December 2000 arXiv papers — page 16

Stefano Mancini

It is shown that ponderomotive force can be used to purify entangled states. The protocol is based on the possibility to exploit such force for a local quantum nondemolition measurement of the total excitation number of continuos variable entangled pairs.

Stefano Mancini, Rodolfo Bonifacio

We investigate the capabilities of a quantum computer based on cold trapped ions in presence of non-dissipative decoherence. The latter is accounted by using the evolution time as a random variable and then averaging on a properly defined probability distribution. Severe bounds on computational performances are found.

Igor V. Volovich

The promise of secure cryptographic quantum key distribution schemes is based on the use of quantum effects in the spin space. We point out that in fact in many current quantum cryptography protocols the space part of the wave function is neglected. However exactly the space part of the wave function describes the behaviour of particles in ordinary real thre

S. Tanzilli, H. de Riedmatten, W. Tittel, H. Zbinden

We report on a new kind of correlated photon-pair source based on a waveguide integrated on a Periodically Poled Lithium Niobate substrate. Using a pump laser of a few micro-Watts at 657 nm, we generate degenerate photon-pairs at 1314 nm. Detecting about 1500 coincidences per second, we can infer a conversion rate of 10-6 pairs per pump photon, which is four

Peng Xue, Yun-Feng Huang, Yong-Sheng Zhang, Chuan-Feng Li

We propose a probabilistic two-party communication complexity scenario with a prior nonmaximally entangled state, which results in less communication than that is required with only classical random correlations. A simple all-optical implementation of this protocol is presented and demonstrates our conclusion.

David D. Song, Richard J. Szabo

Quantum error avoiding codes are constructed by exploiting a geometric interpretation of the algebra of measurements of an open quantum system. The notion of a generalized Dirac operator is introduced and used to naturally construct families of decoherence free subspaces for the encoding of quantum information. The members of the family are connected to each

Jose L. Cereceda

Elaborating on a previous work by Han et al., we give a general, basis-independent proof of the necessity of negative probability measures in order for a class of local hidden-variable (LHV) models to violate the Bell-CHSH inequality. Moreover, we obtain general solutions for LHV-induced probability measures that reproduce any consistent set of probabilities

C. E. Vargas, J. G. Hirsch, J. P. Draayer

The quasi-SU(3) symmetry, as found in shell model calculations, refers to the dominance of the single particle plus quadrupole-quadrupole terms in the Hamiltonian used to describe well deformed nuclei, and to the subspace relevant in its diagonalization. It provides a very efficient basis truncation scheme. It is shown that a small number of SU(3) coupled ir

A. Fabrocini, G. Co'

The one body density matrix, momentum distribution, natural orbits and quasi hole states of 16O and 40Ca are analyzed in the framework of the correlated basis function theory using state dependent correlations with central and tensor components. Fermi hypernetted chain integral equations and single operator chain approximation are employed to sum cluster dia

D. H. E. Gross

The recent paper nucl-th/0012037 by Moretto et al. is commented

L. Tiator, D. Drechsel, O. Hanstein, S. S. Kamalov

A partial wave analysis of pion photoproduction has been obtained in the framework of fixed-t dispersion relations valid from threshold up to 500 MeV. In the resonance region we have precisely determined the electromagnetic properties of the Δ(1232) resonance, in particular the E2/M1 ratio R_{EM}=(-2.5 +- 0.1) %. For pion electroproduction recent experimenta

Lothar Tiator

Results of the recently developed unitary isobar model (MAID) are presented for helicity amplitudes, spin asymmetries, structure functions and relevant sum rules for real and virtual photons in the resonance region. Our evaluation of the energy-weighted integrals is in good agreement for the proton but shows big discrepancies for the neutron.

A. Iomin, George M. Zaslavsky

We show that the breaking time of quantum-classical correspondence depends on the type of kinetics and the dominant origin of stickiness. For sticky dynamics of quantum kicked rotor, when the hierarchical set of islands corresponds to the accelerator mode, we demonstrate by simulation that the breaking time scales as $τ_{\hbar} \sim (1/\hbar)^{1/μ}$ with the

A. Iomin, G. M. Zaslavsky

Semi--classical dynamics of quantum wave packets spreading is studied for a kicked rotor. Quantum flights are established for a specific, "magic" value of a chaos control parameter when the classical stickiness of trajectories is most effective. By studying of survival probability and distribution of the accelerations we identify the presence of quan

V. S. Gerdjikov, I. M. Uzunov

Our previous results on the N-soliton interaction in the adiabatic approximation have been extended. It is shown that the complex Toda chain (CTC) model is an universal one in the sense that it describes the N-soliton train interactions for all NLEE from the NLS hierarchy. We derive the perturbed CTC system and show that the small perturbations affect only t

Harold Steinacker

Noncompact forms of the Drinfeld-Jimbo quantum groups U_q(g) with (H_i)* = H_i, (X_i^{+-})* = s_i X_i^{-+} for s_i= +-1 are studied at roots of unity. This covers g = so(n,2p), su(n,p), so*(2l), sp(n,p), sp(l,R), and exceptional cases. Finite-dimensional unitary representations are found for all these forms, for even roots of unity. Their classical symmetry

Simon Salamon

We classify real 6-dimensional nilpotent Lie algebras for which the corresponding Lie group has a left-invariant complex structure, and estimate the dimensions of moduli spaces of such structures.

Laurent Bartholdi

In 1980 Rostislav Grigorchuk constructed a group $G$ of intermediate growth, and later obtained the following estimates on its growth function: $$e^{\sqrt{n}}\precsim\gamma(n)\precsim e^{n^\beta},$$ where $\beta=\log_{32}(31)\approx0.991$. Using elementary methods we bring the upper bound down to $\log(2)/\log(2/\eta)\approx0.767$, where $\eta\approx0.811$ i

Paul Baum, Stephen Millington, Roger Plymen

Let F be a global field, A its ring of adeles, G a reductive group over F. We prove the Baum-Connes conjecture for the adelic group G(A).

Gregorio Malajovich, J. Maurice Rojas

Let f:=(f^1,\...,f^n) be a sparse random polynomial system. This means that each f^i has fixed support (list of possibly non-zero coefficients) and each coefficient has a Gaussian probability distribution of arbitrary variance. We express the expected number of roots of f inside a region U as the integral over U of a certain mixed volume form. When U = (C^*)

Michael S. Weiss, Bruce Williams

This is a survey paper on spaces of automorphisms of manifolds and spaces of manifolds in a fixed homotopy type. It describes the main theorems of traditional surgery theory, but also the main theorems of pseudoisotopy theory, alias concordance theory, Waldhausen style. It culminates in (an outline of) a synthesis of these two theories, producing algebraic m

Andrew Hassell, Andras Vasy

The purpose of this note is to describe the relationship between two classes of Legendre distributions. These two classes are distributions associated to an intersecting pair of Legendre submanifolds, introduced by one of us by analogy with intersecting Lagrangian distributions of Melrose and Uhlmann, and Legendre distributions associated to a fibred scatter

Gavril Farkas

A Brill-Noether locus is a subvariety of M_g consisting of curves having certain linear series g^r_d. We study the relative position of Brill-Noether loci with respect to the gonality stratification of M_g. We construct smooth curves in P^r of given degree and genus and having the `expected' gonality. As an application we give a new proof of our result a

E. Gava, A. B. Hammou, J. F. Morales, K. S. Narain

We propose CFT descriptions of the D1/D5 system in a class of freely acting Z_2 orbifolds/orientifolds of type IIB theory, with sixteen unbroken supercharges. The CFTs describing D1/D5 systems involve N=(4,4) or N=(4,0) sigma models on $(R^3\times S^1\times T^4\times (T^4)^N/S_N)/Z_2$, where the action of Z_2 is diagonal and its precise nature depends on the

M. Dorca, C. van de Bruck

Using a metric-based formalism to treat cosmological perturbations, we discuss the connection between anisotropic stress on the brane and brane bending. First we discuss gauge-transformations, and draw our attention to gauges, in which the brane-positions remain unperturbed. We provide a unique gauge, where perturbations both on the brane and in the bulk can

E. M. C. Abreu, J. Ananias Neto, W. Oliveira, G. Oliveira-Neto

We embed the O(N) nonlinear sigma model in a non-Abelian gauge theory. As a first class system, it is quantized using two different approaches: the functional Schrödinger method and the non-local field-antifield procedure. Firstly, the quantization is performed with the functional Schrödinger method, for N=2, obtaining the wave functionals for the ground and

J. Niederle, B. Zupnik

We analyze the superfield constraints of the D=4, N=3 SYM-theory using light-cone gauge conditions. The SU(3)/U(1) x U(1) harmonic variables are interpreted as auxiliary spectral parameters, and the transform to the harmonic-superspace representation is considered. The harmonic superfield equations of motion are drastically simplified in our gauge, in partic

Bodo Geyer, Dietmar Muelsch

A superspace formulation is proposed for the osp(1,2)-covariant Lagrangian quantization of general massive gauge theories. Thereby, osp(1,2) is considered as subalgebra of the superalgebra sl(1,2) which is interpreted as conformal algebra acting on two anticommuting coordinates. The mass-dependent (anti)BRST symmetries of the quantum action in the osp(1,2) s

A. Gerhold, J. Grimstrup, H. Grosse, L. Popp

We present the discussion of the energy-momentum tensor of the scalar $ϕ^4$- theory on a noncommutative space. The Noether procedure is performed at the operator level. Additionally, the broken dilatation symmetry will be considered in a Moyal-Weyl deformed scalar field theory at the classical level.

S. Arnone, S. Chiantese, K. Yoshida

Exact Renormalization Group techniques are applied to supersymmetric models in order to get some insights into the low energy effective actions of such theories. Starting from the ultra-violet finite mass deformed N=4 supersymmetric Yang-Mills theory, one varies the regularising mass and compensates for it by introducing an effective Wilsonian action. (Polch

Eric Bergshoeff, Renata Kallosh, Antoine Van Proeyen

We review the construction of actions with supersymmetry on spaces with a domain wall. The latter objects act as sources inducing a jump in the gauge coupling constant. Despite these singularities, supersymmetry can be formulated, maintaining its role as a square root of translations in this singular space. The setup is designed for the application in five d

Liu Yufen

It is proved that fermions can acquire the mass through the additional non-integrable exponential factor. For this propose the special vector potential associated with the spinor field was introduced. Such a vector potential has close relation with the triality property in Dirac spinors and plays crucial role in the construction of massive term. It is shown

Y. S. Myung

We prove that in anti de Sitter space, there is no van Dam-Veltman-Zakharov discontinuity in the graviton propagator. Here we obtain the mass term of $M^2\propto Λ^2$ from the Gauss-Bonnet term, which is a ghost-free one. The condition that the massless limit is smooth is automatically satisfied for this case.

Xiangdong Ji, Richard F. Lebed

We present a simple method to count the number of hadronic form factors based on the partial wave formalism and crossing symmetry. In particular, we show that the number of independent nucleon form factors of spin-n, twist-2 operators (the vector current and energy-momentum tensor being special examples) is n+1. These generalized form factors define the gene

K. Bodoor, H. J. Weber, T. Frederico, M. Beyer

Electromagnetic form factors of the nucleon from relativistic quark models are analyzed: results from null-plane projection of the Feynman triangle diagram are compared with a Bakamjian-Thomas model. The magnetic form factors of the models differ by about 15% at spacelike momentum transfer 0.5 GeV^2, while the charge form factors are much closer. Spurious co

M. Maltoni

A global analysis of atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We consider in our analysis both contained events and upward-going neutrino-induced muon events, including the previous data samples of Frejus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data se

Michael Melles

Future colliders will probe the electroweak theory at energies much larger than the gauge boson masses. Large double (DL) and single (SL) logarithmic virtual electroweak Sudakov corrections lead to significant effects for observable cross sections. Recently, leading and subleading universal corrections for external fermions and transverse gauge boson lines w

G. Moreau

The supersymmetric extension of the Standard Model can contain interactions violating the so-called R-parity symmetry. Such couplings would lead to the lepton and/or baryon number violation and modify deeply the phenomenology of supersymmetry at future particle colliders. We have worked out tests of the R-parity violating interactions. First, we have studied

Jonathan Flynn, C. -J. David Lin

We discuss neutral B_{s,d} meson mixing and b-hadron lifetimes from the perspective of recent lattice calculations. In particular, we consider matrix elements which can be combined with measured ΔM_{s,d} to constrain |V_{td}|, the lifetime ratios τ(Λ_b)/τ(B_d) and τ(B^-)/τ(B_d) and the lifetime difference, ΔΓ_s/Γ_s, in the neutral B_s meson system.

A. Donini

The leptonic CP-violating phase $δ$ can be measured with a Neutrino Factory with $2 \times 10^{20} $ useful muons per year, if the solar neutrino problem is solved by the LMA-MSW solution, with $Δm_{12}^2 \ge 2 \times 10^{-5}$ eV$^2$ (in this analysis a 40 kT magnetized iron detector is considered, taking into account its efficiencies and backgrounds). If LS

John March-Russell

The first part of this lecture quickly touches upon some important but infrequently discussed issues in large extra dimension and warped extra dimension scenarios, with particular reference to effects in the early universe. The second part discusses a modification and extension of an earlier proposal by Brown and Teitelboim to relax the effective cosmologica

Nick van Eijndhoven

Statistical calculations within the Standard Model indicate that at extremely high densities the quarks and gluons will become deconfined, leading to a new state of matter, the so-called Quark-Gluon Plasma (QGP). Recently it was announced at CERN that compelling evidence has been obtained from experimental data that indeed the formation of a deconfined state

I. V. Andreev

Photon emission arising in the course of transition between the states of quark-gluon and hadron plasma has been considered. Single-photon distributions and two-photon correlations in central rapidity region have been calculated for heavy ion collisions at high energies. It has been found that opposite side two-photon correlations can serve as a sign of shar

Yu. S. Kalashnikova, A. V. Nefediev

Strong hadronic decays are discussed in the 't Hooft model for the two-dimensional QCD in the limit of infinite number of colours. Adler selfconsistency condition is derived for decays with pions in the final state and the corresponding amplitude is demonstrated to vanish identically in the chiral limit.

A. V. Nefediev

Properties of light-light mesons are described by the effective Hamiltonian with spinless quarks derived from QCD. The spectrum is computed by the WKB method and shown to reproduce the celebrated linear Regge trajectories even for the lowest levels. The correct string slope of the trajectories naturally appears in the present approach as the string dynamics

B. Machet

By considering its generalization to composite J=0 mesons proposed in a previous work [1], I show how and why a chiral extension of the Glashow-Salam-Weinberg standard model of electroweak interactions calls, there, for right-handed charged W_R's coupled with g_R = e/cos(theta_W), and the masses of which are related to the ones of the left-handed W_L&#39

H. Jung, G. P. Salam

We discuss a practical formulation of backward evolution for the CCFM small-$x$ evolution equation and show results from its implementation in the new Monte Carlo event-generator CASCADE.

Gary Felder, Juan Garcia-Bellido, Patrick B. Greene, Lev Kofman

We reconsider the old problem of the dynamics of spontaneous symmetry breaking using 3d lattice simulations, and develop a theory of tachyonic preheating, which occurs due to the spinodal instability of the scalar field. Tachyonic preheating is so efficient that symmetry breaking typically completes within a single oscillation of the field distribution as it

Shinji Tsujikawa, Kei-ichi Maeda, Shuntaro Mizuno

We study brane-world preheating in massive chaotic inflationary scenario where scalar fields are confined on the 3-brane. Assuming that quadratic contribution in energy densities dominates the Hubble expansion rate during preheating, the amplitude of inflaton decreases slowly relative to the standard dust-dominated case. This leads to an efficient production

Fumiyo Uchiyama

We point out that decoherence parameters in the correlated two neutral kaon system breaks the transformation invariance of basis and their magnitude are stringently limited by the experimentally measured magnitudes of CP violation and of the strangeness non conserving $ΔS = \pm 2$ transitions.

S. Groot Nibbelink, B. J. W. van Tent

In this paper we analyze scalar gravitational perturbations on a Robertson-Walker background in the presence of multiple scalar fields that take values on a (geometrically non-trivial) field manifold during slow-roll inflation. For this purpose modified and generalized slow-roll functions are introduced and their properties examined. These functions make it

George T. Fleming

Supersymmetry, like Poincare symmetry, is softly broken at finite lattice spacing provided the gaugino mass term is strongly suppressed. Domain wall fermions provide the mechanism for suppressing this term by approximately imposing chiral symmetry. We present the first numerical simulations of N=1 supersymmetric SU(2) Yang-Mills on the lattice in four dimens

Rafael G. Campos, Eduardo S. Tututi, L. O. Pimentel

A nonlocal method to obtain discrete classical fields is presented. This technique relies on well-behaved matrix representations of the derivatives constructed on a non--equispaced lattice. The drawbacks of lattice theory like the fermion doubling or the breaking of chiral symmetry for the massless case, are absent in this method.

Ting-Hua Chang

The anuglar distribution of $J/ψ$ decays in the $μ^{+}μ^{-}$ channel in 800 proton-copper collisions has been measured for $x_F$ > 0.25. The polarization parameter $λ$ is extracted in 1 GeV of $p_T$ and 0.1 of $x_F$ bins for two magnet configugrations with different acceptances. The data indicate that the $J/ψ$'s are produced with a slight transverse pol

Y. Inoue

We have studied inclusive muon events using all the data collected by the TOPAZ detector at sqrt(s)=58 GeV with an integrated luminosity of 273pb-1. From 1328 inclusive muon events, we measured the ratio R_qq of the cross section for qq-bar production to the total hadronic cross section and forward-backward asymmetry A^q_FB for b and c quarks. The obtained r

Tevian Dray, George Ellis, Charles Hellaby

Recent work alludes to various `controversies' associated with signature change in general relativity. As we have argued previously, these are in fact disagreements about the (often unstated) assumptions underlying various possible approaches. The choice between approaches remains open.

Alastair D. King, Dmitri Vassiliev

The approach of metric-affine field theory is to define spacetime as a real oriented 4-manifold equipped with a metric and an affine connection. The 10 independent components of the metric tensor and the 64 connection coefficients are the unknowns of the theory. We write the Yang-Mills action for the affine connection and vary it both with respect to the met

Joachim Kupsch, Oleg G. Smolyanov

This paper presents a solution to a problem from superanalysis about the existence of Hilbert-Banach superalgebras. Two main results are derived: 1) There exist Hilbert norms on some graded algebras (infinite-dimensional superalgebras included) with respect to which the multiplication is continuous. 2) Such norms cannot be chosen to be submultiplicative and

Nachum Dershowitz, Naomi Lindenstrauss, Yehoshua Sagiv, Alexander Serebrenik

This paper describes a general framework for automatic termination analysis of logic programs, where we understand by ``termination'' the finitenes s of the LD-tree constructed for the program and a given query. A general property of mappings from a certain subset of the branches of an infinite LD-tree into a finite set is proved. From this result se

Miroslaw Truszczynski

In this paper, we focus on the problem of existence and computing of small and large stable models. We show that for every fixed integer k, there is a linear-time algorithm to decide the problem LSM (large stable models problem): does a logic program P have a stable model of size at least |P|-k. In contrast, we show that the problem SSM (small stable models

L. -M. Martinez, C. A. Angell

A thermodynamic measure of the fragility of liquids has recently (Ito et al ref.1) been defined in terms of the temperature dependence of the excess entropy of liquid over crystal, scaled by the excess entropy at the glass transition temperature, and it has been correlated with kinetic fragility. The correlation has been vigorously contested [2] using dielec

J. M. Schwarz, Daniel S. Fisher

An infinite-range model of an elastic manifold pulled through a random potential by an applied force $F$ is analyzed focusing on inertial effects. When the inertial parameter, $M$, is small, there is a continuous depinning transition from a small-$F$ static phase to a large-$F$ moving phase. When $M$ is increased to $M_c$, a novel tricritical point occurs. F

E. Vidal Russell, N. E. Israeloff

We describe direct observations of molecular cooperativity near the glass transition in poly-vinyl-acetate (PVAc), through nanometer-scale probing of dielectric fluctuations. Molecular clusters switched spontaneously between two to four distinct configurations, producing complex random-telegraph-signals (RTS). Analysis of the RTS and their power spectra show

Tobias Bergsten, Tord Claeson, Per Delsing

We have measured current-voltage characteristics of two-dimensional arrays of small tunnel junctions at temperatures from 1.5 K to 4.2 K. This corresponds to thermal energies larger than the charging energy. We show that 2D-arrays can be used as primary thermometers in the same way as 1D-arrays, and even have some advantages over 1D-arrays. We have carried o

Stephan A. Koehler, Thomas R. Powers

Biological filaments such as DNA or bacterial flagella are typically curved in their natural states. To elucidate the interplay of viscous drag, twisting, and bending in the overdamped dynamics of such filaments, we compute the steady-state torsional stress and shape of a rotating rod with a kink. Drag deforms the rod, ultimately extending or folding it depe

Tobias Bergsten, Tord Claeson, Per Delsing

We have measured the third derivative of the current-voltage characteristics, d^3I/dV^3, in a two-dimensional array of small tunnel junctions using a lock-in amplifier. We show that this derivative is zero at a voltage which scales linearly with the temperature and depends only on the temperature and natural constants, thus providing a primary thermometer. W

Enzo Granato

We study the three-dimensional XY-spin glass as a model for the resistive behavior of granular superconductors containing a random distribution of $π$ junctions, as in high-$T_c$ superconducting materials with d-wave symmetry. The $π$ junctions leads to quenched in circulating currents (chiralities) and to a chiral-glass state at low temperatures, even in th

P. Monceau, F. Ya. Nad, S. Brazovskii

We present experimental evidences for a ferro-electric transition in the family of quasi one- dimensional conductors (TMTTF)2X. We interpret this new transition in the frame of the combined Mott-Hubbard state taking into account the double action of the spontaneous charge disproportionation on the TMTTF molecular stacks and of the X anionic potentials.

A. Krichevsky, M. Schechter, Y. Imry, Y. Levinson

The dc Josephson effect is considered from the thermodynamic point of view. Universal thermodynamic equations, relating both bound and continuum contributions to the Josephson current with the normal electron scattering amplitudes are derived for the single mode case. To derive these equations we use and further develop the method of spatial separation betwe

D. C. Cabra, A. De Martino, P. Pujol, P. Simon

The behavior of a two leg Hubbard ladder in the presence of a magnetic field is studied by means of Abelian bosonization. We predict the appearance of a new (doping dependent) plateau in the magnetization curve of a doped 2-leg spin ladder in a wide range of couplings. We also discuss the extension to N-leg Hubbard ladders.

A. S. Alexandrov, C. J. Dent

The scattering cross section of a Coulomb potential screened by a charged Bose gas (CBG) is calculated both above and below the Bose-Einstein condensation temperature, using the variable phase method. In contrast with the BCS superconductor, the screened scattering potential and quasiparticle lifetime are found to be very different in the superconducting and

A. Naidenov, S. Nechaev

The adsorption of an ideal heteropolymer loop at a potential point well is investigated within the frameworks of a standard random matrix theory. On the basis of semi-analytical/semi-numerical approach the histogram of transition points for the ensemble of quenched heteropolymer structures with bimodal symmetric distribution of types of chain's links is

Vadim M. Loktev, Yuri G. Pogorelov, Julia N. Khalak

Based on a simple model for ordering of hexagons on square planar lattice, an attempt has been made to consider possible structure of C(_{60}) fullerite in its low temperature phase. It is shown that hexagons, imitating fullerens oriented along (C_{3}) axes of \emph{sc} lattice, can be ordered into an ideal structure with four non-equivalent molecules in uni

Gady Frenkel, Moshe Schwartz

We obtain the memory kernel of the generalized Langevin equation, describing a particle interacting with longitudinal phonons in a liquid. The kernel is obtained analytically at T=0 Kelvin and numerically at T>0 Kelvin. We find that it shows some non-trivial structural features like negative correlations for some range of time separations. The system is show

Z. Ropka, R. J. Radwanski

Three fundamentally different electronic structures for 3d electron states in LaCoO3, discussed in the current literature, have been presented. We are in favour of the localized electron atomic- like approach that yields the discrete energy spectrum associated with the atomic-like states of the Co3+ ions in contrary to the continouos energy spectrum yielded

C. Johnston, W. D. McComb

Conditional elimination of degrees of freedom is shown to lead to an exact expression for the rate of turbulent energy dissipation in terms of a renormalized viscosity and a correction. The correction is neglected on the basis of a previous hypothesis [W.D. McComb and C. Johnston, J.Phys.A v33 L15 (2000)] that there is a range of parameters for which a quasi

V. R. Vieira, P. D. Sacramento

We consider a spin coherent states description of a general quantum spin system. It is shown that it is possible to use the spin-1/2 representation to study the general spin-J case. We identify the 1/2 spinor components as the homogeneous coordinates of the projective space associated to the complex variable that labels the coherent states and establish a re

Heinz-Juergen Schmidt, Marshall Luban

We investigate classes of quantum Heisenberg spin systems which have different coupling constants but the same energy spectrum and hence the same thermodynamical properties. To this end we define various types of isospectrality and establish conditions for their occurence. The triangle and the tetrahedron whose vertices are occupied by spins 1/2 are investig

Z. Ropka, R. J. Radwanski

In the commented Letter Vogt et al. (Phys.Rev.Lett. 84 (2000) 2969) claim the existence of a spin-state transition in YBaCo2O5. We think that this claim about the change from the low spin to high spin state upon cooling in YBaCo2O5 is errorneous. Keywords: magnetism, 3d ions, low spin.

Luca Salasnich

After a brief historical introduction to Bose-Einstein condensation and Fermi degeneracy, we discuss theoretical results we have recentely obtained for trapped degenerate quantum gases by means of a thermal field theory approach. In particular, by using Gross-Pitaevskii and Bogoliubov-Popov equations, we consider thermodynamical properties of two Bosonic sys

Leticia F Cugliandolo, D. R. Grempel, Constantino A da Silva Santos

We study a quantum extension of the spherical $p$-spin-glass model using the imaginary-time replica formalism. We solve the model numerically and we discuss two analytical approximation schemes that capture most of the features of the solution. The phase diagram and the physical properties of the system are determined in two ways: by imposing the usual condi

T. Schneider, G. I. Meijer, J. Perret, J. -P. Locquet

We present resistivity data on a high-quality La$_{2-x}$Sr$_{x}$CuO$_{4-δ}$ film measured in a magnetic field of 1 T applied at an angle $δ$ to the c axis. Using these data, the influence of the orientation of the magnetic field and the effective mass anisotropy on the vortex-glass transition can be studied. The variation of $δ$ for a fixed magnitude of the

Ming Yu, C. S. Jayanthi, David A. Drabold, S. Y. Wu

In this work, we address issues pertinent to the understanding of the structural and electronic properties of Si_{1-x} Ge_{x}alloys, namely, (i) how does the lattice constant mismatch between bulk Si and bulk Ge manifests itself in the alloy system? and (ii) what are the relevant strain release mechanisms? To provide answers to these questions, we have carri

Lei Liu, C. S. Jayanthi, S. Y. Wu

The bending of a carbon nanotube is studied by considering the structural evolution of a carbon nanotorus from elastic deformation to the onset of the kinks and eventually to the collapse of the walls of the nanotorus. The changes in the electronic properties due to {\it non-local} deformation are contrasted with those due to {\it local} deformation to bring

Shinsei Ryu, Yasuhiro Hatsugai

The zero mode wave function of a massless Dirac fermion in the presence of a random gauge field is studied. The density correlation function is calculated numerically and found to exhibit power law in the weak randomness with the disorder dependent exponent. It deviates from the power law and the disorder dependence becomes frozen in the strong randomness. A

Lei Liu, C. S. Jayanthi, S. Y. Wu

We present a critical theoretical study of electronic properties of silicon nanoclusters, in particular the roles played by symmetry, relaxation, and hydrogen passivation on the the stability, the gap states and the energy gap of the system using the order-N [O(N)] non-orthogonal tight-binding molecular dynamics and the local analysis of electronic structure

Mallory S. E. Roberts, Roger W. Romani, Nobuyuki Kawai

We present a catalog of 2-10 keV ASCA Gas Imaging Spectrometer images of fields containing bright sources of GeV emission. The images cover $\sim 85%$ of the 95% confidence position contour for 28 of the 30 sources with $> 1$ GeV fluxes above $4\times 10^{-8}$ ph ${\rm cm}^{-2} {\rm s}^{-1}$. We find an excess of hard X-ray sources with $F_{2-10 keV} \ga 10^

N. M. McClure-Griffiths, A. J. Green, John M. Dickey, B. M. Gaensler

The Southern Galactic Plane Survey (SGPS) is a project to image the HI line emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high resolution using the Australia Telescope Compact Array (ATCA) and the Parkes Radio Telescope. In this paper we describe the survey details and goals, present lambda 21-cm continuum data, and discuss HI abs

D. S. Wiebe, W. D. Watson

Calculations are performed for the linear polarization of starlight due to extinction by aligned dust grains when the starlight traverses a medium with irregular magnetic fields. This medium is intended to represent the optically thick components of interstellar clouds which are observed to make little, if any, contribution to the polarization of starlight.

David Branch

In this short review I suggest that recent developments support the conjecture that Type Ia supernovae (SNe Ia) are the complete disruptions of Chandrasekhar-mass carbon-oxygen white dwarfs in single-degenerate binary systems. The causes of the observational diversity of SNe Ia within the context of this standard model, and the implications of the model for

Cecile Gry, Edward B. Jenkins

The composition and physical properties of several local clouds, including the Local Interstellar Cloud (LIC) in which the Sun is embedded, are derived from absorption features in the UV spectrum of the star epsilon CMa. We derive temperatures and densities for three components by combining our interpretations of the ionization balance of magnesium and the r

K. Dimopoulos

A model of quintessential inflation is presented, which manages to achieve the requirements of both inflation and quintessence with natural values of the mass-scales and parameters.

E. Aprile, A. Curioni, V. Egorov, K. -L. Giboni

LXeGRIT is a balloon-borne Compton telescope based on a liquid xenon time projection chamber (LXeTPC) for imaging cosmic \g-rays in the energy band of 0.2-20 MeV. The detector, with 400 cm$^2$ area and 7 cm drift gap, is filled with high purity LXe. Both ionization and scintillation light signals are detected to measure the energy deposits and the three spat

U. G. Oberlack, E. Aprile, A. Curioni, V. Egorov

The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon born experiment sensitive to \g -rays in the energy band of 0.2-20 MeV. The main detector is a time projection chamber filled with high purity liquid xenon (LXeTPC), in which the three-dimensional location and energy deposit of individual \g -ray interactions are accurately measured in one h

G. Meeus, L. B. F. M. Waters, J. Bouwman, M. E. van den Ancker

We present Infrared Space Observatory (ISO) spectra of fourteen isolated Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar dust. These spectra show large star-to-star differences, in the emission features of both carbon-rich and oxygen-rich dust grains. The IR spectra were combined with photometric data ranging from the UV throu

C. N. Sabbey, R. G. Sharp, A. K. Vivas, S. T. Hodgkin

We present preliminary results from a wide field near-IR imaging survey that uses the Cambridge InfraRed Survey Instrument (CIRSI) on the 2.5m Isaac Newton Telescope (INT). CIRSI is a JH-band mosaic imager that contains 4 Rockwell 1024$^{2}$ HgCdTe detectors (the largest IR camera in existence), allowing us to survey approximately 4 deg^2 per night to H ~ 19

M. A. Garrett, T. W. B. Muxlow, S. T. Garrington

We present deep, wide-field European VLBI Network (EVN) 1.6 GHz observations of the Hubble Deep Field (HDF) region with a resolution of 0.025 arcseconds. Above the 210 microJy/beam (5sigma) detection level, the EVN clearly detects two radio sources in a field that encompasses the HDF and part of the Hubble Flanking Fields (HFF). The sources detected are: VLA

Andrea Moneti, Jose Cernicharo, Juan Ramon Pardo

We present observations of CO, 13CO and of H2O in the middle and far-infrared taken with the ISO-SWS and ISO-LWS spectrometers toward two positions in the Galactic Center region (Sgr A* and GCS-3). Both ice and gas phase molecules are detected. The ISO data have been complemented with observations of the J=3-2 and J=7-6 lines of CO carried out at the Caltech

F. A. Aharonian

I discuss the spectral features of pi-0 decay gamma-radiation from clouds/targets located in proximity of relatively young proton accelerators, and speculate that such ``accelerator+target'' systems in our Galaxy can be responsible for a subset of unidentified EGRET sources. Also, I argue that the recent observations of high energy gamma-rays from th

L. E. Pasinetti Fracassini, L. Pastori, S. Covino, A. Pozzi

The Catalogue, available at the Centre de Données Stellaires de Strasbourg, consists of 13573 records concerning the results obtained from different methods for 7778 stars, reported in the literature. The following data are listed for each star: identifications, apparent magnitude, spectral type, apparent diameter in arcsec, absolute radius in solar units, m