July 1999 arXiv papers — page 7

Ansor A. Khelashvili, George A. Khelashvili, Nikoloz Kiknadze, Temur P. Nadareishvili

It is shown that there exist solutions of the quasipotential equations exhibiting the abnormal type behaviour of the Bethe-Salpeter equation.

Andreas Winter

Coding theorems and (strong) converses for memoryless quantum communication channels and quantum sources are proved: for the quantum source the coding theorem is reviewed, and the strong converse proven. For classical information transmission via quantum channels we give a new proof of the coding theorem, and prove the strong converse, even under the extende

Hong-Liang Lu, Xi-Jun Qiu

A set of fixed points of the Hopfield type neural network was under investigation. Its connection matrix is constructed with regard to the Hebb rule from a highly symmetric set of the memorized patterns. Depending on the external parameter the analytic description of the fixed points set had been obtained. And as a conclusion, some exact results of Hopfield

W. C. Haxton, C. -L. Song

We describe a strategy for attacking the canonical nuclear structure problem ---bound-state properties of a system of point nucleons interacting via a two-body potential---which involves an expansion in the number of particles scattering at high momenta, but is otherwise exact. The required self-consistent solutions of the Bloch-Horowitz equation for effecti

C. P. Viazminsky

The elements of the class of non-homogeneous differential operators which are based on the same vector field, when viewed as acting on appropriate Hilbert spaces, are shown to be isomorphic to each other. It shown that the replacement of a non-homogeneous operator by a homogeneous one amouts to appropriately changing the volume element in the manifold. An em

Yasushi Yamashita, Haruko Nishi, Sadayoshi Kojima

In our previous paper, we discussed the hyperbolization of the configuration space of n(> 4) marked points with weights in the projective line up to projective transformations. A variation of the weights induces a deformation. It was shown that this correspondence of the set of the weights to the Teichmüller space when n = 5 and to the Dehn filling space whe

Eugene Polulyakh

Let $X$ be a topological space, $U$ -- opened subset of $X$. We will say that point $x \in \partial U$ is {\it accessible} from $U$ if there exists continuous injective mapping $ϕ: I \to \Cl D$ such that $ϕ(1)=x$, $ϕ([0,1)) \subset \Int U$. We proove the next main theorem. The following conditions are neccesary and suffficient for a compact subset $D$ of $R^

Erik Taflin

A discrete time probabilistic model, for optimal equity allocation and portfolio selection, is formulated so as to apply to (at least) reinsurance. In the context of a company with several portfolios (or subsidiaries), representing both liabilities and assets, it is proved that the model has solutions respecting constraints on ROE's, ruin probabilities a

Sergei V. Shabanov

A general procedure to reveal an Abelian structure of Yang-Mills theories by means of a (nonlocal) change of variables, rather than by gauge fixing, in the space of connections is proposed. The Abelian gauge group is isomorphic to the maximal Abelian subgroup of the Yang-Mills gauge group, but not its subgroup. A Maxwell field of the Abelian theory contains

Shyamoli Chaudhuri

We extend Polchinski's evaluation of the measure for the one-loop closed string path integral to open string tree amplitudes with boundaries and crosscaps embedded in Dbranes. We explain how the nonabelian limit of near-coincident Dbranes emerges in the path integral formalism. We give a careful path integral derivation of the cylinder amplitude includin

G. V. Efimov

The main aim of this paper is to demonstrate the method called "the Bosonization of Nonlocal Currents" (BNC), used for calculations of bound states in a quark model, within the simplest relativistic quantum field model of two scalar fields with the Yukawa type interaction. A second aim is to clarify the relation between BNC and two widely used method

Mayumi Aoki, Noriyuki Oshimo

In the standard model the proton is protected from decay naturally by gauge symmetries, whereas in the ordinary minimal supersymmetric standard model an ad hoc discrete symmetry is imposed for the proton stability. We present a new supersymmetric model in which the proton decay is forbidden by an extra U(1) gauge symmetry. Particle contents are necessarily i

Jonathan L. Rosner

A way is suggested to understand why the average masses of $(d,s,b)$ quarks are smaller than those of $(u,c,t)$ quarks. In contrast to previously proposed mechanisms relying on different Higgs boson vacuum expectation values or different Yukawa couplings, the mass difference is explained as a consequence of mixing of $(d,s,b)$ with exotic quarks implied by t

G. Fabricius, E. Artacho, D. Sanchez-Portal, P. Ordejon

We simulate the liquid silicon surface with first-principles molecular dynamics in a slab geometry. We find that the atom-density profile presents a pronounced layering, similar to those observed in low-temperature liquid metals like Ga and Hg. The depth-dependent pair correlation function shows that the effect originates from directional bonding of Si atoms

C. -T. Liang, M. Y. Simmons, C. G. Smith, G. H. Kim

A shoulder-like feature close to $(0.7\times 2e^{2}/h)$, "the 0.7 structure" at zero magnetic field was observed in clean one-dimensional (1D) channels [K.J. Thomas et al., Phys. Rev. Lett. 77, 135 (1996)]. To provide further understanding of this structure, we have performed low-temperature measurements of a novel design of 1D channel with overlayin

V. V. Prudnikov, A. A. Fedorenko

A field-theoretic description of the critical behaviour of systems with quenched defects obeying a power law correlations $\sim |{\bf x}|^{-a}$ for large separations ${\bf x}$ is given. Directly for three-dimensional systems and different values of correlation parameter $2\leq a \leq 3$ a renormalization analysis of scaling function in the two-loop approxima

M. Pascaud, G. Montambaux

This is a comment to J. Konig, Y. Gefen and G. Schon, Phys. Rev. Lett. 81, 4468 (1998) who consider the coupling of two discrete levels of a dot to the continuum of states in reservoirs. We have generalized this work to the case of several discrete levels.

Ayan Guha, Arindam Ghosh, A. K. Raychaudhuri, S. Parashar

Measurements of the dc transport properties and the low-frequency conductivity noise in films of charge ordered Nd_0.5Ca_0.5MnO_3 grown on Si subtrate reveal the existence of a threshold field in the charge ordered regime beyond which strong non linear conduction sets in along with a large broad band conductivity noise. Threshold-dependent conduction disappe

J. Ellis, K. Farakos, N. E. Mavromatos, V. Mitsou

We discuss possible tests of the constancy of the velocity of light using distant astrophysical sources such as gamma-ray bursters (GRBs), Active Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by some models of quantum fluctuations in the space-time background, and we discuss explicitly how an energy-dependent variation in photon

S. Kubis, M. Kutschera

We study the influence of a high density behaviour of the nuclear symmetry energy on a kaon condensation in neutron stars. We find that the symmetry energy typical for several realistic nuclear potentials, which decreases at high densities, inhibits kaon condensation for weaker kaon-nucleon couplings. There exists a threshold coupling above which the kaon co

G. Gyuk, N. Dalal, K. Griest

All of the proposed explanations for the microlensing events observed towards the LMC have difficulties. One of these proposed explanations, LMC self-lensing, which invokes ordinary LMC stars as the long sought-after lenses, has recently gained considerable popularity as a possible solution to the microlensing conundrum. In this paper, we carefully examine t

S. Y. Choi, H. S. Song, W. Y. Song

We investigate the associated production of neutralinos $e^+e^-\to\tildeχ^0_1\tildeχ^0_2$ accompanied by the neutralino leptonic decay $\tildeχ^0_2\to\tildeχ^0_1 \ell^+\ell^-$, taking into account initial beam polarization and production-decay spin correlations in the minimal supersymmetric standard model with general CP phases but without generational mixin

V. Frolov, D. Singh

We study quantum effects in the presence of a spherical semi-transparent mirror or a system of two concentric mirrors which expand with a constant acceleration in a flat D-dimensional spacetime. Using the Euclidean approach, we obtain expressions for fluctuations and the renormalized value of stress-energy tensor for a scalar non-minimally coupled massless f

Anders Johansen, Didier Sornette

A few key properties of the World-Wide-Web (WWW) has been established indicating the lack of any characteristic scales for the WWW, both in its topology and in its dynamics. Here, we report an experiment which quantifies another power law describing the dynamical response of the WWW to a Dirac-like perturbation, specifically how the popularity of a web site

J. Schaffner-Bielich, V. Koch, M. Effenberger

The medium modifications of antikaons in dense matter are studied in a coupled channel calculation for scenarios more closely related to the environment encountered in heavy-ion collisions. We find that the optical potential of the antikaons turns repulsive or is drastically reduced for finite momenta or finite temperature. Hence, the antikaon mass does not

M. V. Simkin, G. D. Mahan

The phonon thermal conductivity of a multilayer is calculated for transport perpendicular to the layers. There is a cross over between particle transport for thick layers to wave transport for thin layers. The calculations shows that the conductivity has a minimum value for a layer thickness somewhat smaller then the mean free path of the phonons.

N. Kitanine, J. M. Maillet, V. Terras

Using the algebraic Bethe ansatz method, and the solution of the quantum inverse scattering problem for local spins, we obtain multiple integral representations of the $n$-point correlation functions of the XXZ Heisenberg spin-$1 \over 2$ chain in a constant magnetic field. For zero magnetic field, this result agrees, in both the massless and massive (anti-f

R. H. Sanders

The modified Newtonian dynamics (MOND), suggested by Milgrom as an alternative to dark matter, implies that isothermal spheres with a fixed anisotropy parameter should exhibit a near perfect relation between the mass and the fourth power of the velocity dispersion. This is consistent with the observed Faber-Jackson relation for elliptical galaxies-- a lumino

R. A. Briere

We have searched for the rare decays of the eta prime meson to e+ e- eta, e+ e- pizero, e+ e- gamma, and e mu in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb^-1 of e+ e- collisions at the Cornell Electron Storage Ring. We find no signal in any of these modes, and set 90% confidence level upper limits on their branching fraction

Nobuo Furukawa

Low-temperature resistivity of half-metals is investigated. To date it has been discussed that the one-magnon scattering process in half-metals is irrelevant for low-temperature resistivity, due to the fully spin-polarized electronic structure at the ground state. If one takes into account the non-rigid-band behavior of the minority band due to spin fluctuat

J. Nieves, E. Ruiz Arriola

The Bethe-Salpeter equation restores exact elastic unitarity in the $s-$ channel by summing up an infinite set of chiral loops. We use this equation to show how a chiral expansion can be undertaken in the two particle irreducible amplitude and the propagators accomplishing exact elastic unitarity at any step. Renormalizability of the amplitudes can be achiev

Massimo Meneghetti, Micol Bolzonella, Matthias Bartelmann, Lauro Moscardini

We present the results of a set of numerical simulations evaluating the effect of cluster galaxies on arc statistics. We perform a first set of gravitational lensing simulations using three independent projections for each of nine different galaxy clusters obtained from N-body simulations. The simulated clusters consist of dark matter only. We add a populati

S. Borgani, M. Girardi, R. G. Carlberg, H. K. C. Yee

We present the results of the analysis of the internal velocity dispersions, σ_v, for the CNOC sample of distant galaxy clusters, based on an interlopers removal algorithm, which is different from that originally applied by Carlberg et al. (1996, C96). We find that the resulting σ_v values are consistent within <10% with the original C96 estimates. This resu

Alessio Filippetti, Vincenzo Fiorentini

Drawing on the theory of quantum mechanical stress, we introduce the stress density in density functional theory. In analogy with the Chetty-Martin energy density, the stress density provides a spatial resolution of the contributions to the integrated macroscopic stress tensor. We give specific prescriptions for a practical and efficient implementation in th

Domenico Gazzillo, Achille Giacometti, Raffaele G. Della Valle, Elisabetta Venuti

Integral equation of pure liquids, combined with a new &#34;scaling approximation&#34; based on a corresponding states treatment of pair correlation functions, is used to evaluate approximate structure factors for colloidal fluids constituted of uncharged particles with polydispersity in size and energy parameters. Both hard spheres and Lennard-Jones interac

M. P. Anantram, S. Datta, Yongxiang Xue

The modeling of carbon nanotube-metal contacts is important from both basic and applied view points. For many applications, it is important to design contacts such that the transmission is dictated by intrinsic properties of the nanotube rather than by details of the contact. In this paper, we calculate the electron transmission probability from a nanotube t

Hikaru Kawamura

The stability of the three-dimensional vortex-glass order in random type-II superconductors with point disorder is investigated by equilibrium Monte Carlo simulations based on a lattice XY model with a uniform field threading the system. It is found that the vortex-glass order, which stably exists in the absence of screening, is destroyed by the screenng eff

Tetsuro Saso

A new approach is proposed which encompasses the dynamical mean field theory (DMFT) for strongly correlated electron systems and the self-consistent renormalization (SCR) theory of spin fluctuations. The latter is incorporated into DMFT as a $O(1/d)$ correction, where $d$ is the spatial dimensionality, but in a phenomenological way. The DMFT is completely re

S. K. Lamoreaux

A brief review of the recent experimental verifications of the Casimir force between extended bodies is presented. With modern techniques, it now appears feasible to test the force law with 1% precision; I will address the issues relating to the interpretation of experiments at this level of accuracy

V. SunilKumar, B. A. Bambah, R. Jagannathan, P. K. Panigrahi

We present a general unified approach for finding the coherent states of polynomially deformed algebras such as the quadratic and Higgs algebras, which are relevant for various multiphoton processes in quantum optics. We give a general procedure to map these deformed algebras to appropriate Lie algebras. This is used, for the non compact cases, to obtain the

D. Ahn, J. H. Oh, K. Kimm, S. W. Hwang

An exact reduced-density-operator for the output quantum states in time-convolutionless form was derived by solving the quantum Liouville equation which governs the dynamics of a noisy quantum channel by using a projection operator method and both advanced and retarded propagators in time. The formalism developed in this work is general enough to model a noi

A. G. Lisi

The skin of Tursiops Truncatus is corrugated with small, quasi-periodic ridges running circumferentially about the torso. These ridges extend into the turbulent boundary layer and affect the evolution of coherent structures. The development and evolution of coherent structures over a surface is described by the formation and dynamics of vortex filaments. The

G. De Ninno, D. Fanelli

Analyses of betatron coupling can be broadly divided into two categories: the matrix approach that decouples the single-turn matrix to reveal the normal modes and the hamiltonian approach that evaluates the coupling in terms of the action of resonances in perturbation theory. The latter is often regarded as being less exact but good for physical insight. The

Boris Tomasik, Urs Achim Wiedemann, Ulrich Heinz

For a class of analytical parametrizations of the freeze-out state of relativistic heavy ion collisions, we perform a simultaneous analysis of the single-particle m_t-spectra and two-particle Bose-Einstein correlations measured in central Pb+Pb collisions at the CERN SPS. The analysis includes a full model parameter scan with chi^2 confidence levels. A compa

Robert D. Pisarski, Dirk H. Rischke

We review how a classification into representations of color and flavor can be used to understand the possible patterns of symmetry breaking for color superconductivity in dense quark matter. In particular, we show how for three flavors, color-flavor locking is precisely analogous to the usual pattern of chiral symmetry breaking in the QCD vacuum.

P. Podio-Guidugli, S. Sellers, G. Vergara Caffarelli

In order to clarify common assumptions on the form of energy and momentum in elasticity, a generalized conservation format is proposed for finite elasticity, in which total energy and momentum are not specified a priori. Velocity, stress, and total energy are assumed to depend constitutively on deformation gradient and momentum in a manner restricted by a di

Stanislov Volkov

Vertex-Reinforced Random Walk (VRRW), defined by Pemantle (1988a), is a random process in a continuously changing environment which is more likely to visit states it has visited before. We consider VRRW on arbitrary graphs and show that on almost all of them, VRRW visits only finitely many vertices with a positive probability. We conjecture that on all graph

A. an Huef

Let (G,X) be a locally compact transformation group, in which G acts freely on X. We show that the associated transformation-group C^*-algebra is a Fell algebra if and only if X is a Cartan G-space.

J. Böckenhauer, D. E. Evans, Y. Kawahigashi

In this paper we further analyze modular invariants for subfactors, in particular the structure of the chiral induced systems of M-M morphisms. The relative braiding between the chiral systems restricts to a proper braiding on their ``ambichiral&#39;&#39; intersection, and we show that the ambichiral braiding is non-degenerate if the original braiding of the

Brent Everitt

It is shown that any finitely generated non-elementary Fuchsian group has among its homomorphic images all but finitely many of the alternating groups. This settles in the affirmative a conjecture of Graham Higman.

Sadayoshi Kojima

The space of marked n distinct points on the complex projective line up to projective transformations will be called a configuration space in this paper. There are two families of complex hyperbolic structures on the configuration space constructed by Deligne-Mostow and Thurston. We first confirm that these families are the same. Then in view of the deformat

Maciej Dunajski, Paul Tod

We consider four (real or complex) dimensional hyper-Kähler metrics with a conformal symmetry K. The three-dimensional space of orbits of K is shown to have an Einstein-Weyl structure which admits a shear-free geodesics congruence for which the twist is a constant multiple of the divergence. In this case the Einstein-Weyl equations reduce down to a single se

L. Mangiarotti, G. Sardanashvily

We show that, in the framework of covariant Hamiltonian field theory, a degenerate almost regular quadratic Lagrangian $L$ admits a complete set of non-degenerate Hamiltonian forms such that solutions of the corresponding Hamilton equations, which live in the Lagrangian constraint space, exhaust solutions of the Euler--Lagrange equations for $L$. We obtain t

Ludvig Faddeev, Antti J. Niemi

Recently we have proposed a set of variables for describing the physical parameters of SU(N) Yang--Mills field. Here we propose an off-shell generalization of our Ansatz. For this we envoke the Darboux theorem to decompose arbitrary one-form with respect to some basis of one-forms. After a partial gauge fixing we identify these forms with the preimages of ho

M. Chaves, H. Morales

The generalized covariant derivative, that uses both scalar and vector bosons, is defined. It is shown how a grand unified theory of the Standard Model can be constructed using a generalized Yang-Mills theory.

D. Gomez Dumm, J. Vidal

We analyse the muon longitudinal polarization asymmetry Δ_long in the decay K^+ --> π^+ μ^+ mu^-. It is stressed that, since the muon helicities are not Lorentz-invariant quantities, the magnitude of Δ_long depends in general on the reference frame. We consider the muon helicities in the LAB system, and study the sensitivity of the longitudinal polarization

James Pantaleone, T. K. Kuo, Sadek Mansour

Exotic explanations are considered for atmospheric neutrino observations. Our analysis includes matter effects and the mixing of all three neutrinos under the simplifying assumption of only one relevant mixing scale. Constraints from accelerator, reactor and solar neutrinos are included. We find that the proposed mixing mechanisms based on violations of Lore

Hael Collins, Aaron K. Grant, Howard Georgi

We analyze a model of dynamically broken topcolor in the limit in which the number of colors is large. We show that the second order nature of the phase transition, necessary for the success of topcolor models, passes the nontrivial check of consistency with the large N limit. We also identify and discuss a class of theories that generalizes the topcolor phe

John Ellis, G. K. Leontaris, J. Rizos

We analyze the Higgs doublet-triplet mass splitting problem in the version of flipped SU(5) derived from string theory. Analyzing non-renormalizable terms up to tenth order in the superpotential, we identify a pattern of field vev&#39;s that keeps one pair of electroweak Higgs doublets light, while all other Higgs doublets and all Higgs triplets are kept hea

A. Bianconi, S. Boffi, R. Jakob, M. Radici

We investigate the properties of interference fragmentation functions measurable from the distribution of two hadrons produced in the same jet in the current fragmentation region of a hard process. We discuss the azimuthal angular dependences in the leading order cross section of two-hadron inclusive lepton-nucleon scattering as an example how these interfer

Michael Melles

With the LEP II Higgs search approaching exclusion limits on low values of $\tan β\sim 2$ it becomes increasingly important to investigate physical quantities sensitive to large masses of a pseudoscalar Higgs mass. This regime is difficult and over a large range of $\tan β$ impossible to cover at the LHC proton proton collider. In this paper we focus on the

W. L. van Neerven, A. Vogt

We study the next-to-next-to-leading order (NNLO) evolution of flavour non-singlet quark densities and structure functions in massless perturbative QCD. Present information on the corresponding three-loop splitting functions is used to derive parametrizations of these quantities, including Bjorken-x dependent estimates of their residual uncertainties. Compac

V. A. Smirnov

Problems that arise in the application of general prescriptions of the so-called strategy of regions for asymptotic expansions of Feynman integrals in various limits of momenta and masses are discussed with the help of characteristic examples of two-loop diagrams. The strategy is also reformulated in the language of alpha parameters.

M. Stratmann, W. Vogelsang

Di-jet photoproduction in polarized ep collisions at HERA is studied as a possible tool to determine the parton content of circularly polarized photons. The concept of the `effective parton density&#39; approximation is extended to the spin-dependent case.

B. Guberina, B. Melic, H. Stefancic

We extend Voloshin&#39;s recent analysis of charmed and beauty hyperon decays based on SU(3) symmetry and heavy quark effective theory, by introducing a rather moderate model-dependence, in order to obtain more predictive power, e.g. the values of lifetimes of the (Λ_{b},Ξ_{b}) hyperon triplet and the lifetime of Ω_{b}. In this way we obtain an improvement o

M. Stratmann

The present theoretical status of spin-dependent parton densities Delta f^{\gamma}(x,Q^2) of circularly polarized photons is briefly reviewed. It is then demonstrated that measurements of the deep-inelastic spin asymmetry A_1^{\gamma}\simeq g_1^{\gamma}/F_1^{\gamma} and of di-jet rapidity distributions at a future linear e^+e^- collider appear to be particul

J. C. Romao

We review models where R-parity is broken, either spontaneously or explicitly. In this last case we consider the situation where R-parity is broken via bilinear terms in the superpotential. We show that although at tree level only one neutrino gets mass, at one--loop level all three neutrinos became massive. We study the conditions under which bimaximal mixi

M. Stratmann

An updated next-to-leading order (NLO) QCD analysis of all presently available longitudinally polarized deep-inelastic scattering (DIS) data is presented in the framework of the radiative parton model.

V. G. Baryshevsky, K. G. Batrakov, S. L. Cherkas

We consider the effects of the deuteron spin rotation and oscillations at the matter which is proportional to the real part of the deuteron spin-dependent forward scattering amplitude. That gives a possibility of a direct measurement of this quantity. Spin-dependent forward scattering amplitude of the deuteron on an unpolarized proton is discussed in terms o

P. H. Damgaard, U. M. Heller, R. Niclasen, K. Rummukainen

Based on a large number of smearing steps, we classify SU(3) gauge field configurations in different topological sectors. For each sector we compare the exact analytical predictions for the microscopic Dirac operator spectrum of quenched staggered fermions. In all sectors we find perfect agreement with the predictions for the sector of topological charge zer

I. S. Booth, R. B. Mann

We extend the Brown and York notion of quasilocal energy to include coupled electromagnetic and dilaton fields and also allow for spatial boundaries that are not orthogonal to the foliation of the spacetime. We investigate how the quasilocal quantities measured by sets of observers transform with respect to boosts. As a natural application of this work we in

A. M. Gevorkian, R. A. Gevorkian

In Einstein&#39;s equation we suggest a geometrical object substituting the tensor of energy of impulse and tension. The obtained equation, together with the equation for external field, makes up the complete problem of mathematical equations of gravitation, as well as those of inertia. Based on the example of centrally symmetrical field those problems and t

G. Contreras, L. A. Núñez, U. Percoco

The expression of the vector field generator of a Ricci Collineation for diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained. The resulting expressions show that the time and radial first derivatives of the components of the Ricci tensor can be used to classify the collineation, leading to 64 families. Some examples illustrate how to

Charles Hellaby

We show that the only Tolman models which permit a Vaidya limit are those having a dust distribution that is hollow - such as the self-similar case. Thus the naked shell-focussing singularities found in Tolman models that are dense through the origin have no Vaidya equivalent. This also casts light on the nature of the Vaidya metric. We point out a hidden as

K. B. Cooper, M. P. Lilly, J. P. Eisenstein, L. N. Pfeiffer

The intriguing re-entrant integer quantized Hall states recently discovered in high Landau levels of high-mobility 2D electron systems are found to exhibit extremely non-linear transport. At small currents these states reflect insulating behavior of the electrons in the uppermost Landau level. At larger currents, however, a discontinuous and hysteretic trans

Ellen Baake, Wilfried Gabriel

Motivated by present activities in (statistical) physics directed towards biological evolution, we review the interplay of three evolutionary forces: mutation, selection, and genetic drift. The review addresses itself to physicists and intends to bridge the gap between the biological and the physical literature. We first clarify the terminology and recapitul

M. Amoruso, I. Meccoli, A. Minguzzi, M. P. Tosi

We evaluate the small-amplitude excitations of a spin-polarized vapour of Fermi atoms confined inside a harmonic trap. The dispersion law $ω=ω_{f}[l+4n(n+l+2)/3]^{1/2}$ is obtained for the vapour in the collisional regime inside a spherical trap of frequency $ω_{f}$, with $n$ the number of radial nodes and $l$ the orbital angular momentum. The low-energy exc

Jorge Iniguez, Alberto Garcia, J. M. Perez-Mato

Hexagonal BaTiO_3 undergoes a structural phase transition to an orthorhombic C222_1 phase at T_0 = 222 K. The transition is driven by a soft optical mode with E_2u symmetry whose couplings force the appearance of a spontaneous E_2g strain (improper ferroelastic character). Staying within the same E_2u subspace, the system could in principle settle into a sec

Alexander V. Khaetskii, Yuli V. Nazarov

We have studied the physical processes responsible for the spin -flip in GaAs quantum dots. We have calculated the rates for different mechanisms which are related to spin-orbit coupling and cause a spin-flip during the inelastic relaxation of the electron in the dot both with and without a magnetic field. We have shown that the zero-dimensional character of

E. A. Rogacheva

New approach on interpretation and processing of Raman spectra of complex perovskites is suggested. Raman spectra of $PbMg_{1/3}Nb_{2/3}O_{3}$ and $% PbSc_{1/2}Ta_{1/2}O_{3}$ are successfully described on the basis of the phonon-confinement model and validity of the method is demonstrated on good agreement of experimentally obtained and computer simulated sp

Yan Grasselli, Hans J. Herrmann, Gadi Oron, Stefano Zapperi

We study experimentally the shape of a granular heap formed pouring a granular material into a vertical Hele-Shaw cell and analyze the effect of the grain impact energy. We propose a continuous model for the steady profile of the heap that explicitly considers energy dissipation of flowing grains through inelastic collisions. We solve the model analytically

Nobuo Furukawa, Kazuma Hirota

Magnon linewidth of La_1.2 Sr_1.8 Mn_2 O_7 near the Brillouin zone boundary is investigated from both theoretical and experimental points of view. Abrupt magnon broadening is ascribed to a strong magnon-phonon coupling. Magnon broadening observed in cubic perovskite manganites is also discussed.

Yu. P. Gaidukov, N. P. Danilova, N. A. Vassilieva, A. M. Balbashov

The sound velocities dependencies on temperature V(T) were measured by means of resonance method have on the thin plates of quasimonocrystalline manganites La(1-x)Sr(x)MnO3. Results are presented for x=0.1, 0.125, 0.15, 0.175 and 0.2 in the temperature range from 70 to 350K. The V(T) behavior correlates with those of susceptibilities and magnetic moment M(T)

M. V. Feigel&#39;man, A. I. Larkin, M. A. Skvortsov

Keldysh representation of the functional integral for the interacting electron system with disorder is used to derive microscopically an effective action for dirty superconductors. In the most general case this action is a functional of the 8 x 8 matrix Q(t,t&#39;) which depends on two time variables, and on the fluctuating order parameter field and electric

W. Pan, J. -S. Xia, V. Shvarts, E. D. Adams

We report ultra-low temperature experiments on the obscure fractional quantum Hall effect (FQHE) at Landau level filling factor $ν$=5/2 in a very high mobility specimen of $μ=1.7 \times 10^7$ cm$^2$/Vs. We achieve an electron temperature as low as $\sim$ 4~mK, where we observe vanishing $R_{xx}$ and, for the first time, a quantized Hall resistance, $R_{xy}=h

Gang Lu, Nicholas Kioussis, Vasily V. Bulatov, Efthimios Kaxiras

We reexamine two essential issues within the Peierls-Nabarro model which are critical in obtaining accurate values for the Peierls stress. The first issue is related to the sampling scheme of the misfit energy across the glide plane and the second one is the effect of relaxation on the Peierls stress. It is shown that most of the current applications of the

F. M. Ramos, C. Rodrigues Neto, R. R. Rosa

We present a new framework for modeling the statistical behavior of both fully developed turbulence and short-term dynamics of financial markets based on the nonextensive thermostatistics proposed by Tsallis. We also show that intermittency -- strong bursts in the energy dissipation or clusters of high price volatility -- and nonextensivity -- anomalous scal

P. Franzese, L. Zannetti

Separated flows past complex geometries are modelled by discrete vortex techniques. The flows are assumed to be rotational and inviscid, and a new technique is described to determine the streamfunctions for linear shear profiles. The geometries considered are the snow cornice and the backward-facing step, whose edges allow for the separation of the flow and

Pedro Colin, Anatoly Klypin, Andrey V. Kravtsov

We use N-body simulations to study the velocity bias of dark matter halos, the difference in the velocity fields of dark matter and halos, in a flat low- density LCDM model. The high force, 2kpc/h, and mass, 10^9Msun/h, resolution allows dark matter halos to survive in very dense environments of groups and clusters making it possible to use halos as galaxy t

Stephen D. J. Gwyn

Photometric redshifts have been calculated for the Hubble Deep Fields. The redshift distributions of the fields differ; there is a large excess of galaxies in the HDF-North in the redshift range 0.4<z<1.2. The difference is consistent with the presence of a weak cluster in the HDFN and is only slightly larger than the cosmic variance in other fields of simil

Andrea Cattaneo

Quasars are widely believed to be powered by accretion onto supermassive black holes and there is now considerable evidence for a link between mergers, quasars and the formation of spheroids. Cattaneo, Haehnelt & Rees (1999) have demonstrated that a very simple model in which supermassive black holes form and accrete most of their mass in mergers of galaxies

Carla Maceroni, Slavek M. Rucinski

We used the database of eclipsing binaries detected by the OGLE microlensing project in the pencil-beam search volume toward Baade&#39;s Window to define a sample of 74 detached, equal-mass, main-sequence binary stars with short orbital periods in the range 0.19<P<8 days. The logarithmic slope of the period distribution, logN propto (-0.8 pm 0.2) logP, was u

Megan Donahue, G. Mark Voit

We constrain Omega_m through a maximum likelihood analysis of temperatures and redshifts of the high-redshift clusters from the EMSS. We simultaneously fit the low-redshift Markevitch (1998) sample (an all-sky sample from ROSAT with z=0.04- 0.09), a moderate redshift EMSS sample from Henry (1997) (9 clusters with z=0.3- 0.4), and a more distant EMSS sample (

D. A. Smith, A. M. Levine, H. V. Bradt, R. Remillard

The All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE) has been used to localize thirteen confirmed X-ray counterparts to Gamma-Ray Bursts (GRBs) detected over three years of operation. We quantify the errors in ASM localizations of brief transient sources by using observations of persistent sources with well-known locations. We apply the result

Slavek M. Rucinski, Wenxian Lu

Radial velocity data for both components of W Crv are presented. In spite of providing full radial-velocity information, the new data are not sufficient to establish the configuration of this important system because of large seasonal light-curve variations which prevent a combined light-curve/radial-velocity solution. It is noted that the primary minimum is

Paola D&#39;Alessio, Nuria Calvet, Lee Hartmann, Susana Lizano

We construct detailed vertical structure models of irradiated accretion disks around T Tauri stars with interstellar medium dust uniformly mixed with gas. The dependence of the structure and emission properties on mass accretion rate, viscosity parameter, and disk radius is explored using these models. The theoretical spectral energy distributions (SEDs) and

S. Colafrancesco

We discuss the origin of thermal and non-thermal phenomena in galaxy clusters. Specifically, we present some expectations for the non-thermal emission (from radio to gamma ray wavelenghts) expected in a model in which secondary electrons are produced via $pp$ collisions in the intracluster medium. We also discuss the possibility to test this cosmic ray model

Ramesh Narayan

The proposed Laser Interferometer Space Antenna is expected to detect gravitational waves from neutron stars and stellar-mass black holes spiraling into supermassive black holes in distant galactic nuclei. Analysis of the inspiral events will require careful comparison of the observed signals with theoretical waveform templates. The comparison could be serio

Alan P. Smale, Stefanie Wachter

We present results from a campaign of simultaneous X-ray and optical observations of X1254-690 conducted using the Rossi X-ray Timing Explorer and the CTIO 1.5m telescope. We find that the usually-observed deep X-ray dipping is not seen during the times of our observations, with an upper limit of ~2% on any X-ray orbital variation, and that the mean optical

Y. H. Zhang, A. Celotti, A. Treves, L. Chiappetti

(Abridged) We present a detailed power density spectrum and cross-correlation analysis of the X-ray light curves of the BL Lac object PKS 2155-304, observed with BeppoSAX in 1997 and 1996, aimed at exploring the rapid variability properties and the inter-band cross correlations in the X-rays. We also perform the same analysis on the (archival) X-ray light cu