December 1997 arXiv papers — page 3

Marc Henneaux

The cohomological approach to the problem of consistent interactions between fields with a gauge freedom is reviewed. The role played by the BRST symmetry is explained. Applications to massless vector fields and 2-form gauge fields are surveyed.

Kei Ito

A large class of equivalence relations between the moduli spaces of instantons on ALE spaces and the Higgs branches of supersymmetric Yang-Mills theories, are found by means of a certain kind of duality transformation between brane configurations in superstring theories. 4d, N=2 and 5d, N=1 supersymmetric gauge theories with product gauge groups turn out to

Aharon Levy

The differential cross section dsigma/dt of elastic photoproduction of J/Psi at different gamma p center of mass energies W are used to determine the properties of the exchanged trajectory in the reaction gamma p --> J/Psi p. In the region |t| < 1 GeV^2, the resulting trajectory is alpha(t) = (1.153 \pm 0.027) + (-0.001 \pm 0.072)t. The vanishing value of th

Maria Krawczyk

The concept of the structure of the photon is discussed and the progress in the measurement of various structure functions of the photon as well of parton distributions in the photon is shortly reviewed.

E. Gotsman, E. levin, U. Maor

Recent HERA low $Q^2$ data show that the logarithmic slope of the protonstructure function ($\frac{\partial F_2}{\partial \ln Q^2}$) is significantly different from perturbative QCD expectations for smallvalues of $Q^2$ at exeedingly small values of $x$. We show that shadowing (screening) corrections provide a natural explanation for this experimental observ

Lawrence J. Hall, Takeo Moroi, Hitoshi Murayama

The tau sneutrino is proposed as a candidate for galactic halo dark matter, and as the cold dark matter (CDM) component of the universe. A lepton-number-violating sneutrino mass, \tildeν\tildeν, splits the tau sneutrino into two mass eigenstates: \tildeν \rightarrow \tildeν_\pm. The absence of a Z \tildeν_- \tildeν_- coupling implies that the lighter mass ei

A. G. Williams

Recent results by Benayoun et al. comparing the predictions of a range of existing models based on the Vector Meson Dominance hypothesis are summarized and discussed. These are compared with data on e+ e- -> pi+ pi- and e+ e- -> mu+ mu- cross-sections and the phase and near-threshold behavior of the timelike pion form factor, with the aim of determining whic

M. Daoudi

We present preliminary results on two analyses performed by the SLD Collaboration using inclusive B decays: a search for CP violation and a search for the b --> sg transition.

S. O. Alexeyev, M. V. Sazhin

An internal singularity of a string four-dimensional black hole with second order curvature corrections is discussed. A restriction to a minimal size of a neutral black hole is obtained in the frame of the model considered. Vacuum polarization of the surrounding space-time caused by this minimal-size black hole is also discussed.

S. Nakariki, T. Masaki, K. Fukuma, T. Fukui

In this paper we consider a model of Poincaré gauge theory (PGT) in which a translational gauge field and a Lorentz gauge field are actually identified with the Einstein&#39;s gravitational field and a pair of ``Yang-Mills&#39;&#39; field and its partner, respectively.In this model we re-derive some special solutions and take up one of them. The solution rep

Pratip Bhattacharyya

Dynamic properties of a one-dimensional probabilistic cellular automaton are studied by monte-carlo simulation near a critical point which marks a second-order phase transition from a active state to a effectively unique absorbing state. Values obtained for the dynamic critical exponents indicate that the transition belongs to the universality class of direc

A. B. Kuklov, N. Chencinski

It is shown that thermal fluctuations of the normal component induce dephasing -- reversible damping of the low energy collective modes of a confined Bose-Einstein condensate. The dephasing rate is calculated for the isotropic oscillator trap, where Landau damping is expected to be suppressed. This rate is characterized by a steep temperature dependence, and

R. J. Dodd, K. Burnett, Mark Edwards, Charles W. Clark

A simple picture describes the results of recent treatments of partially-condensed, dilute, trapped Bose gases at temperature T > 0. The condensate wavefunction is nearly identical to that of a T=0 condensate with the same number of condensate atoms, N_0. The cloud of non-condensed atoms is described by the statistical mechanics of an ideal Bose gas in the c

T. Ogitsu, K. Kusakabe, S. Tsuneyuki, Y. Tateyama

We present first-principles band calculations as well as structural optimization of the orthorhombic K$_1$C$_{60}$ polymerized phase. We found three-dimensional inter-fullerene bonding/anti-bonding characters consisting of $t_{1u}$ molecular orbitals with $p$-like symmetry in the conduction bands. The formation of the four-membered ring connecting the fuller

N. S. Witte

The Lanczos process has been analytically and exactly carried out for the spin 1/2 isotropic XY chain in the thermodynamic limit, yielding a form for the Lanczos coefficient $β^2(s)$. This coefficient has a monotonic variation for real positive $s$ and confirms a general theorem on the ground state properties of extensive Many-body Systems. The Taylor expans

N. S. Witte

The classical formalism of the Moment Problem has been combined with a cumulant approach and applied to the extensive many-body problem. This has yielded many new exact results for many-body systems in the thermodynamic limit - for the ground state energy, for excited state gaps, and for arbitrary ground state averages. The method applies to any extensive Ha

F. Orsucci, K. Walter, A. Giuliani, C. L. Webber,

A methodology based upon recurrence quantification analysis is proposed for the study of orthographic structure of written texts. Five different orthographic data sets (20th century Italian poems, 20th century American poems, contemporary Swedish poems with their corresponding Italian translations, Italian speech samples, and American speech samples) were su

M. Catanese, C. W. Akerlof, H. M. Badran, S. D. Biller

We present the discovery of >350 GeV gamma-ray emission from the BL Lacertae object 1ES 2344+514 with the Whipple Observatory 10m gamma-ray telescope. This is the third BL Lac object detected at gamma-ray energies above 300 Gev, the other two being Markarian 421 (Mrk 421) and Mrk501. These three active galactic nuclei are all X-ray selected and have the lowe

S. W. Barwick, J. J. Beatty, C. R. Bower, C. J. Chaput

Observations of cosmic-ray electrons and positrons have been made with a new balloon-borne detector, HEAT (the &#34;High-Energy Antimatter Telescope&#34;), first flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach and the data analysis procedures, and we present results from this flight. The measurement has provided a new determinat

G. S. Bisnovatyi-Kogan

Stability of supermassive stars embedded in hot dark matter is investigated on the base of the energetic method. Stability effect of dark mater is compared with rotational stabilization and preference of the last factor is advocated.

Titus J. Galama, Paul J. Groot, Jan van Paradijs, Chryssa Kouveliotou

We present the R_c band light curve of the optical transient (OT) associated with GRB970228, based on re-evaluation of existing photometry. Data obtained until April 1997 suggested a slowing down of the decay of the optical brightness. However, the HST observations in September 1997 show that the light curve of the point source is well represented by a singl

R. Plaga

The possibility that the major part of all extrasolar hadronic cosmic rays with energies above 10 MeV/n is of extragalactic origin is discussed. Recent observational results on the galactocentric cosmic-ray density gradient and very high gamma-ray emission do not support expectations from the simplest models with a Galactic origin of cosmic rays. The hypothe

W. Kluzniak, M. Ruderman

GRBs are thought to arise in relativistic blast-wave shocks at distances of 10 to 1000 AU from the point where the explosive energy is initially released. To account for the observed duration and variability of the gamma-ray emission in most GRBs, a central engine powering the shocks must remain active for several seconds to many minutes but must strongly fl

A. Bondal, D. Orlov

We consider smooth algebraic varieties with ample either canonical or anticanonical sheaf. We prove that such a variety is uniquely determined by its derived category of coherent sheaves. We also calculate the group of exact autoequivalences for these categories. The technics of ample sequences in abelian categories is used.

Adan Cabello

The ladder proof of nonlocality without inequalities for two spin half particles proposed by Hardy et al. (Phys. Rev. Lett. 79 (1997) 2755) works only for nonmaximally entangled states and goes through for 50% of pairs at the most. A similar ladder proof for two spin-1 particles in a maximally entangled state is presented. In its simplest form, the proof goe

M. M. Brisudova, L. Burakovsky, T. Goldman

Using the ``glueball dominance&#39;&#39; picture of the mixing between q\bar{q} mesons of different hidden flavors, we establish new glueball-meson mass relations which serve as a basis for glueball spectral systematics. For the tensor glueball mass 2.3\pm 0.1 GeV used as an input parameter, these relations predict the following glueball masses: M(0^{++})\si

P. Zinn-Justin

A set of coupled non-linear integral equations is derived for a class of models connected with the quantum group $U_q(\hat g)$ ($g$ simply laced Lie algebra), which are solvable using the Bethe Ansatz; these equations describe arbitrary excited states of a system with finite spatial length $L$. They generalize the Destri-De Vega equation for the Sine-Gordon/

Tian-Nan Wang, Rue-Ron Hsu, Han-Tzong Su, Wei-Fu Lin

We analytically derive the correlation functions of the stochastic response of period-p orbits in a generic one-dimensional map system under the influence of weak external, additive white noise. Two approaches, a recurrence scheme and a path integral method, are provided. Beside the supercycle, we recognise that the fluctuations on each elements of the perio

H. Tolga Ilhan, H. Volkan Demir, Philip F. Bagwell

We calculate the electrical currents through a superconductor - insulator - superconductor junction which is also weakly coupled to a normal metal side probe. The voltage $V$ applied to the normal metal terminal controls the occupation of Andreev energy levels $E_n$, and therefore controls the Josephson current flowing through these levels. Whenever the prob

Fernando C. Lombardo, Francisco D. Mazzitelli

We evaluate the influence functional for two dimensional models of dilaton gravity. This functional is exactly computed when the conformal invariance is preserved, and it can be written as the difference between the Liouville actions on each closed-time-path branch plus a boundary term. From the influence action we derive the covariant form of the semiclassi

J. D. Cohn

An overview of some new results in open inflation over the past year, including the calculation of gravity wave contributions to the Cosmic Microwave Background. Proceedings for COSMO-97, held in Ambleside, U.K., hence very short due to space limitations (the version for the web is more than 3 pages because archive numbers have been added for the references)

A. Berkovich, B. M. McCoy, P. A. Pearce

We derive the fermionic polynomial generalizations of the characters of the integrable perturbations $ϕ_{2,1}$ and $ϕ_{1,5}$ of the general minimal $M(p,p&#39;)$ conformal field theory by use of the recently discovered trinomial analogue of Bailey&#39;s lemma. For $ϕ_{2,1}$ perturbations results are given for all models with $2p>p&#39;$ and for $ϕ_{1,5}$ per

D. Bellisai, G. Travaglini

We study instanton effects along the Coulomb branch of an N=2 supersymmetric Yang-Mills theory with gauge group SU(2) on Asymptotically Locally Euclidean (ALE) spaces. We focus our attention on an Eguchi-Hanson gravitational background and on gauge field configurations of lowest Chern class.

Jian-Zhong Ma, Thomas Guhr, Tilo Wettig

The statistical properties of the spectrum of the staggered Dirac operator in an SU(2) lattice gauge theory are analyzed both in the bulk of the spectrum and at the spectrum edge. Two commonly used statistics, the number variance and the spectral rigidity, are investigated. While the spectral fluctuations at the edge are suppressed to the same extent as in t

S. D. Bass

U_A(1) dynamics have the potential to induce a polarised condensate inside a nucleon. The formation of this condensate is related to the realisation of U_A(1) symmetry breaking by tunneling processes such as instantons. If it is present, the polarised condensate induces a term in g_1 which has support only at x=0. Tunneling processes then induce a net transf

A. O. Gattone, D. Abriola, F. T. Avignone, R. L. Brodzinski

A new technique has been used to search for solar axions using a single crystal germanium detector. It exploits the coherent conversion of axions into photons when their angle of incidence satisfies a Bragg condition with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1-kg DEMOS detector in Sierra Grande, Argentina, yields a n

A. S. Belyaev, Ilya L. Shapiro

Starting from the well established form of the Dirac action coupled to the electromagnetic and torsion field we find that there is some additional softly broken local symmetry associated with torsion. This symmetry fixes the form of divergences of the effective action after the spinor fields are integrated out. Then the requirement of renormalizability fixes

Sumathi Rao

We obtain the exact spectrum and the unique ground state of two composite fermions (in a Rajaraman - Sondhi like formulation) in an external magnetic field $B$. We show that the energy eigenvalues decrease with increasing angular momentum, thus making it energetically favourable for composite fermions to stay apart. Generalising this result to a gas of compo

Jonathan L. Feng, Takeo Moroi

In supersymmetric models with gauge-mediated supersymmetry breaking, charged sleptons are the next lightest supersymmetric particles and decay outside the detector for large regions of parameter space. In such scenarios, supersymmetry may be discovered by searches for a number of novel signals, including highly ionizing tracks from long-lived slow charged pa

Eugene A. Mirabelli, Michael E. Peskin

In the strong-coupling limit of the heterotic string theory constructed by Horava and Witten, an 11-dimensional supergravity theory is coupled to matter multiplets confined to 10-dimensional mirror planes. This structure suggests that realistic unification models are obtained, after compactification of 6 dimensions, as theories of 5-dimensional supergravity

S. F. Hassan, Spenta R. Wadia

We study the hypermultiplet moduli space of an N=4, U(Q_1)xU(Q_5) gauge theory in 1+1 dimensions to extract the effective SCFT description of near extremal 5-dimensional black holes modelled by a collection of D1- and D5-branes. On the moduli space, excitations with fractional momenta arise due to a residual discrete gauge invariance. It is argued that, in t

H. W. Griesshammer

A Lagrangean and a set of Feynman rules are presented for non-relativistic QFT&#39;s with manifest power counting in the heavy particle velocity $v$. A régime is identified in which energies and momenta are of order $Mv$. It is neither identical to the ultrasoft régime corresponding to radiative processes with energies and momenta of order $Mv^2$, nor to the

V. S. Matveev

In the present paper we prove, that if the geodesic flow of a metric G on the torus T is quadratically integrable, then the torus T isometrically covers a torus with a Liouville metric on it, and describe the set of quadratically integrable geodesic flows on the Klein bottle.

Metin Gurses

The correspondance is established between the sigma models, the minimal surfaces and the Monge-Ampere equation. The Lax -Pairs of the minimality condition of the minimal surfaces and the Monge-Ampere equations are given. Existance of infinitely many nonlocal conservation laws is shown and some Backlund transformations are also given.

Richard J. Hughes

The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potent

Giuseppe Castagnoli, Dalida Monti

In the diakoptic approach, mechanisms are divided into simpler parts interconnected in some standard way (say by a &#34;mechanical connection&#39;&#39;). We explore the possibility of applying this approach to quantum mechanisms: the specialties of the quantum domain seem to yield a richer result. First parts are made independent of each other by assuming th

David A. Meyer

We continue our analysis of the physics of quantum lattice gas automata (QLGA). Previous work has been restricted to periodic or infinite lattices; simulation of more realistic physical situations requires finite sizes and non-periodic boundary conditions. Furthermore, envisioning a QLGA as a nanoscale computer architecture motivates consideration of inhomog

Andrei Okounkov

In this elementary paper we prove that the extra vanishing property characterizes the BC interpolation Macdonald polynomials inside a very general class of multivariate interpolation polynomials. It follows that they are the only polynomials in this class that admit a tableaux sum formula or a q-integral representation.

Pavel Etingof, Alexander Kirillov

In this note we give a short proof of Cherednik&#39;s generalization of Macdonald-Mehta identities for the root system $A_{n-1}$ using the representation theory of quantum groups. These identities, suggested and proved by Cherednik, give an explicit formula for the integral of a product of Macdonald polynomials with respect to a ``difference analogue of the

Z. Jaskolski

A complete mathematical framework for coalgebraic formulation of supergeometry and its infinite-dimensional extension is proposed. Within this approach a supermanifold is defined as a graded coalgebra endowed with a smooth structure. The category of such coalgebras is constructed and analysed. It is shown that it contains as its full subcategories both the c

Rui Dilao, Joaquim Sainhas

Space and time scales are not independent in diffusion. In fact, numerical simulations show that different patterns are obtained when space and time steps ($Δx$ and $Δt$) are varied independently. On the other hand, anisotropy effects due to the symmetries of the discretization lattice prevent the quantitative calibration of models. We introduce a new class

G. Q. Li, C. Gale

Through the analysis of HELIOS-3 data on dilepton spectra, we demonstrate the importance of secondary processes for the dilepton production in heavy-ion collisions in the intermediate mass region. We find that, while the dilepton spectra in proton-induced reactions can be nicely explained by the decay of primary vector mesons, charmed hadrons, and initial Dr

C. Bennhold, F. X. Lee, T. Mart, L. E. Wright

The formation and excitation of hypernuclei through kaon photoproduction is reviewed. Basic features of the production process are emphasized. The possibility of extracting new information on hypernuclear structure and on the wave function of the bound $Λ$ is discussed. New results are presented for the quasifree production process $A(γ, K Λ)B$. Observables

NA45 Collaboration, G. Agakichiev et al

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounc

Klaus Behrndt, Mirjam Cvetic, Wafic A. Sabra

We give an explicit form of the classical entropy for four-dimensional static near-BPS-saturated black holes of generic N=2 superstring vacua. The expression is obtained by determining the leading corrections in the non-extremality parameter to the corresponding BPS-saturated black hole solutions. These classical results are quantitatively compared with the

J. L. Lucio, M. Ruiz-Altaba

The dual Schrodinger equation for x in terms of psi derived by Faraggi and Matone [hep-th/9606063] with techniques inspired by field theory duality can be derived almost trivially from differential calculus.

M. Veltman

The two-component formulation of quantum electrodynamics is studied. The relation with the usual Dirac formulation is exhibited, and the Feynman rules for the two-component form of the theory are presented in terms of familiar objects. The transformation from the Dirac theory to the two-component theory is quite amusing, involving Faddeev-Popov ghost loops o

Vijay Balasubramanian

N=8 supergravity has a rich spectrum of black holes charged under the 56 U(1) gauge fields of the theory. Duality predicts that the entropy of these black holes is related to the quartic invariant of the E(7,7) group. We verify this prediction in detail by constructing black holes that correspond to supersymmetric bound states of 2-branes at angles and 6-bra

Pawel O. Mazur

A slightly extended version, with a footnote added on December 19, 1997, of a contributed Abstract to the Eight Marcel Grossmann Meeting, Jerusalem, June 1997.

D. Ebert, V. Ch. Zhukovsky

A possibility is discussed that new nontrivial Chern-Simons like terms may be generated in (3+1)--dimensional QED Lagrangian, when induced by quark loops interacting with a non-abelian background field in an SU(2) model of QCD.

C. -P. Yuan

We discuss how to experimentally study the electroweak symmetry breaking (EWSB) sector by observing $WW \to WW$ interactions in the TeV region. We discuss some general features of the event structure in the signal and the background events. Various techniques to enhance the signal-to-background ratio are also presented. We show how to detect longitudinal W-b

Stephen Parke

In this presentation I will primarily focus on top quark physics but I will include a discussion of the W-boson mass and the possibility of discovering a light Higgs boson via associated production at the Tevatron.

S. B. Gerasimov

The phenomenological sum-rule-based approach is used to discuss the quark composition dependence of some static and quasi-static electroweak characteristics of nucleons.The role of nonvalence degrees of freedom, the nucleon sea partons and/or peripheral meson currents, is shown to be important to select and make use of the relevant symmetry parametrization o

Stuart Raby

Lepton flavor violation may be a signature of &#34;GUT scale&#34; physics, if the messenger scale for SUSY breaking is above the &#34;GUT scale.&#34; We elaborate on the details of this simple statement in the following talk.

S. Wallon

We compute the onium-onium scattering amplitude at fixed impact parameter in the framework of the perturbative QCD dipole model. Relying on the conformal properties of the dipole cascade and of the elementary dipole-dipole scattering amplitude, we obtain an exact result for this onium-onium scattering amplitude, which is proved to be identical to the BFKL re

L. Mankiewicz, G. Piller, T. Weigl

We present an analysis of twist-2, leading order QCD amplitudes for hard exclusive leptoproduction of charged vector mesons. These processes are determined by nonforward parton distribution functions which are nondiagonal in quark flavor. We derive relations between flavor diagonal and nondiagonal distribution functions based on isospin symmetry. Furthermore

Juergen Baacke, Katrin Heitmann, Carsten Patzold

We generalize a previously proposed renormalization and computation scheme for nonequilibrium dynamics to include finite temperature and one-loop selfconsistency as arising in the large-N limit. Since such a scheme amounts essentially to tadpole summation, it also includes, at high temperature, the hard mass corrections proportional to T^2. We present some n

Michael Kuhlen

The measurements of the hadronic final state in deep inelastic scattering at HERA are reviewed and discussed in the context of QCD. Covered are the general event properties in terms of energy flows, charged particle production, and charm and strangeness production. Quark fragmentation properties are studied in the Breit frame. Event shape measurements allow

V. V. Anisovich

Recently performed investigations of meson spectra allow us to determine the resonance structure for the waves $IJ^{PC}=00^{++}$, $10^{++}$, $02^{++}$, $12^{++}$ = $IJ^P= 1/2 0^+$ in the mass region up to 1900 MeV, thus establishing the meson multiplets $1^3P_0q\bar q$ and $2^3P_0q\bar q$. Experimental data demonstrate that there are five scalar/isoscalar st

Nita Sinha, Rahul Sinha

We propose a method to determine the angle $γ=arg(V_{ub})$, using the $B\to D^*V$ ($V=K^*, ρ$) modes. The $D^*$ is considered to decay to $D π$. An interference of the $B \to D^{*0}V$ and $B \to \bar {D^{*0}}V$ amplitudes is achieved by looking at a common final state $f$, in the subsequent decays of $D^0/\bar{D^0}$. A detailed analysis of the angular distri

A. T. Davies, C. D. Froggatt, A. Usai

We explore the possibility of spontaneous CP violation within the Next to Minimal Supersymmetric Standard Model. In the most general form of the model, without a discrete $Z_3$ symmetry, we find that even at tree level spontaneous CP violation can occur, while also permitting Higgs masses consistent with experiment.

Yu. S. Kalashnikova, A. V. Nefediev

The two ways of constrained systems quantization are considered from the point of view of their self-consistency at the quantum level. With a transparent example of a particle in the external electromagnetic field we demonstrate that the procedure of gauge fixing turns out rather dangerous and may lead to a quantum anomaly in the operator algebra. We discuss

George Wei-Shu Hou

We discuss the historical development of the gluonic B-penguin, its sensitivity to $H^+$ effects, and $\bsg\sim$ 10--15% as a possible solution to the $\Bsl$ and $n_C$ problems. The latter and the connection of the gluonic penguin to inclusive $B\to η^\prime+ X_s$ production through the gluon anomaly, with the intriguing prospect of 10% inclusive CP asymmetr

B. Foster

Results from the H1 and ZEUS experiments at HERA on deep inelastic scattering are reviewed. The data lead to a consistent picture of a steep rise in the F_2 structure function and in the gluon density within the proton. Important new information on the partonic structure of diffraction is emerging from H1 and ZEUS. The space-like region in which the weak and

S. Baskal

The variational methods implemented on a quadratic Yang-Mills type Lagrangian yield two sets of equations interpreted as the field equations and the energy-momentum tensor for the gravitational field. A covariant condition is imposed on the energy-momentum tensor to represent the radiation field. A generalized pp-wave metric is found to simultaneously satisf

Friedrich W. Hehl, Yuri N. Obukhov

The Minkowski space of special relativity can be understood as a flat 4-dimensional affine space enriched by a constant Minkowski metric. If we gauge the general affine group and `superimpose&#39; the metric, then we arrive at the metric-affine theory of gravity (MAG). The gravitational potentials are the spacetime coframe, the metric, and the linear connect

V. S. Matveev, P. J. Topalov

We show that an invariant surface allows to construct the Jacobi vector field along a geodesic and construct the formula for the normal component of the Jacobi field. If a geodesic is the transversal intersection of two invariant surfaces (such situation we have, for example, if the geodesic is hyperbolic), then we can construct a fundamental solution of the

V. N. Kotov, J. Oitmaa, O. Sushkov

We consider the two-dimensional (2D) quantum Heisenberg antiferromagnet at zero temperature with two types of locally frustrating perturbations - an isolated ferromagnetic bond (FMB) and a quantum impurity spin, coupled symmetrically to the two sublattices. An analytic technique is developed to study strong defect-environment interaction. In the case of a FM

T. A. Vilgis, J. Wilder

This paper discusses the elastic behavior of polyelectrolyte networks. The deformation behavior of single polyelectrolyte chains is discussed. It is shown that a strong coupling between interactions and chain elasticity exists. The theory of the complete crosslinked networks shows that the Flory - Rehner - Hypothesis (FRH) does not hold. The modulus contains

M. V. Milovanovic

We propose an effective low-energy theory for ferromagnetic Hall states. It describes the charge degrees of freedom, on the edge, by a (1 + 1) dimensional chiral boson theory, and the spin degrees of freedom by the (2 + 1)dimensional quantum ferromagnet theory in the spin-wave approximation. The usual chiral boson theory for spinless electrons is modified to

E. N. M. Cirillo, G. Gonnella, A. Pelizzola

We use the cluster variation method (CVM) and Monte Carlo simulations to investigate the phase structure of the 3d gonihedric Ising actions defined by Savvidy and Wegner. This model corresponds to the usual three-dimensional cubic Ising model with nearest, next to the nearest, and plaquette interactions in the region with degenerate lamellar ground states. T

Cristian Micheletti, Jayanth R. Banavar, Amos Maritan, Flavio Seno

A simple lattice model for proteins that allows for distinct sizes of the amino acids is presented. The model is found to lead to a significant number of conformations that are the unique ground state of one or more sequences or encodable. Furthermore, several of the encodable structures are highly designable and are the non-degenerate ground state of severa

Y. Levinson, O. Entin-Wohlman, A. D. Mirlin, P. Woelfle

The interaction of a surface acoustic wave (SAW) with a a two-dimensional electron gas in a periodic electric potential and a classical magnetic field is considered. We calculate the attenuation of the SAW and its velocity change and show that these quantities exhibit Weiss oscillations.

D. H. Cobden, G. Pilling, R. Parthasarathy, P. L. McEuen

We find that, under appropriate conditions, electrons can pass a barrier etched across a two dimensional electron gas (2DEG) by field emission from the GaAs/AlGaAs heterojunction into a second, low-density 2DEG formed deep in the substrate. The current-voltage characteristics exhibit a rapid increase in the current at the field emission threshold and intrins

A. Houghton, I. Vekhter

We derive generalized quasiclassical transport equations which include the terms responsible for the Hall Effect in the vortex state of a clean type-II superconductor, and calculate the conductivity tensor for an s-wave superconductor in the high-field regime. We find that below the superconducting transition the contribution to the transverse conductivity d

Peter A. Heeman

In this thesis, we present a statistical language model for resolving speech repairs, intonational boundaries and discourse markers. Rather than finding the best word interpretation for an acoustic signal, we redefine the speech recognition problem to so that it also identifies the POS tags, discourse markers, speech repairs and intonational phrase endings (

Adam Kilgarriff

Word sense disambiguation has developed as a sub-area of natural language processing, as if, like parsing, it was a well-defined task which was a pre-requisite to a wide range of language-understanding applications. First, I review earlier work which shows that a set of senses for a word is only ever defined relative to a particular human purpose, and that a

Adam Kilgarriff

Lexicon acquisition from machine-readable dictionaries and corpora is currently a dynamic field of research, yet it is often not clear how lexical information so acquired can be used, or how it relates to structured meaning representations. In this paper I look at this issue in relation to Information Extraction (hereafter IE), and one subtask for which both

Adam Kilgarriff

Word sense disambiguation assumes word senses. Within the lexicography and linguistics literature, they are known to be very slippery entities. The paper looks at problems with existing accounts of `word sense&#39; and describes the various kinds of ways in which a word&#39;s meaning can deviate from its core meaning. An analysis is presented in which word s

Yasuhiro Hashimoto, Augustus Oemler, Huan Lin, Douglas L. Tucker

We have used a sample of 15749 galaxies taken from the Las Campanas Redshift Survey to investigate the effects of environment on the rate of star formation (SFR) in galaxies. The size and homogeneity of this data set allows us to sample, for the first time, the entire range of galactic environment, from the voids to the clusters, in a uniform manner, thus, w

L. Bergstrom, P. Ullio, J. Buckley

Recent advances in N-body simulations of cold dark matter halos point to a substantial density enhancement near the center. This means that, e.g., the $γ$ ray signals from neutralino dark matter annihilations would be significantly enhanced compared to old estimates based on an isothermal sphere model with large core radius. Another important development con

Artie P. Hatzes, William D. Cochran, Eric J. Bakker

The discovery of the planet around the solar-type star 51 Pegasi marked a watershed in the search for extrasolar planets. Since then seven other solar-type stars have been discovered, of which several have surprisingly short orbital periods, like the planet around 51 Peg. These planets were detected using the indirect technique of measuring variations in the

Kenneth J. Mighell, Ata Sarajedini, Rica S. French

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (~V) and F450W (~B) of the intermediate-age populous star cluster NGC 416 in the Small Magellanic Cloud galaxy. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these

Artie P. Hatzes, William D. Cochran

An analysis is made of the spectral line shapes of tau Bootis using high resolution (0.026 A) and high signal-to-noise (S/N~400) data in an effort to confirm the planet hypothesis for this star. Changes in the line shape are quantified using spectral line bisectors and line residuals. We detect no variations in either of these quantities above the level of t

Artie P. Hatzes, William D. Cochran

The shape of the Ti I 6303.8 A spectral line of Aldebaran as measured by the line bisector was investigated using high signal-to-noise, high resolution data. The goal of this study was to understand the nature of the 643-day period in the radial velocity for this star reported by Hatzes and Cochran. Variations in the line bisector with the radial velocity pe

Erik Kuulkers, Michiel van der Klis

We report on about 4 hrs of observations made with the Rossi X-ray Timing Explorer on 1997 May 2 of the low-mass X-ray binary and Z source GX 349+2 (Sco X-2). Initially the source was in the normal branch (NB), later it moved to the flaring branch (FB). In the NB the power spectra reveal a broad (FWHM ~16 Hz) noise component peaking near 9 Hz, with a fractio

N. Brouillet, M. Kaufman, F. Combes, A. Baudry

We report about high spatial resolution observations made with the IRAM interferometer of the CO emission from a 1.1x1.1 kpc plane-of-sky field on a spiral arm of Messier 81. With a beam of 5&#39;&#39;(90 pc), we identify 6 giant molecular cloud complexes with virial masses of about 10^6 Msun, including one associated with a giant HII region. The deduced N(H

R. Misra, V. R. Chitnis, F. Melia

We have used the transition disk model to fit the simultaneous broad band ($2-500$ keV) spectrum of Cygnus X-1 from OSSE and Ginga observations. In this model, the spectrum is produced by saturated Comptonization within the inner region of the accretion disk, where the temperature varies rapidly with radius. In an earlier attempt, we demonstrated the viabili

Giovanni Carraro, Cesario Lia, Cesare Chiosi

In this paper we report on PD-SPH the new tree-sph code developed in Padua. The main features of the code are described and the results of a new and independent series of 1-D and 3-D tests are shown. The paper is mainly dedicated to the presentation of the code and to the critical discussion of its performances. In particular great attention is devoted to th

K. Molthagen, N. Bade, H. J. Wendker

RX J0947.0+4721 is a newly discovered example of a narrow-line Seyfert 1 type object with a quasar level luminosity (M_B = -24.8). It was detected in the ROSAT All-Sky Survey (RASS) and later in 17 pointed observations of the ROSAT Position sensitive Proportional Counter (PSPC). The optical spectrum contains strong FeII emission. We apply several spectral mo