April 1997 arXiv papers — page 15

A. R. Denton, J. Hafner

A combination of classical density-functional theory and thermodynamic perturbation theory is applied to a survey of finite-temperature trends in the relative stabilities of one-component crystals and quasicrystals interacting via effective metallic pair potentials derived from pseudopotential theory. Comparing the free energies of several periodic crystals

Stefan Kettemann

The persistent Hall voltage and current in an isolated annulus in a strong perpendicular magnetic field, at odd inverse filling factor, and in the presence of a weak constriction is obtained as a function of temperature, and flux piercing the annulus. A thermodynamic Hall conductance is found which has a universal value even with back scattering at the const

R. K. Kamilla, J. K. Jain, S. M. Girvin

The pair distribution function and the static structure factor are computed for composite fermions. Clear and robust evidence for a $2k_F$ structure is seen in a range of filling factors in the vicinity of the half-filled Landau level. Surprisingly, it is found that filled Landau levels of composite fermions, i.e. incompressible FQHE states, bear a stronger

C. -E. Pfister, Y. Velenik

We apply new techniques developed in a previous paper to the study of some surface effects in the 2D Ising model. We examine in particular the pinning-depinning transition. The results are valid for all subcritical temperatures. By duality we obtained new finite size effects on the asymptotic behaviour of the two-point correlation function above the critical

C. -E. Pfister, Y. Velenik

We show that a class of spin models, containing the Ashkin-Teller model, admits a generalized random-cluster (GRC) representation. Moreover we show that basic properties of the usual representation, such as FKG inequalities and comparison inequalities, still hold for this generalized random-cluster model. Some elementary consequences are given. We also consi

S. Giorgini, L. P. Pitaevskii, S. Stringari

We investigate the thermodynamic behaviour of a Bose gas interacting with repulsive forces and confined in a harmonic anisotropic trap. We develop the formalism of mean field theory for non uniform systems at finite temperature, based on the generalization of Bogoliubov theory for uniform gases. By employing the WKB semiclassical approximation for the excite

Marcel Porta, Carlos Frontera, Eduard Vives, Teresa Castan

The influence of diffusing vacancies on the antiphase domain growth process in a binary alloy is studied by Monte Carlo simulations. The system is modelled by means of a Blume-Emery-Griffiths hamiltonian with a biquadratic coupling parameter K controlling the microscopic interactions between vacancies. We obtain that, independently of K, the vacancies exhibi

Hagai El-Ad

Voids are the most prominent feature of the large-scale structure of the universe. Still, they have been generally ignored in quantitative analysis of it, essentially due to the lack of an objective tool to identify the voids and to quantify them. To overcome this, we have developed the VOID FINDER algorithm, a novel tool for objectively quantifying voids in

Stefanie Wachter

We present optical and near-IR observations of QX Nor, the counterpart to the recurrent soft X-ray transient X1608-52, after its reappearance following the X-ray outburst in February 1996. The object has been seen only once before, during an X-ray outburst in 1977. Data from 3-5 months after the outburst show the counterpart at a mean magnitude of R=20.2 and

Michael S. Turner

The current state of cosmology is easy to summarize: a very successful standard model -- the hot big-bang cosmology -- that accounts for the evolution of the Universe from 10^{-2} sec until the present; bold ideas based upon early-Universe physics -- foremost among them inflation and cold dark matter -- that can extend the standard cosmology to times as earl

Edouard Audit, Romain Teyssier, Jean-Michel Alimi

We investigate some modifications to the Press & Schechter (1974) (PS) prescription resulting from shear and tidal effects. These modifications rely on more realistic treatments of the collapse process than the standard approach based on the spherical model. First, we show that the mass function resulting from a new approximate Lagrangian dynamic (Audit & Al

A. S. Wilson, L. Binette, T. Storchi-Bergmann

We report measurements of the electron temperature at about a dozen locations in the extended emission-line regions of five active (Seyfert and radio) galaxies. Temperatures (T_{[OIII]} and T_{[NII]}) have been determined from both the I([OIII]\lambda4363)/I([OIII]\lambda5007) and I([NII]\lambda5755)/I[NII]\lambda6583) ratios. T_{[OIII]} lies in the range (1

D. Barrado y Navascues, J. R. Stauffer, L. Hartmann, S. C. Balachandran

We estimate here the age of one of the prototypes of the Beta Pic-like stars, Fomalhaut, based on the properties of its common proper motion companion Gl879. By combining constraints derived from the lithium abundance, rotational velocity, HR diagram position, and coronal activity we conclude that the age for Gl879, and hence the age for Fomalhaut, is 200$\p

F. Halzen

Active galaxies and gamma ray bursts are the sources of the highest energy photons detected by astronomical telescopes. We speculate that they may be the sources of the highest energy cosmic rays. This makes them true proton accelerators, where the highest energy photons are the decay products of neutral pions photoproduced when the proton beams interacts wi

Richard S. Ellis

The physical properties of the faint blue galaxy population are reviewed in the context of observational progress made via deep spectroscopic surveys and Hubble Space Telescope imaging of field galaxies at various limits, and theoretical models for the integrated star formation history of the Universe. Notwithstanding uncertainties in the properties of the l

Eelco van Kampen, Peter Katgert

We present a technique to construct a fair sample of simulated galaxy clusters, and build such a sample for a specific cosmological structure formation scenario. Conventionally one extracts such a sample from a single low-resolution large-scale simulation. Here we simulate the clusters individually at high resolution. We construct a model catalogue selected

Enrique Zas

Some neutrino predictions at the highest energies for a number of production mechanisms are comparatively reviewed in the light of future projects for neutrino detection.

S. Sridhar, J. Touma

We construct three dimensional axisymmetric, cuspy density distributions, whose potentials are of Stäckel form in parabolic coordinates. As in Sridhar and Touma (1997), a black hole of arbitrary mass may be added at the centre, without destroying the Stäckel form of the potentials. The construction uses a classic method, originally due to Kuzmin (1956), whic

Rodrigo Ibata, Michael Irwin

We demonstrate the use of a variant of Principal Component Analysis (PCA) for discrimination problems in astronomy. This variant of PCA is shown to provide the best linear discrimination between data classes. As a test case, we present the problem of discrimination between K giant and K dwarf stars from intermediate resolution spectra near the Mg `b' fea

D. Martinez-Delgado, A. Aparicio

In this paper, we show that the optically bright stars above the tip of the first red giant branch (TRGB) in the color magnitude (CM) diagrams of nearby dwarf elliptical (dE) galaxies, commonly interpreted as indication of the existence of an intermediate-age population, may, in certain circumstances, be an artifact of observational effects on a pure old pop

Alexander Braverman, Maxim Braverman

Let $p:R^n\to R$ be a polynomial map. Consider the complex $S'Ω^*(\RR^n)$ of tempered currents on $R^n$ with the twisted differential $d_p=d-dp$ where $d$ is the usual exterior differential and $dp$ stands for the exterior multiplication by $dp$. Let $t\in R$ and let $F_t=p^{-1}(t)$. In this paper we prove that the reduced cohomology $\tilda H^k(F_t;C)$

Carlos R. Cassanello, Eduardo Fradkin

We consider the screening of a magnetic impurity in a $d_{x^2-y^2}$ wave superconductor. The properties of the $d_{x^2-y^2}$ state lead to an unusual behavior in the impurity magnetic susceptibility, the impurity specific heat and in the quasiparticle phase shift which can be used to diagnose the nature of the condensed state. We construct an effective theor

H. Arfaei, M. M. Sheikh-Jabbari

The scale in the D-brane theory is discussed from different points of view. It is shown that scattering of a $D_4$-brane by a $D_0$-brane gives the condition to penetrate beyond the string scale.

J. Blaschke, M. Brack

We present a semiclassical description of the level density of a two-dimensional circular quantum dot in a homogeneous magnetic field. We model the total potential (including electron-electron interaction) of the dot containing many electrons by a circular billiard, i.e., a hard-wall potential. Using the extended approach of the Gutzwiller theory developed b

Vladimir V. Kisil

We describe some connections between three different fields: combinatorics (umbral calculus), functional analysis (linear functionals and operators) and harmonic analysis (convolutions on group-like structures). Systematic usage of cancellative semigroup, their convolution algebras, and tokens between them provides a common language for description of object

M. Potthoff, T. Wegner, W. Nolting

We develop an analytical expression for the self-energy of the infinite-dimensional Hubbard model that is correct in a number of different limits. The approach represents a generalization of the iterative perturbation theory to arbitrary fillings. In the weak-coupling regime perturbation theory to second order in the interaction U is recovered. The theory is

W. Zhang, R. Petre, A. N. Peele, K. Jahoda

We present a conceptual design for a new X-ray all sky monitor (ASM). Compared with previous ASMs, its salient features are: (1) it has a focusing capability that increases the signal to background ratio by a factor of 3; (2) it has a broad-band width: 200 eV to 15 keV; (3) it has a large X-ray collection area: ~100 square cm; (4) it has a duty cycle of near

Michela Petrini

We study the infrared perturbative properties of a class of non supersymmetric gauge theories with the same field content of N=4 Super Yang-Mills and we show that the N=4 supersymmetric model represents an IR unstable fixed point for the renormalization group equations.

J. van den Brink, R. Eder, G. A. Sawatzky

We show that the charge transfer excitons in a Hubbard model system including nearest neighbor Coulomb interactions effectively attain some charge in doped systems and become visible in photoelectron and inverse photoelectron spectroscopies. This shows that the description of a doped system by an extended Hubbard model differs substantially from that of a si

Yasushi Honda, Tsuyoshi Horiguchi

We embody the density matrix renormalization group method for the 19-vertex model on a square lattice; the 19-vertex model is regarded to be equivalent to the XY model for small interaction. The transfer matrix of the 19-vertex model is classified by the total number of arrows incoming into one layer of the lattice. By using this property, we reduce the dime

Hirofumi Yamada

Modified Laplace transformation method is applied to N component $ϕ^4$ theory and the finite temperature problem in the massless limit is re-examined in the large N limit. We perform perturbation expansion of the dressed thermal mass in the massive case to several orders and try the massless approximation with the help of modified Laplace transformation. The

S. P. Strong, J. C. Talstra

We propose a definition for a creation operator for the spinon, the fractional statistics elementary excitation of the Haldane-Shastry model, and give numerical and analytical evidence that our operator creates a single spinon with nearly unit amplitude in the ISE model. We then discuss how the operator is useful in more general contexts such as studying the

Tri Sulistiono

Considerable progress has recently been made in controling the motion of free atomic particles by means of light pressure exerted by laser radiation. The free fall of atoms and bouncing on a reflecting surface made from evanescent wave formed by internal reflection of a quasiresonant laser beam at a curved glass surface in the presence of homogeneous gravita

Y. Aharonov, B. Reznik

The measurability by means of continuous measurements, of an observable $\A(t_0)$, at an instant, and of a time averaged observable, $\bar \A=1/T\int \A(t')dt'$, is examined for linear and in particular for non-linear quantum mechanical systems. We argue that only when the exact (non-perturbative) solution is known, an exact measurement may be possib

Krzysztof Burdzy, Thomas S. Salisbury

Does a minimal harmonic function $h$ remain minimal when it is viewed as a parabolic function? The question is answered for a class of long thin semi-infinite tubes $D\subset \R^d$ of variable width and minimal harmonic functions $h$ corresponding to the boundary point of $D$ ``at infinity.'' Suppose $f(u)$ is the width of the tube $u$ units away fro

Nandor Simányi, Domokos Szász

We consider the system of N (\ge 2) elastically colliding hard balls with masses m_1,..., m_N, radius r, moving uniformly in the flat torus T_L^ν= R^ν/L \cdot Z^ν, ν\ge 2. It is proved here that the relevant Lyapunov exponents of the flow do not vanish for almost every (N+1)-tuple (m_1,...,m_N;L) of the outer geometric parameters.

JM Figueroa-O'Farrill

We apply the techniques of the ``universal string theory'' to the ``manifold'' paradigm for superstring/M-theory and come up with a candidate manifold: the manifold of F-theory vacua, defined in conformal field theoretical terms. It contains the five known superstring theories as particular vacua; although the natural vacua are (10+2)-dimensi

F. A. Berends, W. T. Giele

In this paper the general form of scattering amplitudes for massless particles with equal spins s ($s s \to s s$) or unequal spins ($s_a s_b \to s_a s_b$) are derived. The imposed conditions are that the amplitudes should have the lowest possible dimension, have propagators of dimension $m^{-2}$, and obey gauge invariance. It is shown that the number of mome

E. Gava, K. S. Narain, M. H. Sarmadi

We study bound states of D-p-branes and D-(p+2)-branes. By switching on a large magnetic field F on the (p+2) brane, the problem is shown to admit a perturbative analysis in an expansion in inverse powers of F. It is found that, to the leading order in 1/F, the quartic potential of the tachyonic state from the open string stretched between the p- and (p+2)-b

S. Hyun

We show that the D-brane configurations for the five and four-dimensional black holes give the geometry of two and three-dimensional ones as well. The emergence of these lower dimensional black holes from the D-brane configurations for those of higher dimensions comes from the choice of the integration constant of harmonic functions, which decides the asympt

A. Arhrib, M. Rachidi, E. H Saidi

We introduce a new type of deformation of the chiral symmetry based on the deformation of the Laurent expansion of the conformal energy momentum tensor. Two kinds of solutions of the deformed equations of continuity are worked out. Known results are recovered, others features are also discussed.

Sergei M. Kuzenko

On the base of the notion of N=2 abelian Yang-Mills supergeometry with constant curvature, we propose an off-shell formulation for the massive q-hypermultiplet and complex $ω$-hypermultiplet in the standard harmonic superspase without central charge variables. The corresponding superpropagators are derived.

K. Agashe, M. Graesser

The fine tuning in models of low energy gauge mediated supersymmetry breaking required to obtain the correct $Z$ mass is quantified. To alleviate the fine tuning problem, a model with split $(5+\bar{5})$ messenger fields is presented. This model has additional triplets in the low energy theory which get a mass of $O(500)$ GeV from a coupling to a singlet. Th

Nima Arkani-Hamed, Hsin-Chia Cheng, Jonathan L. Feng, Lawrence J. Hall

In supersymmetric theories the charged sleptons of different generations may oscillate amongst themselves while they decay. In the case of three generation oscillations, superpartner production at the LHC and NLC may lead to an observable $CP$-violating signal $N(e^+μ^-) - N(μ^+e^-)$. This signal is proportional to a $CP$-violating invariant of the slepton m

P. Taxil, J. -M. Virey

In the context of general $SU(2)_L\otimes SU(2)_R\otimes U(1)$ models a relatively light W' is still allowed in some scenarios with a heavy right-handed neutrino and a quark mixing matrix $U^R$ close to unity. We explore the consequences of the presence of this new charged current on the parity violating spin asymmetries which could be induced in one-jet

L. P. A. Haakman, A. B. Kaidalov, J. H. Koch

We consider the production of charm by real and virtual photons. Special attention is paid to diffractive charm production, which provides information on the gluonic content of the Pomeron. Our calculations are based on the gluon distributions of the CKMT-model, which is shown to lead to agreement with the data on open charm production in deep inelastic scat

Janusz Gluza

Doubly charged Higgs s-channel resonances are analyzed in the $e^-e^- \to W^-W^-$ process. In our analysis recent stringent constraint on an effective neutrino mass $<m_ν>$ coming from neutrinoless double-$β$ decay is implemented. It is shown that due to a very restrictive limit on $<m_ν>$ the doubly charged Higgs resonance predicted by the Standard Model wi

Donald E. Neville

Solutions are constructed to the quantum constraints for planar gravity (fields dependent on z and t only) in the Ashtekar complex connection formalism. A number of operators are constructed and applied to the solutions. These include the familiar ADM energy and area operators, as well as new operators sensitive to directionality (z+ct vs. z-ct dependence).

Carlos Pinheiro, Gentil O. Pires, N. Tomimura

We present a 3-dimensional model for massive gravity with masses induced by topological (Chern-Simons) and Proca-like mass terms. Causality and unitarity are discussed at tree-level. Power-counting renormalizability is also contemplated.

Carlos Pinheiro, Gentil O. Pires, Claudio Sasaki

The purpose of this work is to present a model for 3D massive gravity with topological and higher-derivative terms. Causality and unitarity are discussed at tree-level. Power-counting renormalizability is also contemplated.

Daniel Kennefick

This paper examines the historical controversy over whether gravitationally bound systems, such as binary stars, experienced orbital damping due to the emission of gravitational radiation, focusing especially on the period of the 1950s, but also discussing the work of Einstein and Rosen in the 1930s on cylindrical gravitational waves and the later quadrupole

Dae-Yup Song

Recently a restriction (&#34;quantum inequality-type relation&#34;) on the (renormalized) energy density measured by a static observer in a &#34;globally static&#34; (ultrastatic) spacetime has been formulated by Pfenning and Ford for the minimally coupled scalar field, in the extension of quantum inequality-type relation on flat spacetime of Ford and Roman.

P. Agre, I. Horswill

We argue that the analysis of agent/environment interactions should be extended to include the conventions and invariants maintained by agents throughout their activity. We refer to this thicker notion of environment as a lifeworld and present a partial set of formal tools for describing structures of lifeworlds and the ways in which they computationally sim

Ana Lopez, Manuel Fuentes, Eduardo Fradkin

We generalize the bosonization methods for systems in the half line that we discussed elsewhere, to study the effects of interactions on electronic systems coupled to impurities. We introduce a model for a quantum wire coupled with a quantum dot by a purely capacitive interaction. We show that the effect on the quantum wire is a dynamical boundary condition

Michael R. Geller, Daniel Los

Edge states of the quantum Hall fluid provide an almost unparalled opportunity to study mesoscopic effects in a highly correlated electron system. In this paper we develop a bosonization formalism for the finite-size edge state, as described by chiral Luttinger liquid theory, and use it to study the Aharonov-Bohm effect. The problem we address may be realize

Ghyslain Boisvert, Laurent J. Lewis

We use ab initio static relaxation methods and semi-empirical molecular-dynamics simulations to investigate the energetics and dynamics of the diffusion of adatoms, dimers, and vacancies on Cu(100). It is found that the dynamical energy barriers for diffusion are well approximated by the static, 0 K barriers and that prefactors do not depend sensitively on t

E. V. L. de Mello, C. Acha

We make use of a BCS type approach based on the extended Hubbard Hamiltonian to study the superconductor transition and to give a microscopic interpre- tation of the pressure effects on Tc in high temperature superconductors. This novel method suggests that the applied pressure causes an increase of the superconducting gap and this effect is explored in orde

Walter Kob, Jean-Louis Barrat

Using molecular dynamics simulations we study the out of equilibrium dynamic correlations in a model glass-forming liquid. The system is quenched from a high temperature to a temperature below its glass transition temperature and the decay of the two-time intermediate scattering function C(t_w,t+t_w) is monitored for several values of the waiting time t_w af

E. Louis, E. Cuevas, J. A. Verges, M. Ortuno

The elastic mean free path of carriers in a recently introduced model of quantum chaotic billiards in two and three dimensions is calculated. The model incorporates surface roughness at a microscopic scale by randomly choosing the atomic levels at the surface sites between -W/2 and W/2. Surface roughness yields a mean free path l that decreases as L/W^2 as W

Reggie Brown, Nikolai F. Rulkov

We examine synchronization of identical chaotic systems coupled in a drive/response manner. A rigorous criterion is presented which, if satisfied, guarantees that synchronization to the driving trajectory is linearly stable to perturbations. An easy to use approximate criterion for estimating linear stability is also presented. One major advantage of these c

Kyung-Hoon Kwon, Byung-Yoon Park

We study changes in the chaotic properties of a many-body system undergoing a solid-fluid phase transition. To do this, we compute the temperature dependence of the largest Lyapunov exponents $λ_{max}$ for both two- and three-dimensional periodic systems of $N$-particles for various densities. The particles interact through a soft-core potential. The two-dim

A. Naim, K. U. Ratnatunga, R. E. Griffiths

We examine a general framework for visualizing datasets of high (> 2) dimensionality, and demonstrate it using the morphology of galaxies at moderate redshifts. The distributions of various populations of such galaxies are examined in a space spanned by four purely morphological parameters. Galaxy images are taken from the Hubble Space Telescope (HST) Wide F

Leandros Perivolaropoulos

Using analytical methods and Monte Carlo simulations, we analyze a new statistic designed to detect isolated step-like discontinuities which are coherent over large areas of Cosmic Microwave Background (CMB) pixel maps. Such coherent temperature discontinuities are predicted by the Kaiser-Stebbins effect to form due to long cosmic strings present in our pres

J. Greiner

I review the use of ROSAT over the last years for the investigation of well localized gamma-ray burst (GRB) error boxes. In particular, I cover (i) the systematic study of several dozens of IPN locations using the ROSAT All-Sky-Survey data, (ii) results of deep ROSAT pointings of selected small GRB error boxes, (iii) the attempts for and results of quick fol

Michael W. Regan, Stuart N. Vogel, Peter J. Teuben

Mass inflow in barred galaxies has been invoked to account for a wide variety of phenomena, but until now direct evidence for inflow has been lacking. We present Fabry-Perot H-alpha observations of the barred spiral galaxy NGC 1530 from which we determine velocities of the ionized gas for the entire region swept by the bar. We compare the velocity field to m

Mordecai-Mark Mac Low, Thomas H. Chang, You-Hua Chu, Sean D. Points

The large H II complex N11 in the Large Magellanic Cloud contains OB associations at several different stages in their life histories. We have obtained ROSAT PSPC and HRI X-ray observations, Curtis Schmidt CCD images, echelle spectra in H-alpha and [N II] lines, and IUE interstellar absorption line observations of this region. The central bubble of N11 has a

J. Martin-Pintado, P. de Vicente, A. Fuente, P. Planesas

We have mapped the J=1-0 line of SiO in a 1 degree x 12 arcmin. (lxb) region around the Galactic center (GC) with an angular resolution of 2 arcmin. (approx. 4 pc). In contrast to the spatial distribution of other high dipole moment molecules like CS, whose emission is nearly uniform, the SiO emission is very fragmented and it is only associated with some mo

M. Asplund, B. Gustafsson, D. L. Lambert, N. K. Rao

The surface chemical composition of this remarkable star shows that it is hydrogen-deficient, carbon-rich and enriched in the light s-process elements. Spectra taken in May and October 1996 indicate a decrease in the surface hydrogen abundance by 0.7 dex in five months along with an increase in the abundances of Li, Sr, Y and Zr. The abundance changes are in

Ralf Klessen

A method of adapting smoothed particle hydrodynamics (SPH) with periodic boundary conditions for use with the special purpose device GRAPE is presented. GRAPE (GRAvity PipE) solves the Poisson and force equations for an N-body system by direct summation on a specially designed chip and in addition returns the neighbour list for each particle. Due to its desi

M. König, J. Timmer, R. Staubert

In recent years, autoregressive models have had a profound impact on the description of astronomical time series as the observation of a stochastic process. These methods have advantages compared with common Fourier techniques concerning their inherent stationarity and physical background. If autoregressive models are used, however, it has to be taken into a

Paolo Padovani

Active Galactic Nuclei (AGN) are now known to be strong gamma-ray emitters. After briefly describing the different classes of AGN and the basic tenets of unified schemes, I discuss the role of blazars (that is BL Lacs and flat-spectrum radio quasars) as gamma-ray sources. The main properties of blazars and their connection with relativistic beaming are then

R. Guzmán, J. Gallego, D. C. Koo, A. C. Phillips

We present a spectroscopic study of 51 compact field galaxies with redshifts z < 1.4 and apparent magnitudes I < 23.74 in the flanking fields of the Hubble Deep Field. These galaxies are compact in the sense that they have small apparent half-light radii (r_e < 0.5 arcsec) and high surface brightnesses (SB_e < 22.2 mag arcsec^-2). The spectra, taken at the K