December 1999 arXiv papers — page 9

S. Capozziello, G. Lambiase

Higher-order corrections of Einstein-Hilbert action of general relativity can be recovered by imposing the existence of a Noether symmetry to a class of theories of gravity where Ricci scalar R and its d'Alembertian $\Box R$ are present. In several cases, it is possible to get exact cosmological solutions or, at least, to simplify dynamics by recovering

S. Capozziello, G. Lambiase

The existence of a Noether symmetry for a given minisuperspace cosmological model is a sort of selection rule to recover classical behaviours in cosmic evolution since oscillatory regimes for the wave function of the universe come out. The so called Hartle criterion to select correlated regions in the configuration space of dynamical variables can be directl

Daniele Oriti

We analyse the quantization procedure of the spinor field in the Rindler spacetime, showing the boundary conditions that should be imposed to the field, in order to have a well posed theory. We then investigate the relationship between this construction and the usual one in Minkowski spacetime. This leads to the concept of "Unruh effect", that is the

Kerstin E. Kunze, Ruth Durrer

In this letter we investigate whether the isotropy problem is naturally solved in inflationary cosmologies inspired by string theory, so called pre-big-bang cosmologies. We find that, in contrast to what happens in the more common 'potential inflation' models, initial anisotropies do not decay during pre-big-bang inflation.

Marcus Gaul, Carlo Rovelli

This series of lectures gives a simple and self-contained introduction to the non-perturbative and background independent loop approach of canonical quantum gravity. The Hilbert space of kinematical quantum states is constructed and a complete basis of spin network states is introduced. An application of the formalism is provided by the spectral analysis of

Mauricio Bellini

A second-order expansion for the quantum fluctuations of the matter field was considered in the framemork of the warm inflation scenario. The friction and Hubble parameters were expanded by means of a semiclassical approach. The fluctuations of the Hubble parameter generates fluctuations of the metric. These metric fluctuations produce an effective term of c

Marshall Bern, David Eppstein

The regression depth of a hyperplane with respect to a set of n points in R^d is the minimum number of points the hyperplane must pass through in a rotation to vertical. We generalize hyperplane regression depth to k-flats for any k between 0 and d-1. The k=0 case gives the classical notion of center points. We prove that for any k and d, deep k-flats exist,

Kagan Tumer, David H. Wolpert

In an Ideal Shortest Path Algorithm (ISPA), at each moment each router in a network sends all of its traffic down the path that will incur the lowest cost to that traffic. In the limit of an infinitesimally small amount of traffic for a particular router, its routing that traffic via an ISPA is optimal, as far as cost incurred by that traffic is concerned. W

David H. Wolpert, Sergey Kirshner, Chris J. Merz, Kagan Tumer

Adaptivity, both of the individual agents and of the interaction structure among the agents, seems indispensable for scaling up multi-agent systems (MAS's) in noisy environments. One important consideration in designing adaptive agents is choosing their action spaces to be as amenable as possible to machine learning techniques, especially to reinforcemen

K. Vollmayr-Lee, W. Kob, K. Binder, A. Zippelius

We investigate a binary Lennard-Jones mixture with molecular dynamics simulations. We consider first a system cooled linearly in time with the cooling rate gamma. By varying gamma over almost four decades we study the influence of the cooling rate on the glass transition and on the resulting glass. We find for all investigated quantities a cooling rate depen

D. P. Landau, Alex Bunker, Hans Gerd Evertz, M. Krech

Spin-dynamics techniques can now be used to study the deterministic time-dependent behavior of magnetic systems containing over 10^5 spins with quite good accuracy. This approach will be introduced, including the theoretical foundations of the methods of analysis. Then newly developed, improved techniques based upon Suzuki-Trotter decomposition methods will

D. P. Landau, Shan-Ho Tsai, Alex Bunker

Spin-dynamics simulations have been used to investigate the dynamic behavior of RbMnF_3, treating it as a classical Heisenberg antiferromagnet on a simple cubic lattice. Time-evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a new algorithm which is based on Suzuki-Trotter decompositions

D. P. Landau, Shan-Ho Tsai, M. Krech, Alex Bunker

Using Suzuki-Trotter decompositions of exponential operators we describe new algorithms for the numerical integration of the equations of motion for classical spin systems. These techniques conserve spin length exactly and, in special cases, also conserve the energy and maintain time reversibility. We investigate integration schemes of up to eighth order and

Rochus Klesse, Ady Stern

We study Coulomb drag in a pair of parallel one-dimensional electron systems within the framework of the Tomanaga-Luttinger model. We find that Coulomb coupling has a much stronger effect on one dimensional wires than on two-dimensional layers: At zero temperature the trans-resistivity {\em diverges}, due to the formation of locked charge density waves. At t

V. T. Petrashov, I. A. Sosnin, I. Cox, A. Parsons

The proximity effect in mesoscopic ferromagnet/superconductor ($FS$) Ni/Al structures of various geometries was studied experimentally on both $F$- and $S$-sides of the structures. Samples with a wide range of interface transparency were fabricated. The dependence of the effect on $FS$ interface transparency was investigated. The amplitude of this effect was

J. Dobes

The SU(4) algebraic model of high-temperature superconductivity is studied employing the boson mapping techniques. The bosonization of the model enables us to get exact numerical solution of the model. The order parameters are discussed. The situation close to the SO(5) dynamical symmetry limit is interpreted as a modelling case for the behaviour of $D$-wave

M. Disertori, V. Rivasseau

Using the method of continuous constructive renormalization group around the Fermi surface, it is proved that a jellium two-dimensional interacting system of Fermions at low temperature $T$ remains analytic in the coupling constant $λ$ for $|λ| |\log T| \le K $ where $K$ is some numerical constant and $T$ is the temperature. Furthermore in that range of para

X. S. Chen, V. Dohm

We study the large-$r$ behavior of the bulk order-parameter correlation function $G(\bf{r})$ for $T>T_c$ within the lattice $ϕ^4$ theory. We also study the large-$L$ behavior of the susceptibility $χ$ of the confined lattice system of size $L$ with periodic boundary conditions. The large-$L$ behavior of $χ$ is closely related to the large-$r$ behavior of $G(

J. Wilke, A. D. Mirlin, D. G. Polyakov, F. Evers

We study the low-frequency behavior of the {\it ac} conductivity $σ(ω)$ of a two-dimensional fermion gas subject to a smooth random potential (RP) or random magnetic field (RMF). We find a non-analytic $\propto|ω|$ correction to ${\rm Re} σ$, which corresponds to a $1/t^2$ long-time tail in the velocity correlation function. This contribution is induced by r

Kun Yang, D. F. Agterberg

Due to the difference in the momenta of the superconducting order parameters, the Josephson current in a Josephson junction between a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS superconductor is suppressed. We show that the Josephson current may be recovered by applying a magnetic field in the junction. The field strength a

S. de Gironcoli, S. Scandolo, G. Ballabio, G. Santoro

We show that two distinct $3 \times 3$ ground states, one nonmagnetic, metallic, and distorted, the other magnetic, semimetallic (or insulating) and undistorted, compete in $α$-phase adsorbates on semiconductor (111) surfaces. In Sn/Ge(111), LSDA/GGA calculations indicate, in agreement with experiment, that the distorted metallic ground state prevails. The r

U. Tutsch, P. Schweiss, R. Hauff, B. Obst

The specific heat of Nd(Y)Ba2Cu3Ox single crystals without substitution of Nd for Ba has been measured for various oxygen contents. In comparison with YBa2Cu3Ox, the maximum attainable transition temperature of the crystals is about 4 K higher and shifted from x = 6.92 to x = 7.0, the highest possible oxygen content. In spite of the difference in the Tc(x) d

Charles W. Wolgemuth, Thomas R. Powers, Raymond E. Goldstein

Motivated by diverse phenomena in cellular biophysics, including bacterial flagellar motion and DNA transcription and replication, we study the overdamped nonlinear dynamics of a rotationally forced filament with twist and bend elasticity. Competition between twist injection, twist diffusion, and writhing instabilities is described by a novel pair of coupled

K. Grube, H. Leibrock, W. H. Fietz, S. I. Schlachter

The linear compressibilities and the thermal expansion of an untwinned, nearly optimal doped YBa2Cu3O6.94 single crystal were measured along the three crystallographic axes with a high-resolution dilatometer mounted in a high-pressure cell. The measurements were performed in a temperature range from 50 K to 320 K under hydrostatic gas pressure of maximal 0.6

C. Honerkamp, M. Salmhofer, N. Furukawa, T. M. Rice

We study the renormalization group flow of the interactions in the two-dimensional t-t' Hubbard model near half filling in a N-patch representation of the whole Fermi surface. Starting from weak to intermediate couplings the flows are to strong coupling with different character depending on the choice of parameters. In a large parameter region elastic Um

S. I. Schlachter, K. -P. Weiss, W. H. Fietz, K. Grube

We studied Tc of YBa2Cu3Ox (Y123), Y0.89Ca0.11Ba2Cu3Ox (YCa123) and NdBa2Cu3Ox (Nd123) single crystals with various oxygen contents x. Compared to Tc(x) of Y123 the Tc(x) curves of YCa123 are shifted to lower oxygen contents and the maximum transition temperature Tc,max decreases with increasing Ca content whereas in Nd123 Tc(x) is shifted to higher oxygen c

Walter H. Fietz, Frank W. Hornung, Kai Grube, Sonja I. Schlachter

The lattice parameters and Tc of Y1-yCayBa2Cu3Ox have been determined under pressure up to 10 GPa using a diamond anvil cell. The results are used to test the extended charge transfer model that connects the pressure effect on Tc to an intrinsic dTc,max/dp and a pressure induced hole doping dnh/dp, the latter being caused by charge transfer from the CuO chai

G. M. Zhao, D. J. Kang, W. Prellier, M. Rajeswari

Oxygen isotope effects on the transport properties have been studied in high-quality epitaxial thin films of La_{0.75}Ca_{0.25}MnO_{3} and Nd_{0.7}Sr_{0.3}MnO_{3}. In the paramagnetic state, the resistivity can be well fitted by ρ(T) = (A/\sqrt{T})\exp(E_ρ/k_{B}T) with the parameters A and E_{a} depending strongly on the oxygen isotope mass. The resistivity

V. Yu. Irkhin, M. I. Katsnelson

Electron spectrum of 2D and 3D antiferromagnetic metals is calculated with account of spin-fluctuation corrections within perturbation theory in the s-f exchange model. Effects of the interaction of conduction electrons with spin waves in thermodynamic and transport properties are investigated. At lowest temperatures $T<T^{*}\sim (Δ/E_F)T_N$ ($Δ$ is the AFM

Frank O. Pfeiffer, Heiko Rieger

We investigate the effects of topological defects (dislocations) to the ground state of the solid-on-solid (SOS) model on a simple cubic disordered substrate utilizing the min-cost-flow algorithm from combinatorial optimization. The dislocations are found to destabilize and destroy the elastic phase, particularly when the defects are placed only in partially

D. Foerster

We transpose an idea of &#39;t Hooft from its context of Yang and Mills&#39; theory of strongly interacting quarks to that of strongly correlated electrons in transition metal oxides and show that a Hubbard model of N interacting electron species reduces, to leading orders in N, to a sum of almost planar diagrams. The resulting generating functional and inte

C. -T. Liang, M. Pepper, M. Y. Simmons, C. G. Smith

We describe the transport properties of a 5 $μ$m long one-dimensional (1D) quantum wire. Reduction of conductance plateaux due to the introduction of weakly disorder scattering are observed. In an in-plane magnetic field, we observe spin-splitting of the reduced conductance steps. Our experimental results provide evidence that deviation from conductance quan

S. Daul, I. Ciofini, C. Daul, Steven R. White

We describe how density-matrix renormalization group (DMRG) can be used to solve the full-CI problem in quantum chemistry. As an illustration of the potential of this method, we apply it to a paramagnetic molecule. In particular, we show the effect of various basis set, the scaling as the fourth power of the size of the problem, and compare the DMRG with oth

A. Yu. Galkin, Y. Kopelevich, P. Esquinazi, A. Setzer

Magnetization hysteresis loop $M(H)$ measurements performed on a single crystalline Ba$_{0.63}$K$_{0.37}$BiO$_3$ superconducting thick film reveal pronounced sample geometry dependence of the &#34;second magnetization peak&#34; (SMP), i.e. a maximum in the width of $M(H)$ occurring at the field $H_{\rm SMP}(T)$. In particular, it is found that the SMP vanish

Erik Koch, Olle Gunnarsson, Richard M. Martin

We study the Mott transition in Hubbard models with a degenerate band on different 3-dimensional lattices. While for a non-degenerate band only the half-filled system may exhibit a Mott transition, with degeneracy there can be a transition for any integer filling. We analyze the filling dependence of the Mott transition and find that $U_c$ (the Hubbard inter

V. Ya. Demikhovskii, A. A. Perov, D. V. Khomitsky

In the tight-binding approximation the Harper like equation describing an electron in 3D crystal subject to a uniform magnetic field is obtained. It is supposed that the vector H can be oriented along several directions in the lattice. The Fermi surfaces relevant to a magnetic flux p/q=1/2 in a simple cubic lattice are built. The quantization rules in magnet

R. Kuhne

This paper has been withdrawn by the author due to unspecified problems.

Joachim Buschle, Philipp Maass, Wolfgang Dieterich

We propose a new and general method for deriving exact density functionals in one dimension for lattice gases with finite-range pairwise interactions. Corresponding continuum functionals are derived by applying a proper limiting procedure. The method is based on a generalised Markov property, which allows us to set up a rather transparent scheme that covers

Shinji Watanabe

The magnetization process in the one-dimensional Kondo lattice model for the doped (n_{c}<1) case is studied by the density matrix renormalization group (DMRG) method. A rapid increase of the magnetization is caused by the collapse of the intersite incommensurate correlation of f spins. On the contrary, the intrasite f-c singlet correlation survives in the l

Jose L. Mateos

We address the problem of the classical deterministic dynamics of a particle in a periodic asymmetric potential of the ratchet type. We take into account the inertial term in order to understand the role of the chaotic dynamics in the transport properties. By a comparison between the bifurcation diagram and the current, we identify the origin of the current

J. Main, P. A. Dando, Dz. Belkic, H. S. Taylor

We present and compare three generically applicable signal processing methods for periodic orbit quantization via harmonic inversion of semiclassical recurrence functions. In a first step of each method, a band-limited decimated periodic orbit signal is obtained by analytical frequency windowing of the periodic orbit sum. In a second step, the frequencies an

Laszlo Matyas, Tamas Tel, Jurgen Vollmer

We give a thermodynamically consistent description of simultaneous heat and particle transport, as well as of the associated cross-effects, in the framework of a chaotic dynamical system, a generalized multibaker map. Besides the density, a second field with appropriate source terms is included in order to mimic, after coarse graining, a spatial temperature

Christopher L. Gerardy, Robert A. Fesen, Peter Hoeflich, J. Craig Wheeler

Near-infrared spectra (0.95 -- 2.4 micron) of the peculiar Type IIn supernova 1998S in NGC 3877 from 95 to 355 days after maximum light are presented. K-band data taken at days 95 and 225 show the presence of the first overtone of CO emission near 2.3 micron, which is gone by day 355. An apparent extended blue wing on the CO profile in the day 95 spectrum co

Patricia B. Tissera

Using cosmological hydrodynamical simulations, we investigate the effects of hierarchical aggregation on the triggering of star formation in galactic-like objects. We include a simple star formation model to transform the cold gas in dense regions into stars. Simulations with different parameters have been performed in order to quantify the dependence of the

S. Casassus, L. Bronfman, J. May, L. -A. Nyman

The population of newly formed massive stars, while still embedded in their parent molecular clouds, is studied on the galactic disk scale. We analyse the luminosity function of IRAS point-like sources, with far-infrared (FIR) colours of ultra-compact HII regions, that have been detected in the CS(2-1) line - a tracer of high density molecular gas. The FIR l

S. Heinz, M. C. Begelman

We explore the possibility that extragalactic radio jets might be accelerated by highly disorganized magnetic fields that are strong enough to dominate the dynamics until the terminal Lorentz factor is reached. Following the twin-exhaust model by Blandford & Rees (1974), the collimation under this scenario is provided by the stratified thermal pressure from

C. A. Trujillo, D. C. Jewitt, J. X. Luu

We present the discovery of three new Scattered Kuiper Belt Objects (SKBOs) from a wide-field survey of the ecliptic. This continuing survey has to date covered 20.2 square degrees to a limiting red magnitude of 23.6. We combine the data from this new survey with an existing survey conducted at the University of Hawaii 2.2m telescope to constrain the number

Ivo Saviane, Enrico V. Held, Gianpaolo Bertelli

(abridged) We present B,V,I CCD photometry of about 40000 stars in four regions of the Fornax dSph. Using the resultant CMDs, many already known age-tracers are investigated, and new CMD features are also detected: we show that blue HB stars may be present in the outer regions, and measure the luminosity of the AGB bump. We measure a corrected distance modul

O. Straniero, M. Limongi, A. Chieffi, I. Dominguez

We present a set of models of AGB stars with initial mass larger than 5 Mo as obtained with the FRANEC code. It includes models of Z=0.02 and Z=0.001, with and without mass loss.

I. Dominguez, O. Straniero, M. Limongi, A. Chieffi

We have studied the evolution of intermediate mass (M.ge.5Mo) zero metal (Z=0) stars with particular attention to the AGB phase. At variance with previous claims we find that these stars experience thermal instability (the so called thermal pulses). The critical quantity which controls the onset of a thermally pulsing phase is the amount of CNO in the envelo

N. Masetti

Optical and near-infrared observations of the GRB990705 error box were carried out with ESO telescopes at La Silla and Paranal in Chile and with the NOAO SPIREX 0.6-meter telescope in Antarctica. We detected the counterpart of this GRB in the near-infrared H band and optical V band. The power-law decline of the near-infrared lightcurve is rather steep with a

Martin White, John Carlstrom, Mark Dragovan, S. W. L. Holzapfel

We present an optimized layout of horn positions for the Degree Angular Scale Interferometer (DASI), which provides good coverage of the u-v plane and 3-fold symmetry. We investigate how an optimal subspace filtering analysis of a single pointing of DASI could be used to determine the anisotropies in the cosmic microwave background over a range of angular sc

Thomas W. Berghoefer, Stuart Bowyer, Eric Korpela

We present results of a re-analysis of archival EUVE data of the central region of the Virgo cluster. We employ the new analysis method developed by Bowyer, Berghöfer & Korpela (1999) and find diffuse emission reaching out to a distance of $\approx 13\arcmin$. The spatial distribution of this flux is incompatible with a thermal plasma origin. We investigate

Gavin Ramsay

We have extracted spectra of 20 magnetic Cataclysmic Variables (mCVs) from the RXTE archive and fitted them using the X-ray continuum method of Cropper et al to determine the mass of the accreting white dwarf in each system. We find evidence that the mass distribution of these mCVs is significantly different to that of non-magnetic isolated white dwarfs, wit

Agnieszka Janiuk, Piotr T. Zycki, Bozena Czerny

We consider the role of advection in the two-temperature accreting corona with an underlying optically thick disc. The properties of coronal solutions depend significantly on the description of advection. Local parameterization of advection by a constant coeficient $δ$ replacing the radial derivatives lead to complex topology of solutions, similar to some ex

Robert Braun, Butler Burton

Six examples of the compact, isolated high-velocity HI clouds (CHVCs) identified by Braun and Burton (1999) have been imaged with the WSRT. The 65 confirmed objects in this class define a dynamically cold system, with a global minimum for the velocity dispersion of only 70 km/s, found in the Local Group Standard of Rest, while in-falling at 100 km/s toward t

Daniel Thomas, Laura Greggio, Ralf Bender

Uncertainties in stellar nucleosynthesis and their impact on models of chemical evolution are discussed. Comparing the Type II supernova nucleosynthesis prescriptions from Woosley & Weaver (1995) and Thielemann, Nomoto, & Hashimoto (1996), it turns out that the latter predict higher Mg/Fe ratios that are more favorable in reproducing the observed abundance f

T. R. Geballe, F. Najarro, D. F. Figer

H and K band moderate resolution and 4 $μ$m high resolution spectra have been obtained for FMM#362, a bright star in the Quintuplet Cluster near the Galactic Center. The spectral features in these bands closely match those of the Pistol Star, a luminous blue variable and one of the most luminous stars known. The new spectra and previously-obtained photometry

Norimasa Sugiura, Ken-ichi Nakao, Daisuke Ida, Nobuyuki Sakai

Propagation of light in a clumpy universe is examined. As an inhomogeneous matter distribution, we take a spherical void surrounded by a dust shell where the ``lost mass&#39;&#39; in the void is compensated by the shell. We study how the angular-diameter distance behaves when such a structure exists. The angular-diameter distance is calculated by integrating

F. de Felice, O. Zanotti

We study the processes of particle acceleration which take place in the field of a rotating black hole as part of a mechanism of formation of galactic jets within the first parsec from the central source, where gravitation is supposed to be dominant. We find the Lorentz factor that a stream of particles acquires as function of distance, when the orbital para

J. E. Hibbard, W. D. Vacca, M. S. Yun

We have mapped the neutral atomic gas (HI) in the three disk-disk merger systems NGC 520, Arp 220, and Arp 299. These systems differ from the majority of the mergers mapped in HI, in that their stellar and gaseous tidal features do not coincide. In particular, they exhibit large stellar tidal features with little if any accompanying neutral gas and large gas

F. R. Klinkhamer

We consider chiral gauge theories defined over a four-dimensional spacetime manifold with a Cartesian product structure for at least one compact spatial dimension. For a simple setup, we calculate the effective gauge field action by integrating out the chiral fermions, while maintaining gauge invariance. Due to a combination of infrared and ultraviolet effec

M. A. McLaughlin, J. M. Cordes

We apply a likelihood analysis to pulsar detections, pulsar upper limits, and diffuse background measurements from the OSSE and EGRET instruments on the Compton Gamma Ray Observatory to constrain the luminosity law for gamma-ray pulsars and some properties of the gamma-ray pulsar population. We find that the dependence of luminosity on spin period and dipole

Hector Figueroa, Jose M. Gracia-Bondia

We give a new formula for the antipode of the algebra of rooted trees, directly in terms of the bialgebra structure. The equivalence, proved in this paper, among the three available formulae for the antipode, reflects the equivalence among the Bogoliubov-Parasiuk-Hepp, Zimmermann, and Dyson-Salam renormalization schemes.

David M. Goldberg, David N. Spergel

We introduce a new method for generating initial conditions consistent with highly nonlinear observations of density and velocity fields. Using a variant of the Least Action method, called Perturbative Least Action (PLA), we show that it is possible to generate several different sets of initial conditions, each of which will satisfy a set of highly nonlinear

A. Ali Khan, T. Bhattacharya, S. Collins, C. T. H. Davies

We present lattice results for the spectrum of mesons containing one heavy quark and of baryons containing one or two heavy quarks. The calculation is done in the quenched approximation using the NRQCD formalism for the heavy quark. We analyze the dependence of the mass splittings on both the heavy and the light quark masses. Meson P-state fine structure and

H. Bravo-Alfaro, V. Cayatte, J. H. van Gorkom, C. Balkowski

We have obtained 21cm images of 19 spiral galaxies in the Coma cluster, using the VLA in its C and D configurations. The sample selection was based on morphology, brightness, and optical diameters of galaxies within one Abell radius (1.2 degrees). The HI detected, yet deficient galaxies show a strong correlation in their HI properties with projected distance

V. B. Bezerra, G. L. Klimchitskaya, V. M. Mostepanenko

The finite conductivity corrections to the Casimir force in two configurations are calculated in the third and fourth orders in relative penetration depth of electromagnetic zero oscillations into the metal. The obtained analytical perturbation results are compared with recent computations. Applications to the modern experiments are discussed.

E. V. Tsiper

Variational procedure is developed that yields lowest frequencies of small-amplitude oscillations of classical Hamiltonian systems. Genuine Lanczos recursion is generalized to treat related non-Hermitian eigenvalue problems.

Joseph C. Varilly

We examine some recent developments in noncommutative geometry, including spin geometries on noncommutative tori and their quantization by the Shale-Stinespring procedure, as well as the emergence of Hopf algebras as a tool linking index theory and renormalization calculations

M. Hayakawa

Here we discuss the ultraviolet and infrared aspects of the noncommutative counterpart of QED, which is called as noncommutative QED, as well as some infrared dynamics of noncommutative Yang-Mills (NCYM) theory. First we demonstrate that the divergence in the theory can be subtracted by the similar counterterms as in ordinary theory at one loop level. Then t

Hartmut Wittig

The status of lattice calculations in Quantum Field Theory is reviewed. A major part is devoted to recent progress in formulating exact chiral symmetry on the lattice. Another topic which has received a lot of attention is the influence of dynamical quark effects. Attempts to quantify these effects for the light hadron spectrum and flavour singlet amplitudes

H. E. Montgomery

Over the course of the past years the experimental measurements performed by the two large collaborations, CDF and DØ, at the Fermilab Tevatron Collider have fueled advances in our understanding of physics at the energy frontier. At the present time the accelerator complex and the two detectors are undergoing substantial improvements. In this paper, we provi

J-P. Gazeau, M. V. Takook

We present in this paper a covariant quantization of the ``massive&#39;&#39; vector field on de Sitter (dS) space based on analyticity in the complexified pseudo-Riemanian manifold. The correspondence between unitary irreducible representations of the de Sitter group and the field theory on de Sitter space-time is essential in our approach. We introduce the

H. C. Rosu

If stationary, the spectrum of vacuum field noise (VFN) is an important ingredient to get information about the curvature invariants of classical worldlines (relativistic classical trajectories). For scalar quantum field vacua there are six stationary cases as shown by Letaw some time ago, these are reviewed here. However, the non-stationary vacuum noises ar

Julien Vidal, Dominique Mouhanna, Thierry Giamarchi

Although the effects of interactions in solid state systems still remains a widely open subject, some limiting cases such as the three dimensional Fermi liquid or the one-dimensional Luttinger liquid are by now well understood when one is dealing with interacting electrons in {\it periodic} crystalline structures. This problem is much more fascinating when p

A. Malatesta, Gaetano Senatore

We report on a diffusion Monte Carlo investigation of model electron systems in low dimensions, which should be relevant to the physics of systems obtainable nowadays in semiconductor heterostructures. In particular, we present results for a one dimensional electron gas, at selected values of the coupling strength and confinement parameter, briefly analyzing

Xiao-Hong Wang, Shlomo Havlin, Moshe Schwartz

We present systematic numerical simulations for directed polymers at finite temperatures in 1+1 and 2+1 dimensions. The transverse fluctuations and free energy fluctuations tend to the strong coupling limit at any temperature in both 1+1 and 2+1 dimensions for long time t. Two different definitions for energy fluctuations at finite temperatures, which are th

M. A. McLaughlin, J. M. Cordes, T. H. Hankins, D. A. Moffett

We derive an upper limit of 3 mJy (95% confidence) for the flux density at 317 MHz of the Geminga pulsar (J0633+1746). Our results are based on 7 hours of fast-sampled VLA data, which we averaged synchronously with the pulse period using a period model based on CGRO/EGRET gamma-ray data. Our limit accounts for the fact that this pulsar is most likely subject

Jonathan Granot, Mark Miller, Tsvi Piran, Wai-Mo Suen

We describe fully relativistic three dimensional calculations of the slowing down and spreading of a relativistic jet by an external medium like the ISM. We calculate the synchrotron spectra and light curves using the conditions determined by the hydrodynamic calculations. Preliminary results with a moderate resolution are presented here. Higher resolution c

M. Plionis, S. Basilakos, M. Rowan-Robinson, S. J. Maddox

Comparing the gravitational acceleration induced on the Local Group of galaxies by different tracers of the underline density field we estimate, within the linear gravitational instability theory and the linear biasing ansatz, their relative bias factors. Using optical SSRS2 galaxies, IRAS (PSCz) galaxies and Abell/ACO clusters, we find b_{O,I} ~ 1.21 +- 0.0

Shawn Snider, Yuan Qu, Carlos Allende Prieto, Ted von Hippel

New generation large-aperture telescopes, multi-object spectrographs, and large format detectors are making it possible to acquire very large samples of stellar spectra rapidly. In this context, traditional star-by-star spectroscopic analysis are no longer practical. New tools are required that are capable of extracting quickly and with reasonable accuracy i

Christopher J. Miller, Adrian L. Melott, Robert C. Nichol

We examine the relationship between the total X-ray and optical luminosities of groups and clusters of galaxies taken from various samples in the literature. The clusters and groups were drawn from four different catalogs: (1) the Abell/ACO catalog, (2) the Edinburgh-Durham Cluster Catalog, (3) the RASS Bright Cluster Sample, and (4) galaxy groups selected f

Ralph L. Cohen, Paulo Lima-Filho

Using symmetrized Grassmannians we give an algebraic geometric presentation, in the level of classifying spaces, of the Chern character and its relation to Chern classes. This allows one to define, for any projective variety $X$, a Chern character map from the "holomorphic K-theory of X to its morphic cohomology (introduced by Friedlander and Lawson). The ho

Aparna Venkatesan

Current data of high-redshift absorption-line systems imply that hydrogen reionization occurred before redshifts of about 5. Previous works on reionization by the first stars or quasars have shown that such scenarios are described by a large number of cosmological and astrophysical parameters. Here, we adopt a semi-analytic model of stellar reionization in o

Dieter Brill

Exact solutions of Einstein's equations in 2+1-dimensional anti-de Sitter space containing any number of black holes are described. In addition to the black holes these spacetimes can possess ``internal'' structure. Accordingly the generic spacetime of this type depends on a large number of parameters. Half of these can be taken as mass parameters, and the r

C. Pinzari, Y. Watatani, K. Yonetani

To any periodic, unital and full C*-dynamical system (A, α, R) an invertible operator s acting on the Banach space of trace functionals of the fixed point algebra is canonically associated. KMS states correspond to positive eigenvectors of s. A Perron-Frobenius type theorem asserts the existence of KMS states at inverse temperatures equal the logarithms of t

Berthold-Georg Englert, Nasser Metwally

The state of an entangled q-bit pair is specified by 15 numerical parameters that are naturally regarded as the components of two 3-vectors and a $3\times3$-dyadic. There are easy-to-use criteria to check whether a given pair of 3-vectors plus a dyadic specify a 2-q-bit state; and if they do, whether the state is entangled; and if it is, whether it is a sepa

R. Drimmel, R. L. Smart, M. G. Lattanzi

The kinematics of distant OB stars perpendicular to the Galactic plane, inferred from proper motions in the Hipparcos catalogue, are analysed and compared to the kinematic signature that would be induced by a long-lived Galactic warp. Previously we reported that the kinematics of the OB stars toward the anticenter were inconsistent with the assumption of a l

Kazutaka Sudoh, Toshiyuki Morii

We studied the photoproduction of $ψ^{\prime}$ in the forward regions in polarized $γp$ collisions at relevant HERA energies. We found that this reaction is very effective to test the color-octet mechanism which is based on the NRQCD factorization formalism. Furthermore we found that the value of the NRQCD matrix elements can be severely constrained by measu

Mark Mineev-Weinstein, Anton Zabrodin

The Laplacian growth problem in the limit of zero surface tension is proved to be equivalent to finding a particular solution to the dispersionless Toda lattice hierarchy. The hierarchical times are harmonic moments of the growing domain. The Laplacian growth equation itself is the quasiclassical version of the string equation that selects the solution to th

Theodore E. Liolios

The conflict in Yugoslavia has been a source of great concern due to the radiological and toxic hazard posed by the alleged presence of depleted uranium in NATO weapons. In the present study some worst-case scenaria are assumed in order to assess the risk for Yugoslavia and its neighboring countries . The risk is proved to be negligible for the neighboring c

Mark Mineev-Weinstein, Gary D. Doolen, John E. Pearson, Silvina Ponce Dawson

Within a class of exact time-dependent non-singular N-logarithmic solutions (Mineev-Weinstein and Dawson, Phys. Rev. E 50, R24 (1994); Dawson and Mineev-Weinstein, Phys. Rev. E 57, 3063 (1998)), we have found solutions which describe the development and pinching off of viscous droplets in the Hele-Shaw cell in the absence of surface tension.

H. Blaine Lawson,, Paulo Lima-Filho, Marie-Louise Michelsohn

Algebraic cycles on complex projective space P(V) are known to have beautiful and surprising properties. Therefore, when V carries a real or quaternionic structure, it is natural to ask for the properties of the groups of real or quaternionic algebraic cycles on P(V). In this paper and its sequel the homotopy structure of these cycle groups is determined. Th

Ralph L. Cohen, Paulo Lima-Filho

In this paper we study the &#34;holomorphic K-theory&#34; of a projective variety, which is defined in terms of the homotopy type of spaces of holomorphic maps from the variety to Grassmannians and loop groups. This theory was introduced by Lawson, Lima-Filho and Michelsohn, and also by Friedlander and Walker, and a related theory was considered by Karoubi.

Ignasi Mundet i Riera

Our aim in this work is to study a system of equations which generalises at the same time the vortex equations of Yang-Mills-Higgs theory and the holomorphicity equation in Gromov theory of pseudoholomorphic curves. We extend some results and definitions from both theories to a common setting. We introduce a functional generalising Yang-Mills-Higgs functiona

Mihail N. Kolountzakis

Consider a collection $λ_1<...<λ_N$ of distinct positive integers and the quantities $$ M_1 = M_1(λ_1,...,λ_N) = \max_{0\le x \le 2π} |\sum_{j=1}^N \sin{λ_j x}| $$ and $$ M_2 = M_2(λ_1,...,λ_N) = - \min_{0\le x \le 2π} \sum_{j=1} \cos{λ_j x}. $$ Prompted by a discussion with G. Benke we prove that collections of frequencies $λ_j$ which have $M_1 = o(N)$ or $

Mihail N. Kolountzakis

Let $Ω\subseteq {\bf R}^d$ be an open set of measure 1. An open set $D \subseteq {\bf R}^d$ is called a ``tight orthogonal packing region&#39;&#39; for $Ω$ if $D-D$ does not intersect the zeros of the Fourier Transform of the indicator function of $Ω$ and $D$ has measure 1. Suppose that $Λ$ is a discrete subset of ${\bf R}^d$. The main contribution of this p

Mihail N. Kolountzakis

A conjecture of Fuglede states that a bounded measurable set $Ω$ in space, of measure 1, can tile space by translations if and only if the Hilbert space $L^2(Ω)$ has an orthonormal basis consisting of exponentials. If $Ω$ has the latter property it is called spectral. We generalize a result of Fuglede, that a triangle in the plane is not spectral, proving th

Amol S. Dighe

We analyze the neutrino conversions inside a supernova in the 3$ν$ mixing scheme, and their effects on the neutrino spectra observed at the earth. We find that the observations of the energy spectra of neutrinos from a future galactic supernova may enable us to identify the solar neutrino solution, to determine the sign of $Δm^2_{32}$, and to probe the mixin