June 1997 arXiv papers — page 10

Tamas G. Kovacs, Zsolt Schram

We used a renormalisation group based smoothing to address two questions related to abelian dominance. Smoothing drastically reduces short distance fluctuations but it preserves the long distance physical properties of the SU(2) configurations. This enabled us to extract the abelian heavy-quark potential from time-like Wilson loops on Polyakov gauge projecte

A. H. Bougourzi

In this paper, we present a detailed analysis of the diagonalization of the higher spin Heisenberg model using its quantum affine symmetry $U_q(\hat{sl(2)})$. In particular, we describe the bosonizations of the latter algebra, its highest weight representations, vertex operators and screening operators. Finally, we use this bosonization method to compute the

Wolfgang Poeschl, Dario Vretenar, Peter Ring

A C++ code for the solution of the relativistic Hartree-Bogoliubov theory in coordinate space is presented. The theory describes a nucleus as a relativistic system of baryons and mesons. The RHB model is applied in the self-consistent mean-field approximation to the description of ground state properties of spherical nuclei. Finite range interactions are inc

Sangmin Lee, Soo-Jong Rey

Inclusive absorption cross section of fundamental IIB string to D-string is calculated perturbatively. The leading order result agrees with estimate based on stringy Higgs mechanism via Cremmer-Scherk coupling. It is argued that the subleading order correction is dominated by purely planar diagrams in the large mass limit. The correction represents conversio

Alexander Ushveridze

A new class of completely integrable models is constructed. These models are deformations of the famous integrable and exactly solvable Gaudin models. In contrast with the latter, they are quasi-exactly solvable, i.e. admit the algebraic Bethe ansatz solution only for some limited parts of the spectrum. An underlying algebra responsible for both the phenomen

Hongsu Kim

Classical solutions of the self-interacting, non-abelian antisymmetric tensor gauge theory of Freedman and Townsend coupled to Einstein gravity is discussed. Particularly, it is demonstrated that the theory admits a classical metric solution which, depending on the value of the gauge coupling parameter of the theory, exhibits a black hole with an exotic non-

A. Restuccia, R. Torrealba

Families of solutions to the field equations of the covariant BRST invariant effective action of the membrane theory are constructed. The equations are discussed in a double dimensional reduction, they lead to a nonlinear equation for a one dimensional extended object. One family of solutions of these equations are solitary waves with several properties of s

L. Ya. Glozman

An implication of the spontaneous chiral symmetry breaking in QCD is that at low energy and resolution there appear quasiparticles - constituent quarks and Goldstone bosons. Thus, light and strange baryons should be considered as systems of three constituent quarks with confining interaction and a chiral interaction that is mediated by Goldstone bosons betwe

Sushan Konar, Avijit Kumar Ganguly

The transport properties of the quark-gluon plasma is important both from the point of view of the astrophysical systems and the heavy ion collisions. Therefore, accurate calculations of the elastic scattering cross-sections of $qq' \to qq'$ and $ q\qbar' \to q\qbar'$ processes are required. At the tree-diagram level exchange of massless gluo

Hongsu Kim

It has recently been argued that non-trivial Brans-Dicke black hole solutions different from the usual Schwarzschild solution could exist. We attemt here to ``censor'' these non-trivial Brans-Dicke black hole solutions by examining their thermodynamic properties. Quantities like Hawking temperature and entropy of the black holes are computed. Analysi

Y. J. Uemura

Combining (1) the universal correlations between $T_{c}$ and $n_{s}/m^{*}$ (superconducting carrier density / effective mass) and (2) the pseudo-gap behavior in the underdoped region, we obtain a picture to describe superconductivity in cuprate systems in evolution from Bose-Einstein to BCS condensation. Overdoped and Zn-substituted cuprate systems show sign

Abhijit Kar Gupta, Asok K. Sen

We study dielectric breakdown in a semi-classical bond percolation model for nonlinear composite materials introduced by us and the related breakdown exponent near the percolation threshold in two dimensions. The breakdown exponent after doing finite size scaling analysis is found to be $t_B \simeq$ 1.42. We discuss in detail the differences in our model fro

A. Burrows

Though it is agreed that the post-bounce, pre-explosion cores of massive stars are unstable to transonic, Rayleigh-Taylor-like instabilities, the role convective motions may play in igniting the supernova explosion itself is not yet clear. Whatever that role, the morphology and nucleosynthetic yields of the explosion, the recoil of the protoneutron star, the

S. Katz, P. Mayr, C. Vafa

Using geometric engineering in the context of type II strings, we obtain exact solutions for the moduli space of the Coulomb branch of all N=2 gauge theories in four dimensions involving products of SU gauge groups with arbitrary number of bi-fundamental matter for chosen pairs, as well as an arbitrary number of fundamental matter for each factor. Asymptotic

Edward Witten

A brane configuration is described that is relevant to understanding the dynamics of N=1 supersymmetric Yang-Mills theory. Confinement and spontaneous breaking of a discrete chiral symmetry can be understood as consequences of the topology of the brane. Because of the symmetry breaking, there can be domain walls separating different vacua; the QCD string can

Astrid Orr, S. Molendi, F. Fiore, P. Grandi

We report on soft X-ray observations of the Seyfert 1 galaxy MCG-6-30-15 with the Low and Medium Energy Concentrator Spectrometers on board BeppoSAX. The time averaged 0.1-4 keV spectrum shows evidence for a complex warm absorber. K-edges of highly ionized oxygen (O vii and O viii) can only partly describe the soft X-ray spectrum below 2 keV. A spectral vari

Christoph J. Halboth, Walter Metzner

We show that the spectral function for single-particle excitations in a two-dimensional Fermi liquid has Lorentzian shape in the low energy limit. Landau quasi-particles have a uniquely defined spectral weight and a decay rate which is much smaller than the quasi-particle energy. By contrast, perturbation theory and the T-matrix approximation yield spurious

M. Lagerholm, C. Peterson, B. Söderberg

A statistical analysis is performed for a random unrestricted local crew scheduling problem, expressed in terms of pairing arrivals with departures. The analysis is aimed at understanding the structure of similar problems with global restrictions, and estimating their difficulty. The methods developed are of a general nature and can be of use in other proble

Gregory Brown, Per Arne Rikvold, Mark Sutton, Martin Grant

The statistical properties of coherent radiation scattered from phase-ordering materials are studied in detail using large-scale computer simulations and analytic arguments. Specifically, we consider a two-dimensional model with a nonconserved, scalar order parameter (Model A), quenched through an order-disorder transition into the two-phase regime. For such

Lov K. Grover

Quantum mechanics can speed up a range of search applications over unsorted data. For example imagine a phone directory containing N names arranged in completely random order. To find someone's phone number with a probability of 50%, any classical algorithm (whether deterministic or probabilistic) will need to access the database a minimum of O(N) times. Qua

A. Feinstein, J. Ibáñez, R. Lazkoz

We construct exact solutions to Einstein equations which represent relativistic disks immersed into an expanding FRW Universe. It is shown that the expansion influences dynamical characteristics of the disks such as rotational curves, surface mass density, etc. The effects of the expansion is exemplified with non-static generalizations of Kuzmin-Curzon and g

A. Angelow

The quantum optical problem of the propagation of electromagnetic waves in a nonlinear waveguide is related to the solutions of the classical nonstationary harmonic oscillator using the method of linear integrals of motion [ Malkin et.al., Phys Rev. 2D (1970) p.1371 ]. An explicit solution of the classical oscillator with a varying frequency, corresponding t

Angel Ballesteros, Francisco J. Herranz, Preeti Parashar

A non-standard quantum deformation of the two-photon algebra $h_6$ is constructed, and its quantum universal R-matrix is given. Representations of this new quantum algebra are studied on the Fock space and translated into Fock-Bargmann realizations that provide a direct formalism for the definition of deformed states of light. Finally, the isomorphism betwee

Priyamvada Natarajan, Jean-Paul Kneib, Ian Smail, Richard S. Ellis

We present a new wide field image of the distant cluster AC114 ($z=0.31$) obtained with Wide Field and Planetary Camera II onboard the Hubble Space Telescope. This image considerably extends our knowledge of the lensing properties of the cluster beyond those derived by Smail \et (1995a) from a single WF/PC-1 pointing. In conjunction with published ground-bas

Miguel Navarro

The symmetries of generic 2D dilaton models of gravity with (and without) matter are studied in some detail. It is shown that $δ_2$, one of the symmetries of the matterless models, can be generalized to the case where matter fields of any kind are present. The general (classical) solution for some of these models, in particular those coupled to chiral matter

Brian Chaboyer, P. Demarque, Peter J. Kernan, Lawrence M. Krauss

We review five independent techniques which are used to set the distance scale to globular clusters, including subdwarf main sequence fitting utilizing the recent Hipparcos parallax catalogue. These data together all indicate that globular clusters are farther away than previously believed, implying a reduction in age estimates. This new distance scale estim

M. K. Volkov, E. A. Kuraev, D. Blaschke, G. Roepke

The photon pair production by pion annihilation in a hot and dense medium at the chiral phase transition is investigated within a chiral quark model. As a direct consequence of this transition the $σ$ meson appears as a bound state in the domain of temperatures and chemical potentials where the condition $M_σ(T,μ) \approx 2 M_π(T,μ)$ is fulfilled. This effec

Dongsu Bak, Hyuk-jae Lee

The moduli space dynamics of vortices in the Jackiw-Pi model where a non-relativistic Schrodinger field couples minimally to Chern-Simons gauge field, is considered. It is shown that the difficulties in direct application of Manton's method to obtain a moduli-space metric in the first order system can be circumvented by turning the Lagrangian into a seco

Borge Nodland, John P. Ralston

Recently, J. P. Leahy commented (astro-ph/9704285) on the indication of anisotropy in the propagation of radio waves over cosmological distances, published by Nodland and Ralston (B. Nodland and J. P. Ralston, Phys. Rev. Lett. 78, 3043 (1997); astro-ph/9704196). Unfortunately, Leahy ignores the need for a statistical comparison, egregiously selects data, com

Doug Beeferman, Adam Berger, John Lafferty

This paper introduces new methods based on exponential families for modeling the correlations between words in text and speech. While previous work assumed the effects of word co-occurrence statistics to be constant over a window of several hundred words, we show that their influence is nonstationary on a much smaller time scale. Empirical data drawn from En

Adrian P. Gentle, Warner A. Miller

We describe the first discrete-time 4-dimensional numerical application of Regge calculus. The spacetime is represented as a complex of 4-dimensional simplices, and the geometry interior to each 4-simplex is flat Minkowski spacetime. This simplicial spacetime is constructed so as to be foliated with a one parameter family of spacelike hypersurfaces built of

Iwana Inukai, Masaharu Tanabashi, Koichi Yamawaki

We propose a top quark condensate scenario embedded in grand unified theories (GUTs), stressing that the gauged Nambu-Jona-Lasinio model has a nontrivial continuum limit (``renormalizability'') under certain condition which is actually satisfied in all sensible GUTs with simple group. The top quark mass prediction in this scenario is shown to be inse

J. I. Cirac, M. Lewenstein, K. Moelmer, P. Zoller

We propose a scheme to create a macroscopic ``Schödinger cat'' state formed by two interacting Bose condensates. In analogy with quantum optics, where the control and engineering of quantum states can be maintained to a large extend, we consider the present scheme to be an example of quantum atom optics at work.

F. Benatti, R. Floreanini

We study the modified dynamical evolution of the neutral kaon system under the condition of complete positivity. The accuracy of the data from planned future experiments is expected to be sufficiently precise to test such a hypothesis.

N. Lütkenhaus, J. I. Cirac, P. Zoller

The interaction of an atomic two-level system and a squeezed vacuum leads to interesting novel effects in atomic dynamics, including line narrowing in resonance fluorescence and absorption spectra, and a suppressed (enhanced) decay of the in-phase and out-of phase component of the atomic polarization. On the experimental side these predictions have so far el

Dorje C. Brody, Lane P. Hughston

A novel geometric formalism for statistical estimation is applied here to the canonical distribution of classical statistical mechanics. In this scheme thermodynamic states, or equivalently, statistical mechanical states, can be characterised concisely in terms of the geometry of a submanifold ${\cal M}$ of the unit sphere ${\cal S}$ in a real Hilbert space

D. A. Trifonov

Overcomplete families of states of the type of Barut-Girardello coherent states (BG CS) are constructed for noncompact algebras $u(p,q)$ and $sp(N,C)$ in quadratic bosonic representation. The $sp(N,C)$ BG CS are obtained in the form of multimode ordinary Schrödinger cat states. A set of such macroscopic superpositions is pointed out which is overcomplete in

Masanao Ozawa

An operational approach to quantum state reduction, the state change of the measured system caused by a measurement of an observable conditional upon the outcome of measurement, is founded without assuming the projection postulate in any stages of the measuring process. Whereas the conventional formula assumes that the probe measurement satisfies the project

D. V. Averin

We propose a new variant of the controlled-NOT quantum logic gate based on adiabatic level-crossing dynamics of the q-bits. The gate has a natural implementation in terms of the Cooper pair transport in arrays of small Josephson tunnel junctions. An important advantage of the adiabatic approach is that the gate dynamics is insensitive to the unavoidable spre

J. Avan, L. Frappat, M. Rossi, P. Sorba

We construct operators t(z) in the elliptic algebra introduced by Foda et al. ${\cal A}_{q,p}({\hat sl}(2)_c)$. They close an exchange algebra when p^m=q^{c+2} for m integer. In addition they commute when p=q^{2k} for k integer non-zero, and they belong to the center of ${\cal A}_{q,p}({\hat sl}(2)_c)$ when k is odd. The Poisson structures obtained for t(z)

A. Aguado, A. Ayuela, J. M. Lopez, J. A. Alonso

A systematic theoretical study of stoichiometric clusters (NaI)n up to n=15 is performed using the ab initio Perturbed-Ion (PI) model. The structures obtained are compared to previous pair potential results, and observed differences between (NaI)n clusters and previous ab initio results for other alkali halide clusters are discussed. (NaI)n clusters with n u

J. A. Acebron, L. L. Bonilla

A two-time scale asymptotic method has been introduced to analyze the multimodal mean-field Kuramoto-Sakaguchi model of oscillator synchronization in the high-frequency limit. The method allows to uncouple the probability density in different components corresponding to the different peaks of the oscillator frequency distribution. Each component evolves towa

S. Ulrych, H. Müther

The Dirac structure of the nucleon self-energy in asymmetric nuclear matter cannot reliably be deduced from the momentum dependence of the single-particle energies. It is demonstrated that such attempts yield an isospin dependence with even a wrong sign. Relativistic studies of finite nuclei have been based on such studies of asymmetric nuclear matter. The e

LSND Collaboration, C. Athanassopoulos, L. B. Auerbach, R. L. Burman

A search for nu_mu -> nu_e oscillations has been conducted at the Los Alamos Meson Physics Facility using nu_mu from pi^+ decay in flight. An excess in the number of beam-related events from the C(nu_e,e^-)X inclusive reaction is observed. The excess is too large to be explained by normal nu_e contamination in the beam at a confidence level greater than 99%.

Richard Grimm, Maximilian Hasler, Carl Herrmann

We present a new, alternative interpretation of the vector-tensor multiplet as a 2-form in central charge superspace. This approach provides a geometric description of the (non-trivial) central charge transformations ab initio and is naturally generalized to include couplings of Chern-Simons forms to the antisymmetric tensor gauge field, giving rise to a N=2

Fedele Lizzi, Richard J. Szabo

The structure of spacetime duality and discrete worldsheet symmetries of compactified string theory is examined within the framework of noncommutative geometry. The full noncommutative string spacetime is constructed using the Frohlich-Gawedzki spectral triple which incorporates the vertex operator algebra of the string theory. The duality group appears natu

M. N. Stoilov

It is shown that in some cases higher (covariant) derivative regularization for spinor field is equivalent to the gauge invariant Pauli-Villars one.

Lionel Carminati, Bruno Iochum, Thomas Schucker

Connes' view at Yang-Mills theories is reviewed with special emphasis on the gauge invariant scalar product. This landscape is shown to contain Chamseddine and Connes' noncommutative extension of general relativity restricted to flat space-time, if the top mass is between 172 and 204 GeV. Then the Higgs mass is between 188 and 201 GeV.

A. K. Chaudhuri

We have explored the possibility that the universe at very early stage was dominated by (macroscopic) heterotic strings. We have found that the dimensionless parameter $Gμ$ for the heterotic strings varies from $10^{-2}$ to $10^{-4}$ as the universe evolve from the matter dominance to radiation dominance. This led to the interesting consequence of epoch depe

R. L. P. G. Amaral, L. V. Belvedere, K. D. Rothe, F. G. Scholtz

We analyse the BRST constraints and corresponding Hilbert-space structure of chiral QCD$_2$ in the decoupled formulation for the case of the Jackiw-Rajaraman parameter $a=2$. We show that despite formal similarities this theory is not equivalent to QCD$_2$, and that its extension to U(N) does not lead to an infinite vacuum degeneracy.

Spencer Klein, Evan Scannapieco

The Relativistic Heavy Ion Collider (RHIC) will be the first heavy ion accelerator energetic enough to produce hadronic final states via coherent \gamgam, \gampom, and \pompom interactions. Because the photon flux scales as $Z^2$, up to an energy of about $γ\hbar c/R\approx 3$ GeV/c, the \gamgam\ interaction rates are large. RHIC $γP$ interactions test how P

Dieter Zeppenfeld

Effective $eeqq$ contact interactions can enhance event rates in $e^+p$ scattering at HERA at high $Q^2$. Present constraints from atomic parity violation measurements and from Drell Yan events at the Tevatron are discussed.

Edmond L. Berger, Harry Contopanagos

We discuss the motivation for resummation of the effects of initial-state soft-gluon radiation, to all orders in the strong coupling strength, for processes in which the near-threshold region in the partonic subenergy is important. We summarize our calculation of the total cross section for top quark production at hadron colliders. Comments are included on t

L. E. Gordon

The cross section for photoproduction of a prompt photon in association with a jet is studied in Next-to-Leading Order at the DESY $ep$ collider HERA. The effect of various cuts imposed on the cross section by the ZEUS collaboration including isolation cuts on the photon is examined. Comparisons with the ZEUS preliminary data using various parametrizations o

W. Buchmueller, A. Hebecker, M. F. McDermott

The diffractive production of high-$p_{\perp}$ jets in deep-inelastic scattering is studied in the semiclassical approach. The $p_{\perp}$-spectra of $q {\bar q}$ and $q {\bar q} g$ diffractive final states are found to be qualitatively different. For $q {\bar q}$ final states, which are produced by `hard' colour-singlet exchange, the $p_{\perp}$-spectru

O. Benhar, S. Fantoni, G. I. Lykasov, N. V. Slavin

Deep inelastic scattering of leptons off nuclear targets is analized within the convolution model taking into account nucleon-nucleon correlations. We show that in the nuclear medium nucleons are distributed according to a function that exhibits a sizeable Q**2-dependence and reduces to the ordinary light-cone distribution in the Bjorken limit. At Q**2 < 50

Yoav Achiman, Susanne Bielefeld

RH rotations of the fermionic mass matrices are not observable in the standard model, but dictate the details of the proton decay in GUTs. $P_{LR}$ symmetry in the two light families leads to a full RH mixing. We give two versions of suitable broken $P_{LR}$ invariant SO(10) which leads to nucleon decay modes similar to those of SUSY-GUTs with rates in the r

T. Gehrmann

A summary of new experimental results and recent theoretical developments presented in the ``Spin Physics&#39;&#39; working group is given.

L. Houra-Yaou, P. Kessler, J. Parisi, F. Murgia

We present an approach that generalizes in a natural way the perturbative QCD formalism developed by Brodsky and Lepage for the study of exclusive hadronic processes to the case of $L\neq 0$ mesons. As an application of our approach we consider here the production of meson pairs, involving tensor and pseudotensor mesons, in photon-photon collisions.

S. M. H. Wong

The dependence of the equilibration of the parton plasma on the value of the strong coupling is studied in Au+Au collisions at LHC and at RHIC energies. With increasing coupling, the following are found to happen: 1) both thermal and chemical equilibration speed up, 2) in the final degree of equilibration, only quarks and antiquarks show obvious improvements

A. L. Ayala Filho, M. B. Gay Ducati, E. M. Levin

In this paper we re-analyse the situation with the shadowing corrections (SC) in QCD for the proton deep inelastic structure functions. We reconsider the Glauber - Mueller approach for the SC in deep inelastic scattering (DIS) and suggest a new nonlinear evolution equation. We argue that this equation solves the problem of the SC in the wide kinematic region

Adrian Patrascioiu, Erhard Seiler

We report the results of a Monte Carlo study of the continuum limit of the two dimensional O(3) non-linear $σ$ model. The notable finding is that it agrees very well with both the prediction inspired by Zamolodchikovs&#39; S-matrix ansatz and with the continuum limit of the dodecahedron spin model. The latter finding renders the existence of asymptotic freed

ALEPH Collaboration

A search for pair-production of long-lived, heavy, singly-charged particles has been performed with data collected by the ALEPH detector at a centre-of-mass energy of 172 GeV. Data at \sqrt{s} = 161, 136, and 130 GeV are also included to improve the sensitivity to lower masses. No candidate is found in the data. A model-independent 95% confidence level upper

V. K. Shchigolev, V. M. Zhuravlev, S. V. Chervon

Exact solutions corresponding to spherically symmetric inhomogeneous nonstationary Tolman metrics are obtained for the self-consistent

Pawel Nurowski

Given a conformally nonflat Einstein spacetime we define a fibration $P$ over it. The fibres of this fibration are elliptic curves (2-dimensional tori) or their degenerate counterparts. Their topology depends on the algebraic type of the Weyl tensor of the Einstein metric. The fibration $P$ is a double branched cover of the bundle of null direction over the

Pawel Nurowski

We define a certain differential system on an open set of $R^6$. The system locally defines a Lorentzian 4-manifold satisfying the Einstein equations. The converse statement is indicated and its details are postponed to the furthcoming paper.

Jean-Pierre De Villiers

Cosmic strings are topological defects thought to have formed early in the life of the universe. If such objects exist, a study of their interaction with black holes is of interest. The equations of motion of a cosmic string have the form of highly non-linear wave equations. General analytic solutions, except for motion in certain backgrounds such as flat an

J. A. Smoller, A. G. Wasserman

We prove that any asymptotically flat solution to the spherically symmetric SU(2) Einstein-Yang/Mills equations is globally defined. This result applies in particular to the interior of colored black holes.

R. Loll

The volume operator plays a central role in both the kinematics and dynamics of canonical approaches to quantum gravity which are based on algebras of generalized Wilson loops. We introduce a method for simplifying its spectral analysis, for quantum states that can be realized on a cubic three-dimensional lattice. This involves a decomposition of Hilbert spa

M. Gasperini

The decay of the string perturbative vacuum into our present cosmological state is associated to the transition from a phase of growing curvature and growing dilaton, to a phase of decreasing curvature and frozen dilaton. The possible approaches to a classical and quantum description of such a transition are introduced and briefly discussed.

A. Zheludev, S. Maslov, G. Shirane, Y. Sasago

We report an observation of a commensurate-incommensurate phase transition in the Dzyaloshinskii-Moriya spiral antiferromagnet Ba_2 Cu Ge_2 O_7. The transition is induced by an external magnetic field applied along the c-axis of the tetragonal structure, i. e., in the plane of spin rotation. Bulk magnetic measurements and neutron diffraction experiments show

T. Startseva, T. Timusk, A. V. Puchkov, D. N. Basov

The ab plane optical spectra of two single crystals of La(2-x)Sr(x)Cu(4), one overdoped and one underdoped, were investigated. We observe a gap-like depression of the effective scattering rate below 700 cm(-1) in both systems. This feature persists up to 300 K in the underdoped sample with the concentration of Sr x=0.14 but loses prominance at temperatures a

P. Orellana, E. Anda, F. Claro

We show that the addition of a magnetic field parallel to the current induces self sustained intrinsic current oscillations in an asymmetric double barrier structure. The oscillations are attributed to the nonlinear dynamic coupling of the current to the charge trapped in the well, and the effect of the external field over the local density of states across

M. Lagerholm, C. Peterson, B. Söderberg

A novel method is presented and explored within the framework of Potts neural networks for solving optimization problems with a non-trivial topology, with the airline crew scheduling problem as a target application. The key ingredient to handle the topological complications is a propagator defined in terms of Potts neurons. The approach is tested on artifici

D. M. Gaitonde, T. V. Ramakrishnan

We present here a calculation of the inertial mass of a moving vortex in cuprate superconductors. This is a poorly known basic quantity of obvious interest in vortex dynamics. The motion of a vortex causes a dipolar density distortion and an associated electric field which is screened. The energy cost of the density distortion as well as the related screened

G. Chaboussant, M. -H. Julien, Y. Fagot-Revurat, L. P. Levy

The proton hyperfine shift K and NMR relaxation rate $1/T_1$ have been measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap $Δ\simeq J_\perp-J_\parallel$ in this strongly coupled ladder ($J_\parallel < J_\perp$) is supported by the K and $1/T_1$ results. By comparing $1/T_1$ at tw

U. E. Volmar, U. Weber, R. Houbertz, U. Hartmann

Monte Carlo simulations and an analytical approach within the framework of a semiclassical model are presented which permit the determination of Coulomb blockade and single electron charging effects for multiple tunnel junctions coupled in series. The Coulomb gap in the I(V) curves can be expressed as a simple function of the capacitances in the series. Furt

J. Abad, M. Ríos

The general expression for the local matrix $t(θ)$ of a quantum chain with the site space in any representation of su(3) is obtained. This is made by generalizing $t(θ)$ from the fundamental representation and imposing the fulfillment of the Yang-Baxter equation. Then, a non-homogeneous spin chain combining different representations of su(3) is solved by dev

M. Yu. Kuchiev, P. V. Shevchenko, O. P. Sushkov

We consider the implications of the small Fermi surface for the ab-plane microwave absorption. The small Fermi surface results in two superconducting condensates. Linear combinations of these condensates correspond to the d- and g-wave pairings. Microwave electric field applied in the ab-plane induces Josephson transitions between the condensates. Dependence

Shinji Watanabe, Yoshio Kuramoto

A new kind of phase transition is proposed for lattice fermion systems with simplified f^2 configurations at each site. The free energy of the model is computed in the mean-field approximation for both the itinerant state with the Kondo screening, and a localized state with the crystalline electric field (CEF) singlet at each site. The presence of a first-or

Hideaki Ujino

The Calogero model is a one-dimensional quantum integrable system with inverse-square long-range interactions confined in an external harmonic well. It shares the same algebraic structure with the Sutherland model, which is also a one-dimensional quantum integrable system with inverse-sine-square interactions. Inspired by the Rodrigues formula for the Jack p

Ya. B. Bazaliy, B. A. Jones, Shou-Cheng Zhang

We derive a continuum equation for the magnetization of a conducting ferromagnet in the presence of a spin-polarized current. Current effects enter in the form of a topological term in the Landau-Lifshitz equation . In the stationary situation the problem maps onto the motion of a classical charged particle in the field of a magnetic monopole. The spatial de

Marilyn Walker, Donald Hindle, Jeanne Fromer, Giuseppe Di Fabbrizio

This paper reports experimental results comparing a mixed-initiative to a system-initiative dialog strategy in the context of a personal voice email agent. To independently test the effects of dialog strategy and user expertise, users interact with either the system-initiative or the mixed-initiative agent to perform three successive tasks which are identica

Victor S. L&#39;vov, Evgenii Podivilov, Itamar Procaccia

The phenomenology of the scaling behavior of higher order structure functions of velocity differences across a scale $R$ in turbulence should be built around the irreducible representations of the rotation symmetry group. Every irreducible representation is associated with a scalar function of $R$ which may exhibit different scaling exponents. The common pra

M. Catanese, P. J. Boyle, J. H. Buckley, A. M. Burdett

Two active galactic nuclei have been detected at TeV energies using the atmospheric Cherenkov imaging technique. The Whipple Observatory gamma-ray telescope has been used to observe all the BL Lacertae objects in the northern hemisphere out to a redshift of 0.1. We report the tentative detection of VHE emission from a third BL Lac object, 1ES 2344+514. Progr

E. Kuulkers, A. N. Parmar, S. Kitamoto, L. R. Cominsky

We present data from different epochs in 1978, 1987-1991 and 1996 from the black-hole candidate 4U1630-47. For the first time we present almost complete coverage of the outbursts which started in 1987, 1988 and 1996. We find that the outburst behaviour of 4U1630-47 is more complex than previously realized. The source shows outbursts with durations on the ord

Ronald E. Taam, Xingming Chen, Jean H. Swank

The light curves of GRS 1915+105 observed with RXTE on October 15, 1996 reveal a wide range of transient activity including regular bursts with a recurrence time of about 1 minute, irregular bursts, and dips. In contrast to bursts from other sources, a secondary (and a tertiary) weaker burst immediately following the primary burst are observed. Detailed ener

P. J. Boyle, J. H. Buckley, A. M. Burdett, J. Bussons Gordo

Based on BACODINE network notification the Whipple Observatory gamma-ray telescope has been used to search for the delayed TeV counterpart to BATSE-detected gamma-ray bursts. In the fast slew mode, any point in the sky can be reached within two minutes of the burst notification. The search strategy, necessary because of the uncertainty in burst position and

R. W. Lessard, P. J. Boyle, S. M. Bradbury, J. H. Buckley

If supernova remnants (SNRs) are the sites of cosmic-ray acceleration, the associated nuclear interactions should result in observable fluxes of TeV gamma-rays from the nearest SNRs. Measurements of the gamma-ray flux from six nearby, radio-bright, SNRs have been made with the Whipple Observatory gamma-ray telescope. No significant emission has been detected

Paul P. van der Werf

Surveys of redshifted emission lines in the near-infrared will provide unique information on the cosmic star formation history. Near-infrared Halpha surveys will probe the cosmic star formation density and the evolution of the luminosity function of star forming galaxies out to z\sim2.5, including the important z=1.5-2.0 epoch, where according to current kno

Pedro M. Rodriguez-Pascual, J. Miguel Mas-Hesse, Maria Santos-Lleo

We have analyzed new and archival IUE observations of narrow-line Seyfert 1 galaxies (NLS1) in order to revise the ultraviolet (UV) properties of this sub-group of Active Galactic Nuclei (AGN). We have found broad wings in the strongest UV emission lines, ruling out the hypothesis that there is no broad line emission region in this type of objects. Since the

J. E. McEnery, I. H. Bond, P. J. Boyle, S. M. Bradbury

Markarian 421 was the first extragalactic source to be detected with high statistical certainty at TeV energies. The Whipple Observatory gamma-ray telescope has been used to observe the Active Galactic Nucleus, Markarian 421 in 1996 and 1997. The rapid variability observed in TeV gamma rays in previous years is confirmed. Doubling times as short as 15 minute

Ansar Fayyazuddin, Michael Spalinski

The form of the Seiberg-Witten differential is derived from the M-theory approach to N=2 supersymmetric Yang-Mills theories by directly imposing the BPS condition for twobranes ending on fivebranes. The BPS condition also implies that the pullback of the Kahler form onto the space part of the twobrane world-volume vanishes.

Steven S. Gubser

The absorption of photons and fermions into four-dimensional black holes is described by equations which in certain cases can be analyzed using dyadic index techniques. The resulting absorption cross-sections for near-extremal black holes have a form at low energies suggestive of the effective string model. A coupling to the effective string is proposed for

T. Plewa, J. Ma. Marti, E. Mueller, M. Rozyczka

We present simulations of relativistic jets propagating in a nonuniform medium. Specifically, we study the bending of jets propagating obliquely to the vector of the density-gradient. Our results are applied to the NGC 4258, where such a medium is assumed to be provided by the atmosphere of the sub-parsec accretion disk tilted with respect to the original di

Paul Thompson, Christopher C. Dozier

The main application of name searching has been name matching in a database of names. This paper discusses a different application: improving information retrieval through name recognition. It investigates name recognition accuracy, and the effect on retrieval performance of indexing and searching personal names differently from non-name terms in the context

Giuseppe Albertini

The transition from the ordered commensurate phase to the incommensurate gaussian phase of the antiferroelectric asymmetric six-vertex model is investigated by keeping the temperature constant below the roughening point and varying the external fields $(h,v)$. In the $(h,v)$ plane, the phase boundary is approached along straight lines $δv=k δh$, where $(δh,δ

Sergio Ferrara, Juan M. Maldacena

In extended supergravity theories there are $p$-brane solutions preserving different numbers of supersymmetries, depending on the charges, the spacetime dimension and the number of original supersymmetries (8, 16 or 32). We find U-duality invariant conditions on the quantized charges which specify the number of supersymmetries preserved with a particular cha

Klaus Behrndt, Ingo Gaida, Dieter Lust, Swapna Mahapatra

We discuss the T-duality between the solutions of type IIA versus IIB superstrings compactified on Calabi-Yau threefolds. Within the context of the N=2, D=4 supergravity effective Lagrangian, the T-duality transformation is equivalently described by the c-map, which relates the special Kahler moduli space of the IIA N=2 vector multiplets to the quaternionic

A. Kovner, M. Shifman, A. Smilga

We present a detailed analysis of the domain walls in supersymmetric gluodynamics and SQCD. We use the (corrected) Veneziano-Yankielowicz effective Lagrangians to explicitely obtain the wall profiles and check recent results of Dvali and Shifman (Phys. Lett. B396, (1997) 64: (i) the BPS-saturated nature of the walls; (ii) the exact expressions for the wall e