October 1998 arXiv papers — page 6

I. F. Mirabel, O. Laurent, D. B. Sanders, M. Sauvage

We report observations at mid-infrared and sub-millimeter wavelengths of Centaurus A (CenA, NGC 5128), the giant elliptical galaxy that harbors the closest radio loud Active Galactic Nucleus (AGN) to Earth. The dust emission from the deep interior of CenA reveals a bisymmetric structure with a diameter of 5' (5 kpc), centred at the AGN. This structure is

R. Della Ceca, R. E. Griffiths, T. M. Heckman, M. D. Lehnert

We report ASCA GIS and SIS observations of the nearby (D = 11.6 Mpc), nearly edge-on, starburst galaxy NGC 2146. These X-ray spectral data complement ROSAT PSPC and HRI imaging discussed by Armus et al., 1995. The broad band (0.6-9 keV) X-ray spectrum of NGC 2146 is best described by a two component model: the soft X-ray emission with a Raymond-Smith thermal

Michael R. Merrifield, Konrad Kuijken

The disks of galaxies are primarily stellar systems, and fundamentally dynamical entities. Thus, to fully understand galactic disks, we must study their stellar kinematics as well as their morphologies. Observational techniques have now advanced to a point where quite detailed stellar-kinematic information can be extracted from spectral observations. This re

J. Magueijo, P. Ferreira, K. Gorski

In a recent Letter we have shown how COBE-DMR maps may be used to disprove Gaussianity at a high confidence level. In this report we digress on a few issues closely related to this Letter. We present the general formalism for surveying non-Gaussianity employed. We present a few more tests for systematics. We wonder about the theoretical implications of our r

I. Georgantopoulos, O. Almaini, T. Shanks, G. C. Stewart

We use UKIRT and ASCA observations to determine the nature of a high redshift (z=2.35) narrow-line AGN, previously discovered by Almaini et al. (1995). The UKIRT observations show a broad Halpha line while no Hbeta line is detected. This together with the red colour (B-K=5.4) suggest that our object is a moderately obscured QSO (Av>3), in optical wavelengths

Carlo R. Contaldi, Mark Hindmarsh, Joao Magueijo

We evaluate the two point functions of the stress energy from the largest string simulations carried out so far. The two point functions are used to calculate the cosmic microwave background (CMB) and cold dark matter (CDM) power spectra from local cosmic string models for structure formation. We find that our spectra differ significantly from those previous

V. V. Usov, M. V. Smolsky

It is suggested that the outflowing plasma in the jets of active galactic nuclei (AGNs) is inhomogeneous and consists of separate clouds. These clouds are strongly magnetized and move away from the central engine at relativistic speeds. The clouds interact with an ambient medium which is assumed to be at rest. In the process of this interaction, particles of

Carsten van de Bruck

We discuss structure formation in cosmic string theories. Emphasis is laid on the properties of the peculiar velocity field, non-gaussian features and clusters of galaxies. It is found that the predicted peculiar velocity field is quiet ($v<150$ km/s for $L>30 h^{-1}$ Mpc) for models with ($Ω_0 h \leq 0.2$) which is in disagreement with the results from POTE

S. Charlot

The Next Generation Space Telescope (NGST) will gather unprecedented spectro-photometric data on galaxies out to the highest redshifts. It is therefore crucial to identify the spectro-photometric diagnostics within reach of NGST, which will allow us to best constrain the history of star formation and evolution of galaxies. The primary parameters to be determ

Robert A. Fesen, Christopher L. Gerardy, Alexei V. Filippenko, Thomas Matheson

A low-dispersion Keck I spectrum of SN 1980K taken in August 1995 (t = 14.8 yr after explosion) and a November 1997 MDM spectrum (t = 17.0 yr) show broad 5500 km s^{-1} emission lines of Hα, [O I] 6300,6364 A, and [O II] 7319,7330 A. Weaker but similarly broad lines detected include [Fe II] 7155 A, [S II] 4068,4072 A, and a blend of [Fe II] lines at 5050--54

Michael A. Nowak, Joern Wilms, Brian A. Vaughan, James B. Dove

We have recently shown that a `sphere+disk' geometry Compton corona model provides a good description of Rossi X-ray Timing Explorer (RXTE) observations of the hard/low state of Cygnus X--1. Separately, we have analyzed the temporal data provided by RXTE. In this paper we consider the implications of this timing analysis for our best-fit `sphere+disk' Compto

D. V. Shantsev, M. E. Gaevski, R. A. Suris, A. V. Bobyl

Temperature and magnetic field dependences of the conductivity of YBaCuO films in the transition region are analyzed taking into account spatial inhomogeneity in transition temperature, Tc. (i) An expression for the superconducting contribution to conductivity, σ_s(T,H,Tc), of a homogeneous superconductor for H<<Hc2(T=0) is obtained using the solution of the

Youngjai Kiem, Dahl Park

We show that the five-dimensional general relativity with a negative cosmological constant allows the solutions of the form M_3 \times M_g where M_3 is the three-dimensional BTZ black hole and M_g is a higher genus (g>1) Riemann surface with a fixed size. It is shown that this type of spontaneous compactification on a Riemann surface is possible only for the

J. P. Gauntlett, R. C. Myers, P. K. Townsend

We discuss some general features of black holes of five-dimensional supergravity, such as the first law of black hole mechanics. We also discuss some special features of rotating supersymmetric black holes. In particular, we show that the horizon is a non-singular, and {\sl non-rotating}, null hypersurface whose intersection with a Cauchy surface is a squash

Cheongho Han

When a microlensing light curve is contaminated by blended light from unresolved stars near the line of sight to the lensed star, the light curve shape and corresponding parameterization for the event will differ from the values expected when the event is not affected by blending. As a result, blending makes it difficult to identify the major lens population

Oliver Rudolph

In the first part of this paper the general perspective of history quantum theories is reviewed. History quantum theories provide a conceptual and mathematical framework for formulating quantum theories without a globally defined Hamiltonian time evolution and for introducing the concept of space time event into quantum theory. On a mathematical level a hist

Jack Button

Not all Schottky groups of Moebius transformations are classical Schottky groups. In this paper we show that all Fuchsian Schottky groups are classical Schottky groups, but not necessarily on the same set of generators.

Martin R. Bridson

If a class of finitely generated groups Curly(G) is closed under isometric amalgamations along free subgroups, then every G in Curly(G) can be quasi-isometrically embedded in a group Hat(G) in Curly(G) that has no proper subgroups of finite index. Every compact, connected, non-positively curved space X admits an isometric embedding into a compact, connected,

B. H. Bowditch

We consider splittings of groups over finite and two-ended subgroups. We study the combinatorics of such splittings using generalisations of Whitehead graphs. In the case of hyperbolic groups, we relate this to the topology of the boundary. In particular, we give a proof that the boundary of a one-ended strongly accessible hyperbolic group has no global cut

F. G. Garashchenko, O. M. Bashniakov, V. V. Pichkur

We prove the necessary and sufficient conditions for practical stability of nonlinear dynamical system at general phase restrictions. In such a case the Lyapunov function is nondifferentiable. But if the set of initial data is starry compact, then it is possible building Lyapunov function which belongs to differentiable functions class. We also estimate the

Herbert S. Wilf

A theorem of Mina evaluates the determinant of a matrix with entries $D^j(f(x)^i)$. We note the important special case where the matrix entries are evaluated at $x=0$ and give a simple proof of it, and some applications. We then give a short proof of the general case.

Efrain J. Ferrer, Vivian de la Incera

By solving the gap equation in the quenched, ladder approximation for an Abelian gauge model with Yukawa interaction in the presence of a constant magnetic field, we show that the Yukawa interactions enhance the dynamical generation of fermion mass. The theory is then studied at finite temperature, where we prove that the critical magnetic field, required fo

S. M. Gerasyuta

The D-and F-wave quark-quark amplitudes are constructed in the framework of the dispersion N/D-method. The mass values of meson multiplets with $J^{PC}=1^{--},2^{--},2^{-+},3^{--}$ and $J^{PC}=2^{++},3^{++},3^{+-},4^{++}$ are calculated. The Regge trajectories of mesonic resonances with orbital numbers L=0,1,2,3 are obtained.

N. Haba, N. Okamura, M. Sugiura

The Superkamiokande experiment suggests the large flavor mixing between nu_mu and nu_tau. We show that the mixing angle receives significant corrections from the renormalization group equation (RGE) when both the second and the third generation neutrino masses are larger than O(0.1eV). This means that the mixing angle must be small at the decoupling scale of

A. Markou

It is proposed to search for free quarks near their production thresholds. If the current-quark masses for u, d quarks are smaller than the pion mass, $u\bar{u}$ and $d\bar{d}$ pairs produced below the pion pair threshold, would not have sufficient energy to hadronize and could be observable. In the case of large u,d quark masses and also for the heavy quark

G. E. Volovik

The problem of the energy-momentum conservation for matter in the gravitational field is discussed on the example of the effective gravity, which arises in superfluids. The &#34;gravitational&#34; field experienced by the relativistic-like massless quasiparticles which form the &#34;matter&#34; (phonons in superfluid 4He and low-energy fermions in superfluid

B. Shapiro

The theory of orbital magnetism in disordered metals is reviewed, and extended to include a broad range of temperatures and fields. Sample-to-sample fluctuations in the orbital magnetic susceptibility are studied. In a given sample these fluctuations manifest themselves in aperiodic sample-specific oscillations of susceptibility and magnetization, when the s

Patricia M. Knezek

An unexpected characteristic of low surface brightness galaxies (LSBGs) is that a significant number are massive and possess substantial amounts of atomic gas. We present preliminary results of an ongoing program to obtain BVRIJHK imaging, along with some nuclear spectroscopy, of a well-defined sample of LSBGs which are gas-rich and of similar size to giant,

Amnon Stupp

We investigate wave amplification through the Electron Cyclotron Maser mechanism. We derive a semi-analytic approximation formula giving the frequencies at which the absorption coefficient is negative. The coefficients still need to be computed to obtain the largest, and therefore the dominant, coefficient.

Z. G. Dai, T. Lu

Millisecond pulsars with strong magnetic fields may be formed through several processes, e.g. accretion-induced collapse of magnetized white dwarfs, merger of two neutron stars. During the birth of such a pulsar, an initial fireball available for a gamma-ray burst (GRB) may occur. We here study evolution of a postburst relativistic fireball with energy injec

Ariel Caticha

The objective of the consistent-amplitude approach to quantum theory has been to justify the mathematical formalism on the basis of three main assumptions: the first defines the subject matter, the second introduces amplitudes as the tools for quantitative reasoning, and the third is an interpretative rule that provides the link to the prediction of experime

I. H. Stairs, S. E. Thorsett, F. Camilo

We present a large sample of high-precision, coherently-dedispersed polarization profiles of millisecond pulsars (MSPs) at frequencies between 410 and 1414 MHz. These data include the first polarimetric observations of several of the pulsars, and the first low-frequency polarization profiles for others. Our observations support previous suggestions that the

G. Jackeli, N. M. Plakida

The dynamic charge susceptibility and the optical conductivity are calculated in the planar t-J model within the memory function method, working directly in terms of Hubbard operators. The density fluctuation spectrum consists of a damped sound-like mode for small wave vectors and a broad high energy peak ($\sim t$) for large momenta. The study of the optica

Rychard J. Bouwens, Tom Broadhurst, Joseph Silk

In a companion paper we outlined a methodology for generating parameter-free, model-independent ``no-evolution&#39;&#39; fields of faint galaxy images, demonstrating the need for significant evolution in the HDF at faint magnitudes. Here we incorporate evolution into our procedure, by transforming the input bright galaxy images with redshift, for comparison

Jan M. Rost

The description of threshold fragmentation under long range repulsive forces is presented. The dominant energy dependence near threshold is isolated by decomposing the cross section into a product of a back ground part and a barrier penetration probability resulting from the repulsive Coulomb interaction. This tunneling probability contains the dominant ener

Antoine Balan

We construct quantum deformations of the integrals of motion of the generalized mKdV equations for $\hat {\SL}_2$. For this, we give the relevant vertex operator algebra and prove quantum Serre relations for vertex operators, it allows to construct a $q$-BGG resolution and to deform the classical integrals of motion in a commutativ family.

Lawrence J. Hall, Hitoshi Murayama

If the correct interpretation of the Super-Kamiokande atmospheric neutrino data is ν_μ-> ν_τoscillation, the contained data sample should already have more than 10 tau appearance events. We study the challenging task of detecting the tau, focussing on the decay chain τ^\pm -> ρ^\pm -> π^\pm π^0 in events with quasi-elastic tau production. The background leve

Lucas Taylor, David O. Williams

This paper assesses the feasibility of exploiting commercial satellite television technologies to broadcast video signals and data from major High Energy Physics facilities to collaborating institutes throughout the world.

Jeff Erickson, Leonidas J. Guibas, Jorge Stolfi, Li Zhang

We develop a class of new kinetic data structures for collision detection between moving convex polytopes; the performance of these structures is sensitive to the separation of the polytopes during their motion. For two convex polygons in the plane, let $D$ be the maximum diameter of the polygons, and let $s$ be the minimum distance between them during their

David G. Sedrakyan, Ara G. Sedrakyan

Two component superlattice film of 2N layers is considered and dimensionally quantised spectrum of phonon-s is found. The problem of localization of phonon-s in the superlattice with random thicknesses of the layers is investigated. The Landauer resistance of the transport of phonon-s is calculated exactly. For short range disorder the numerical analyses sho

Gabor Fath, Stephen B. Haley

The Schrodinger equation for an interacting spinless electron gas in a nonuniform magnetic field admits an exact solution in Jastrow product form when the fluctuations in the magnetic field track the fluctuations in the scalar potential. For tracking realizations in a two-dimensional electron gas, the degeneracy of the lowest Landau level persists, and the `

Imre Derenyi, Tamas Vicsek

The origin of biological motion can be traced back to the function of molecular motor proteins. Cytoplasmic dynein and kinesin transport organelles within our cells moving along a polymeric filament, the microtubule. The motion of the myosin molecules along the actin filaments is responsible for the contraction of our muscles. Recent experiments have been ab

Elena Pian, Eliana Palazzi, Lucio Chiappetti, Laura Maraschi

The BL Lac object Mkn 501 was observed with the BeppoSAX satellite at three epochs in April-May 1998, simultaneously with the Whipple and HEGRA Cherenkov telescopes. The X-ray spectrum is well detected up to 70 keV and it exhibits, at all epochs, a continuous curvature, which is here modeled with three power-laws of increasingly steeper index at larger energ

Matthew R. Bate

We present results from the first three-dimensional calculations ever to follow the collapse of a molecular cloud core (~ 10^{-18} g cm^{-3}) to stellar densities (> 0.01 g cm^{-3}). The calculations resolve structures over 7 orders of magnitude in spatial extent (~ 5000 AU - 0.1 R_\odot), and over 17 orders of magnitude in density contrast. With these calcu

Rychard J. Bouwens, Tom Broadhurst, Joseph Silk

We present a model-independent method of quantifying galaxy evolution in high-resolution images, which we apply to the Hubble Deep Field (HDF). Our procedure is to k-correct all pixels belonging to the images of a complete set of bright galaxies and then to replicate each galaxy image to higher redshift by the product of its space density, 1/V_{max}, and the

David R. Morrison, M. Ronen Plesser

We formulate an extension of Maldacena&#39;s AdS/CFT conjectures to the case of branes located at singular points in the ambient transverse space. For singularities which occur at finite distance in the moduli space of M or F theory models with spacetime-filling branes, the conjectures identify the worldvolume theory on the p-branes with a compactification o

Amanda W. Peet, Simon F. Ross

Banks, Douglas, Horowitz and Martinec [hep-th/9808016] recently argued that in the microcanonical ensemble for string theory on AdS_m xS^n, there is a phase transition between a black hole solution extended over the S^n and a solution localized on the S^n. If we think of this AdS_m x S^n geometry as arising from the near-horizon limit of a black m-2 brane, t

A. V. Radyushkin

Extending the concept of parton densities onto nonforward matrix elements <p&#39;|O(0,z)|p> of quark and gluon light-cone operators, one can use two types of nonperturbative functions: double distributions (DDs) f(x,α;t), F(x,y;t) and skewed (off&nonforward) parton distributions (SPDs) H(x,ξ;t), F_ζ(X,t). We treat DDs as primary objects producing SPDs after

G. F. Marani, R. J. Nemiroff, J. P. Norris, K. Hurley

If dark matter in the form of compact objects comprises a large fraction of the mass of the universe, then gravitational lensing effects on gamma-ray bursts are expected. We utilize BATSE and Ulysses data to search for lenses of different mass ranges, which cause lensing in the milli, pico, and femto regimes. Null results are used to set weak limits on the c

May Chiao, R. W. Hill, Christian Lupien, Bojana Popic

The effect of vortices on quasiparticle transport in cuprate superconductors was investigated by measuring the low temperature thermal conductivity of YBa_2Cu_3O_6.9 in magnetic fields up to 8 T. The residual linear term (as T \to 0) is found to increase with field, directly reflecting the occupation of extended quasiparticle states. A study for different Zn

M. J. Menon, A. E. Motter, B. M. Pimentel

Making use of a recursive approach, derivative dispersion relations are generalized for an arbitrary number of subtractions. The results for both cross even and odd amplitudes are theoretically consistent at sufficiently high energies and in the region of small momentum transfer.

Adel Bilal, Chong-Sun Chu

Recently, Douglas and Taylor proposed to identify the Higgs vev of the Coulomb branch of the 4 dimensional N=4 super Yang-Mills theory with the positions of D3 branes in the AdS_5 x S^5 string theory. We extend this identification to more general configurations that preserve less supersymmetry. We show that a single D3 brane in AdS_5 x S^5 string theory can

G. Bonelli

In this paper it is shown how the AdS/CFT correspondence extends to a more general situation in which the first theory is defined on (d+1)-dimensional manifold $\tilde M$ defined as the filling in of a compact d-dimensional manifold M. The stability of the spectral correspondence mass/conformal-weight under such geometry changes is also proven.

Daniel Ueltschi

The Hubbard model describes a lattice system of quantum particles with local (on-site) interactions. Its free energy is analytic when βt is small, or βt^2/U is small; here, βis the inverse temperature, U the on-site repulsion and t the hopping coefficient. For more general models with Hamiltonian H = V + T where V involves local terms only, the free energy i

R. Ketzmerick, K. Kruse, D. Springsguth, T. Geisel

We find that a 2D periodic potential with different modulation amplitudes in x- and y-direction and a perpendicular magnetic field may lead to a transition to electron transport along the direction of stronger modulation and to localization in the direction of weaker modulation. In the experimentally accessible regime we relate this new quantum transport phe

Martin Janssen, Marcus Metzler, Martin R. Zirnbauer

On the basis of the Chalker-Coddington network model, a numerical and analytical study is made of the statistics of point-contact conductances for systems in the integer quantum Hall regime. In the Hall plateau region the point-contact conductances reflect strong localization of the electrons, while near the plateau transition they exhibit strong mesoscopic

A. Werthenbach, L. M. Sehgal

The reaction $ e^+e^- \to W^+W^-$ produces a $W$-boson pair with a non-trivial spin correlation at threshold. This correlation leads to a characteristic angular correlation between the leptons produced in $W^{\pm} \to \ell ^{\pm} ν$ (angles relative to the $e^-$ beam direction): $d σ/d \cos θ_+ d \cos θ_- \sim (1-\cos θ_+) (1+ \cos θ_-) (1+\cos θ_- \cos θ_+)

Einan Gardi, Georges Grunberg

In both QCD and supersymmetric QCD (SQCD) with N_f flavors there are conformal windows where the theory is asymptotically free in the ultraviolet while the infrared physics is governed by a non-trivial fixed-point. In SQCD, the lower N_f boundary of the conformal window, below which the theory is confining is well understood thanks to duality. In QCD there i

R. Hofmann, M. Schumann, R. D. Viollier

A novel technique based on Schwinger&#39;s proper time method is applied to the Casimir problem of the M.I.T. bag model. Calculations of the regularized vacuum energies of massless scalar and Dirac spinor fields confined to a static and spherical cavity are presented in a consistent manner. While our results agree partly with previous calculations based on a

A. J. Green, L. E. Cram, M. I. Large, Taisheng Ye

The first epoch Molonglo Galactic Plane Survey (MGPS1) is a radio continuum survey made using the Molonglo Observatory Synthesis Telescope (MOST) at 843 MHz with a resolution of 43&#34; X 43&#34; cosec |delta|. The region surveyed is 245 deg < l < 355 deg, |b| < 1.5 deg. The thirteen 9 deg X 3 deg mosaic images presented here are the superposition of over 45

Andrew W. Blain, Ole Moeller, Ariyeh H. Maller

The high-magnification gravitational lensing cross-section of a galaxy is enhanced significantly if a baryonic disc is embedded in its dark matter halo. We investigate the effects of a population of such disks on the probability of detecting strongly lensed images of distant galaxies and quasars. The optical depth to lensing is always more than doubled. The

Edward Witten

By exploiting recent arguments about stable nonsupersymmetric D-brane states, we argue that D-brane charge takes values in the K-theory of spacetime, as has been suspected before. In the process, we gain a new understanding of some novel objects proposed recently - such as the Type I zerobrane - and we describe some new objects - such as a -1-brane in Type I

Csaba Csaki, Yaron Oz, Jorge Russo, John Terning

We study large N SU(N) Yang-Mills theory in three and four dimensions using a one-parameter family of supergravity models which originate from non-extremal rotating D-branes. We show explicitly that varying this &#34;angular momentum&#34; parameter decouples the Kaluza-Klein modes associated with the compact D-brane coordinate, while the mass ratios for ordi

N. A. Slavnov

The correlation functions of the quantum nonlinear Schrodinger equation can be presented in terms of a Fredholm determinant. The explicit expression for this determinant is found for the large time and long distance.

P. Stovicek, O. Vana

A basic analysis is provided for the differential cross section characterizing Aharonov--Bohm effect with non standard (non regular) boundary conditions imposed on a wave function at the potential barrier. If compared with the standard case two new features can occur: a violation of rotational symmetry and a more significant backward scattering.

E. Paspalakis, C. H. Keitel, P. L. Knight

We discuss the spontaneous emission from a coherently prepared and microwave driven doublet of potentially closely spaced excited states to a common ground level. Multiple interference mechanisms are identified which may lead to fluorescence inhibition in well-separated regions of the spectrum or act jointly in cancelling the spontaneous emission. In additio

Georg Junker

A supersymmetric method for the construction of so-called conditionally exactly solvable quantum systems is reviewed and extended to classical stochastic dynamical systems characterized by a Fokker-Planck equation with drift. A class of drift-potentials on the real line as well as on the half line is constructed for which the associated Fokker-Planck equatio

Bernhard Bodmann, Hajo Leschke, Simone Warzel

Adapting ideas of Daubechies and Klauder we derive a continuum path-integral formula for the time evolution generated by a spin Hamiltonian. For this purpose we identify the finite-dimensional spin Hilbert space with the ground-state eigenspace of a suitable Schödinger operator on $L^2({\mathbb{R}}^2)$, the Hilbert space of square-integrable functions on the

J. L. Cohen, B. Dubetsky, P. R. Berman

We propose a laser field configuration which acts as a quasiperiodic atom optical diffraction grating. Analytical and computational results for the atomic center-of-mass wavefunction after the grating reveal a quasiperiodic density pattern, a semiclassical focusing effect, and a quasiperiodic self-imaging of the atomic wavefunction analogous to a Talbot effe

Eric Lewin Altschuler

The question of the authorship of Shakespeare&#39;s plays has long been debated. The two leading contenders are W. Shakspere (1564-1616) and Edward de Vere the 13th Earl of Oxford (1550-1604). Here I note that Shakespeare&#39;s references to important events and discoveries in astronomy and geophysics in 1572 and 1600, but not to similarly important events o

Nelson P. Andion

An approach to the teaching of electromagnetism to senior undergraduate students, designed for overcoming the fragmentation of the theory is described. As usual it starts from the static case, but it is strictly based on Helmholtz theorem of uniqueness of vector fields, on primary experimental observations upon the sources of electric and magnetic fields, on

E. Nielsen, D. V. Fedorov, A. S. Jensen

We propose to observe the Efimov effect experimentally by applying an external electric field on atomic three-body systems. We first derive the lowest order effective two-body interaction for two spin zero atoms in the field. Then we solve the three-body problem and search for the extreme spatially extended Efimov states. We use helium trimers as an illustra

Ch. Jung, B. Huke, M. Luecke

Convection structures in binary fluid mixtures are investigated for positive Soret coupling in the driving regime where solutal and thermal contributions to the buoyancy forces compete. Bifurcation properties of stable and unstable stationary square, roll, and crossroll (CR) structures and the oscillatory competition between rolls and squares are determined

A. Recktenwald, M. Luecke

Realistic boundaries of finite heat conductivity Realistic boundaries of finite heat conductivity for thermoconvection in a Rayleigh-Bénard setup with magnetized ferrofluids are investigated. A linear stability analysis of the conductive state is performed with a shooting method. It shows that the critical wave number is for any magnetic field stronly influe

D. E. Kahana, S. H. Kahana

We reexamine the production of J/Psi and other charmonium states for a variety of target-projectile choices at the SPS, in particular for the interesting comparison between S+U at 200 GeV/c and Pb+Pb at 158 GeV/c as observed in the experiments NA38 and NA50 respectively. The result is a description of the NA38 and NA50 data in terms of a conventional, quasi-

J. Toke, W. U. Schroeder

A novel mechanism of prompt nuclear fragmentation is proposed. Assuming micro-canonical or canonical equilibrium, it is shown that a strong enhancement of the accessible phase space volume, due to the diffuceness of the nuclear surface, leads to dynamical instabilities of hot nuclei and to prompt fragmentation. Equations are derived for the transition temper

H. Sagawa, P. F. Bortignon, G. Colo`

Explicit relations between the isospin mixing probability, the spreading width $Γ_{IAS}^{\downarrow}$ of the Isobaric Analog State (IAS) and the statistical decay width $Γ_c$ of the compound nucleus at finite excitation energy, are derived by using the Feshbach projection formalism. The temperature dependence of the isospin mixing probability is discussed qu

V. Muccifora, N. Bianchi, A. Deppman, E. De Sanctis

The energy and nuclear mass dependences of the total hadronic cross section in the energy range 0.5-2.6 GeV have been measured at Bonn using the SAPHIR tagged photon beam. The measurement, performed on C, Al, Cu, Sn and Pb, provides the first photoabsorption data in the region 1.2-1.7 GeV. The results show a significant reduction of the photoabsorption stren

T. Krajewski

In complete analogy with the classical case, we define the Chern-Simons action functional in noncommutative geometry and study its properties under gauge transformations. As usual, the latter are related to the connectedness of the group of gauge transformations. We establish this result by making use of the coupling between cyclic cohomology and K-theory an

James W. Anderson

We give a brief overview of the current state of the study of the deformation theory of Kleinian groups. The topics covered include the definition of the deformation space of a Kleinian group and of several important subspaces; a discussion of the parametrization by topological data of the components of the closure of the deformation space; the relationship

James Howie

We show that a group presented by a labelled oriented tree presentation in which the tree has diameter at most three is an HNN extension of a finitely presented group. From results of Silver, it then follows that the corresponding higher dimensional ribbon knots admit minimal Seifert manifolds.

Guillermo Cortiñas

We study a noncommutative version of the infinitesimal site of Grothendieck. A theorem of Grothendieck establishes that the cohomology of the structure sheaf on the infinitesimal topology of a scheme of characteristic zero is de Rham cohomology. We prove that, for the noncommutative infinitesimal topology of an associative algebra over a field of characteris

Harald Helfgott, Ira M. Gessel

We show how to count tilings of Aztec diamonds and hexagons with defects using determinants. In several cases these determinants can be evaluated in closed form. In particular, we obtain solutions to problems 1, 2, and 10 in James Propp&#39;s list of problems on enumeration of matchings.

C. D. Fosco, G. L. Rossini, F. A. Schaposnik

We calculate the exact parity odd part of the effective action ($Γ_{odd}^{2d+1}$) for massive Dirac fermions in 2d+1 dimensions at finite temperature, for a certain class of gauge field configurations. We consider first Abelian external gauge fields, and then we deal with the case of a non-Abelian gauge group containing an Abelian U(1) subgroup. For both cas

Jean Zinn-Justin

In these lecture notes prepared for the 11th Taiwan Spring School, Taipei 1997}, and updated for the Saalburg summer school 1998, we review the solutions of O(N) or U(N) models in the large N limit and as 1/N expansions, in the case of vector representations. The general idea is that invariant composite fields have small fluctuations for N large. Therefore t

F. T. Brandt, Ashok Das, J. Frenkel

In this brief report, we analyze a generalized theory of massless scalar QED_2 and show that, unlike the conventional scalar QED_2, it is free from infrared divergence problems. The model is exactly soluble and may describe, in an 1+1 dimensional space-time, noninteracting spin-one tachyons.

Jean Zinn-Justin

Path integrals have played a fundamental role in emphasizing the profound analogies between Quantum Field Theory (QFT), and Classical as well as Quantum Statistical Physics. Ideas coming from Statistical Physics have then led to a deeper understanding of Quantum Field Theory and open the way for a wealth of non-perturbative methods. Conversely QFT methods ar

B. Chakraborty, A. S. Majumdar

Recently it was shown by Cho and Kimm that the gauged $CP^1$ model, obtained by gauging the global $SU(2)$ group and adding a corresponding Chern-Simons term, has got its own soliton. These solitons are somewhat distinct from those of pure $CP^1$ model as they cannot always be characterised by $π_2(CP^1)=Z$. In this paper, we first carry out a detailed Hamil

Y. Takimoto, H. Igarashi, H. Kurokawa, T. Fujiwara

Locality is analyzed for Toda field theories by noting novel chiral description in the conventional nonchiral formalism. It is shown that the canonicity of the interacting to free field mapping described by the classical solution is automatically guaranteed by the locality. Quantum Toda theories are investigated by applying the method of free field quantizat

Laura Andrianopoli, Sergio Ferrara

We consider some long multiplets describing bulk massive excitations of M-theory two-branes and IIB string three-branes which correspond to ``non chiral&#39;&#39; primary operators of the boundary OSp(8/4) and SU(2,2/4) superconformal field theories. Examples of such multiplets are the ``radial&#39;&#39; modes on the branes, including up to spin 4 excitation

J. Pantaleone

Observations of atmospheric neutrinos by the SuperKamiokande collaboration have demonstrated large mixing of the muon-neutrino. However the present atmospheric neutrino data does not significantly constrain the associated mixing of the electron-neutrino, or the sign of the mass-squared difference. Here we identify the diagnostics for these quantities and the

Basarab Nicolescu

We review recent theoretical and phenomenological results on both the perturbative and non-perturbative Odderon. The HERA type of experiments constitutes a direct probe of the Odderon.

B. Pötter

I review recent results on NLO calculations in QCD for inclusive jet production in γ^*γ-scattering at e+e- colliders. I discuss the region of large Q^2 (DIS regime) and the transition to small Q^2 (virtual photoproduction regime). The limit to real photoproduction is performed and compared with existing calculations.

Lucas Taylor

This paper reviews the theoretical predictions for and the experimental measurements of the anomalous magnetic and electric dipole moments of the tau lepton. In particular, recent analyses of the $\eettg$ process from the L3 and OPAL collaborations are described. The most precise results, from L3, for the anomalous magnetic and electric dipole moments respec

A. V. Sidorov

Power corrections both to the strong coupling constant and to the structure function itself are estimated on the basis of the LO, NLO and NNLO QCD analysis of $xF_3$ structure function data. The sign of correction to the coupling constant is found to be negative. The x-shape of a higher twist contribution to the structure function is stable up to NNLO.

Ana Achúcarro, Julian Borrill, Andrew R. Liddle

We review recent simulations of the formation of a particular class of non-topological defects known as semilocal strings during a phase transition. Semilocal strings have properties that are intermediate between topological cosmic strings and stable electroweak strings, and therefore the observation that they could form in substantial quantities during a co

Qing Hong Cao, Chong Sheng Li, Shou Hua Zhu

We calculate the leading electroweak corrections to the light neutral Higgs boson production via $q\bar q&#39;\to WH$ at the Fermilab Tevatron in both the standard model and the minimal supersymmetric model, which arise from the top-quark and Higgs boson loop diagrams. We found that the leading electroweak corrections can exceed the QCD corrections for favor

Chi-Keung Chow

Discretizations of the Laplacian operator on non-hypercubical lattices are discussed in a systematic approach. It is shown that order $a^2$ errors always exist for discretizations involving only nearest neighbors. Among all lattices with the same density of lattice sites, the hypercubical lattices always have errors smaller than other lattices with the same

Jochen Fingberg

The early idea that a non-perturbative gluon condensate affects the spectrum of heavy quarks is revisited in the light of modern simulation techniques. We evaluate the low lying spectrum of bound states of two heavy quarks for large hypothetical quark mass, m_Q > m_b, using non-relativistic QCD and compare with other models to test the consistency.

S. Bilke, G. Thorleifsson

We extend a model of four-dimensional simplicial quantum gravity to include degenerate triangulations in addition to combinatorial triangulations traditionally used. Relaxing the constraint that every 4-simplex is uniquely defined by a set of five distinct vertexes, we allow triangulations containing multiply connected simplexes and distinct simplexes define