June 1997 arXiv papers — page 8

Fred Popowich, Davide Turcato, Olivier Laurens, Paul McFetridge

Colloquial English (CE) as found in television programs or typical conversations is different than text found in technical manuals, newspapers and books. Phrases tend to be shorter and less sophisticated. In this paper, we look at some of the theoretical and implementational issues involved in translating CE. We present a fully automatic large-scale multilin

G. Neumann, R. Backofen, J. Baur, M. Becker

This paper describes SMES, an information extraction core system for real world German text processing. The basic design criterion of the system is of providing a set of basic powerful, robust, and efficient natural language components and generic linguistic knowledge sources which can easily be customized for processing different tasks in a flexible manner.

H. van Beijeren, J. R. Dorfman, H. A. Posch, Ch. Dellago

We use the kinetic theory of gases to compute the Kolmogorov-Sinai entropy per particle for a dilute gas in equilibrium. For an equilibrium system, the KS entropy, h_KS is the sum of all of the positive Lyapunov exponents characterizing the chaotic behavior of the gas. We compute h_KS/N, where N is the number of particles in the gas. This quantity has a dens

Leonid M. Ozernoy, Reinhard Genzel, Vladimir V. Usov

We point out that a high number density of stars in the core of a dense star cluster such as the central stellar cluster at the Galactic center, where many stars possess strong stellar winds, should result in collisions of those winds. The wind collisions in the dense stellar core at the Galactic center would result in production of strong X-ray flares with

J. Greiner, E. Morgan, R. Remillard

We report on extensive X-ray observations of the galactic superluminal motion source GRS 1915+105 with the RXTE satellite over the last year. More than 130 RXTE pointings have been performed. GRS 1915+105 displays drastic X-ray intensity variations on a variety of time scales ranging from sub-seconds to days. In general, the intensity changes are accompanied

Karl D. Rakos, Andrew P. Odell, James M. Schombert

This paper presents deep narrow band photometry of the cluster A2317 (z=0.211) carried out using KPNO 4 m and Steward 2.3 m telescopes. Using rest frame Stromgren photometry, it is determined that A2317 has an unusually high fraction of blue galaxies (the Butcher-Oemler effect) for its redshift (f_B=0.35). We demonstrate that the ratio of blue to red galaxie

Ben Dorman, Robert W. O'Connell

We consider the extent to which broadband mid-UV (2000 - 3000 Angstrom) colors can give superior constraints on the ages and abundances of old stellar populations than can their optical counterparts. The ultraviolet colors directly measure the turnoff component of old populations. They vary much more strongly with t and Z and give much tighter constraints fo

M. Fukugita, N. Hata

It is shown that the metal abundance in the solar interior is constrained from the current solar neutrino experiment, even if one allows neutrino conversion in the sun due to neutrino oscillation. The result shows that the metal abundance in the interior should be within the range 0.4 - 1.4 times that in the surface, supporting the idea that the sun formed b

S. Benetti, E. Cappellaro, I. J. Danziger, M. Turatto

Extensive photometric and spectroscopic observations of SN1994aj until 540d after maximum light have been obtained. The photometry around maximum suggests that the SN belongs to the Type II Linear class, with a peak absolute magnitude of Mv ~ -17.8 (assuming Ho=75 km/s/Mpc). The spectra of SN1994aj were unusual with the presence of a narrow line with a P-Cyg

G. Fossati, A. Celotti, G. Ghisellini, L. Maraschi

The average Spectral Energy Distributions (SED) of different classes of blazars from the radio to the gamma-ray band are studied adopting a "complete-sample" approach. The SED are globally similar, despite systematic differences in specific frequency ranges, showing two broad peaks. However, i) the first and second peak occur in different frequency r

Hagai Netzer, J. Turner

Previous X-ray and ultraviolet spectroscopy suggested that the Fe/O abundance ratio in NGC 1068 may be abnormally high. We have measured some 15 X-ray lines in NGC 1068, to an accuracy better than a factor 2, and modeled the continuum in two different ways. The first assumes that the hard X-ray continuum is the reflection of the nuclear source by two, extend

T. Oosterbroek, A. N. Parmar, D. D. E. Martin, U. Lammers

We present 0.1-10 keV observations of Her X-1 obtained with the Low-Energy Spectrometer Concentrator instrument onboard the BeppoSAX satellite during the main on-state of the 35 day cycle. We confirm the existence of an intense 0.093 keV blackbody component and a broad emission feature at 0.94 keV. The pulse phase dependence of these components is similar, s

J. C. Papaloizou, G. J. Savonije

We describe a generalization of the asymptotic calculation of the tidal torques experienced by a massive star as a result of a companion in circular orbit originally considered by Zahn (1975,1977) to the case of a rotating star when the forcing frequency is small and in the inertial regime, that is it is less than twice the rotation frequency in magnitude. T

G. J. Savonije, J. C. Papaloizou

We study the fully non-adiabatic tidal response of a uniformly rotating unevolved 20 Msun star to the dominant l=m=2 component of the companion's perturbing potential. This is done numerically with a 2D implicit finite difference scheme. We assume the star is rotating slowly, so that the centrifugal force can be neglected, but the Coriolis force is taken

Peter Schneider

The gravitational lens equation resulting from a single (non-linear) mass concentration (the main lens) plus inhomogeneities of the large-scale structure is shown to be strictly equivalent to the single-plane gravitational lens equation without the cosmological perturbations. The deflection potential (and, by applying the Poisson equation, also the mass dist

Matthias Bartelmann, Tsafrir S. Kolatt

The projected gravitational potential of galaxy clusters is reflected in both their X-ray emission and their imprint on the images of background sources due to their gravitational lensing effects. Since these projections of the potential are weighted differently along the line-of-sight, we propose a method to combine them and remove the degeneracy between tw

R. Muller, K. Lippert, A. Kuhnel, U. Behn

We investigate a system of harmonically coupled identical nonlinear constituents subject to noise in different spatial arrangements. For global coupling we find for infinitely many constituents the coexistence of several ergodic components and a bifurcation behaviour like in first order phase transitions. These results are compared with simulations for finit

Patrick N. McGraw

We describe a numerical simulation of the evolution of an $S_3$ cosmic string network which takes fully into account the non-commutative nature of the cosmic string fluxes and the topological obstructions which hinder strings from moving past each other or intercommuting. The influence of initial conditions, string tensions, and other parameters on the netwo

E. Abdalla, Roya Mohayaee

We use de Vaucouleurs' power-law density-distance relation, to study a hierarchical perturbation of the Friedmann universe. We solve the Einstein equation and obtain the density contrast and the amplification factor for the perturbation. It is shown that, scale-invariant inhomogeneities decay in Einstein-de-Sitter universe. On the contrary, in an open un

Glennys R. Farrar

Measurements of the total hadronic cross section in e+e- annihilation are shown to be capable of severely limiting the possibility that gauginos have negligible tree level masses. A combined analysis of 1997 and earlier LEP data, considering simultaneously conventional SUSY signatures and purely hadronic final states, should achieve a 95% cl sensitivity to t

A. Brandhuber, N. Itzhaki, V. Kaplunovsky, J. Sonnenschein

We use the M theory approach of Witten to investigate N=1 SU($N_c$) SQCD with $N_f$ flavors. We reproduce the field theoretical results and identify in M theory the gluino condensate and the eigenvalues of the meson matrix. This approach allows us to identify the constant piece of the effective field theory coupling from which the coefficient of the one-loop

Fabio Gavarini

Let $ \mathfrak{g} $ be an untwisted affine Kac-Moody algebra over the field $ K \, $, and let $ U_q(\mathfrak{g}) $ be the associated quantum enveloping algebra; let $ \mathfrak{U}_q(g) $ be the Lusztig's integer form of $ U_q(\mathfrak{g}) \, $, generated by $ q $-divided powers of Chevalley generators over a suitable subring $ R $ of $ K(q) \, $. We p

Paolo Padoan, Mika Juvela, John Bally, AAke Nordlund

In this work we use models of molecular clouds (MC), and non-LTE radiative transfer calculations, to obtain a theoretical calibration of the relation between LTE 13CO column density and true column density in MCs. The cloud models consist of 3 dimensional grids of density and velocity fields obtained as solutions of the compressible magneto-hydrodynamic equa

Hajime Tanaka

We propose that glass-forming liquids are intrinsically under the influences of both fluctuating interactions and random fields well-known in the field of spin systems. This is due to the frustration between the isotropic and anisotropic parts of effective intermolecular interactions. Our model indicates the existence of two key temperatures relevant to glas

Stefano Forte

We briefly summarize some recent theoretical developments in perturbative QCD, emphasizing new ideas which have led to widening the domain of applicability of perturbation theory. In particular, it is now possible to calculate efficiently processes with many partons; the high order behavior of perturbation theory can be at least partly understood by going be

R. Bijker, A. Leviatan

We reanalyze the world data on the electromagnetic form factors of the nucleon. The calculations are performed in the framework of an algebraic model of the nucleon combined with vector meson dominance.

Michele Maggiore, Riccardo Sturani

We examine the effect of spatial curvature in the pre-big-bang inflationary model suggested by string theory. We study $O(α')$ corrections and we show that, independently of the initial curvature, they lead to a phase of exponential inflation. The amount of inflation in this phase is long enough to solve the horizon and flatness problems if the evolution

Lewis P. Fulcher

Baker, Ball and Zachariasen have developed an elegant formulation of the dual superconducting model of quantum chromodynamics (QCD), which allows one to use the field equations to eliminate the gluon and Higgs degrees of freedom and thus to express the interaction between quarks as an effective potential. Carrying out an expansion in inverse powers of the co

D. S. Dean, R. R. Horgan, D. Sentenac

We use the functional integral technique of Edwards and Lenard to solve the statistical mechanics of a one dimensional Coulomb gas with boundary interactions leading to surface charging. The theory examined is a one dimensional model for a soap film. Finite size effects and the phenomenon of charge regulation are studied. We also discuss the pressure of disj

Jihn E. Kim, P. Ko

In the framework of the minimal supersymmetric standard model (MSSM) with $R-$parity violation, the high--$Q^2$ HERA events can be interpreted as the $s-$channel production of a single stop of $M_{\tilde{t}_1} \approx 200$ GeV, whose dominant decay modes are assumed to be the $R-$parity violating $e^+ + d $ and the $R-$parity conserving $χ^+ + b$. Assuming o

D. Syer, HongSheng Zhao

Galactic nuclei are now generally thought to have density cusps in their centres, and the evidence is mounting that as a consequence they are unlikely to be triaxial. Self-consistent stellar dynamical models of non-axisymmetric cusps would be an interesting counter-argument to this conclusion. We consider 2-d analogues of triaxial cusps: a sequence of non-ax

Carel Faber

We describe algorithms for computing the intersection numbers of divisors and of Chern classes of the Hodge bundle on the moduli spaces of stable pointed curves. We also discuss the implementations and the results obtained. There are several applications. We discuss one in particular: the calculation of the projection in the tautological ring of the moduli s

K. Maki, S. Orito

Prospects are examined for the detection of a slow decay of the lightest neutralino (or any other longlived particles) at the CERN LHC and at Very Large Hadron Collider (VLHC). We first point out that such hadron colliders will become the ``neutralino factory'' producing 10^6--10^9 neutralinos/yr, if gluinos and/or squarks actually exist below O(1) T

Q. H. Zhang, X. Q. Li

We use a recently derived result to extract from two-pion interferometry data from $p\bar{p}$ collisions the radius of the coherent component in the source. We find a coherent source radius of about $2 fm$.

Olivier Schiffmann

Using recent results of P. Etingof and A. Varchenko on the Classical Dynamical Yang-Baxter equation, we reduce the classification of dynamical r-matrices r on a commutative subalgebra l of a Lie algebra g to a purely algebraic problem under some technical conditions on the symmetric part of r. Using this, we then classify all non skew-symmetric dynamical r-m

R. A. Alanakyan

In the framework of models with Higgs triplets, doubly and singly charged triplet Higgs boson production in the processes $e^-e^-\toδ^{--}_{L,R}Z^0$ and $e^-e^-\toδ^{-}_{L}W^-_L$ are considered.

Dong-Shin Shin

We apply a new coordinate space method for the evaluation of lattice Feynman diagrams suggested by Lüscher and Weisz to field theories in two dimensions. Our work is to be presented for the theories with massless propagators. The main idea is to deal with the integrals in position space by making use of the recursion relation for the free propagator $G(x)$ w

Peter Skala, Manfried Faber, Martin Zach

We modify the standard Wilson action of SU(3) lattice gauge theory by adding an extra term which suppresses colour magnetic currents. We present numerical results of simulations at zero and finite temperature and show that colour magnetic currents strongly influence the confining properties of SU(3) lattice gauge theory.

Gerald H. Ristow

The solid--fluid phase transition of a granular material shaken horizontally is investigated numerically. We find that it is a second-order phase transition and propose two order parameters, namely the averaged kinetic energy and the averaged granular temperature, to determine the fluidization point precisely. It scales with the acceleration of the external

Yuri Shtanov

Recently the issue of EPR-like correlations in the mutual probability of detecting neutrino together with accompanying charged lepton has received a new impetus. In this paper we describe this effect using the propagators of the particles involved in the Schwinger's parametric integral representation. We find this description more simple and more suitabl

Robert R. Tucci

We begin with a review of a well known class of networks, Classical Bayesian (CB) nets (also called causal probabilistic nets by some). Given a situation which includes randomness, CB nets are used to calculate the probabilities of various hypotheses about the situation, conditioned on the available evidence. We introduce a new class of networks, which we ca

L. Lanz, O. Melsheimer

It is argued that setting isolated systems as primary scope of field theory and looking at particles as derived entities, the problem of an objective anchorage of quantum mechanics can be solved and irreversibility acquires a fundamental role. These general ideas are checked in the case of the Boltzmann description of a dilute gas.

Dorje C. Brody, Lane P. Hughston

A geometric framework for quantum statistical estimation is used to establish a series of higher order corrections to the Heisenberg uncertainty relations associated with pairs of canonically conjugate variables. These corrections can be expressed in terms of linear combinations of higher order cumulants for the distributions, and thus vanish for Gaussian di

Tomasz Brzezinski, Shahn Majid

The q-monopole bundle introduced previously is extended to a general construction for quantum group bundles with non-universal differential calculi. We show that the theory applies to several other classes of bundles as well, including bicrossproduct quantum groups, the quantum double and combinatorial bundles associated to covers of compact manifolds.

Sergei Kozyrev

Free coherent states for a system with p degrees of freedom are defined. An isomorphism of the space of free coherent states to the space of distributions on p-adic disk is constructed.

Saburo Kakei

Operators that intertwine representations of a degenerate version of the double affine Hecke algebra are introduced. Each of the representations is related to multi-variable orthogonal polynomials associated with Calogero-Sutherland type models. As applications, raising operators and shift operators for such polynomials are constructed.

R. Debbe, S. Gushue, B. Moskowitz, J. Olness

A ring imaging Cherenkov counter, to be read out by four 100-channel PMTs, is a key element of the BRAHMS experiment. We report here the most recent results obtained tested at the BNL AGS using several radiator gases, including the heavy fluorocarbon C4F10. Ring radii were measured for different particles (pions, muons, and electrons) for momenta ranging fro

J. R. Mureika

Recently, a simple model was derived to account for a sprinter's energy loss around a curve, based on previous sprint models for linear races. This paper offers a quick test of the model's precision by comparing split times from Donovan Bailey's 150m ``Challenge of Champions'' race at Skydome on June 1st, 1997. The discrepancy in the trac

R. Balian, H. Flocard, M. Vénéroni

Extensions of the Hartree-Fock-Bogoliubov theory are worked out which are tailored for, (i) the consistent evaluation of fluctuations and correlations and (ii) the restoration through projection of broken symmetries. For both purposes we rely on a single variational principle which optimizes the characteristic function. The Bloch equation is used as a constr

Zhenping Li

The recent Investigations in the chiral quark model show that kaon productions of nucleon play an important role in understanding the structure of baryons. The evidences of a third $S_{11}$ resonance in the second resonance region and two narrow states around 2 GeV suggest a set of the molecular type baryons with hidden strangeness. Confirming these states r

R. A. Eramzhyan, G. G. Ryzhikh, Yu. M. Tchuvil'sky

A modified version of the Multicluster Dynamic Model of nuclei is proposed to construct completely antisymmetrized wave functions of multicluster systems. An overlap kernel operator is introduced to renormalize the total wave function after antisymmetrization between nucleons in different clusters. A group-theoretical method is developed to analyze the role

NA44 Collaboration, M Murray

Proton and deuteron m_T spectra and rapidity densities at y=1.9-2.3 are presented for central SS, SPb and PbPb collisions. The inverse slopes increase with system size and mass. The radius parameter, R_G, extracted from ratios of the spectra increases with system size. R_G is proportional to 1/\sqrt{m_T} consistent with transverse flow and NA44's HBT res

John Ellis, N. E. Mavromatos, D. V. Nanopoulos

We have argued previously that black holes may be represented in a D-brane approach by monopole and vortex defects in a sine-Gordon field theory model of Liouville dynamics on the world sheet. Supersymmetrizing this sine-Gordon system, we find critical behaviour in 11 dimensions, due to defect condensation that is the world-sheet analogue of D-brane condensa

X. -H. Guo, T. Muta

In the heavy quark limit, the heavy baryon $Λ_Q$ (Q=b or c) can be regarded as composed of a heavy quark and a scalar light diquark which has good spin and flavor quantum numbers. Based on this picture we establish the Bethe-Salpeter (B-S) equation for $Λ_Q$ in the leading order of $1/m_Q$ expansion. With the kernel containing both the scalar confinement and

Z. Bern, J. Rozowsky, B. Yan

Two-loop four-gluon N=4 susy amplitudes are evaluated via cutting techniques as a testing ground for QCD. A conjecture for four-point amplitudes to all loop orders is described. We also present a new conjecture for the leading-color part of the two-loop five-gluon amplitudes.

R. Jeannerot

We construct supersymmetric unified models which automatically lead to a period of inflation. The models all involve a U(1) symmetry which does not belong to the MSSM. We consider three different types of models depending on whether this extra U(1) is the subgroup of a non abelian gauge group, is a U(1) factor belonging to the visible sector or is a U(1) fac

J. R. Espinosa

Light stops can give a strong first order electroweak phase transition in the Minimal Supersymmetric Standard Model (MSSM) satisfying one of the necessary conditions for electroweak baryogenesis. I discuss the region of parameter space where this occurs using a perturbative analysis of the Higgs effective potential. Two-loop QCD corrections associated with s

A. Denner, S. Dittmaier

We determine the accuracy of various approximations to the O(alpha) corrections for on-shell W-pair production. While an approximation based on the universal corrections arising from initial-state radiation, from the running of alpha, and from corrections proportional to m_t^2 fails in the Linear-Collider energy range, a high-energy approximation improved by

P. Aurenche

In the following some aspects of inclusive hard processes in photon induced reactions are reviewed. After a discussion on the properties of hard processes, the phenomenology of jet production and of charmonium production is presented in the context of the next-to-leading logarithm approximation of QCD.

G. Lazarides, Q. Shafi, N. D. Vlachos

In a supersymmetric left-right symmetric model, inflation, baryogenesis (via leptogenesis) and neutrino oscillations can become closely linked. A familiar ansatz for the neutrino Dirac masses and mixing of the two heaviest families, together with the MSW resolution of the solar neutrino puzzle, imply that 1 eV <_\sim m_{ν_{τ}<_\sim 9 eV. The predicted range

Berthold Stech

Non-leptonic two-body decays are discussed on the basis of a generalized factorization approach. It is shown that a satisfactory description of numerous decay processes can be given using the same two parameters a_1^{eff} and a_2^{eff}. Although in general process-dependent, these parameters are not expected to change markedly. In fact, within error limits,

C. S. Kim, T. Morozumi, A. I. Sanda

We propose a new method to extract the value of |Vtd/Vts| from the ratio of the decay distributions dBr/ds[B->Xd l^+ l^-}] and dBr/ds[B Xs l^+ l^-].

S. Y. Choi, C. S. Kim, Jake Lee

The T-odd top-quark chromoelectric dipole moment (tCEDM) is probed through top-quark-pair production via gluon fusion at the CERN Large Hadron Collider (LHC) by considering the possibility of having polarized protons. The complete analytic expressions for the tree-level helicity amplitudes of gg-> ttbar is also presented. For the derived analytic results we

Bo Feng, Jianming Li, Xingchang Song

In this paper we propose a new approach to formulate the field theory on a lattice. This approach can eliminate the Fermion doubling problem, preserve the chiral symmetry and get the same dispersion relation for both Fermion and Boson fields. This gives us the possibility to write down the chiral model (such as the Weinberg-Salam model) on a lattice.

A. Ghosh, P. Mitra

The entropy of a black hole can differ from a quarter of the area of the horizon because of quantum corrections. The correction is related to the contribution to the Euclidean functional integral from quantum fluctuations but is not simply equal to the correction to the effective action. A (2+1) dimensional rotating black hole is explicitly considered.

J. H. Yoon, S. K. Oh, C. M. Kim, Y. M. Cho

The Kaluza-Klein formalism of the Einstein&#39;s theory, based on the (2,2)-fibration of a generic 4-dimensional spacetime, describes general relativity as a Yang-Mills gauge theory on the 2-dimensional base manifold, where the local gauge symmetry is the group of the diffeomorphisms of the 2-dimensional fibre manifold. As a way of illustrating how to use th

Alex Kumjian, Paul S. Muhly, Jean N. Renault, Dana P. Williams

We define the Brauer group $\Br(G)$ of a locally compact groupoid $G$ to be the set of Morita equivalence classes of pairs $(\A,α)$ consisting of an elementary C*-bundle $\A$ over $G^{(0)}$ satisfying Fell&#39;s condition and an action $α$ of $G$ on $\A$ by $*$-isomorphisms. When $G$ is the transformation groupoid $X\times H$, then $\Br(G)$ is the equivarian

Siegfried Echterhoff, Dana P. Williams

Suppose that $G$ has a representation group $H$, that $G_{ab}:= G/\bar{[G,G]}$ is compactly generated, and that $A$ is a \cs-algebra for which the complete regularization of $\Prim(A)$ is a locally compact Hausdorff space $X$. In a previous article, we showed that there is a bijection $α\mapsto (Z_α,f_α)$ between the collection of exterior equivalence classe

Siegfried Echterhoff, Dana P. Williams

We make a detailed study of locally inner actions on C*-algebras whose primitive ideal spaces have locally compact Hausdorff complete regularizations. We suppose that $G$ has a representation group and compactly generated abelianization $G_{ab}$. Then if the complete regularization of $\Prim(A)$ is $X$, we show that the collection of exterior equivalence cla

Ruy Exel

We show that a Fell bundle B = {B_t}_{t \in F}, over an arbitrary free group F, is amenable, whenever it is orthogonal (in the sense that B_x^* B_y = 0, if x and y are distinct generators of F) and semi-saturated (in the sense that B_{ts} coincides with the closed linear span of B_t B_s, when the multiplication ``ts&#39;&#39; involves no cancelation).

Daniel W. Hone, Roland Ketzmerick, Walter Kohn

Quantum systems subject to time periodic fields of finite amplitude, lambda, have conventionally been handled either by low order perturbation theory, for lambda not too large, or by exact diagonalization within a finite basis of N states. An adiabatic limit, as lambda is switched on arbitrarily slowly, has been assumed. But the validity of these procedures

Yu. G. Gurevich, V. B. Yurchenko

A general description is given of a process of formation of an emf in a medium with nonequilibrium carriers. The appearance of anomalous emfs is predicted for several semiconductor structures. Such emfs appear as a result of photogeneration of the majority carriers or, for example, due to homogeneous heating of electrons and holes along the whole circuit. An

Yu. G. Gurevich, G. N. Logvinov, O. Yu. Titov

The flow of a thermoelectric current through a semiconductor of submicron dimensions is analyzed. The rate of surface relaxation of the energy is assumed to be much higher than the rate of electron-electron collisions. Under these conditions, it is incorrect to describe the electron gas by means of a Maxwellian distribution and thus to describe the thermoele

H. R. Shea, M. Tinkham

We report measurements of the dependence on magnetic field and array size of the resistive transition of Josephson junction arrays with long-range interaction. Because every wire in these arrays has a large number of nearest-neighbors (9 or 18 in our case), a mean-field theory should provide an excellent description of this system. Our data agree well with t

Yu. G. Gurevich, G. N. Logvinov, O. Yu. Titov

The symmetric part of the distribution of the electrons in a semiconductor submicron film, placed between a heater and refrigeration unit, is derived and analyzed. It is shown that, in general, it is of non-Fermi (non-Maxwellian) nature. A new mechanism is proposed to account for the non-Maxwellian form of the symmetric part of the distribution function. Thi

M. Takigawa, O. A. Starykh, A. W. Sandvik, R. R. P. Singh

The NMR relaxation data on Sr_2CuO_3 [Phys. Rev. Lett. 76, 4612 (1996)] are reexamined and compared with the analytic theory of the dynamic susceptibility in the S=1/2 antiferromagnetic Heisenberg chain including multiplicative logarithmic corrections [Phys. Rev. Lett. 78, 539 (1997); cond-mat/9610015]. Comparisons of the spin-lattice and the gaussian spin-e

Hajime Tanaka

Because of the isotropic and disordered nature of liquids, the anisotropy hidden in intermolecular interactions are often neglected. Accordingly, the order parameter describing a simple liquid has so far been believed to be only density. In contrast to this common sense, we propose that two order parameters, namely, density and bond order parameters, are req

Stefan Feldkemper, Werner Weber

Using a Rayleigh-Schrödinger perturbation expansion of multi-band Hubbard models, we present analytic expressions for the super-exchange coupling constants between magnetic transition metal ions of arbitrary separation in Mott-Hubbard insulators. The only restrictions are i) all ligand ions are closed shell anions and ii) all contributing interaction paths a

F. F. Assaad, M. Imada, D. J. Scalapino

To the Hubbard model on a square lattice we add an interaction, $W$, which depends upon the square of a near-neighbor hopping. We use zero temperature quantum Monte Carlo simulations on lattice sizes up to $16 \times 16$, to show that at half-filling and constant value of the Hubbard repulsion, the interaction $W$ triggers a quantum transition between an ant

G. E. Volovik

Superfluid phases of 3He are quantuim liquids with the interacting fermionic and bosonic fields. In many respects they can simulate the interacting quantum fields in the phyiscal vacuum. One can observe analogs of such phenomena as axial anomaly, vacuum polarization, zero-charge effect, fermionic charge of the vacuum, baryogenesis, ergoregion, vacuum instabi

M. Azuma, M. Takano, R. S. Eccleston

An inelastic neutron scattering study was performed on a Zn-substituted spin-1/2 Heisenberg 2-leg ladder compound Sr(Cu1-xZnx)2O3 (x < 0.04) to investigate nonmagnetic impurity effects on the quantum spin system with a large spin gap of about 400 K. The magnitude of the spin gap was found to be independent of Zn concentration, 33 meV, while the integrated ma

Nikolai Prokof&#39;ev, Boris Svistunov

We present the phase diagram of the system obtained by continuous-time worldline Monte Carlo simulations, and demonstrate that the actual phase diagram is in sharp contrast with that found in Phys. Rev. Lett., 76 (1996) 2937.

P. Lecheminant, B. Bernu, C. Lhuillier, L. Pierre

A group symmetry analysis of the low lying levels of the spin-1/2 kagomé Heisenberg antiferromagnet is performed for small samples up to N=27. This approach allows to follow the effect of quantum fluctuations when the sample size increases. The results contradict the scenario of ``order by disorder&#39;&#39; which has been advanced on the basis of large S ca

K. Schoutens

We propose a new method for investigating the exclusion statistics of quasi-particles in Conformal Field Theory (CFT) spectra. The method leads to one-particle distribution functions, which generalize the Fermi-Dirac distribution. For the simplest $su(n)$ invariant CFTs we find a generalization of Gentile parafermions, and we obtain new distributions for the

Ji-Min Duan, D. P. Arovas, L. J. Sham

In the Anderson lattice model for a mixed-valent system, the $d-f$ hybridization can possess a $p$-wave symmetry. The strongly-correlated insulating phase in the mean-field approximation is shown to be a $p$-wave Bose condensate of excitons with a spontaneous lattice deformation. We study the equilibrium and linear response properties across the insulator-me

Michael Collins

In this paper we first propose a new statistical parsing model, which is a generative model of lexicalised context-free grammar. We then extend the model to include a probabilistic treatment of both subcategorisation and wh-movement. Results on Wall Street Journal text show that the parser performs at 88.1/87.5% constituent precision/recall, an average impro

Carolyn Penstien Rose&#39;, Alon Lavie

Although Minimum Distance Parsing (MDP) offers a theoretically attractive solution to the problem of extragrammaticality, it is often computationally infeasible in large scale practical applications. In this paper we present an alternative approach where the labor is distributed between a more restrictive partial parser and a repair module. Though two stage

Paul B. Eskridge, Raymond E. White, III

We have analysed archival ROSAT PSPC and Einstein HRI data for the x-ray point source in the bar of NGC 6822. The source decreased in x-ray flux by at least half an order of magnitude in the 13 years between the HRI and PSPC observations. It has a PSPC flux of f_X = 8 x 10E-14 erg/cm^2/s, giving L_X = 2.4 x 10E36 erg/s for a distance of 500 kpc. The source a

Arkadiusz Olech

We report CCD observations of the dwarf nova V485~Cen during its 1997 superoutburst. The long lasting outburst with characteristic slope, brightness dip and presence of clear superhumps give evidence that V485 Cen belongs to the group of SU UMa-type variables. The superhump period is equal to 0.042156 +/- 0.000004 d (60.7 min). Thus V485 Cen has the shortest

Gerhardt R. Meurer

Our recent work on starbursts, particularly in the ultraviolet (UV), is summarized. The intrinsic UV fluxes of UV selected starbursts can be derived from UV data alone because, to first order, their dust behaves like a foreground screen. This allows a comparison of the bolometric effective surface brightness S_e of UV selected starbursts to other starburst s

J. H. Buckley, P. J. Boyle, S. M. Bradbury, A. M. Burdett

The ~70 unidentified sources of the EGRET sky survey may be one of its most important legacies. The identification of these sources at other wavelengths is critical to understanding their nature. Many have flat spectra out to 10 GeV which, if extrapolated to TeV energies, would be easily detectable relative to the steeply falling diffuse background. The Whip

Paolo Padoan, AAke Nordlund

Supersonic random motions are observed in dark clouds and are traditionally interpreted as Alfvén waves, but the possibility that these motions are super-Alfvenic has not been ruled out. In this work we report the results of numerical experiments in two opposite regimes: beta ~1 and beta << 1, where beta is the ratio of gas pressure and magnetic pressure: be

Katsuyo Thornton, Michael Gaudlitz, Hans-Thomas Janka, Matthias Steinmetz

We present the results of numerical studies of supernova remnant evolution and their effects on galactic and globular cluster evolution. We show that parameters such as the density and the metallicity of the environment significantly influence the evolution of the remnant, and thus change its effects on the global environment (e.g., globular clusters, galaxi

Joshua S. Bloom, Steinn Sigurdsson, Ralph A. M. J. Wijers, Omar Almaini

A recent spectrum of the optical afterglow of GRB 970508 suggests that gamma-ray bursts (GRBs) are cosmological in origin and it is of crucial importance to derive an accurate distance to each burst. If GRBs occur near their host galaxies then Lyman limit absorption should be observable in roughly half the GRB afterglow spectra. Here we outline the methodolo

Alan B. Whiting, Mike J. Irwin, George K. T. Hau

We report the discovery of new member of the Local Group in the constellation of Antlia. Optically the system appears to be a typical dwarf spheroidal galaxy of type dE3.5 with no apparent young blue stars or unusual features. A color-magnitude diagram in I, V-I shows the tip of the red giant branch, giving a distance modulus of 25.3 +/- 0.2 (1.15 Mpc +/- 0.

Amir Levinson, Maurice H. P. M. van Putten

We study the formation, evolution and structure of dissipative fronts produced by overtaking collisions of relativistic streams, with emphasis on strongly magnetized flows. The evolution of the system is followed using analytical approach in the simple wave regime and numerical simulations in the non-simple wave regime, until a steady-state is reached. The s

S. D. Vrtilek, B. Boroson, F. H. Cheng, R. McCray

We present first results from simultaneous ultraviolet (UV; HST/GHRS) and X-ray (ASCA) observations of the 13.5s pulsar LMC X-4 taken in 1996 May. The GHRS data are the highest resolution (both temporal and spectral) UV spectra ever taken of LMC X-4. Fits to the UV continuum using a model that incorporates X-ray heating of the companion star and the accretio

Tomislav Kundic, David W. Hogg, Roger D. Blandford, Judith G. Cohen

In a number of multiply imaged quasar systems, a significant contribution to the lensing potential is provided by groups and clusters of galaxies associated with the primary lens. As part of an ongoing effort to gather observational data on these systems, we present spectroscopy and near-infrared and optical photometry of galaxies in the field of the quadrup

V. Maillot

En nous appuyant sur une construction due à Bedford et Taylor, et certains résultats récents de Demailly, nous présentons une extension (partielle) de la géométrie d&#39;Arakelov aux fibrés en droites intégrables. (Ces derniers sont les fibrés en droites hermitiens sur une variété arithmétique $X$ pouvant se décomposer sous la forme $\ov{E} = \ov{E}_{1}\otim

M. J. Duff, J. M. Evans, R. R. Khuri, J. X. Lu

We generalize the supermembrane solution of D=11 supergravity by permitting the 4-form $G$ to be either self-dual or anti-self-dual in the eight dimensions transverse to the membrane. After analyzing the supergravity field equations directly, and also discussing necessary conditions for unbroken supersymmetry, we focus on two specific, related solutions. The