March 1998 arXiv papers — page 9

Boris Körs, Michael G. Schmidt

Using the Worldline formalism of QED we compute the two-loop effective action induced by a charged scalar, respectively spinor particle in a general constant electromagnetic field.

Matthias Klein, Jan Louis

In this paper we discuss quantum modified moduli spaces in supergravity. We examine a model suggested by Izawa and Yanagida and by Intriligator and Thomas that breaks global supersymmetry by a quantum deformation of the classical moduli space. We determine the minimum of the supergravity potential when the gauge coupling is taken to depend on a dynamical fie

G. Degrassi, G. F. Giudice

We employ an effective Lagrangian approach to derive the leading-logarithm two-loop electroweak contributions to the muon anomalous magnetic moment, a_mu. We show that these corrections can be obtained using known results on the anomalous dimensions of composite operators. We confirm the result of Czarnecki et al. for the bosonic part and present the complet

M. Dasgupta, G. E. Smye, B. R. Webber

We investigate the power-suppressed corrections to the fragmentation functions of the current jet in non-singlet deep inelastic lepton-hadron scattering. The current jet is defined by selecting final-state particles in the current hemisphere in the Breit frame of reference. Our method is based on an analysis of one-loop Feynman graphs containing a massive gl

Yu. M. Shabelski, D. Treleani

By evaluating all the contributions of the intermediate states of the multiple scattering theory diagrams, we compute the integrated stripping cross sections of collisions among light nuclei. The resulting expressions have the simple form of a combination of total inelastic cross sections of nuclear reactions with projectile nuclei differing in the atomic ma

V. I. Shevchenko, Yu. A. Simonov

The cancellation of perturbative contributions to the string tension in gluodynamics in the framework of vacuum field correlators method is shown at the order $O(g^4)$ by explicit calculation. The general pattern of these cancellations at all orders and relation with the renormalization properties of the Wilson loop is discussed.

K. Urbanowski

CPT-symmetry properties of the exact effective Hamiltonian H(eff) governing the time evolution in the K(0), K(O)-bar (neutral K mesons) subspace implied by such properties of the total Hamiltonian of the system under consideration are examined. We show that H(eff) can commute with CPT - operator only if H does not commute with it. We also find that, in contr

A. Jacholkowska, J. Kalinowski, Z. Was

The process e+e- to nu barnu + gamma with a distinctive ``photon-plus-missing-energy'' signal can serve as an important tool to search for new physics at LEP2. It can be exploited to measure the WW gamma coupling, or to search for weakly interacting and invisible (s)particles. For meaningful comparisons of experimental data with theoretical predictio

A. Martinez, D. M. Tun, A. Garcia, G. Sanchez-Colon

We show that the radiative corrections containing terms up to order $αq / πM_1$ for unpolarized semileptonic decays of baryons with positron emission can be obtained by simply reversing the sign of the axial-vector form factors in the corresponding final expressions of such decays with electron emission. This rule is valid regardless of the final kinematical

V. I. Shevchenko

The leading perturbative contributions into the two-point gauge-invariant correlator $Tr<gF(x)U(x,0)U(0,y)F(y)U(y,0)U(0,x)>$ are calculated at the one-loop order. It is shown, that nonlocal condensate is nonzero at this order. The relation with the renormalization properties of Wilson loops is discussed.

Walter Wilcox

An evaluation of charged pion polarizability using correlation functions measured on a 16^{3}\times 24 lattice in the context of the Das, Mathur, Okubo (DMO) sum rule is carried out. The calculation is limited to the so-called intrinsic part of the polarizability. This contribution, equivalent to a Euclidean time integral over vector and axial vector momentu

Donald E. Neville

Smolin has pointed out that the spin network formulation of quantum gravity will not necessarily possess the long range correlations needed for a proper classical limit; typically, the action of the scalar constraint is too local. Thiemann&#39;s length operator is used to argue for a further restriction on the action of the scalar constraint: it should not i

G W Gibbons

I review some recent progress in String/M-theory

Tin-Lun Ho

In an optical trap, the ground state of spin-1 Bosons such as $^{23}$Na, $^{39}$K, and $^{87}$Rb can be either a ferromagnetic or a &#34;polar&#34; state, depending on the scattering lengths in different angular momentum channel. The collective modes of these states have very different spin character and spatial distributions. While ordinary vortices are sta

D. A. Garanin

The field-dependent magnetization m(H,T) of 1- and 2-dimensional classical magnets described by the $D$-component vector model is calculated analytically in the whole range of temperature and magnetic fields with the help of the 1/D expansion. In the 1-st order in 1/D the theory reproduces with a good accuracy the temperature dependence of the zero-field sus

Lucia Reining, Giovanni Onida, R. W. Godby

We present a new method for the computation of self-energy corrections in large supercells. It eliminates the explicit summation over unoccupied states, and uses an iterative scheme based on an expansion of the Green&#39;s function around a set of reference energies. This improves the scaling of the computational time from the fourth to the third power of th

Massimiliano Corradini, Rodolfo Del Sole, Giovanni Onida, Maurizia Palummo

We present an analytical expression for the local field factor G(q) of the homogeneous electron gas which reproduces recently published Quantum Monte--Carlo data by S. Moroni, D.M. Ceperley, and G. Senatore [Phys. Rev. Lett. 75, 689 (1995)], reflects the theoretically known asymptotic behaviours for both small and large q limits, and allows to express the ex

A. V. Postnikov, G. Borstel

With the aim to get an insight in the origin of differences in the earlier reported calculation results for KNbO3 and to test the recently proposed implementation of the FP-LMTO method by Methfessel and van Schilfgaarde, we perform a comparative study of the ferroelectric instability in KNbO3 by FP-LMTO and LAPW methods. It is shown that a high precision in

Ugo Bastolla, Giorgio Parisi

Attractors in asymmetric neural networks with deterministic parallel dynamics were shown to present a &#34;chaotic&#34; regime at symmetry eta < 0.5, where the average length of the cycles increases exponentially with system size, and an oscillatory regime at high symmetry, where the typical length of the cycles is 2. We show, both with analytic arguments an

Makoto Kuwabara, Yukihiro Shimoi, Shuji Abe

Competition between polaron and bipolaron inconjugated polymers with nondegenerate ground state is systematically studied in the extended Hubbard-Peierls model with the symmetry-breaking Brazovskii-Kirova term, using the density matrix renormalization group method combined with lattice optimization in the adiabatic approximation. We demonstrate that the rela

N. S. Branco, Luciano Bachmann

The degenerate Blume-Emery-Griffiths (DBEG) model has recently been introduced in the study of martensitic transformation problems. This model has the same Hamiltonian as the standard Blume-Emery-Griffiths (BEG) model but, to take into account vibrational effects on the martensitic transition, it is assumed that the states S=0 have a degeneracy p (p=1 corres

Beate Paulus

Ab initio multi-reference configuration interaction calculations are performed for the Si(100) surface using a cluster approach. The convergence with respect to the cluster size is checked and the final results are taken from a $Si_{32} H_{28}$ cluster which models two dimers and six bulk layers. We find for the ideal as well as for the p($1\times 2$) recons

Y. F. Lim, Kan Chen

We perform extended numerical simulation of the dynamics of dry friction, based on a model derived from the phenomenological description proposed by T. Baumberger et al.. In the case of small deviation from the steady sliding motion, the model is shown to be equivalent to the state- and rate-dependent friction law which was first introduced by Rice and Ruina

M. Naraschewski, D. M. Stamper-Kurn

Present experiments with Bose condensed gases can be largely described by a semi-ideal two-gas model. In this model, the condensate is influenced only by the mean-field repulsion among condensed atoms, while the thermal cloud is considered an ideal gas confined by an effective potential that consists of the external trap and the mean-field repulsion by the c

Heng Fan, Bo-yu Hou, Kang-jie Shi

In the framework of the graded quantum inverse scattering method (QISM), we obtain the eigenvalues and eigenvectors of the supersymmetric $t-J$ model with reflecting boundary conditions in FFB background. The corresponding Bethe ansatz equations are obtained.

C. Stanghellini, C. P. O&#39;Dea, D. Dallacasa, S. A. Baum

We define a complete sample of thirty-three GHz-Peaked-Spectrum (GPS) radio sources based on their spectral properties. We present measurements of the radio spectra and polarization of the complete sample and a list of additional GPS sources which fail one or more criteria to be included in the complete sample. The majority of the data have been obtained fro

H. J. Rocha-Pinto, W. J. Maciel

We show that there is a relationship between the age excess, defined as the difference between the stellar isochrone and chromospheric ages, and the metallicity as measured by the index [Fe/H] for late-type dwarfs. The chromospheric age tends to be lower than the isochrone age for metal-poor stars, and the opposite occurs for metal-rich objects. We suggest t

Marcelo B. Ribeiro, Alexandre Y. Miguelote

This paper presents a review of the fractal approach for describing the large scale distribution of galaxies. We start by presenting a brief, but general, introduction to fractals, which emphasizes their empirical side and applications rather than their mathematical side. Then we discuss the standard correlation function analysis of galaxy catalogues and man

Shiho Kobayashi, Tsvi Piran, Re&#39;em Sari

We study numerically the evolution of an adiabatic relativistic fireball expanding into a cold uniform medium. We follow the stages of initial free expansion and acceleration, coasting and then deceleration and slowing down to a non-relativistic velocity. We compare the numerical results with simplified analytical estimates. We show that the relativistic sel

M. Turatto, P. A. Mazzali, T. R. Young, K. Nomoto

SN 1997D in NGC 1536 is possibly the least luminous and energetic Type II supernova discovered to date. The entire light curve is subluminous, never reaching $M_V = -14.65$. The radioactive tail follows the 56Co decay slope. In the case of nearly complete trapping of the $γ$-rays, the 56Ni mass derived from the tail brightness is extremely small, $\sim 0.002

Marco Spaans, David Neufeld, Stephen Lepp, Gary J. Melnick

We report an upper limit of 9 x 10^{12} cm-2 on the column density of water in the translucent cloud along the line of sight toward HD 154368. This result is based upon a search for the C-X band of water near 1240 Åcarried out using the Goddard High Resolution Spectrograph of the Hubble Space Telescope. Our observational limit on the water abundance together

F. E. Marshall, E. V. Gotthelf, W. Zhang, J. Middleditch

We present the serendipitous discovery of 16 ms pulsed X-ray emission from the Crab-like supernova remnant N157B in the Large Magellanic Cloud. This is the fastest spinning pulsar associated with a supernova remnant (SNR). Observations with the Rossi X-ray Timing Explorer (RXTE), centered on the field containing SN1987A, reveal an X-ray pulsar with a narrow

P. Savic, V. Celebonovic

In the sixties,the first author and R.Kasanin have started developing a mean field theory of dense matter.This paper presents a short review of the basic ideas of the theory,and discusses some examples of its applications,which range from DAC experiments to modelling of planetary interiors.

Vladimir N. Lukash

In this brief review I will touch upon the main points and thends of observational and theoretical cosmology, that influence and change today our understanding of the Universe.

David Merritt

Supermassive black holes containing ~0.5% of the stellar mass of their host galaxies appear to be ubiquitous components of galactic nuclei. The gravitational force from these central singularities can influence the motion of stars far outside the nucleus in non-axisymmetric, i.e. barred or triaxial, galaxies. Here, recent work concerning the influence of nuc

Ilse M. van Bemmel, Peter D. Barthel, Min S. Yun

We try to explain the unusually high far-infrared emission seen by IRAS in the double-lobed radio-loud quasars 3C47, 3C207 and 3C334. High resolution cm--mm observations were carried out to determine their radio core spectra, which are subsequently extrapolated to the far-infrared in order to determine the strength of the synchrotron far-infrared emission. T

Weihsueh A. Chiu, B. T. Draine

We derive an analytic expression for the intensity of resonance-line radiation ``trapped&#39;&#39; in a semi-infinite medium. Given a source function and destruction probability per scattering, the radiation pressure due to trapped photons can be calculated by numerically integrating over analytic functions. We apply this formalism to a plane-parallel model

David A. Buote, Claude R. Canizares

We present analysis of the shape and radial mass distribution of the E4 galaxy NGC 3923 using archival X-ray data from the ROSAT PSPC and HRI. The X-ray isophotes are significantly elongated with ellipticity e_x=0.15 (0.09-0.21) (90% confidence) for semi-major axis a\sim 10h^{-1}_70 kpc and have position angles aligned with the optical isophotes within the e

Zurab Kakushadze, Gary Shiu, S. -H. Henry Tye

We consider six dimensional N=1 space-time supersymmetric Type IIB orientifolds with non-zero untwisted NS-NS sector B-field. The B-field is quantized due to the requirement that the Type IIB spectrum be left-right symmetric. The presence of the B-field results in rank reduction of both 99 and 55 open string sector gauge groups. We point out that in some of

Murat Gunaydin

We review the oscillator construction of the unitary representations of noncompact groups and supergroups and study the unitary supermultiplets of OSp(1/32,R) in relation to M-theory. OSp(1/32,R) has a singleton supermultiplet consisting of a scalar and a spinor field. Parity invariance leads us to consider OSp(1/32,R)_L X OSp(1/32,R)_R as the &#34;minimal&#

A. L. Kagan, M. Neubert

We argue that the observation of a sizable direct CP asymmetry A_{CP} in the inclusive decays B -> X_s gamma would be a clean signal of New Physics. In the Standard Model, A_{CP} can be calculated reliably and is found to be below 1% in magnitude. In extensions of the Standard Model with new CP-violating couplings, large CP asymmetries are possible without c

D. M. Appleby

The accuracy of the Arthurs-Kelly model of a simultaneous measurement of position and momentum is analysed using concepts developed by Braginsky and Khalili in the context of measurements of a single quantum observable. A distinction is made between the errors of retrodiction and prediction. It is shown that the distribution of measured values coincides with

John Brodie

We examine the effects of instantons in four dimensional N=1 supersymmetric gauge theory by including D0-branes in type IIA brane constructions. We examine instanton generated superpotentials in supersymmetric QCD and find that they are due to a repulsive force between D4-branes bound to D0-branes ending on NS 5-branes. We study situations where instanton ef

Manuel H. Tiglio

It is shown that in 2+1 dimensional gravity an open spacetime with timelike sources and total energy momentum cannot have a stable compactly generated Cauchy horizon. This constitutes a proof of a version of Kabat&#39;s conjecture and shows, in particular, that not only a Gott pair cannot be formed from processes such as the decay of a single cosmic string a

S. A. Bass, M. Belkacem, M. Bleicher, M. Brandstetter

In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended col

A. Brandhuber, N. Itzhaki, J. Sonnenschein, S. Yankielowicz

Using a proposal of Maldacena we compute in the framework of the supergravity description of N coincident D3 branes the energy of a quark anti-quark pair in the large N limit of U(N) N=4 SYM in four dimensions at finite temperature.

P. F. L. Maxted, T. R. Marsh

The white dwarf stars WD1614+136 and WD1353+409 are not sufficiently massive to have formed through single star evolution. However, observations to date have not yet found any evidence for binarity. It has therefore been suggested that these stars are the result of a merger. In this paper we place an upper limit of approximately 50kms on the projected rotati

Dietmar Klemm, Luciano Vanzo

We examine quantum properties of topological black holes which are asymptotically anti--de Sitter. First, massless scalar fields and Weyl spinors which propagate in the background of an anti--de Sitter black hole are considered in an exactly soluble two--dimensional toy model. The Boulware--, Unruh--, and Hartle--Hawking vacua are defined. The latter results

Peter Coles, Francesco Lucchin, Sabino Matarrese, Lauro Moscardini

We calculate the statistical clustering of Lyman-break galaxies predicted in a selection of currently-fashionable structure formation scenarios. These models are all based on the cold dark matter model, but vary in the amount of dark matter, the initial perturbation spectrum, the background cosmology and in the presence or absence of a cosmological constant

Ian C. Percival

The method of transfer functions is developed as a tool for studying Bell inequalities, alternative quantum theories and the associated physical properties of quantum systems. Non-negative probabilities for transfer functions result in Bell-type inequalities. The method is used to show that all realistic Lorentz-invariant quantum theories, which give unique

L. Gerland, L. Frankfurt, M. Strikman, H. Stöcker

The hard contributions to the heavy quarkonium-nucleon cross sections are calculated based on the QCD factorization theorem and the nonrelativistic quarkonium model. We evaluate the nonperturbative part of these cross sections which dominates at $\sqrt{s_{NN}}\approx 20$ GeV at the Cern Super Proton Synchrotron (SPS) and becomes a correction at $\sqrt{s_{NN}

K. Kajantie, M. Karjalainen, M. Laine, J. Peisa

We study non-perturbatively and from first principles the thermodynamics of vortices in 3d U(1) gauge+Higgs theory, or the Ginzburg-Landau model, which has frequently been used as a model for cosmological topological defect formation. We discretize the system and introduce a gauge-invariant definition of a vortex passing through a loop on the lattice. We the

Lior M. Burko

We study the singularity created in the supercritical collapse of a spherical massless scalar field. We first model the geometry and the scalar field to be homogeneous, and find a generic solution (in terms of a formal series expansion) describing a spacelike singularity which is monotonic, scalar polynomial and strong. We confront the predictions of this an

O. M. Kurth, U. Fritze - v. Alvensleben, K. J. Fricke

We construct evolutionary synthesis models for simple stellar populations using the evolutionary tracks from the Padova group (1993, 1994), theoretical colour calibrations from Lejeune et al., and fit functions for stellar atmospheric indices from Worthey et al.. A Monte-Carlo technique allows us to obtain a smooth time evolution of both broad band colours i

Yuichi Oyama

A long-baseline neutrino-oscillation experiment using a well-defined neutrino beam is in preparation at KEK. Neutrinos generated at KEK will be detected by the Super-kamiokande detector 250 km away. The design of the neutrino beam line, beam monitors and detector are briefly presented. The sensitivities for neutrino oscillations are also discussed.

Kei-Ichi Kondo

We show that the four-dimensional U(1) gauge theory in the continuum formulation has a confining phase (exhibiting area law of the Wilson loop) in the strong coupling region above a critical coupling $g_c$. This result is obtained by taking into account topological non-trivial sectors in U(1) gauge theory. The derivation is based on the reformulation of gaug

CDF Collaboration, F. Abe et al

We report the observations of the decays B^+ -> psi(2S) K^+ and B^0 -> psi(2S) K^*(892)^0 in ppbar collisions at a center-of-mass energy of 1.8 TeV using a 110 pb^{-1} data sample recorded by the Collider Detector at Fermilab. We also reconstruct the decays B^+ -> J/psi K^+ and B^0 -> J/psi K^*(892)^0 and measure the six ratios of branching fractions of thes

Andrew G. Cohen, David B. Kaplan, Ann E. Nelson

Bekenstein has proposed the bound S < pi M_P^2 L^2 on the total entropy S in a volume L^3. This non-extensive scaling suggests that quantum field theory breaks down in large volume. To reconcile this breakdown with the success of local quantum field theory in describing observed particle phenomenology, we propose a relationship between UV and IR cutoffs such

D. M. Appleby

The concept of experimental accuracy is investigated in the context of the unbiased joint measurement processes defined by Arthurs and Kelly. A distinction is made between the errors of retrodiction and prediction. Four error-disturbance relationships are derived, analogous to the single error-disturbance relationship derived by Braginsky and Khalili in the

David Vitali, Paolo Tombesi, Gerard J. Milburn

We show how an initially prepared quantum state of a radiation mode in a cavity can be preserved for a long time using a feedback scheme based on the injection of appropriately prepared atoms. We present a feedback scheme both for optical cavities, which can be continuously monitored by a photodetector, and for microwave cavities, which can be monitored only

Pedro F. Gonzalez-Diaz

Rabi frequencies for multiphoton absorption by atoms or molecules that can be characterized as two- or three-level systems are obtained in the cases of single and double laser perturbations. If the ambiguity in the origin of absolute energy is conveniently gauged off in the three-level model, there appears an additional non linear frequency which is originat

David J. Raymond

If potential energy is the timelike component of a four-vector, then there must be a corresponding spacelike part which would logically be called the potential momentum. The potential four-momentum consisting of the potential momentum and the potential energy taken together is just the gauge field of the associated force times the charge associated with that

M. V. Medvedev, P. H. Diamond, M. N. Rosenbluth, V. I. Shevchenko

A fully nonlinear, time-asymptotic theory of resonant particle trapping in large-amplitude quasi-parallel Alfven waves is presented. The effect of trapped particles on the nonlinear dynamics of quasi-stationary Alfvenic discontinuities and coherent Alfven waves is highly non-trivial and forces to a significant departure of the theory from the conventional DN

Christian Elphick, Aric Hagberg, Ehud Meron

Multiplicity of phase states within frequency locked bands in periodically forced oscillatory systems may give rise to front structures separating states with different phases. A new front instability is found within bands where $ω_{forcing}/ω_{system}=2n$ ($n>1$). Stationary fronts shifting the oscillation phase by $π$ lose stability below a critical forcin

A. S. Cattaneo, P. Cotta-Ramusino, M. Rinaldi

We study the differential geometry of principal G-bundles whose base space is the space of free paths (loops) on a manifold M. In particular we consider connections defined in terms of pairs (A,B), where A is a connection for a fixed principal bundle P(M,G) and B is a 2-form on M. The relevant curvatures, parallel transports and holonomies are computed and t

D. Shklyarov, S. Sinel&#39;shchikov, L. Vaksman

This work considers a formal deformation of the quantum disc (it is developed via an application of the Berezin method) and presents an explicit formula for this deformation.

Pasha Belorousski, Rahul Pandharipande

A new codimension 2 relation among descendent strata in the moduli space of stable, 3-pointed, genus 2 curves is found. The space of pointed admissible double covers is used in the calculation. The resulting differential equations satisfied by the genus 2 gravitational potentials of varieties in Gromov-Witten theory are described. These are analogous to the

Benjamin Grinstein, Detlef R. Nolte

We complete the process of classifying all supersymmetric theories with quantum modified moduli. We present all the supersymmetric gauge theories based on a simple orthogonal or exceptional group that exhibit a quantum modified moduli space. The quantum modified constraints of theories derived from s-confining theories are invariant under all symmetries. How

A. De Martino, M. Moriconi

We study the integrable and supersymmetric massive $\hatϕ_{(1,3)}$ deformation of the tricritical Ising model in the presence of a boundary. We use constraints from supersymmetry in order to compute the exact boundary $S$-matrices, which turn out to depend explicitly on the topological charge of the supersymmetry algebra. We also solve the general boundary Y

E. I. Guendelman, A. B. Kaganovich

We study gauge theories in the context of a gravitational theory without the cosmological constant problem (CCP). The theory is based on the requirement that the measure of integration in the action is not necessarily $\sqrt{-g}$ but it is determined dynamically through additional degrees of freedom. Realization of these ideas in the framework of the first o

Michael Faux

The construction of effective field theories describing M-theory compactified on $S^1/{\bf Z}_2$ is revisited, and new insights into the parameters of the theory are explained. Particularly, the web of constraints which follow from supersymmetry and anomaly cancelation is argued to be more rich than previously understood. In contradistinction to the lore on

J. L. Hewett

The ability of present and future experiments to test the Standard Model in the $B$ meson sector is described. We examine the loop effects of new interactions in flavor changing neutral current $B$ decays and in $Z\to b\bar b$, concentrating on supersymmetry and the left-right symmetric model as specific examples of new physics scenarios. The procedure for p

J. L. Hewett

The ability of high energy lepton and photon colliders to probe the gauge couplings of the top-quark is summarized.

Chao-Shang Huang, Qi-Shu Yan

We perform a detailed study of the inclusive branching ratio and the forward-backward asymmetry of the rare B decay process $B \longrightarrow X_{s} τ^{+} τ^{-}$ in the flipped SU(5) model, a predictive model which has only two free parameters, plus the sign of the higgs mixing mass $μ$, to describe mass spectrum and mixings of about 30 sparticles. In contra

CDF Collaboration, F. Abe et al

We have searched in $p \bar{p}$ collisions at $\sqrt{s}$ = 1.8 TeV for events with three charged leptons and missing transverse energy. In the Minimal Supersymmetric Standard Model, we expect trilepton events from chargino-neutralino ($\chione \chitwo$) pair production, with subsequent decay into leptons. We observe no candidate $e^+e^-e^\pm$, $e^+e^-μ^\pm$,

F. Bunchaft, S. Carneiro

Mishra has recently established, using a generic static metric, the relative local proper-time 3-acceleration of a test-particle in one-dimensional free fall relative to a static reference frame in any static spacetime. In this paper, on the grounds of gravitoelectromagnetism we establish, in a covariant spacetime form, the relative 4-acceleration for the ge

M. O. Terra, M. L. Tiago, M. A. M. de Aguiar

We study the magnetic susceptibility of an ensemble of non-interacting electrons confined by parabolic potentials and subjected to a perpendicular magnetic field at finite temperatures. We show that the behavior of the average susceptibility is qualitatively different from that of billiards. When averaged over the Fermi energy the susceptibility exhibits a l

P R A Campos, J F Fontanari

We use finite-size scaling to investigate the critical behavior of the quasiespecies model of molecular evolution in the single-sharp-peak replication landscape. This model exhibits a sharp threshold phenomenon at Q=Q_c=1/a, where Q is the probability of exact replication of a molecule of length L and a is the selective advantage of the master string. We inv

Matthias Vojta, Klaus W. Becker

We study frequency- and wave-vector dependent charge correlations in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The ground state is expressed within a cumulant formalism which has been successfully applied to study magnetic properties of the weakly doped system. Within this

G. Montambaux

In a recent letter, Yi et al. PRL 78, 3523 (1997), have considered the stability of a Charge Density Wave in a one-dimensional ring, in the presence of an Aharonov-Bohm flux. This comment shows that, in one dimension, the stability of the Charge Density Wave depends on the parity of the number of electrons in the ring. This effect is similar to the parity ef

B. -D. Doerfel, St. Meissner

Based on our previous analysis \cite{doerfel3} of the anisotropic integrable chain consisting of spins $s=1/2$ and $s=1$ we compare the dispersion relations for the sectors with infinite Fermi zones. Further we calculate the speeds of sound for regions close to sector borders, where the Fermi radii either vanish or diverge, and compare the results.

Th. Jonckheere, J. M. Luck

We investigate the AC conductivity of binary random impedance networks, with emphasis on its dependence on the ratio of the complex conductances of both phases. We propose an algorithm to determine the conductance of a finite network, in terms of its poles and of the associated residues. A numerical implementation of the algorithm, on the example of the squa

P. J. Klar, D. Wolverson, J. J. Davies, W. Heimbrodt

Quantum disc structures (with diameters of 200 nm and 100 nm) were prepared from a Zn_{0.72}Mn_{0.28}Se/ZnSe single quantum well structure by electron beam lithography followed by an etching procedure which combined dry and wet etching techniques. The quantum disc structures and the parent structure were studied by photoluminescence and photoluminescence exc

A. J. Williamson, Randolph Q. Hood, R. J. Needs, G. Rajagopal

The band structure of silicon is calculated at the Gamma, X, and L wave vectors using diffusion quantum Monte Carlo methods. Excited states are formed by promoting an electron from the valence band into the conduction band. We obtain good agreement with experiment for states around the gap region and demonstrate that the method works equally well for direct

M. T. Batchelor, K. A. Seaton

On the basis of features observed in the exact perturbation approach solution for the eigenspectrum of the dilute A_3 model, we propose expressions for excitations in the dilute A_4 and A_6 models. Principally, we require that these expressions satisfy the appropriate inversion relations. We demonstrate that they give the expected E_7 and E_6 mass spectra, a

L. V. Popovich, M. V. Medvedev

We propose a systematic way to investigate the low-temperature thermodynamic properties of quantum spin systems subject to the restriction that only a finite number of bosons may occupy a single lattice site. Such a kinematical interaction results in appearance of a temperature dependent chemical potential. Its low-temperature asymptotics is calculated self-

C. Impey, E. Falco, C. Kochanek, J. Lehar

Hubble Space Telescope observations of the gravitational lens PG 1115+080 in the infrared show the known z =0.310 lens galaxy and reveal the z = 1.722 quasar host galaxy. The main lens galaxy G is a nearly circular (ellipticity < 0.07) elliptical galaxy with a de Vaucouleurs profile and an effective radius of R_e = 0.59 +/- 0.06 arcsec (1.7 +/- 0.2 h^{-1} kp

H. Netzer, T. J. Turner, I. M. George

This paper discusses the properties of scattering--dominated active galactic nuclei (AGN). We define these to be AGN for which the direct line-of-sight to the continuum source is obscured by Compton-thick material. The aim is to construct, for the first time, a model consistent with X-ray line luminosities, line ratios and various luminosity indicators. The

N. Bade, V. Beckmann, N. G. Douglas, P. D. Barthel

We present a new well defined sample of BL Lac objects selected from the ROSAT All-Sky Survey (RASS). The sample consists of 39 objects with 35 forming a flux limited sample down to f_X = 8 x 10^{-13} cgs, redshifts are known for 33 objects (and 31 of the complete sample). X-ray spectral properties were determined for each object individually with the RASS d

Sheldon L. Glashow

We posit a second massless photon, uncoupled to known forms of matter but undergoing Lorentz non-invariant velocity mixing with ordinary photons. Our speculation within a speculation suffers from the sin of implausibility but enjoys the virtue of verifiability. To avoid unacceptable distortion of the well-measured microwave background spectrum, the velocity

H. Spruit, E. S. Phinney

RADIO pulsars are thought to born with spin periods of 0.02-0.5 s and space velocities of 100-1000 km/s, and they are inferred to have initial dipole magnetic fields of 10^{11}-10^{13}. The average space velocity of a normal star in the Milky Way is only 30 km/s, which means that pulsars must receive a substantial &#39;kick&#39; at birth. Here we propose tha

F. De Paolis, G. Ingrosso, Ph. Jetzer, M. Roncadelli

Recent observations of microlensing events in the Large Magellanic Cloud suggest that a sizable fraction of the galactic halo is in the form of Massive Astrophysical Compact Halo Objects (MACHOs). Although the average MACHO mass is presently poorly known, the value $\sim 0.1 M_{\odot}$ looks as a realistic estimate, thereby implying that brown dwarfs are a v

Hector G. Arce, Alyssa A. Goodman, Pierre Bastien, Nadine Manset

We present a study of the polarizing power of the dust in cold dense regions (dark clouds) compared to that of dust in the general interstellar medium (ISM). Our study uses new polarimetric, optical, and spectral classification data for 36 stars to carefully study the relation between polarization percentage (p) and extinction (A_V) in the Taurus dark cloud

B. Giebels, R. Bazer-Bachi, H. Bergeret, A. Cordier

The CELESTE experiment will be an Atmospheric Cherenkov detector designed to bridge the gap in energy sensitivity between current satellite and ground-based gamma-ray telescopes, 20 to 300 GeV. We present test results made at the former solar power plant, Themis, in the French Pyrenees. The tests confirm the viability of using a central tower heliostat array

Kari Enqvist

The explanation of the observed galactic magnetic fields may require the existence of a primordial magnetic field. Such a field may arise during the early cosmological phase transitions, or because of other particle physics related phenomena in the very early universe reviewed here. The turbulent evolution of the initial, randomly fluctuating microscopic fie

D. Narasimha, Anwesh Mazumdar

A measurement of the distance to Virgo Cluster by a direct method along with a realistic error analysis is important for a reliable determination of the value of Hubble Constant. Cepheid variables in the face-on spiral M100 in the Virgo Cluster were observed with the Hubble Space Telescope in 1994 under the HST Key Project on the Extragalactic Distance Scale

Anwesh Mazumdar, D. Narasimha

An analysis of the observed characteristics of the Galactic Cepheid variables is carried out in the framework of their period-luminosity relation being used as a standard candle for distance measurement. The variation of the observed number density of Galactic Cepheids as function of their period and amplitude along with stellar pulsation characteristics is

William H. Press, George B. Rybicki

Radio observations establish the B/A magnification ratio of gravitational lens 0957+561 at about 0.75. Yet, for more than 15 years, the optical magnfication ratio has been between 0.9 and 1.12. The accepted explanation is microlensing of the optical source. However, this explanation is mildly discordant with (i) the relative constancy of the optical ratio, a

Michal Chodorowski

I present recent progress in theoretical modelling of cosmological density--velocity relations in the weakly nonlinear regime. The relations are local, based on rigorous perturbation theory and include the effects of smoothing of the density and the velocity fields. For small smoothing scales, they can be improved by slight adjustments based on N-body result

Stefanie Komossa, Hartmut Schulz, Jochen Greiner

We report the detection of luminous extended X-ray emission in NGC 6240 on the basis of ROSAT HRI observations of this ultraluminous IR galaxy. The spatial structure and temporal behavior of the X-ray source were analyzed. We find that >= 70% of the soft X-ray emission is extended beyond a radius of 5 arcsec. Strong emission can be traced out to a radius of