

A low energy action for double-layer quantum Hall systems at filling fractions $ν= 2/m$ ($m$ an odd integer) is introduced. Interlayer antiferromagnetic exchange induces a phase with canted spin order, and also a spin-singlet phase. Universal properties of zero and finite temperature transitions are obtained. We compute the critical temperature at which the

Michael Henseler, Andreas Wirzba, Thomas Guhr

Most discussions of chaotic scattering systems are devoted to two-dimensional systems. It is of considerable interest to extend these studies to the, in general, more realistic case of three dimensions. In this context, it is conceptually important to investigate the quality of semiclassical methods as a function of the dimensionality. As a model system, we

Mark L. Giroux, J. Michael Shull

Recent measurements of Si IV/C IV ratios in the high-redshift Ly-alpha forest (Songaila & Cowie, AJ, 112, 335 [1996a]; Savaglio et al., A&A, in press [1997]) have opened a new window on chemical enrichment and the first generations of stars. However, the derivation of accurate Si/C abundances requires reliable ionization corrections, which are strongly depen

Mario Mateo

I review observational data on the kinematic properties of dwarf spheroidal galaxies in the halo of the Milky Way and beyond. The present data confirm previous claims that these galaxies have unusually large central velocity dispersions. `Simple' sources of bias such as binary stars, internal atmospheric motions, measurement errors, and small sample size

Ben Dorman

Since the discovery of the Ultraviolet Upturn Phenomenon (``UVX&#39;&#39;) in early-type galaxies it has been clear that the stellar populations of such systems contain an unexpected hot component. Recent work has provided strong circumstantial evidence that the stars radiating at short wavelengths (< 2000 Angstrom) is in fact due to hot horizontal branch, p