July 1999 arXiv papers — page 10

M. Boettcher, C. D. Dermer

We present simple analytical expressions for the predicted spectral and temporal behavior of the early afterglow radiation from gamma-ray bursts in radiative regimes intermediate between the adiabatic and the fully radiative solutions of the blastwave hydrodynamic equations. Our expressions are valid as long as the relativistic electrons responsible for the

M. G. Cosenza, K. Tucci

General hierarchical lattices of coupled maps are considered as dynamical systems. These models may describe many processes occurring in heterogeneous media with tree-like structures. The transition to turbulence via spatiotemporal intermittency is investigated for these geometries. Critical exponents associated to the onset of turbulence are calculated as f

Dave Allen, Fabian H. L. Essler, Alexander A. Nersesyan

We study a weakly coupled, frustrated two-leg spin-1/2 Heisenberg ladder. For vanishing coupling between the chains, elementary excitations are deconfined, gapless spin-1/2 objects called spinons. We investigate the fate of spinons for the case of a weak interchain interaction. We show that despite a drastic change in ground state, which becomes spontaneousl

M. B. Hastings

The eigenvalues of an arbitrary quaternionic matrix have a joint probability distribution function first derived by Ginibre. We show that there exists a mapping of this system onto a fermionic field theory and then use this mapping to integrate over the positions of the eigenvalues and obtain eigenvalue density as well as all higher correlation functions for

Matteo Beccaria

We apply a recently proposed Green Function Monte Carlo to the study of Hamiltonian lattice gauge theories. This class of algorithms computes quantum vacuum expectation values by averaging over a set of suitable weighted random walkers. By means of a procedure called Stochastic Reconfiguration the long standing problem of keeping fixed the walker population

S. Daul, D. J. Scalapino, Steven R. White

Pairing correlations on generalized t-U-J two-leg ladders are reported. We find that the pairing correlations on the usual t-U Hubbard ladder are significantly enhanced by the addition of a nearest-neighbor exchange interaction J. Likewise, these correlations are also enhanced for the t-J model when the onsite Coulomb interaction is reduced from infinity. Mo

T. E. O. Ericson, B. Loiseau, A. W. Thomas

We critically evaluate the isovector GMO sumrule for the charged $\pi N N$ coupling constant using recent precision data from $\pi ^-$p and $\pi^-$d atoms and with careful attention to systematic errors. From the $\pi ^-$d scattering length we deduce the pion-proton scattering lengths ${1/2}(a_{\pi ^-p}+a_{\pi ^-n})=(-20\pm 6$(statistic)$ \pm 10$ (systematic

Gautam Bhattacharyya, H. V. Klapdor-Kleingrothaus, Heinrich Päs

We consider the generation of neutrino Majorana mass and transition magnetic moment by the lepton-number violating $λ$ and/or $λ'$ couplings in R-parity-violating supersymmetric models. We update (and improve) the existing upper limits on the relevant couplings using the most recent data on neutrino masses and mixings, indicating also the possible improv

J. Fleischer, M. Yu. Kalmykov

A FORM based package (ON-SHELL2) for the calculation of two loop self-energy diagrams with one nonzero mass in internal lines and the external momentum on the same mass shell is elaborated. The algorithm, based on recurrence relations obtained from the integration-by-parts method, allows us to reduce diagrams with arbitrary indices (powers of scalar propagat

Ashoke Sen, Barton Zwiebach

F-theory on K3 admits non-BPS states that are represented as string junctions extending between 7-branes. We classify the non-BPS states which are guaranteed to be stable on account of charge conservation and the existence of a region of moduli space where the 7-branes supporting the junction can be isolated from the rest of the branes. We find three possibi

P. A. Zizzi

We interpret the Holographic Conjecture in terms of quantum bits (qubits). N-qubit states are associated with surfaces that are punctured in N points by spin networks' edges labeled by the spin-1/2 representation of SU(2), which are in a superposed quantum state of spin "up" and spin "down". The formalism is applied in particular to de Si

Fumiharu Kato

In this paper we discuss log blow-up's, introduced by Kazuya Kato, and define the concept of log modifications. Using this concept we prove that any morphism f: X ---> Y of locally noetherian fs log schemes with underlying structures of f and Y quasi-compact can be modified to an exact morphism, and moreover to an integral morphism. By a well-known fact on t

Dae-Yup Song

For a time-dependent $τ$-periodic harmonic oscillator of two linearly independent homogeneous solutions of classical equation of motion which are bounded all over the time (stable), it is shown, there is a representation of states cyclic up to multiplicative constants under $τ$-evolution or $2τ$-evolution depending on the model. The set of the wave functions

M. Lutz, B. Friman, Ch. Appel

We construct an equation-of-state for nuclear matter based on the chiral Lagrangian. The relevant scales are discussed and an effective chiral power expansion scheme, which is constructed to work around the nuclear saturation density, is presented. A realistic equation-of-state is obtained by adjusting one free parameter, when the leading and subleading term

P. A. Grassi, T. Hurth, M. Steinhauser

A practical approach is presented which allows the use of a non-invariant regularization scheme for the computation of quantum corrections in perturbative quantum field theory. The theoretical control of algebraic renormalization over non-invariant counterterms is translated into a practical computational method. We provide a detailed introduction into the h

Thomas Schick

The canonical trace on the reduced C*-algebra of a discrete group gives rise to a homomorphism from the K-theory of this C^*-algebra to the real numbers. This paper addresses the range of this homomorphism. For torsion free groups, the Baum-Connes conjecture and Atiyah's L2-index theorem implies that the range consists of the integers. If the group is not to

Paulo F. Bedaque, Harald W. Griesshammer

The real and imaginary part of the quartet S wave phase shift in nd scattering (^4 S_{3/2}) for centre-of-mass momenta of up to 300 MeV (E_cm \approx 70 MeV) is presented in effective field theory, using both perturbative pions and a theory in which pions are integrated out. As available, the calculation agrees with both experimental data and potential model

Vinay Ambegaokar

Assertions by Overhauser of error in accepted calculations of the temperature dependence of the Josephson current are shown to be without merit.

V. Barger, T. Han, T. Li, T. Plehn

At a future Linear Collider one will be able to determine the masses of charginos and neutralinos and their pair production cross sections to high accuracies. We show how systematically including the cross sections into the analysis improves the measurement of the underlying mass parameters, including potential CP violating phases. In addition, we investigat

Thomas Durt

We study in this short comment the analogies and the differences that exist between several local hidden variable models.

G. A. Natanzon

Original English Summary. - A systematic method of constructing potentials, for which the one-variable Schroedinger equation can be solved in terms of the hypergeometric (HGM) function, is presented. All the potentials, obtained by energy-independent transformations of the HGM equation, are determined together with eigenvalues and eigenfunctions. A class of

P. Sule

We present a perturbative approach within the scope of Kohn-Sham density functional theory (DFT). The method is based on the exact exchange-only optimized effective potential method, and correlation is included via perturbation expansion using Rayleigh-Schrodinger (RS) perturbation theory (PT). The correlation potential is constructed from Moller-Plesset for

H. Mueller, J. R. Shepard

Properties of hypernuclei are studied in the context of a chiral Lagrangian which successfully describes ordinary nuclei. Lambda-Sigma^0 mixing arises from nondiagonal vertices in flavor space induced by the vector mesons and by the electromagnetic field. The set of Dirac equations for the coupled hyperon system is discussed. Results are presented for energy

B. M. Abramov, S. A. Bulychjov, I. A. Dukhovskoy, A. I. Khanov

In experiment on the study of the quasielastic pion-proton scattering at large momentum transfer on nuclei the proton Fermi-momentum distributions have been analysed in plane-wave approximation for light nuclei $^6$Li, $^7$Li and $^{12}$C. It was found that, contrary to (e,e') experiments, that the oscillator model gives slightly better description of ou

David Eppstein

It is known that any planar graph with diameter D has treewidth O(D), and this fact has been used as the basis for several planar graph algorithms. We investigate the extent to which similar relations hold in other graph families. We show that treewidth is bounded by a function of the diameter in a minor-closed family, if and only if some apex graph does not

M. Irac-Astaud, C. Quesne

We propose a q-deformation of the su(2)-invariant Schrodinger equation of a spinless particle in a central potential, which allows us not only to determine a deformed spectrum and the corresponding eigenstates, as in other approaches, but also to calculate the expectation values of some physically-relevant operators. Here we consider the case of the isotropi

M. Irac-Astaud, C. Quesne

We propose a q-deformation of the su(2)-invariant Schrodinger equation of a spinless particle in a central potential, which allows us not only to determine a deformed spectrum and the corresponding eigenstates, as in other approaches, but also to calculate the expectation values of some physically-relevant operators. Here we consider the case of the isotropi

Pan Jianzhong, Woo Moo Ha

In this note, we attack a question posed ten years ago by Tsukiyama about the injectivity of the so- called Forgetable map. We show that we can insert the Forgetable map in an exact sequence and that the problem can be reduced to the computation of the sequence which turns out unexpectedly to be related to the phantom map problem and the famous Halperin conj

Toshiyuki Abe

Fusion rules among irreducible modules of the free bosonic orbifold vertex operator algebra are completely determined.

J. C. George, R. S. Sanders

In this paper we determine partial answers to the question given in the title, thereby significantly extending results of Broere and Hattingh. We characterize completely those pairs of complete graphs whose tensor products are circulant. We establish that if the orders of these circulant graphs have greatest common divisor of 2, the product is circulant when

Paul M. N. Feehan, Thomas G. Leness

This is the third installment in our series of articles (dg-ga/9712005, dg-ga/9710032) on the application of the PU(2) monopole equations to prove Witten's conjecture (hep-th/9411102) concerning the relation between the Donaldson and Seiberg-Witten invariants of smooth four-manifolds. The moduli space of solutions to the PU(2) monopole equations provides

D. Kaledin

We consider the quotients $X = V/G$ of a symplectic complex vector space $V$ by a finite subgroup $G \subset Sp(V)$ which admit a smooth crepant resolution $Y \to X$. For such quotients, we prove the homological McKay correspondence conjectured by M. Reid. Namely, we construct a natural basis in the homology space $H_\cdot(Y,\Q)$ whose elements are numbered

Xi Chen

We proved that every rational curves in the primitive class of a general K3 surface of any genus is nodal.

Carlos Lozano, Marcos Marino

Using the u-plane integral of Moore and Witten, we derive a simple expression for the Donaldson invariants of $Σ_g \times S^2$, where $Σ_g$ is a Riemann surface of genus g. This expression generalizes a theorem of Morgan and Szabo for g=1 to any genus g. We give two applications of our results: (1) We derive Thaddeus' formulae for the intersection pairin

Tim Prestidge

The thermodynamic properties of Schwarzschild-anti-de Sitter black holes confined within finite isothermal cavities are examined. In contrast to the Schwarzschild case, the infinite cavity limit may be taken which, if suitably stated, remains double valued. This allows the correspondence between non-existence of negative modes for classical solutions and loc

E. J. Copeland, P. M. Saffin, O. Tornkvist

We present the results of lattice computations of collisions of two expanding bubbles of true vacuum in the Abelian Higgs model with a first-order phase transition. New time-dependent analytical solutions for the Abelian field strength and the phase of the complex field are derived from initial conditions inferred from linear superposition and are shown to b

E. Kh. Akhmedov

Neutrino oscillations in matter can exhibit a specific resonance enhancement -- parametric resonance, which is different from the MSW resonance. Oscillations of atmospheric and solar neutrinos inside the earth can undergo parametric enhancement when neutrino trajectories cross the core of the earth. In this paper we review the parametric resonance of neutrin

Carlo Ewerz, Bryan R. Webber

We derive closed expressions for the mean and variance of the (mini-)jet multiplicity distribution in hard scattering processes at low x. Here (mini-)jets are defined as those due to initial-state radiation of gluons with transverse momenta greater than some resolution scale m_R, where Lambda^2 << m_R^2 << Q^2, Lambda being the intrinsic QCD scale and Q the

S. V. Goloskokov

We consider the dependencies of spin asymmetries in the diffractive $J/Ψ$ and $Q \bar Q$ leptoproduction at HERA energies on the structure of the pomeron-proton coupling. It is shown that it is difficult to study the spin structure of the pomeron coupling with the proton from the $A_{ll}$ asymmetry. The $A_{lT}$ asymmetry is an appropriate object for this in

Konrad Baranowski, Mikolaj Misiak

We evaluate the O(alpha_em/alpha_s) correction to the rate of B -> X_s gamma decay, i.e. we resum all the 0[ alpha_em ln M_W^2/m_b^2 x (alpha_s ln M_W^2/m_b^2)^n ] corrections for n=0,1,2,... Our calculation differs from the previously available one by that it takes into account the complete relevant set of operators. The correction is found to be negligible

Giancarlo D&#39;Ambrosio

We review some recent theoretical results on rare kaon decays. Particular attention is devoted to establish the short distance (direct CP violating) contribution to K_L => π^0 e \bar{e}. This is achieved by a careful study of the long distance part. As byproduct, we discuss interesting chiral tests.

C. Destri, E. Manfredini

The $λϕ^4$ model in a finite volume is studied in the infinite $N$ limit and within a non-gaussian Hartree-Fock approximation both at equilibrium and out of equilibrium, with particular attention to certain fundamental features of the broken symmetry phase. The numerical solution of the dynamical evolution equations show that the zero-mode quantum fluctuatio

M. E. Berbenni-Bitsch, M. Göckeler, H. Hehl, S. Meyer

Recently, the chiral logarithms predicted by quenched chiral perturbation theory have been extracted from lattice calculations of hadron masses. We argue that the deviations of lattice results from random matrix theory starting around the so-called Thouless energy can be understood in terms of chiral perturbation theory as well. Comparison of lattice data wi

H. V. Klapdor-Kleingrothaus

Nuclear double beta decay provides an extraordinarily broad potential to search for beyond Standard Model physics, probing already now the TeV scale, on which new physics should manifest itself. These possibilities are reviewed here.

The SLD Collaboration, K. Abe

We present a direct measurement of the parity-violation parameter A_c. The measurement is based on 550k Z^0 decays collected by the SLD detector. The mean electron-beam polarization is |P_e| = 73 %. The tagging of c-quark events was performed using two methods: The exclusive reconstruction of D^*+, D^+, and D^0 mesons, and the inclusive P_T spectrum of soft-

David Eppstein

A fractal construction shows that, for any beta>0, the beta-skeleton of a point set can have arbitrarily large dilation. In particular this applies to the Gabriel graph.

Paolo Allegrini, Jack F. Douglas, Sharon C. Glotzer

The length-scale dependence of the dynamic entropy is studied in a molecular dynamics simulation of a binary Lennard-Jones liquid above the mode-coupling critical temperature $T_c$. A number of methods exist for estimating the entropy of dynamical systems and we utilize an approximation based on calculating the mean first-passage time (MFPT) for particle dis

R. K. Koleva, A. Widom, D. Garelick, Meredith Harris

Postural body sway displacements for quiet standing subjects (measured with a new ultrasonic device) are reported. Two of the well known strategies for balancing, namely ankle and hip movements were probed. The data is modeled using a Fokker-Plank-Langevin stochastic theory. Both analytic and computer simulation techniques are employed. The Kramers transitio

M. Mola, S. Hill, P. Goy, M. Gross

We describe instrumentation for conducting high sensitivity millimeter-wave cavity perturbation measurements over a broad frequency range (40-200 GHz) and in the presence of strong magnetic fields (up to 33 tesla). A Millimeter-wave Vector Network Analyzer (MVNA) acts as a continuously tunable microwave source and phase sensitive detector (8-350 GHz), enabli

G. A. Levin, C. C. Almasan

We show that the resistive anisotropy of an anisotropic medium is determined by the ratio of the phase coherence lengths. In layered crystals in which the interlayer transport is incoherent, the out-of-plane phase coherence length is fixed and temperature independent. This leads to a temperature dependent resistive anisotropy and to the coexistence of metall

L. Vasiliu-Doloc, S. Rosenkranz, R. Osborn, S. K. Sinha

X-ray and neutron scattering measurements directly demonstrate the existence of polarons in the paramagnetic phase of optimally-doped colossal magnetoresistive oxides. The polarons exhibit short-range correlations that grow with decreasing temperature, but disappear abruptly at the ferromagnetic transition because of the sudden charge delocalization. The &#3

M. J. Graf, A. V. Balatsky, J. A. Sauls

We show that an isolated impurity in a spin singlet d_{x2-y2} superconductor generates a d_{xy} order parameter with locally broken time-reversal symmetry. The origin of this effect is a coupling between the d_{x2-y2} and the d_{xy} order parameter induced by spin-orbit scattering off the impurity. The signature of locally broken time-reversal symmetry is an

Semjon Stepanow, Michael Schulz

We consider the drift of a polymer chain in a disordered medium, which is caused by a constant force applied to the one end of the polymer, under neglecting the thermal fluctuations. In the lowest order of the perturbation theory we have computed the transversal fluctuations of the centre of mass of the polymer, the transversal and the longitudinal size of t

Bruce M. Boghosian, Peter V. Coveney, Peter J. Love

We describe a three-dimensional hydrodynamic lattice-gas model of amphiphilic fluids. This model of the non-equilibrium properties of oil-water-surfactant systems, which is a non-trivial extension of an earlier two-dimensional realisation due to Boghosian, Coveney and Emerton [Boghosian, Coveney, and Emerton 1996, Proc. Roy. Soc. A 452, 1221-1250], can be st

Andrew Matacz, Jean-Philippe Bouchaud

In this paper we study empirically the Forward Rate Curve (FRC) of 5 different currencies. We confirm and extend the findings of our previous investigation of the U.S. Forward Rate Curve. In particular, the average FRC follows a square-root law, with a prefactor related to the spot volatility, suggesting a Value-at-Risk like pricing. We find a striking corre

Andrea Cavagna, Juan P. Garrahan, Irene Giardina

We compute the distribution of the number of negative eigenvalues (the index) for an ensemble of Gaussian random matrices, by means of the replica method. This calculation has important applications in the context of statistical mechanics of disordered systems, where the second derivative of the potential energy (the Hessian) is a random matrix whose negativ

Sang-Hoon Kim

The trapped Bose system can be regarded as two-dimensional if the thermal fluctuation energy is less than the lowest energy in the perpendicular direction. Under this assumption, we derive an expression for the maximum thickness of an effective two-dimensional trapped Bose system.

P. Sule, S. Kurth, V. Van Doren

The optimized effective potential (OEP) method allows for calculation of the local, effective single particle potential of density functional theory for explicitly orbital-dependent approximations to the exchange-correlation energy functional. In the present work the OEP method is used together with the approximation due to Krieger, Li and Iafrate (KLI). We

D. Guery-Odelin, S. Stringari

We investigate the oscillation of a dilute atomic gas generated by a sudden rotation of the confining trap (scissors mode). This oscillation reveals the effects of superfluidity exhibited by a Bose-Einstein condensate. The scissors mode is investigated also in a classical gas above T_c in various collisional regimes. The crucial difference with respect to th

P. Estrela, T. Naka, A. de Visser, F. R. de Boer

Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa). At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum develops in rho(T). A study of the field dependenc

Jysoo Lee

We use molecular dynamics simulations to study the formation of surface waves in vertically vibrated granular material. We find that horizontal movements of particles, which are essential for the formation of the waves, consist of two distinct processes. First, the movements sharply increase while the particles are colliding with a bottom plate, where the du

Trinh Van Khoa

In this paper we constructed new model of plastic deformation. The knot theory was used to classify the plastic state.

V. A. Kulbachinskii, V. G. Kytin, R. A. Lunin, A. V. Golikov

We have prepared a number of GaAs structures delta-doped by Sn using the well-known molecular beam epitaxy growth technique. The samples obtained for a wide range of Sn doping densities were characterised by magnetotransport experiments at low temperatures and in high magnetic fields up to 38 T. Hall-effect and Shubnikov-de Haas measurements show that the el

J. L. Alonso, Ph. Boucaud, V. Martin-Mayor, A. J. van der Sijs

The phase diagram at zero temperature of a lattice SU(2) scalar-fermion model in (2+1) dimensions is studied numerically and with Mean-Field methods. Special attention is devoted to the strong coupling regime. We have developed a new method to adaptate the Hybrid Monte Carlo algorithm to the O(3) non-linear $σ$ model constraint. The charged excitations in th

Wei-Min Zhang

In this Letter, we develop a microscopic theory to describe the close proximity between the insulating antiferromagnetic (AF) order and the d-wave superconducting (dSC) order in cuprates. We show that the cuprate ground states form a configuration of coherent pairing states consisting of extended singlet Cooper pairs and triplet $π$ pairs, which can simultan

B. Noheda, J. A. Gonzalo, A. Caballero, C. Moure

Recently a new monoclinic phase in the PbZr(1-x)TixO3 ceramic system has been reported by Noheda et al. for the composition x= 0.48. In the present work, samples with Ti contents of x= 0.47 and 0.50, which are both tetragonal below their Curie points, have been investigated. In the sample with x= 0.50, the tetragonal phase was found to transform to a monocli

Benoit des Ligneris, Marcel Aubin, Julian Cave, When Zhu

The ac losses in a silver-gold alloy sheathed Bi-2223 tape were measured by the null calorimetric method while a dc current was superimposed onto the ac current. As expected through computer simulations, a Clem valley was observed for the larger ac currents. A reduction of ac losses of approximately 50% at the valley minimum is observed in accord with the ca

Vassilios M. Rothos

We describe and characterize rigorously the chaotic behavior of the sine-Gordon equation. The existence of invariant manifolds and the persistence of homoclinic orbits for a perturbed sine--Gordon equation are established. We apply a geometric method based on Mel&#39;nikov&#39;s analysis to derive conditions for the transversal intersection of invariant mani

K. D. Borne, L. Colina, H. Bushouse, R. A. Lucas

We have used HST I-band images to identify Mrk 273X, the very unusual high-redshift X-ray-luminous Seyfert 2 galaxy found by ROSAT in the same field-of-view as Mrk 273. We have measured the photometric properties of Mrk 273X and have also analyzed the luminosity distribution of the faint galaxy population seen in the HST image. The luminosity of the galaxy a

H. Li, J. M. Finn, R. V. E. Lovelace, S. A. Colgate

In earlier work we identified a global, non-axisymmetric instability associated with the presence of an extreme in the radial profile of the key function ${\cal L}(r) \equiv (ΣΩ/κ^2) S^{2/Γ}$ in a thin, inviscid, nonmagnetized accretion disk. Here, $Σ(r)$ is the surface mass density of the disk, $Ω(r)$ the angular rotation rate, $S(r)$ the specific entropy,

L. van Zee, J. Bryant

We have analyzed high velocity resolution HI synthesis observations of the nearly face-on Sc galaxy NGC 1232. The neutral gas distribution extends well beyond the optical extent of the galaxy. As expected, local peaks in the HI column density are associated with the spiral arms. Further, the HI column density drops precipitously near the center of the galaxy

H. Ozawa, F. Nagase, Y. Ueda, T. Dotani

We observed the HH24-26 region in the L1630 Orion molecular cloud complex with the X-ray observatory ASCA in the 0.5$-$10 keV band. X-ray emission was detected from the T Tauri star SSV61 and from the region where the Class I protostars SSV63E and SSV63W are located (hereafter SSV63E+W). The spectra of both SSV63E+W and SSV61 are well explained by an optical

J. B. Peterson, J. E. Carlstrom, E. S. Cheng, M. Kamionkowski

The Microwave Anisotropy Probe and Planck missions will provide low noise maps of the temperature of the cosmic microwave background (CMB). These maps will allow measurement of the power spectrum of the CMB with measurement noise below cosmic variance for l < 1500. It is anticipated that no further all sky CMB temperature observations will be needed after Pl

Marcel Arnould, Nikos Prantzos

Radionuclides with half-lives ranging from some years to billions of years presumably synthesized outside of the solar system are now recorded in ``live&#39;&#39; or ``fossil&#39;&#39; form in various types of materials, like meteorites or the galactic cosmic rays. They bring specific astrophysical messages the deciphering of which is briefly reviewed here,

G. Martinez-Pinedo, K. Langanke

We have performed large-scale shell-model calculations of the half-lives and neutron-branching probabilties of the r-process waiting point nuclei at the magic neutron number N=82. We find good agreement with the measured half-lives of 129Ag and 130Cd. Our shell-model half-lives are noticeably shorter than those currently adopted in r-process simulations. Our

David C. Koo

I review the early history of photometric redshifts; specify a working definition that encompasses a broader range of approaches than commonly adopted; discuss the pros and cons of template fitting versus empirically-based techniques; and summarize some past applications. Despite its relatively long history, the technique of photometric redshifts remains far

B. J. Mochejska, J. Kaluzny

We present the results of our search for variable stars in the intermediate-age open cluster NGC 7789. We have found 45 variable stars: 35 eclipsing binaries, five pulsating variables and five miscellaneous variables. Most of the eclipsing binaries show W UMa type of variability, with periods shorter than one day. Four systems exhibit unusual behavior: two,

Sidney van den Bergh

The young populous cluster NGC 1866 in the Large Magellanic Cloud LMC), which is probably one of the most massive object formed in the LMC during the last ~ 3 Gyr, appears to have an unexpectedly high mass-to-light ratio. From its velocity dispersion Fischer et al. (1992) find its mass to be (1.35 &#34; 0.25) x 105 Mu. The luminosity of this cluster is MV =

A. J. Barth, H. D. Tran, M. S. Brotherton, A. V. Filippenko

The detection of polarized continuum and line emission from the nucleus of NGC 4258 by Wilkes et al. (1995) provides an intriguing application of the unified model of Seyfert nuclei to a galaxy in which there is known to be an edge-on, rotating disk of molecular gas surrounding the nucleus. Unlike most Seyfert nuclei, however, NGC 4258 has strongly polarized

Piero Madau

I review the constraints imposed by the observed extragalactic background light (EBL) on the history of the stellar birthrate in galaxies. At faint magnitudes, the logarithmic slope of the galaxy counts is flatter than 0.4 in all seven UBVIJHK optical bandpasses of the Hubble Deep Field-South imaging survey. The integration of the number counts provides a lo

M. Tagger, R. Pellat

We present an instability occurring in the inner part of disks threaded by a moderately strong vertical (poloidal) magnetic field. Its mechanism is such that a spiral density wave in the disk, driven by magnetic stresses (rather than self-gravity as in galactic spirals), becomes unstable by exchanging angular momentum with a Rossby vortex it generates at its

M. Girardi, S. Borgani, G. Giuricin, F. Mardirossian

We analyze a sample of 105 clusters having virial mass homogeneously estimated and for which galaxy magnitudes are available with a well defined high degree of completeness. In particular, we consider a subsample of 89 clusters with B_j band galaxy magnitudes taken from the COSMOS/UKST Southern Sky Object Catalogue. We compute cluster luminosities L_{B_j} wi

J. J. M. in &#39;t Zand, J. Heise, E. Kuulkers, A. Bazzano

The broad band X-ray spectrum of the low-mass X-ray binary (LMXB) GS1826-238 was measured with the narrow-field instruments on BeppoSAX on April 6 and 7, 1997. The spectrum is consistent with the Comptonization of a 0.6 keV thermal spectrum by a hot cloud of temperature equivalent kT=20 keV. During the observation two type I X-ray bursts were detected. From

T. J. Galama, N. Tanvir, P. M. Vreeswijk, R. A. M. J. Wijers

We present B-, V-, R_c-, I_c-, J-, H-, K- and K&#39;-band observations of the optical transient (OT) associated with GRB970228, based on a reanalysis of previously used images and unpublished data. In order to minimize calibration differences we have collected and analyzed most of the photometry and consistently determined the magnitude of the OT relative to

M. D&#39;Vali, I. H. Bond, S. M. Bradbury, J. H. Buckley

Only BL Lac objects have been detected as extragalactic sources of very high energy (E > 300 GeV) gamma rays. Using the Whipple Observatory Gamma-ray Telescope, we have attempted to detect more BL Lacs using three approaches. First, we have conducted surveys of nearby BL Lacs, which led to the detections of Mrk 501 and 1ES 2344+514. Second, we have observed

U. Heber, I. N. Reid, K. Werner

PG 1605+072 has unique pulsational properties amongst the members of the new class of pulsating sdB (EC 14026) stars. It has the longest periods and the richest, most puzzling frequency spectrum (55 periods). We present a quantitative analysis of a Keck HIRES spectrum using NLTE and LTE model atmospheres. Atmospheric parameters (Teff, log g, log(He/H)), meta

T. Oka, N. Kawai, T. Naito, T. Horiuchi

CO J=1-0 mapping observations of the dark nebula Lynds 227, which is possibly associated with the unidentified EGRET source 2EG J1811-2339, are presented. We detected a large amount of molecular gas along Lynds 227 with a total mass of (1-2)E4 Msun surrounding an X-ray synchrotron nebula, which was detected by the ASCA satellite within the error circle of 2E

Mark Walker, Mark Wardle

Modelling of Extreme Scattering Events suggests that the Galaxy&#39;s dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture -- thermal/non-thermal emission, extinction and lensing -- are problematic. The theoretical situation is less comfortable, but still satisfacto

J. A. Holtzman, J. S. Gallagher, A. A. Cole, J. R. Mould

We present derivations of star formation histories based on color-magnitude diagrams of three fields in the LMC from HST/WFPC2 observations. A significant component of stars older than 4 Gyr is required to match the observed color-magnitude diagrams. Models with a dispersion-free age-metallicity relation are unable to reproduce the width of the observed main

L. V. E. Koopmans, C. D. Fassnacht

EDITED FROM PAPER: We present mass models of the four-image gravitational lens system B1608+656. A mass model for the lens galaxies has been determined that reproduces the image positions, two out of three flux-density ratios and the model time delays. Using the time delays determined by Fassnacht et al. (1999a), we find that the best isothermal mass model g

C. D. Fassnacht, T. J. Pearson, A. C. S. Readhead, I. W. A. Browne

We present the results of a program to monitor the four-image gravitational lens B1608+656 with the VLA. The system was observed over a seven month period from 1996 October to 1997 May. The 64 epochs of observation have an average spacing of 3.6~d. The light curves of the four images of the background source show that the flux density of the background sourc

N. Kataoka, K. Kaneko

The articulation process of dynamical networks is studied with a functional map, a minimal model for the dynamic change of relationships through iteration. The model is a dynamical system of a function $f$, not of variables, having a self-reference term $f \circ f$, introduced by recalling that operation in a biological system is often applied to itself, as

N. Kataoka, K. Kaneko

Functional dynamics, introduced in a previous paper, is analyzed, focusing on the formation of a hierarchical rule to determine the dynamics of the functional value. To study the periodic (or non-fixed) solution, the functional dynamics is separated into fixed and non-fixed parts. It is shown that the fixed parts generate a 1-dimensional map by which the dyn

Steven G. Harris

A method is presented for imputing a topology for any chronological set, i.e., a set with a chronology relation, such as a spacetime or a spacetime with some sort of boundary. This topology is shown to have several good properties, such as replicating the manifold topology for a spacetime and replicating the expected topology for some simple examples of spac

Amol S. Dighe, Alexei Yu. Smirnov

We study the role that the future detection of the neutrino burst from a galactic supernova can play in the reconstruction of the neutrino mass spectrum. We consider all possible 3$ν$ mass and flavor spectra which describe the solar and atmospheric neutrino data. For each of these spectra we find the observable effects of the supernova neutrino conversions b

Ian Affleck, Shaojin Qin

The effect of a BULK marginal operator on BOUNDARY critical phenomena in two space-time dimensions is considered. The particular case of an open S=1/2 antiferromagnetic Heisenberg chain, corresponding to a Wess-Zumino-Witten non-linear sigma model, is solved. In this case, the needed renormalization group coefficient is associated with a novel operator produ

A. B. Shick, W. E. Pickett, C. S. Fadley

Effects of electron correlation on the electronic structure and magnetic properties of the Gd(0001) surface are investigated using of the full-potential linearized augmented plane wave implementation of correlated band theory (&#34;LDA+U&#34;). The use of LDA+U instead of LDA (local density approximation) total energy calculations produces the correct ferrom

V. Barger, J. G. Learned, P. Lipari, M. Lusignoli

We reconsider neutrino decay as an explanation for atmospheric neutrino observations. We show that if the mass-difference relevant to the two mixed states ν_μand ν_τis very small (< 10^{-4} eV^2), then a very good fit to the observations can be obtained with decay of a component of ν_μto a sterile neutrino and a Majoron. We discuss how the K2K and MINOS long

Hsuan-Yi Chen, David Jasnow, Jorge Vinals

A coarse grained description of a two phase fluid is used to study the steady state configuration of the interface separating the coexisting phases, and the motion of the contact line at which the interface intersects a solid boundary. The fluid is set in motion by displacing two parallel, infinite solid boundaries along their own plane. Dissipative relaxati

N. N. Kuzma, P. Khandelwal, S. E. Barrett, L. N. Pfeiffer

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu=1/3. Below 0.5K, the spectra provide evidence that spin-reversed charged excitations of the nu=1/3 ground state are localized over the NMR time scale of ~40 micro