February 2001 arXiv papers — page 18

P. P. Avelino, S. Esposito, G. Mangano, C. J. A. P. Martins

Higher-dimensional theories have the remarkable feature of predicting a time (and hence redshift) dependence of the `fundamental' four dimensional constants on cosmological timescales. In this paper we update the bounds on a possible variation of the fine structure constant alpha at the time of BBN (z =10^10) and CMB (z=10^3). Using the recently-released

R. Senesi, C. Andreani, D. Colognesi, A. Cunsolo

For the first time, an experimental determination of the single-particle mean kinetic energies for 3He along the T=2.00 K isotherm in the dense liquid and in the solid hcp and bcc phases is reported. Deep Inelastic Neutron Scattering measurements at exchanged wavevectors ranging from 90.0 A^-1 to 140.0 A^-1 have been performed in order to evaluate, within th

M. Dube, P. C. E. Stamp

We briefly review the oscillator and spin bath models of quantum environments, which can be used to describe the low-energy dynamics of open quantum systems. We then use them to discuss both the mechanisms causing decoherence at low $T$, and the dynamics of this decoherence. This is done first for a central 2-level system coupled to these environments- the r

M. Hirsch, S. F. King

We consider how well current theories can predict neutrino mass and mixing parameters, and construct a statistical discriminator which allows us to compare different models to each other. As an example we consider see-saw models based on family symmetry, and single right-handed neutrino dominance, and compare them to each other and to the case of neutrino an

T. S. Kosmas, Sergey Kovalenko, Ivan Schmidt

We study nuclear muon-electron (mu-e) conversion in the general framework of effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation (LFV). All the possible types of short range interactions (non-photonic mechanisms), i.e. (pseudo-)scalar, (axial-)vector

Marc Freitag, Willy Benz

We have developed a new simulation code aimed at studying the stellar dynamics of a galactic central star cluster surrounding a massive black hole. In order to include all the relevant physical ingredients (2-body relaxation, stellar mass spectrum, collisions, tidal disruption,...), we chose to revive a numerical scheme pioneered by Henon in the 70's. It

M. V. Cheremisin

Based on a thermodynamic approach, we have calculated the resistivity of a 2D electron gas, assumed $dissipationless$ in a strong quantum limit. Standard measurements, with extra current leads, define the resistivity caused by a combination of Peltier and Seebeck effects. The current causes heating(cooling) at the first(second) sample contacts, due to the Pe

Cornelius Paufler, Hartmann Romer

Multisymplectic geometry - which originates from the well known de Donder-Weyl theory - is a natural framework for the study of classical field theories. Recently, two algebraic structures have been put forward to encode a given theory algebraically. Those structures are formulated on finite dimensional spaces, which seems to be surprising at first. In this

M. Dvornikov, A. Studenikin

Within the Lorentz invariant formalizm for description of neutrino evolution in electromagnetic fields and matter we consider neutrino spin oscillations in the circular polarized electromagnetic wave, the amplitude of which is a modulated function of time. It is shown for the first time that the parametric resonance of neutrino oscillations can occur in such

Alain Barrat, Ludovic Berthier

The out of equilibrium dynamics of finite dimensional spin glasses is considered from a point of view going beyond the standard `mean-field theory' versus `droplet picture' debate of the last decades. The main predictions of both theories concerning the spin glass dynamics are discussed. It is shown, in particular, that predictions originating from m

Georg Goeppert, Hermann Grabert

We study the energy relaxation of quasiparticles in voltage biased mesoscopic wires in presence of magnetic impurities. The renormalization of the exchange interaction of Kondo impurities coupled to conduction electrons is extended to the case of a nonequilibrium electron distribution, which is determined self-consistently from a Boltzmann equation with a co

J. Ellis, T. Falk, G. Ganis, K. A. Olive

We extend previous combinations of LEP and cosmological relic density constraints on the parameter space of the constrained MSSM, with universal input supersymmetry-breaking parameters, to large tan beta. We take account of the possibility that the lightest Higgs boson might weigh about 115 GeV, but also retain the possibility that it might be heavier. We in

Andreas Glatz, Sanjay Kumar, Mai Suan Li

The effect of disorder on the static and dynamic behaviour of one-dimensional charge density waves at low temperatures is studied by analytical and numerical approaches. In the low temperature region the spatial behaviour of the phase-phase correlation function is dominated by disorder but the roughness exponent remains the same as in the pure case. Contrary

Daijiro Suematsu, George Zoupanos

We propose a solution to the $\mu$-problem due to the non-universal soft supersymmetry breaking in a class of supersymmetric extensions of the SM with an extra U(1) and the NMSSM. Our scenario resembles an earlier one which has been proposed as a solution to the $\mu$-problem in the framework of similar models but it has rather different features from that.

F. Arleo, P. -B. Gossiaux, T. Gousset, J. Aichelin

We compute the total cross section of a heavy quarkonium on a hadron target in leading twist QCD, including target mass corrections. Our method relies on the analytical continuation of the operator product expansion of the scattering amplitude, obtained long ago by Bhanot and Peskin. The cross section has a simple partonic form, which allows us to investigat

K. E. Feldman

We present a solution of the generalized Hirzebruch problem on the relations between the Chern numbers of a stably almost complex manifold and the Chern numbers of its virtual Chern submanifolds.

L. Consoli, H. J. F. Knops, A. Fasolino

We show that invariance properties of the Lagrangian of an incommensurate system, as described by the Frenkel Kontorova model, imply the existence of a generalized angular momentum which is an integral of motion if the system remains floating. The behavior of this quantity can therefore monitor the character of the system as floating (when it is conserved) o

S. Esposito

We consider photonic tunnelling through evanescent regions and obtain general analytic expressions for the transit (phase) time $τ$ (in the opaque barrier limit) in order to study the recently proposed ``universality'' property according to which $τ$ is given by the reciprocal of the photon frequency. We consider different physical phenomena (corresp

M. Marklund, D. Anderson, F. Cattani, M. Lisak

Fermat's principle and variational analysis is used to analyze the trajectories of light propagating in a radially inhomogeneous medium with a singularity in the center. It is found that the light trajectories are similar to those around a black hole, in the sense that there exists a critical radius within which the light cannot escape, but spirals into

Martin Servin, Gert Brodin, Mattias Marklund

We study the propagation of gravitational waves in a collisionless plasma with an external magnetic field parallel to the direction of propagation. Due to resonant interaction with the plasma particles the gravitational wave experiences cyclotron damping or growth, the latter case being possible if the distribution function for any of the particle species de

Joseph C. Varilly

We show that the noncommutative spheres of Connes and Landi are quantum homogeneous spaces for certain compact quantum groups. We give a general construction of homogeneous spaces which support noncommutative spin geometries.

David Beckman, Daniel Gottesman, M. A. Nielsen, John Preskill

We examine constraints on quantum operations imposed by relativistic causality. A bipartite superoperator is said to be localizable if it can be implemented by two parties (Alice and Bob) who share entanglement but do not communicate; it is causal if the superoperator does not convey information from Alice to Bob or from Bob to Alice. We characterize the gen

E. Cerboneschi, F. Renzoni, E. Arimondo

We investigate theoretically the slow group velocity of a pulse probe laser propagating through a cold sample and interacting with atoms in a three-level $Λ$ configuration having losses towards external states. The EIT phenomenon produces very small group velocities for the probe pulse in presence of a strong coupling field even in presence of the population

Matteo G. A. Paris

We present a conditional experiment involving a parametric amplifier and an avalanche photodetector to generate highly nonclassical states of the radiation field. The nonclassicality is robust against amplifier gain, detector efficiency and dark counts. At the output all the generalized Wigner functions have negative values, and this is exploited in order to

C. Y. Chen

A nonperturbative procedure of solving the time-dependent Schrödinger equation, called the multi-projection approach or phase dynamics of quantum mechanics, is derived and illustrated. In addition to introducing a method with that time-dependent systems become solvable (under the assumption that corresponding time-independent systems are solvable), the new a

Evgueni V. Kovarski

The time-dependent electromagnetic field can results both pair waves and pair particles. It can be for mathematical relations between two functions with identical argument and difference of phases equal to $π$. Two examples both the opportunity of phase synchronism for different frequencies of at atom-field interaction with known abnormal dispersion of refra

K. C. Chung, C. S. Wang, A. J. Santiago

The extraction of nuclear matter properties from measured nuclear masses is investigated in the energy density functional formalism of nuclei. It is shown that the volume energy $a_1$ and the nuclear incompressibility $K_0$ depend essentially on $μ_n N+\barμ_p Z-2E_N$, whereas the symmetry energy $J$ and the density symmetry coefficient $L$ as well as symmet

A. Lavagno, P. Quarati

We show that in weakly non-ideal plasmas, like the solar interior, both non-extensivity and quantum uncertainty (a' la Galitskii and Yakimets) should be taken into account to derive equilibrium ion distribution functions and to estimate nuclear reaction rates and solar neutrino fluxes.

R. Shyam, P. Danielewicz

Within the pure Coulomb breakup mechanism, we investigate the one-neutron removal reaction of the type A(a,b$γ$)X with $^{11}$Be and $^{19}$C projectiles on a heavy target nucleus $^{208}$Pb at the beam energy of 60 MeV/nucleon. Our intention is to examine the prospective of using these reactions to study the structure of neutron rich nuclei. Integrated part

H. Akaike, Y. Tsue, C. Providencia, J. da Providencia

The su(2)-algebraic model interacting with an environment is investigated from a viewpoint of treating the dissipative system. By using the time-dependent variational approach with a coherent state and with the help of the canonicity condition, the time-evolution of this quantum many-body system is described in terms of the canonical equations of motion in t

J. Arrington, C. S. Armstrong, T. Averett, O. K. Baker

Inclusive electron scattering data are presented for ^2H and Fe targets at an incident electron energy of 4.045 GeV for a range of momentum transfers from Q^2 = 1 to 7 (GeV/c)^2. Data were taken at Jefferson Laboratory for low values of energy loss, corresponding to values of Bjorken x greater than or near 1. The structure functions do not show scaling in x

Paolo Giuliani, Mogens H. Jensen, Victor Yakhot

We investigate the GOY shell model within the scenario of a critical dimension in fully developed turbulence. By changing the conserved quantities, one can continuously vary an ``effective dimension'' between $d=2$ and $d=3$. We identify a critical point between these two situations where the flux of energy changes sign and the helicity flux diverges

V. I. Karpman, J. J. Rasmussen, A. G. Shagalov

The dynamics of soliton and quasisoliton solutions of cubic third order nonlinear Schrödinger equation is studied. The regular solitons exist due to a balance between the nonlinear terms and (linear) third order dispersion; they are not important at small $α_3$ ($α_3$ is the coefficient in the third derivative term) and vanish at $α_3 \to 0$. The most essent

Peter Gacs

Toom's north-east-self voting cellular automaton rule R is known to suppress small minorities. A variant which we call R^+ is also known to turn an arbitrary initial configuration into a homogenous one (without changing the ones that were homogenous to start with). Here we show that R^+ always increases a certain property of sets called thickness. This r

Hans Frisk, Serge de Gosson

The motion in the complex plane of the zeros to various zeta functions is investigated numerically. First the Hurwitz zeta function is considered and an accurate formula for the distribution of its zeros is suggested. Then functions which are linear combinations of different Hurwitz zeta functions, and have a symmetric distribution of their zeros with respec

A. Berkovich, P. Paule

The object of this paper is to propose and prove a new generalization of the Andrews-Gordon identities, extending a recent result of Garrett, Ismail and Stanton. We also give a combinatorial discussion of the finite form of their result, which appeared in the work of Andrews, Knopfmacher, and Paule.

Boris Vaillant

Generalizing work of W. Müller we investigate the spectral theory for the Dirac operator D on a noncompact manifold X with generalized fibred cusps $$ C(M)=M\times [A,\infty[_r, g= d r^2+ ϕ^*g_Y+ e^{-2cr}g_Z, $$ at infinity. Here $ϕ:M^{h+v}\to Y^h$ is a compact fibre bundle with fibre Z and a distinguished horizontal space HM. The metric $g_Z$ is a metric in

N. A. Gromov, I. V. Kostyakov, V. V. Kuratov

Possible contractions of quantum orthogonal groups which correspond to different choices of primitive elements of Hopf algebra are considered and all allowed contractions in Cayley--Klein scheme are obtained. Quantum deformations of kinematical groups have been investigated and have shown that quantum analog of (complex) Galilei group G(1,3) do not exist in

Justin R. Smith

This paper extends the results of "Operads and Algebraic Homotopy" in giving algebraic invariants for the stable homotopy type of a pointed simply-connected simplicial set.

Odile Sauzet

We construct explicitly APF extensions of finite extensions of $\qp$ for which the Galois group is not a p-adic Lie group and which do not have any open subgroup with $\zp$-quotient.

Jean-Louis Loday, Maria O. Ronco

In "Hopf algebra of the planar binary trees", Adv. Math. 139 (1998), no. 2, 293--309, we constructed by induction a graded associative product on the vector space generated by the planar binary trees (resp. the permutations). In the present paper we prove an explicit formula for this product in terms of a partial order on the set of planar binary tre

Lin WENG

In this paper, we introduce (local and) global non-abelian zeta functions for general curves. As an example, we compute the so-called rank two zeta functions for genus two curves by studying non-abelian Brill-Noether loci and their infinitesimal structures.

Michael Anshelevich

The objects under investigation are the stochastic integrals with respect to free Levy processes. We define such integrals for square-integrable integrands, as well as for a certain general class of bounded integrands. Using the product form of the Ito formula, we prove the full functional Ito formula in this context.

Lev Borisov, Anatoly Libgober

Orbifold elliptic genus and elliptic genus of singular varieties are introduced and relation between them is studied. Elliptic genus of singular varieties is given in terms of a resolution of singularities and extends the elliptic genus of Calabi-Yau hypersurfaces in Fano Gorenstein toric varieties introduced earlier. Orbifold elliptic genus is given in term

E. T. Akhmedov

AdS/CFT-correspondence establishes a relationship between supersymmetric gravity (SUGRA) on Anti-de-Sitter (AdS) space and supersymmetric Yang-Mills (SYM) theory which is conformaly invariant (CFT). The AdS space is the solution of the Einstein-Hilbert equations with a constant negative curvature. Why is this relationship important? What kind of relationship

A. A. Bichl, J. M. Grimstrup, L. Popp, M. Schweda

We investigate the quantization of the theta-expanded noncommutative U(1) Yang-Mills action, obtained via the Seiberg-Witten map. As expected we find non-renormalizable terms. The one-loop propagator corrections are gauge independent, and lead us to a unique extention of the noncommutative classical action. We interpret our results as a requirement that also

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

We discuss spectra of $AdS_3$ supergravities, arising in the near horizon geometry of D1/D5 systems in orbifolds/orientifolds of type IIB theory with 16 supercharges. These include models studied in a recent paper (hep-th/0012118), where the group action involves also a shift along a transversal circle, as well as IIB/$ΩI_4$, which is dual to IIB on $K3$. Af

Mahiko Suzuki

Isospin breaking correction to the $ΔI = {1/2}$ decay of $K\toππ$ generates a large enough contribution to $ε'$ through an induced $ΔI = {3/2}$ amplitude in $K_L$ decay. Aside from the $π$-$η$ and $π$-$η'$ mixing contributions, there is a correction of kinematical origin due to the final-state $π^{\pm}$-$π^0$ mass difference, which is unambiguously c

Ulrich Heinz

Multi-boson symmetrization effects on two-particle Bose-Einstein interferometry are studied for ensembles with arbitrary multiplicity distributions. In the general case one finds interesting residual correlations which require a modified framework for extracting information on the source geometry from two-particle correlation measurements. In sources with hi

Marieke Postma

Sources of ultrahigh energy photons operating at high red shift produce a diffuse background of neutrinos. At high red shift, when the cosmic microwave background radiation has a higher temperature, an electromagnetic cascade originated by an energetic photon can generate neutrinos via muon and pion production and decay. We have calculated numerically the ne

M. Hirsch

Recently Hall, Murayama and Weiner (Phys. Rev. Lett. 84 (2000) 2572, [hep-ph/9911341]) claimed that neutrino oscillation data are well accounted for by a neutrino mass matrix which appears to have random entries. Here this claim is disputed by constructing a specific counter example. Structure in the neutrino mass matrix is clearly preferred over random matr

Michael Melles

At energies ($\sqrt{s}$) much higher than the electroweak gauge boson masses ($M$) large logarithmic corrections of the scale ratio $\sqrt{s}/M$ occur. While the electroweak Sudakov type double (DL) and universal single (SL) logarithms have recently been resummed, at higher orders the electroweak renormalization group (RG) corrections are folded with the DL

C. S. Kim

Here I summarize P5-WG (New/Alternative Physics Working Group) of LCWS2000@FNAL, held on Oct 24-28, 2000. There were 13 talks altogether, 7 talks on collider signals from new particles/interactions and 6 talks on extra dimensional physics. We had very active and hot discussions among participants for those new/alternative physics/ideas.

Michael G. Albrow

We have studied events with a high-x_F antiproton and two central jets with E_T>7 GeV in CDF, in p+p_bar collisions at sqrt(s) = 1800 GeV. From the di-jet kinematics we derive the diffractive structure function of the antiproton. We also find an excess of events with a rapidity gap at least 3.5 units wide in the proton direction, which we interpret as di-jet

D. P. Roy

I discuss LHC signatures of the charged Higgs boson of the MSSM, focussing mainly on the case of the charged Higgs boson being heavier than top quark.

Christian W. Bauer, Michael Luke, Thomas Mannel

We construct the higher twist structure functions that describe inclusive b hadron decays in regions of phase space where the hadronic decay products carry high energy but have low invariant mass. We show that, for B meson decays, there are four new non-vanishing matrix elements of non-local operators. We show that to subleading twist these decays are parame

H. Tajima

Charmed and beauty meson lifetimes have been measured using data collected with the Belle detector at KEKB.

Enric Verdaguer

Stochastic semiclassical gravity is a theory for the interaction of gravity with quantum matter fields which goes beyond the semiclassical limit. The theory predicts stochastic fluctuations of the classical gravitational field induced by the quantum fluctuations of the stress energy tensor of the matter fields. Here we use an axiomatic approach to introduce

O. Sarbach, E. Winstanley

Using a recently developed perturbation formalism based on curvature quantities, we investigate the linear stability of black holes and solitons with Yang-Mills hair and a negative cosmological constant. We show that those solutions which have no linear instabilities under odd- and even- parity spherically symmetric perturbations remain stable under odd-pari

I. G. Dymnikova, A. Dobosz, M. L. Fil'chenkov, A. Gromov

We address the question of universes inside a $Λ$ black hole which is described by a spherically symmetric globally regular solution to the Einstein equations with a variable cosmological term $Λ_{μν}$, asymptotically $Λg_{μν}$ as $r\to 0$ with $Λ$ of the scale of symmetry restoration. Global structure of spacetime contains an infinite sequence of black and

R. M. Avakyan, E. V. Chubaryan, A. H. Yeranyan

The gravitation field of the flat plate was investigated. It have been shown that there exist the internal solution of Einstein equations sewed together with external one, which described a ''homogeneous'' gravitational field.

Richie Chih-Nan Chuang, Ashim Garg, Xin He, Ming-Yang Kao

Let G be a plane graph of n nodes, m edges, f faces, and no self-loop. G need not be connected or simple (i.e., free of multiple edges). We give three sets of coding schemes for G which all take O(m+n) time for encoding and decoding. Our schemes employ new properties of canonical orderings for planar graphs and new techniques of processing strings of multipl

S. Aubry, G. Kopidakis

We describe results concerning the existence proofs of Discrete Breathers (DBs) in the two classes of dynamical systems with optical linear phonons and with acoustic linear phonons. A standard approach is by continuation of DBs from an anticontinuous limit. A new approach, which is purely variational, is presented. We also review some numerical results on in

M. Heinrich, H. -A. Krug von Nidda, V. Fritsch, A. Loidl

The perovskite-like transition-metal oxide Gd$_{1-x}$Sr$_x$TiO$_3$ is investigated by measurements of resistivity, specific-heat, and electron paramagnetic resonance (EPR). Approaching the metal-to-insulator transition from the metallic regime ($x \geq 0.2$), the Sommerfeld coefficient $γ$ of the specific heat becomes strongly enhanced and the resistivity in

Lorenz Bartosch

We review the density of states and related quantities of quasi one-dimensional disordered Peierls systems in which fluctuation effects of a backscattering potential play a crucial role. The low-energy behavior of non-interacting fermions which are subject to a static random backscattering potential will be described by the fluctuating gap model (FGM). Recen

M. L. Polianski, P. W. Brouwer

We consider adiabatic pumping of electrons through a quantum dot. There are two ways to operate the pump: to create a dc current ${\bar I}$ or to create a dc voltage ${\bar V}$. We demonstrate that, for very slow pumping, ${\bar I}$ and ${\bar V}$ are not simply related via the dc conductance $G$ as $\bar I = \bar V G$. For the case of a chaotic quantum dot,

Andrea Gabrielli, Miguel A. Munoz, Bernard Sapoval

We propose a phenomenological field theoretical approach to the chemical etching of a disordered-solid. The theory is based on a recently proposed dynamical etching model. Through the introduction of a set of Langevin equations for the model evolution, we are able to map the problem into a field theory related to isotropic percolation. To the best of the aut

Y. Liu, R. Jin, Z. Q. Mao, K. D. Nelson

We report the results of Hall coefficient R_H and magnetoresistance (MR) measurements on single crystalline samples of Sr3Ru2O7 grown by the floating zone method. R_H was found to be positive over the entire temperature range studied (0.3 - 300K). Its temperature (T) dependence follows closely that of the magnetic susceptibility, including a maximum at a cha

S. Oberholzer, M. Henny, C. Strunk, C. Schonenberger

We realized an equivalent Hanbury Brown and Twiss experiment for a beam of electrons in a two dimensional electron gas in the quantum Hall regime. A metallic split gate serves as a tunable beam splitter which is used to partition the incident beam into transmitted and reflected partial beams. The current fluctuations in the reflected and transmitted beam are

H. Suderow, P. Martinez-Samper, S. Vieira, N. Luchier

We present new measurements about the tunneling conductance in the borocarbide superconductor TmNi$_2$B$_2$C. The results show a very good agreement with weak coupling BCS theory, without any lifetime broadening parameter, over the whole sample surface. We detect no particular change of the tunneling spectroscopy below 1.5K, when both the antiferromagnetic (

J. E. Williams

The Josephson oscillations between condensates in a double-well trap are known theoretically to be strongly effected by the mean field interaction in dilute atomic gases. The most important effect is that the amplitude of oscillation in the relative population of the two wells is greatly suppressed due to the mean field interaction, which can make it difficu

A. Weber, S. Koerner, E. -W. Scheidt, S. Kehrein

We have studied the role of disorder in the non-Fermi liquid system UCu4Pd using annealing as a control parameter. Measurement of the lattice parameter indicates that this procedure increases the crystallographic order by rearranging the Pd atoms from the 16e to the 4c sites. We find that the low temperature properties depend strongly on annealing. Whereas t

P. Galatola, J. -B. Fournier

We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality ar

E. Mariani, M. Sassetti, B. Kramer

The bosonisation technique is used to calculate the resonant Raman spectrum of a quantum wire with two electronic sub-bands occupied. Close to resonance, the cross section at frequencies in the region of the inter sub-band transitions shows distinct peaks in parallel polarisation of the incident and scattered light that are signature of collective higher ord

Akira Furusaki, Masashige Matsumoto, Manfred Sigrist

In a chiral superconductor with broken time-reversal symmetry a ``spontaneous Hall effect'' may be observed. We analyze this phenomenon by taking into account the surface properties of a chiral superconductor. We identify two main contributions to the spontaneous Hall effect. One contribution originates from the Bernoulli (or Lorentz) force from spon

Ross H. McKenzie, J. Merino, J. B. Marston, O. P. Sushkov

We consider the electronic properties of layered molecular crystals of the type theta-D$_2$A, where A is an anion and D is a donor molecule such as BEDT-TTF [where BEDT-TTF is bis-(ethylenedithia-tetrathiafulvalene)] which is arranged in the theta type pattern within the layers. We argue that the simplest strongly correlated electron model that can describe

G. Steigman, J. P. Kneller, A. Zentner

Primordial nucleosynthesis provides a probe of the universal abundance of baryons when the universe was only a few minutes old. Recent observations of anisotropy in the cosmic microwave background (CMB) probe the baryon abundance when the universe was several hundred thousand years old. Observations of type Ia supernovae and clusters of galaxies in the very

F. K. Baganoff, Y. Maeda, M. Morris, M. W. Bautz

We present results of our Chandra observation with the ACIS-I instrument centered on the position of Sagittarius A* (Sgr A*), the compact nonthermal radio source associated with the massive black hole (MBH) at the dynamical center of the Milky Way Galaxy. We have obtained the first high-spatial-resolution (~1 arcsec), hard X-ray (0.5-7 keV) image of the cent

Adolf N. Witt, Randall K. Smith, Eli Dwek

Recent observations with dust detectors on board the interplanetary spacecraft Ulysses and Galileo have recorded a substantial flux of large interstellar grains with radii between 0.25 and 2.0 mu entering the solar system from the local interstellar cloud. The most commonly used interstellar grain size distribution is characterized by a a^-3.5 power law in g

B. P. Wakker, P. M. W. Kalberla, H. van Woerden, K. S. de Boer

We show 21-cm line profiles in the direction of stars and extragalactic objects, lying projected on high- and intermediate-velocity clouds (HVCs and IVCs). About half of these are from new data obtained with the Effelsberg 100-m telescope, about a quarter are extracted from the Leiden-Dwingeloo Survey (LDS) and the remaining quarter were observed with other

B. P. Wakker

A table is presented that summarizes published absorption line measurements for the high- and intermediate velocity clouds (HVCs and IVCs). New values are derived for N(HI) in the direction of observed probes, in order to arrive at reliable abundances and abundance limits (the HI data are described in Paper II). Distances to stellar probes are revisited and

Dayton L. Jones, Ann E. Wehrle, B. Glenn Piner, David L. Meier

The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption (by ionized gas in the disk) of background emission from a radio counterjet. We report high angular resolution VLBI observations of the nearby (about 40 Mpc) radio galaxy NGC 4261 that conf

N. J. Turner, J. M. Stone

A module for the ZEUS-2D code is described which may be used to solve the equations of radiation hydrodynamics to order unity in v/c, in the flux-limited diffusion (FLD) approximation. In this approximation, the tensor Eddington factor f which closes the radiation moment equations is chosen to be an empirical function of radiation energy density. This is eas

Piero Cipriani, Marco Pettini

The dynamical justifications which lie at the basis of an effective Statistical Mechanics for self gravitating systems are formulated, analyzing some among the well known obstacles thought to prevent a rigorous Statistical treatment. It is shown that N-body gravitational systems satisfy a strong chaos criterion, so supporting the assumption of an increasingl

A. Ulla, M. R. Zapatero Osorio, F. Perez Hernandez, J. MacDonald

BVRI CCD-based and near-IR (J) imaging, together with unfiltered photometry of the hot subdwarf B star PG 0856+121 are reported. Two close, faint, red, point-like sources are resolved. They account for the previously reported IR excess observed in this hot subdwarf. In addition, the new unfiltered differential photometry of PG 0856+121 confirms its previousl

N. Ivanova, Ph. Podsiadlowski, H. Spruit

We study the merging of massive stars inside a common envelope for binary systems consisting of a red supergiant with a mass of 15-20 Msun and a main-sequence companion of 1-5 Msun. We are particularly interested in the stage when the secondary, having overfilled its Roche lobe inside the common envelope, starts to transfer mass to the core of the primary at

Sangeeta Malhotra, James Rhoads, Arjun Dey, Buell Jannuzi

Strong Lyman-alpha emission is a signpost of young stars and the absence of dust and thus indicates young galaxies. To find such a population of young galaxies at z=4.5 we started the Large Area Lyman Alpha survey (LALA). This survey achieves an unprecedented combination of volume and sensitivity by using narrow-band filters on a large format (36x36 square-a

L. A. Popa, C. Burigana, N. Mandolesi

We study the complementarity between the cosmological information obtainable with the Planck surveyour and the large scale structure (LSS) redshift surveys in LambdaCHDM cosmologies. We compute the initial full phase-space neutrino distribution function for LambdaCHDM models by using numerical simulations. As initial condition we adopt the HDM density fluctu

P. P. Petrov, G. F. Gahm, J. F. Gameiro, R. Duemmler

(Abridged) High-resolution spectroscopic monitoring of RW Aur A was carried out in 1996, 1998 and 1999 with simultaneous B, V photometry. A multicomponent spectrum is revealed with a veiled photospheric spectrum, broad emissions, narrow emission lines of helium, and accretion, wind and shell features. Periodic modulations in many spectral features were found

V. G. Gurzadyan, A. Mazure

The mean redshift of the core of the Coma cluster - cz = 6953 km s^{-1} and its dispersion σ=949 km s^{-1} are obtained by means of the analysis of the substructures of this cluster by using the S-tree method. The existence of three subgroups of galaxies is revealed, one of them is associated with the cD galaxy NGC 4874, the other -- with NGC 4889. It is arg

T. Bloecker

The evolution on the AGB and beyond is reviewed with respect to the origin of Wolf-Rayet central stars. We focus on thermal pulses due to their particular importance for the evolution of hydrogen deficient stars. It is shown that overshoot applied to all convection regions is a key ingredient to model these objects leading to intershell abundances already cl

Cristina Chiappini, Francesca Matteucci, Donatella Romano

In this paper we adopt a chemical evolution model, which is an improved version of the Chiappini, Matteucci and Gratton (1997) model, assuming two main accretion episodes for the formation of the Galaxy. The present model takes into account in more detail than previously the halo density distribution and explores the effects of a threshold density in the sta

C. Adami, A. Mazure, M. P. Ulmer, C. Savine

We have analyzed the galaxy number density and luminosity density profiles of rich clusters of galaxies from redshifts z=0 to z=0.5. We show that the luminosity profile computed with bright galaxies is significantly cusped in the center of the clusters, whatever the redshift. This is in agreement with the dark matter profiles predicted by numerical simulatio

L. A. N. da Costa

The start of operation of several large-aperture telescopes has motivated several groups around the world to conduct deep large imaging surveys, complementing other wide-area but shallower surveys. A special class of imaging surveys are the public ones such as those being conducted by the ESO Imaging Survey (EIS) project established with the primary objectiv

Francesco Palla, Steven W. Stahler

Observations of binaries have traditionally provided the means for ascertaining stellar masses. Here, we use the published data on 8 pre-main-sequence pairs to gauge the accuracy of our own, recently calculated, evolutionary tracks (Palla & Stahler 1999). We consider both eclipsing, double-lined spectroscopic binaries, which provide the mass of each star sep

Cornelia C. Lang, W. M. Goss, Mark Morris

The VLA has been used at 8.3 GHz in the DnC and CnB array configurations to carry out an H92alpha recombination line study (at 8.3 GHz) of the ionized gas in the Arched Filaments H II complex, which defines the western edge of the Galactic center Radio Arc. The H92alpha line properties of the ionized gas are consistent with photoionization from hot stars,and

Una Hwang

This brief review of recent X-ray observations of young supernova remnants highlights results obtained by the Chandra and XMM Newton Observatories since their launch last year. Their impressive capabilities are illustrated by results for spectral imaging, and for spatially resolved spectroscopy that isolates emission from individual ejecta knots and from the

Arnon Dar, A. De Rujula

Recent observations suggest that gamma-ray bursts (GRBs) and their afterglows are produced by jets of highly relativistic cannonballs (CBs), emitted in supernova explosions. The fully ionized CBs cool to a temperature below 4500 K within a day or two, at which point electron-proton recombination produces an intense Lyman-$α$ emission. The line energy is Dopp

J. E. Hirsch

The theory of hole superconductivity explains high temperature superconductivity in cuprates as driven by pairing of hole carriers in oxygen $pπ$ orbitals in the highly negatively charged $Cu-O$ planes. The pairing mechanism is hole undressing and is Coulomb-interaction driven. We propose that the planes of $B$ atoms in $Mg B_2$ are akin to the $Cu-O$ planes

Pinaki Sengupta, Anders W. Sandvik, David K. Campbell

We use a stochastic series expansion quantum Monte Carlo method to study the phase diagram of the one-dimensional extended Hubbard model at half filling for small to intermediate values of the on-site (U) and nearest-neighbor (V) repulsions. We confirm the existence of a novel, long-range-ordered bond-order-wave (BOW) phase recently predicted by Nakamura (J.