June 2000 arXiv papers — page 11

Stefan Forste, Zygmunt Lalak, Stéphane Lavignac, Hans Peter Nilles

We point out several subtleties arising in brane-world scenarios of cosmological constant cancellation. We show that solutions with curvature singularities are inconsistent, unless the contribution to the effective four-dimentional cosmological constant of the physics that resolves the singularities is fine-tuned. This holds for both flat and curved branes.

Sonia Stanciu

We show that a D-brane in a group manifold given by a (twisted) conjugacy class is characterised by a gauge invariant two-form field determined in terms of the matrix of gluing conditions. Using a quantisation argument based on the path integral one obtains the known quantisation condition for the corresponding D-branes. We find no evidence for the existence

I. L. Buchbinder, D. M. Gitman, V. D. Pershin

We investigate the structure of equations of motion and lagrangian constraints in a general theory of massive spin 2 field interacting with external gravity. We demonstrate how consistency with the flat limit can be achieved in a number of specific spacetimes. One such example is an arbitrary static spacetime though equations of motion in this case may lack

Daniel Liberzon, A. Stephen Morse, Eduardo D. Sontag

This paper introduces and studies the notion of output-input stability, which represents a variant of the minimum-phase property for general smooth nonlinear control systems. The definition of output-input stability does not rely on a particular choice of coordinates in which the system takes a normal form or on the computation of zero dynamics. In the spiri

Jialun Ping, Fan Wang, T. Goldman

We study the questions of the existence and mass of the proposed $d' (IJ^P=00^-)$ dibaryon in the quark-delocalization, color-screening model (QDCSM). The transformation between physical and symmetry bases has been extended to the cases beyond the SU(2) orbital symmetry. Using parameters fixed by baryon properties and $NN$ scattering, we find a mild attr

Ping Chen

We present results for the mass spectrum of $c{\bar c}$ mesons simulated on anisotropic lattices where the temporal spacing $a_t$ is only half of the spatial spacing $a_s$. The lattice QCD action is the Wilson gauge action plus the clover-improved Wilson fermion action. The two clover coefficients on an anisotropic lattice are estimated using mean links in L

J. Bub

A quantum key distribution scheme whose security depends on the features of pre- and post-selected quantum states is described.

Carlos A. Ramirez

A critical review is presented of the attempts to estimate the Strong Interactions contributions to the parameter $S$ ($L_{10}$ in the QCD Chiral Version). In particular it is discussed why the estimations done for Technicolor are unreliable. $S$ is calculated for heavy doublets of Techniquarks using the Nonrelativistic Quark Model and keeping $v\simeq 0.25$

R. Kerger

The $e^+p$-data collected with the ZEUS (${\cal L}=47.7$ pb$^{-1}$) and the H1 (${\cal L}=37$ pb$^{-1}$) detectors at HERA in 1994--1997 are analysed for signals of lepton flavour violation mediated by leptoquark exchange, both in the muon and the tau channels. No evidence for lepton flavour violation is found and limits on the leptoquarks' Yukawa coupli

I. Ennes, C. Lozano, S. Naculich, H. Schnitzer

We analyze the large N supergravity descriptions of the class of type IIB models T-dual to elliptic type IIA brane configurations containing two orientifold 6-planes and up to two NS 5-branes. The T-dual IIB configurations contain N D3-branes in the background of an orientifold 7-plane and, in some models, a Z_2 orbifold and/or D7-branes, which give rise to

S. Kalyana Rama

Tsallis has proposed a generalisation of the standard entropy, which has since been applied to a variety of physical systems. In the canonical ensemble approach that is mostly used, average energy is given by an unnromalised, or normalised, $q$-expectation value. A Lagrange multiplier $β$ enforces the energy constraint whose physical interpretation, however,

Manabu Miyamoto

The time operator, an operator which satisfies the canonical commutation relation with the Hamiltonian, is investigated, on the basis of a certain algebraic relation for a pair of operators T and H, where T is symmetric and H self-adjoint. This relation is equivalent to the Weyl relation, in the case of self-adjoint T, and is satisfied by the Aharonov-Bohm t

F. Alet, E. Sorensen

Open segments of S=1 antiferromagnetic spin chains are studied at finite temperatures and fields using continuous time Quantum Monte Carlo techniques. By calculating the resulting magnetization profiles for a large range of chain lengths with fixed field and temperature we reconstruct the experimentally measured NMR spectrum of impurity doped Y$_2$BaNi$_{1-x

I. Goidenko, G. Plunien, S. Zschocke, L. Labzowsky

The equivalence of the covariant renormalization and the partial-wave renormaliz ation (PWR) approach is proven explicitly for the one-loop self-energy correction (SE) of a bound electron state in the presence of external perturbation potentials. No spurious correctio n terms to the noncovariant PWR scheme are generated for Coulomb-type screening potentia ls

Vittorio Giovannetti, David Vitali

We study the dynamics of an optical mode in a cavity with a movable mirror subject to quantum Brownian motion. We study the phase noise power spectrum of the output light, and we describe the mirror Brownian motion, which is responsible for the thermal noise contribution, using the quantum Langevin approach. We show that the standard quantum Langevin equatio

Neven Bilic, Hrvoje Nikolic

A system of charged bosons at finite temperature and chemical potential is studied in a general-relativistic framework. We assume that the boson fields interact only gravitationally. At sufficiently low temperature the system exists in two phases: the gas and the condensate. By studying the condensation process numerically we determine the critical temperatu

J. Kowalski-Glikman

Following the procedure proposed recently by Martin and Brandenberger we investigate the spectrum of the cosmological perturbations in the case when the ``trans-Plackian'' dispersion relations are motivated by the quantum $κ$-Poincaré algebra. We find that depending on the choice of initial conditions of the perturbations, the spectrum either differs

Mariano Mendez, Michiel van der Klis, Eric C. Ford

We study the kilohertz quasi-periodic oscillations (kHz QPOs) in the low-mass X-ray binaries 4U 1728-34, 4U 1608-52, and Aql X-1. Each source traces out a set of nearly parallel lines in a frequency vs. X-ray count rate diagram. We find that between two of these tracks, for similar QPO frequency, the source count rate can differ by up to a factor of ~ 4, whe

T. Asaka, T. Yanagida

In a large class of supersymmetric (SUSY) axion model the mass of axino $\axino$ (a fermionic superpartner of the axion) is predicted as $m_{\axino} \lesssim {\cal O}(1)$ keV. Thus, the axino is the lightest SUSY particle (LSP). We pointed out that such a light axino provides a natural solution to the gravitino problem, if the gravitino is the next LSP. We d

M. Havukainen

Canonical quantization of electromagnetic field is traditionally done using plane waves. It is possible to formulate the quantization using other complete set of basis functions. Wavelets are a special kind of functions which are localized in real as well as in Fourier space. In this paper we show how wavelets can be used as basis functions in canonical quan

Alexander R. Kessel, Vladimir L. Ermakov

It is suggested to map the qubits into solid state NMR spin system collective states instead of the states of the individual spin. Such an approach introduces the stable computational basis without any additional actions and allows to obtain the universal set of quantum gates, which operation time is determined only by a RF pulse duration.

Vladimir Savichev

A series of high presicion atomic experiments was carried out last decade to get a better estimate for the electron (anti)neutrino mass $m_ν$. The reaction to be observed is molecular tritium $β$- decay. The $m_ν$ value serves as one of the tune parameters to fit $β$- electrons spectrum via reference theoretical one. The unexpected message consists of that p

Robert Alicki

The previously proposed Heisenberg-type relation $ E_c t_c >> \hbar {\cal C}$ for the energy used by a quantum computer, the total computation time and the logical ("classical") complexity of the problem is verified for the following examples of quantum computations: preparation of the input state, two Hamiltonian versions of the Grover's algorit

Michael L. Stein, Jean M. Quashnock, Ji Meng Loh

Motivated by the study of an important data set for understanding the large-scale structure of the universe, this work considers the estimation of the reduced second moment function, or K-function, of a stationary point process observed over a large number of segments of possibly varying lengths. Theory and simulation are used to compare the behavior of isot

Kirk T. McDonald

Scalar Bessel beams are derived both via the wave equation and via diffraction theory. While such beams have a group velocity that exceeds the speed of light, this is a manifestation of the "scissors paradox" of special relativty. The signal velocity of a modulated Bessel beam is less than the speed of light. Forms of Bessel beams that satisfy Maxwel

M. Ohlsson, C. Peterson, M. Ringner, R. Blankenbecler

A novel approach for structure alignment is presented, where the key ingredients are: (1) An error function formulation of the problem simultaneously in terms of binary (Potts) assignment variables and real-valued atomic coordinates. (2) Minimization of the error function by an iterative method, where in each iteration a mean field method is employed for the

Afsar Abbas

Non-locality or entanglement is an experimentally well established property of quantum mechanics. Here we study the role of quantum entanglement for higher symmetry group like $ SU(3_c) $, the gauge group of quantum chromodynamics (QCD). We show that the hitherto unexplained property of confinement in QCD arises as a fundamental feature of quantum entangleme

L. Ya. Kobelev

As well known rest masses of elementary particles and physical fields appear when temperature of Universe become low enough and symmetry broke. Are there another sources of rest masses that are consequences of other nature of rest masses or it is the only methods for generating rest masses? What will be with massless fields when the laws of symmetry are not

A. Garcia, J. L. Garcia-Luna, G. Lopez Castro

Measurements of neutron beta decay observables required to determine $|V_{ud}|$ are reaching the 0.1% accuracy. In this paper we review the calculation of the decay rate of this process, discuss its relevant uncertainties, and obtain an expression that is precise at the $10^{-4}$ level. Our analysis clearly shows the necessity of measurements of $λ$, the rat

G. A. Sokol, T. A. Aibergenov, A. V. Koltsov, A. V. Kravtsov

First experimental results on photoproduction of eta-mesic nuclei are analyzed. In an experiment performed at the 1 GeV electron synchrotron of the Lebedev Physical Institute, correlated pi+n pairs arising from the reaction gamma + 12C -> N + eta(A-1) -> N + pi+ + n + (A-2) and flying transversely to the photon beam have been observed. When the photon energy

Aristophanes Dimakis, Folkert Muller-Hoissen

We associate bicomplexes with several integrable models in such a way that conserved currents are obtained by a simple iterative construction. Gauge transformations and dressings are discussed in this framework and several examples are presented, including the nonlinear Schrodinger and sine-Gordon equations, and some discrete models.

Wieslaw Krolikowski, Ole Bang

We investigate the propagation of one-dimensional bright and dark spatial solitons in a nonlocal Kerr-like media, in which the nonlocality is of general form. We find an exact analytical solution to the nonlinear propagation equation in the case of weak nonlocality. We study the properties of these solitons and show their stability.

Emil J. Straube

We show that if the closure of a smooth pseudoconvex domain admits a "sufficiently nice" Stein neighborhood basis, then the d-bar Neumann problem on the domain is globally regular.

Fedor Bogomolov, Yuri Tschinkel

We construct examples of algebraic surfaces with interesting fundamental groups.

Charles A. Akemann, Soren Eilers

The concept of regularity in the meta-topological setting of projections in the double dual of a C*-algebra addresses the interrelations of a projection p with its closure, for instance in the form that such projections act identically, in norm, on elements of the C*-algebra. This concept has been given new actuality with the recent plan of Peligrad and Zsid

Karen L. Collins

It is shown that any finite, rank-connected, dismantlable lattice is lexicographically shellable (hence Cohen-Macaulay). A ranked, interval-connected lattice is shown to be rank-connected, but a rank-connected lattice need not be interval-connected. An example of a planar, rank-connected lattice that is not admissible is given.

Vera V. Dmitrieva

Point transformations of the 3-rd order ordinary differential equations are considered. Special classes of ordinary differential equations that are invariant under the general point transformations are constructed.

S. V. Astashkin

Necessary and sufficient conditions for the equivalence of the Rademacher chaos to the canonical basis of l_2 and also for the complementability of the corresponding generated subspace are derived. In particular, we obtain the unimprovability of the exponential integrability of functions from this space.

Y. Louzoun, H. Atlan, I. R. Cohen

A sharp TH1/TH2 dichotomy has often been used to define the effects of cytokines on autoimmune diseases. However contradictory results in recent research indicate that the situation may be more complex. We build here a simple mathematical model aimed at settling the contradictions. The model is based on a neural network paradigm, and is applied using Partial

Victor Alexandrov

We study the existence problem for a local implicit function determined by a system of nonlinear algebraic equations in the particular case when the determinant of its Jacobian matrix vanishes at the point under consideration. We present a system of sufficient conditions that implies existence of a local implicit function as well as another system of suffici

Ruslan Sharipov

Explicit description for arbitrary Newtonian dynamical system admitting the normal shift in Riemannian manifold of the dimension $n\geq 3$ is found. On the base of this result the kinematics of normal shift of hypersurfaces along trajectories of such system is studied.

Chen Ying, He Bing, Lin He, Wu Ji-Min

The purpose of this paper is to investigate the gauge symmetry of classical field theories in integral formalism. A gauge invariant theory is defined in terms of the invariance of the physical observables under the coordinate transformations in principal bundle space. Through the detailed study on the property of non-Abelian parallel transportor under gauge

M. Ramon Medrano, N. Sanchez

A {\cal R} "dual" transform is introduced which relates Quantum Field Theory and String regimes, both in a curved background with D-non compact dimensions. This operation maps the characteristic length of one regime into the other (and, as a consequence, mass domains as well). The {\cal R}-transform is not an assumed or {\it a priori} imposed symmetr

Carlos Pinheiro, F. C. Khanna

We write the Hamiltonian for a gravitational spherically symmetric scalar field collapse with massive scalar field source, and we discuss the application of Wheeler De Witt equation as well as the appearence of time in this context. Using an Ansatz for Wheeler De Witt equation, solutions are discussed including the appearence of time evolution.

I. Ennes, C. Lozano, S. Naculich, H. Rhedin

Methods are reviewed for computing the instanton expansion of the prepotential for N=2 Seiberg-Witten theory with non-hyperelliptic curves. These results, when compared with the instanton expansion obtained from the microscopic Lagrangian, provide detailed tests of M-theory. Group theoretic regularities of F_ 1-inst allow one to "reverse engineer" a

J. S. Dowker

The divergence found by Nesterenko, Lambiase and Scarpetta in the Casimir energy on a semi-circular cylinder is attributed to the existence of edges.

Lee Smolin

We find evidence for a duality between the standard matrix formulations of M theory and a background independent theory which extends loop quantum gravity by replacing SU(2) with a supersymmetric and quantum group extension of SU(16). This is deduced from the recently proposed cubic matrix model for M theory which has been argued to have compactifications wh

A. M. Polyakov

This article, based on the Klein lecture, contains some new results and new speculations on various topics. They include discussion of open strings in the AdS space, unusual features of D-branes, conformal gauge theories in higher dimensions. We also comment on the infrared screening of the cosmological constant and on the "brane worlds"

Carlos Pinheiro, Cintia G. Pinheiro, F. C. Khanna

The purpose of this paper is to study static solution configuration which describes the magnetic monopoles in a scenary where the gravitation is coupled with Higgs, Yang-Mills and fermions. We are looking for analysis of the energy functional and Bogomol'nyi equations. The Einstein equations now take into consideration the fermions' contribution for

Kevin Cahill

Neutrino masses and mixings are analyzed in terms of left-handed fields and a 6x6 complex symmetric mass matrix whose singular values are the neutrino masses. An angle theta_nu characterizes the kind of the neutrinos, with theta_nu=0 for Dirac neutrinos and theta_nu=pi/2 for Majorana neutrinos. At theta_nu = 0 baryon-minus-lepton number is conserved. If thet

Todd Fugleberg

In an effective Lagrangian approach to QCD we nonperturbatively calculate an analytic approximation to the decay rate of a false vacuum per unit volume, $Γ/V$. We do so for both zero and high temperature theories. This result is important for the study of the early universe at around the time of the QCD phase transition. It is also important in order to dete

Markus A. Luty, John Terning, Aaron K. Grant

We construct models in which electroweak symmetry is spontaneously broken by supersymmetric strong dynamics at the TeV scale. The order parameter is a composite of scalars, and the longitudinal components of the W and Z are strongly-coupled bound states of scalars. The usual phenomenological problems of dynamical electroweak symmetry breaking are absent: the

V. Barger, T. Han, J. Jiang

We study the production at future $e^+e^-$ linear colliders of the heavy neutral Higgs bosons $H$ and $A$ of the minimal supersymmetric standard model in association with top and bottom quarks. The cross sections have a strong dependence on the parameter $\tanβ$, and thus provide a good way to determine it. At a linear collider with $\sqrt s = 0.5-1$ TeV and

U. Ellwanger, C. Hugonie

We give the upper bounds on the masses of the lightest and second lightest CP even Higgs bosons in the NMSSM, the MSSM extended by a gauge singlet. The dominant two loop corrections are included. Since the coupling R of the lightest Higgs scalar to gauge bosons can be small, we study in detail the relation between masses and couplings of both lightest scalar

V. A. Nikonov, J. Nyiri

Model independent verification of the quark combinatorics rules, which govern the ratios of the yields of secondaries, is presented for jet processes. Because of a large number of produced resonances in the hadron jets, a test of the quark combinatorics rules is hardly possible in the central region, x_{hadron} < 0.2. However, a model-independent verificatio

I. Schienbein

Parameter-free and perturbatively stable leading order (LO) and next-to-leading order (NLO) parton densities for real and virtual photons are presented.

Shinji Ejiri, Jisuke Kubo, Michika Murata

Pure lattice SU(2) Yang-Mills theory in five dimensions is considered, where an extra dimension is compactified on a circle. Monte-Carlo simulations indicate that the theory possesses a continuum limit with a non-vanishing string tension if the compactification radius is smaller than a certain value $R_M$ which is $O(1/10)$ of the inverse of the square root

A. Ringwald, F. Schrempp

In view of the new (preliminary) search results for instanton-induced events at HERA from the H1 collaboration, we present a brief discussion of (controllable) theoretical uncertainties, both in the event topology and the calculated rate.

Harry Lehmann, Per Osland, Tai Tsun Wu

When the electron density is a linear function of distance, it is known that the MSW equations for two neutrino species can be solved in terms of known functions. It is shown here that more generally, for any number of neutrino species, these MSW equations can be solved exactly in terms of single integrals. While these integrals cannot be expressed in terms

M. Wakamatsu

The spin-dependent structure functions g_2 (x, Q^2) are investigated within the framework of the chiral quark soliton model. It turns out that the twist-3 part of g_2 (x, Q^2) gives nonnegligible contributions to the total distributions at the energy scale of Q^2 = 5 {GeV}^2 but mainly in the smaller x region only, so that the corresponding third moments \in

Giovanni Amelino-Camelia, Tsvi Piran

It has been recently observed that small violations of Lorentz invariance, of a type which may arise in quantum gravity, could explain both the observations of cosmic rays above the GZK cutoff and the observations of 20-TeV gamma rays from Markarian 501. We show here that different pictures of the short-distance structure of space-time would lead to differen

D. Müller

Skewed parton distributions contain new non-perturbative information about hadronic states. Thus, their extraction from experimental data is an important goal. Properties and models for skewed parton distributions as well as their extraction, based on perturbative leading-order results, are shortly reviewed.

S. Ambrosanio, H. Baer, A. Brignole, A. Castro

There are many low-energy models of supersymmetry breaking parameters which are motivated by theoretical and experimental considerations. Here, we discuss some of the lesser-known theories of low-energy supersymmetry, and outline their phenomenological consequences. In some cases, these theories have more gauge symmetry or particle content than the Minimal S

S. Ying

A stable soliton configuration for a nucleon emerges when the nucleon stability and $Σ_N$ term discrepancy problems are studied semi-quantitatively within a local theory developed recently. The approach developed here goes beyond the mean field or Hartree-Fock approximation by taking into account of the non-perturbative wave function renormalization in a way

S. Hands, I. Montvay, S. Morrison, M. Oevers

We identify the global symmetries of SU(2) lattice gauge theory with N flavors of staggered fermion in the presence of a quark chemical potential mu, for fermions in both fundamental and adjoint representations, and anticipate likely patterns of symmetry breaking at both low and high densities. Results from numerical simulations of the model with N=1 adjoint

K. Vesely, J. Podolsky

A Hamiltonian system with a modified Henon-Heiles potential is investigated. This describes the motion of free test particles in vacuum gravitational pp-wave spacetimes with both quadratic (&#34;homogeneous&#34;) and cubic (&#34;non-homogeneous&#34;) terms in the structural function. It is shown that, for energies above a certain value, the motion is chaotic

Milan Stefanik, Jan Horsky

We will show that the Nariai metric, i.e. the static spherically symmetric vacuum spacetime with a cosmological constant, admits a conformally Kerr-Schild spacetime representation. We find the vacuum solutions of the Einstein-Maxwell equations for the Nariai metric using the Horsky-Mitskievich generating conjecture.

Manfred Requardt

In the following we undertake to derive quantum theory as a stochastic low-energy and coarse-grained theory from a more primordial discrete and basically geometric theory living on the Planck scale and which (as we argue) possibly underlies also \tit{string theory}. We isolate the so-called \tit{ideal elements} which represent at the same time the cornerston

Patrick B. Warren

Phase separation in charged systems may involve the replacement of critical points by microphase separated states, or charge-density-wave states. A density functional theory for highly charged colloids at low ionic strength is developed to examine this possibility. It is found that the lower critical solution point is most susceptible to microphase separatio

C. Bernhard, J. L. Tallon, Th. Blasius, A. Golnik

The doping dependence of the superconducting condensate density, n_{s}^{o}, has been studied by muon-spin-rotation for Y_{0.8}Ca_{0.2}Ba_{2}(Cu_{1-z}Zn_{z})_{3}O_{7-δ} and Tl_{0.5-y}Pb_{0.5+y}Sr_{2}Ca_{1-x}Y_{x}Cu_{2}O_{7}. We find that n_{s}^{o} exhibits a pronounced peak at a unique doping state in the slightly overdoped regime. Its position coincides with

German Drazer, Joel Koplik

The permeability of two-dimensional fractures with self-affine fractal roughness is studied via analytic arguments and numerical simulations. The limit where the roughness amplitude is small compared with average fracture aperture is analyzed by a perturbation method, while in the opposite case of narrow aperture, we use heuristic arguments based on lubricat

G. B. Martins, C. Gazza, E. Dagotto

The hole-doped standard and extended t-J models on ladders with anisotropic Heisenberg interactions are studied computationally in the interval $0.0 \leq λ\leq 1.0$ ($λ=0$, Ising; $λ=1$, Heisenberg). It is shown that the approximately half-doped stripes recently discussed at $λ=1$ survive in the anisotropic case ($λ$$<$1.0), particularly in the &#34;extended

Claudio Chamon, Eduardo R. Mucciolo

We find a non-perturbative saddle-point solution for the non-linear sigma model proposed by Finkelstein for interacting and disordered electronic systems. Spin rotation symmetry, present in the original saddle point solution, is spontaneously broken at one-loop, as in the Coleman-Weinberg mechanism. The new solution is singular in both the disorder and tripl

T. Borzsonyi, T. Toth-Katona, A. Buka, L. Granasy

The dynamic response of dendritic solidification to spatially homogeneous time-periodic forcing has been studied. Phase-field calculations performed in two dimensions (2D) and experiments on thin (quasi 2D) liquid crystal layers show that the frequency of dendritic side-branching can be tuned by oscillatory pressure or heating. The sensitivity of this phenom

Joerg Buenemann, Florian Gebhard, Werner Weber

Multi-band Gutzwiller-correlated wave functions reconcile the contrasting concepts of itinerant band electrons versus electrons localized in partially filled atomic shells. The approximate evaluation of these variational ground states becomes exact in the limit of large coordination number. The result allows the identification of quasi-particle band structur

A. Levy Yeyati, M. Buttiker

The properties of scattering phases in quantum dots are analyzed with the help of lattice models. We first derive the expressions relating the different scattering phases and the dot Green functions. We analyze in detail the Friedel sum rule and discuss the deviation of the phase of the transmission amplitude from the Friedel phase at the zeroes of the trans

Markus Lazar

We consider the static elastoplastic theory of dislocations in an elastoplastic material. We use a Yang-Mills type Lagrangian (the teleparallel equivalent of Hilbert-Einstein Lagrangian) and some Lagrangians with anisotropic constitutive laws. The translational part of the generalized affine connection is utilized to describe the theory of elastoplasticity i

T. J. Inagaki, M. Aihara, A. Takahashi

We present a unified theory of luminescence spectra for highly excited semiconductors, which is applicable both to the electron-hole BCS state and to the exciton Bose-Einstein condensate. The crossover behavior between electron-hole BCS state and exciton Bose-Einstein condensate clearly manifests itself in the calculated luminescence spectra. The analysis is

Ren-Bao Liu, Bang-fen Zhu

The dynamic Fano resonance (DFR) between discrete quasienergy excitons and sidebands of their ionization continua is predicted and investigated in dc- and ac-driven semiconductor superlattices. This DFR, well controlled by the ac field, delocalizes the excitons and opens an intrinsic decay channel in nonlinear four-wave mixing signals.

J. S. Dodge, C. P. Weber, J. Corson, J. Orenstein

We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO_3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, w

S. A. Mikhailov

I present variational solutions of the many-body Schrödinger equation for a two-dimensional electron system in strong magnetic fields, which have, at $ν=1$, the energy about 46% lower than the energy of the Laughlin liquid. At $ν=2/3$, I obtain the energy, about 29% lower than was reported so far.

Thomas Matheson, Alexei V. Filippenko, Luis C. Ho, Aaron J. Barth

We present a detailed study of line structure in early to late-time spectra of Supernova (SN) 1993J. Spectra during the nebular phase, but within the first two years after explosion, exhibit small-scale structure in the emission lines of some species, notably oxygen and magnesium, showing that the ejecta of SN 1993J are clumpy. On the other hand, a lack of s

T. Matheson, A. V. Filippenko, A. J. Barth, L. C. Ho

We present 42 low-resolution spectra of Supernova (SN) 1993J, our complete collection from the Lick and Keck Observatories, from day 3 after explosion to day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J began as an apparent SN II, albeit an unusual one. After a few weeks, a dramatic transition took place, as prominent helium line

Robert L. Hurt, Tom H. Jarrett, J. Davy Kirkpatrick, Roc M. Cutri

We present the basic properties of three objects near the Galactic Plane - a large galaxy and two candidate globular clusters - discovered in the Two Micron All Sky Survey (2MASS) dataset. All were noted during spot-checks of the data during 2MASS quality assurance reviews. The galaxy is a late-type spiral galaxy (Sc-Sd), ~11 Mpc distant. We estimate an exti

Geraint F. Lewis, Rodrigo A. Ibata

We present a new method to identify and probe planetary companions of stars in the Galactic Bulge and Magellanic Clouds using gravitational microlensing. While spectroscopic studies of these planets is well beyond current observational techniques, monitoring polarization fluctuations during high magnification events induced by binary microlensing events will

Jon P. Fulbright

We describe observations and abundance analysis of a high-resolution, high-S/N survey of 168 stars, most of which are metal-poor dwarfs. We follow a self-consistent LTE analysis technique to determine the stellar parameters and abundances, and estimate the effects of random and systematic uncertainties on the resulting abundances. Element-to-iron ratios are

F. Wyrowski, C. M. Walmsley, W. M. Goss, A. G. G. M. Tielens

The VLA and the BIMA array were used to obtain high resolution (10-20&#34;) observations of C+, traced by the C91a recombination line at 8.6 GHz, and the dense molecular gas, traced by HCN and HCO+(1-0), of the photon dominated region (PDR) associated with the reflection nebula NGC 2023. Using the VLA, continuum emission is detected at 8.6 GHz from a faint H

Ilaria Cagnoni, Annalisa Celotti, Davide Poccecai

We present the aim and the status of the BLEIS project currently under development at SISSA. This project consists in selecting a complete Blazar sample from deep optical data, down to B=24.6, V=24.4 and I=23.7 (80% completness). The optical images are taken from the ESO Imaging Survey (EIS - Wide), a public survey covering ~16 deg2 of the Southern Emisphere

Ilaria Cagnoni, Annalisa Celotti, Martin Elvis, Dong-Woo Kim

The X-ray sky is not as well known as is sometimes thought. We report on our search of minority populations (Kim & Elvis 1999). One of the most intriguing is that of `blank field sources&#39;, i.e. bright ROSAT sources (F(X)>1e-13 erg/cm2/s) with no optical counterpart on the Palomar Sky Survey (to O=21.5) within their 39&#34;(99%) radius error circle. The n

Ilaria Cagnoni, Antonella Fruscione, Iossif E. Papadakis

The Extreme Ultraviolet Explorer (EUVE) satellite accumulated ~one million seconds of public data between 1994 and 1997 for the BL Lacertae object Markarian 421. This is the second of two papers in which we present the results of spectral and temporal analysis of this EUVE data set. We analyze in the present paper the imaging data by means of power spectrum

K. O&#39;Neil

Recent surveys have discovered hundreds of low surface brightness galaxies in the local (z < 0.1) Universe. Plots of the surface brightness distribution (the space density of galaxies plotted against central surface brightness) show a flat distribution from the bright-end cutoff of 21.65 through the current observational limit of 25.0 B mag arcsec^{-2}. As n

Claus Kiefer

According to the inflationary scenario, all structure in the Universe can be traced back to quantum fluctuations of the metric and scalar field(s) during inflation. The seeds of this structure can be observed as classical anisotropies in the cosmic microwave background. I briefly review how the transition from the inherent quantum nature of these fluctuation

G. Bono, F. Caputo, S. Cassisi, M. Marconi

We present a comprehensive theoretical investigation of the evolutionary properties of intermediate-mass stars. The evolutionary sequences were computed from the Zero Age Main Sequence up to the central He exhaustion and often up to the phases which precede the carbon ignition or to the reignition of the H-shell which marks the beginning of the thermal pulse

S. Mereghetti, D. Cremonesi, M. Feroci, M. Tavani

We have observed with the BeppoSAX satellite the quiescent counterpart of the Soft Gamma-ray Repeater SGR 1806-20. Observations performed in October 1998 and in March 1999 showed that this pulsar continued its long term spin-down trend at an average rate of ~8 10e-11 s/s while its flux and spectrum remained remarkably constant between the two observations, d

M. Vivekanand

Time-scales of radio emission are studied in PSR J0437-4715 at 327 MHz using almost half a million periods of high quality data from Ooty Radio Telescope. The radio emission in this milli second pulsar occurs on a short (s) time-scale of approximately 0.026 +- 0.001 periods, and on a (l) time-scale that is much longer than the widths of the components of the

I. Marquez, F. Durret, J. Masegosa, M. Moles

We present the analysis of morphological and photometric properties of a sample of isolated spirals with (18) and without (11) an active nucleus, based on near-infrared imaging in the J and K&#39; bands. The aim of this analysis is to find the differential properties that could be directly connected with the phenomenon of nuclear activity. We stress the impo

Floris F. S. van der Tak, Ewine F. van Dishoeck

Recent models of the envelopes of seven massive protostars are used to analyze observations of H3+ infrared absorption and H13CO+ submillimeter emission lines toward these stars, and to constrain the cosmic-ray ionization rate zeta. The H13CO+ gives best-fit values of zeta=(2.6+/- 1.8) x 10^-17 s^-1, in good agreement with diffuse cloud models and with recen

Mariano Mendez

I describe a new technique that we have been using in the past few years to get precise measurements of the frequency separation of the kHz QPOs in some Low-mass X-ray binaries. I show how this technique (that we call &#34;shift-and-add&#34;) works, and I present some of the results we obtained using it.

Mariano Mendez, Michiel van der Klis

We use data from the Rossi X-ray Timing Explorer to search for harmonics and sidebands of the two simultaneous kilohertz quasi-periodic oscillations (kHz QPOs) in Sco X-1. We do not detect any of these harmonics or sidebands, with 95% confidence upper limits to their power between ~ 1% and ~ 10% of the power of the upper kHz QPO. The oscillations produced at

J. E. Avron, A. Gordon

The standard Born Oppenheimer theory does not give an accurate description of the wave function near points of level crossing. We give such a description near an isotropic conic crossing, for energies close to the crossing energy. This leads to the study of two coupled second order ordinary differential equations whose solution is described in terms of the g