November 1997 arXiv papers — page 15

P. A. Caraveo, G. F. Bignami

The EGRET catalogue of unidentified X-ray sources has more objects along the galactic disk than at high galactic latitude, where identifications are comparatively easier. On the other hand, the Egret/GRO mission has already identified several known radio pulsars as gamma-ray sources as well as discovering Geminga's nature as a pulsar. If Geminga is not a

F. Natali, E. Giallongo, S. Cristiani, F. La Franca

The average optical-UV continuum shape of QSOs has been investigated using spectra of 62 QSOs having good relative photometric calibrations. The QSO spectra were extracted from two complete color selected samples in the magnitude intervals B ~ 16-20. The analysis was performed fitting power-law continua (f proportional to nu^(alpha)) in well defined rest-fra

Heino Falcke, Peter L. Biermann

We summarize recent results presented in the astrophysics session during a conference on ``Frontiers of Contemporary Physics''. We will discuss three main fields (High-Energy Astrophysics, Relativistic Astrophysics, and Cosmology), where Astrophysicists are pushing the limits of our knowledge of the physics of the universe to new frontiers. Since the

J. K. Kotilainen, R. Falomo, R. Scarpa

We present the results of a high resolution (0.27 arcsec/px) near-infrared H band (1.65 micron) imaging survey of a complete sample of 20 flat spectrum radio quasars (FSRQ) extracted from the 2Jy catalogue of radio sources. The observed objects are intrinsically luminous with median M(B) = -25.5. The median redshift of the objects in the sample is z = 0.65.

P. A. Caraveo, R. P. Mignani, G. F. Bignami

In view of the data gathered in September 1997, we review the flux values collected so far for the "fuzziness" seen in the optical counterpart of GRB970228. Comparison between the ground based data collected in March and the data of September 1997 suggests a fading of the fuzz. Given the diversity of the data in hand, the magnitude of the effect and

V. G. Gurzadyan, S. Torres

The geodesics followed by cosmic microwave background (CMB) photons show different behaviours depending on the geometry of space. Namely, the effect of `mixing geodesics' predicts a distinct signature in CMB maps: threshold-independent elongated anisotropy spots in negatively curved geometries. We have found statistically significant sign for spot elonga

Fred Hamann, Ross D. Cohen, Joseph Shields, E. M. Burbidge

NeVIII 774 is an important tracer of the high-ionization gas in QSOs. We examine the NeVIII emission-line properties using new HST-FOS spectra of four sources, mean spectra derived from two QSO samples in the HST archives, and new photoionization calculations. The results support our previous claim that broad NeVIIIlines are common in QSOs, with an average f

Michael Gronau, and Jonathan L. Rosner

The ratio of partial decay rates for charged and neutral $B$ mesons to $K π$ final states provides information on the weak phase $γ\equiv {\rm Arg} (V_{ub}^*)$ when augmented with information on the CP-violating asymmetry in the $K^\pm π^\mp$ mode. The requirements for a useful determination of $γ$ are examined in the light of present information about the d

Oyvind Tafjord, Vipul Periwal

We evaluate one-loop finite-time amplitudes for graviton scattering in Matrix theory and compare to the corresponding amplitudes in supergravity. We find agreement for arbitrary time intervals at leading order in distance, providing a functional agreement between supergravity and Matrix theory. At subleading order, we find corrections to the effective potent

Adam K. Leibovich, Iain W. Stewart

Exclusive semileptonic Lambda_b decays to excited charmed Lambda_c baryons are investigated at order Lambda_{QCD}/m_Q in the heavy quark effective theory. The differential decay rates are analyzed for the J^π=1/2^- Lambda_c(2593) and the J^π=3/2^- Λ_c(2625). They receive 1/m_{c,b} corrections at zero recoil that are determined by mass splittings and the lead

E. G. Floratos, G. K. Leontaris, A. P. Polychronakos, R. Tzani

We present some methods of determining explicit solutions for self-dual supermembranes in 4+1 and 8+1 dimensions with spherical or toroidal topology. For configurations of axial symmetry, the continuous SU(\infty) Toda equation turns out to play a central role, and a specific method of determining all the periodic solutions are suggested. A number of example

Miquel Dorca

In a recent work on the quantization of a massless scalar field in a particular colliding plane wave space-time, we computed the vacuum expectation value of the stress-energy tensor on the physical state which corresponds to the Minkowski vacuum before the collision of the waves. We did such a calculation in a region close to both the Killing-Cauchy horizon

Martin Markl

Barton Zwiebach constructed the `string products' on the Hilbert space of combined conformal field theory of matter and ghosts. It is well-known that the `tree level' specialization of these products forms a strongly homotopy Lie algebra. A strongly homotopy Lie algebra is given by a square zero coderivation on the cofree cocommutative connected coal

Stefan Forste, Debashis Ghoshal

We construct models in 1+1 dimensions with chiral (0,N) supersymmetry by taking orientifolds of type IIB on an eight-torus identified by different numbers of reflections. The resulting models have Dirichlet strings, fivebranes and ninebranes stretched along different directions. The cases we study in detail have residual chiral supersymmetry (0,8), (0,4) and

Eric Bergshoeff, Joaquim Gomis, Paul K. Townsend

It is known that the M-branes of M-theory correspond to p-form charges in the D=11 spacetime supersymmetry algebra. Here we show that their intersections are encoded in the p-form charges of their worldvolume supersymmetry algebras. Triple intersections are encoded in double intersection worldvolume algebras with eight supercharges.

B. Carazza

We examine the reduced density matrix of the centre of mass on position basis considering a one-dimensional system of $N$ non-interacting distinguishable particles in a infinitely deep square potential well. We find a class of pure states of the system for which the off-diagonal elements of the matrix above go to zero as $N$ increases. This property holds to

S. W. Hawking, M. M. Taylor-Robinson

Eleven dimensional supergravity has electric type currents arising from the Chern-Simon and anomaly terms in the action. However the bulk charge integrates to zero for asymptotically flat solutions with topological trivial spatial sections. We show that by relaxing the boundary conditions to generalisations of the ALE and ALF boundary conditions in four dime

S. Brian Edgar, Anders Höglund

We prove that a Lanczos potential L_abc for the Weyl candidate tensor W_abcd does not generally exist for dimensions higher than four. The technique is simply to assume the existence of such a potential in dimension n, and then check the integrability conditions for the assumed system of differential equations; if the integrability conditions yield another n

E. Ivanov, E. Sokatchev

We propose a harmonic superspace description of the non-linear vector-tensor N=2 multiplet. We show that there exist two inequivalent version: the old one in which one of the vectors is the field-strength of a gauge two-form, and a new one in which this vector satisfies a non-linear constraint and cannot be expressed in terms of a potential. In this the new

Anindya K. Biswas, Alok Kumar, Gautam Sengupta

We present a class of BPS solutions of the IIB Matrix Theory which preserve 1/4 supersymmetry. The solutions desrcibe D-string configurations with left-moving oscillations. We demonstrate that the one-loop quantum effective action of Matrix Theory vanishes for this solution, confirming its BPS nature. We also study the world-volume gauge theory of oscillatin

C. Helminen

The exchange charge density operators that correspond to the Fermi-invariant decomposition of quark-quark interactions have been constructed. Their effect on the electromagnetic charge radii of the nucleons, in combination with that of the relativistic corrections to the single-quark operator, has been studied with a constituent quark model with a spin and f

Jorge Berger, Jacob Rubinstein

We predict the existence of a quantum vortex for an unusual situation. We study the order parameter in doubly connected superconducting samples embedded in a uniform magnetic field. For samples with perfect cylindrical symmetry, the order parameter has been known for long and no vortices are present in the linear regime. However, if the sample is not symmetr

Zoltan Ligeti, Iain W. Stewart, Mark B. Wise

The prospects for determining $|V_{ub}|$ from exclusive B semileptonic decay are discussed. The double ratio of form factors $(f^{B\toρ}/f^{B\to K^*})/ (f^{D\toρ}/f^{D\to K^*})$ is calculated using chiral perturbation theory. Its deviation from unity due to contributions that are non-analytic in the symmetry breaking parameters is very small. Combining exper

Kirill Ilinski, Alexander Stepanenko

In the comment we give references to our papers where the problem was solved for more general case of time-dependent finite temperature correlators.

Masanao Ozawa

A new approach to the problem of measurement in quantum mechanics is proposed. In this approach, the process of measurement is described in the Heisenberg picture and divided into two stages. The first stage is to transduce the measured observable to the probe observable. The second stage is to amplify the probe observable to the macroscopic meter observable

A. R. Porter, R. W. Godby

We present the results of over 90 tight-binding molecular-dynamics simulations of collisions between three- and five-atom silicon clusters, at a system temperature of 2000K. Much the most likely products are found to be two 'magic' four-atom clusters. We show that previous studies, which focused on the equilibrium binding energies of clusters of diff

Konrad Banaszek, Krzysztof Wodkiewicz, Wolfgang P. Schleich

A phase space description of the fractional Talbot effect, occurring in a one-dimensional Fresnel diffraction from a periodic grating, is presented. Using the phase space formalism a compact summation formula for the Wigner function at rational multiples of the Talbot distance is derived. The summation formula shows that the fractional Talbot image in the ph

A. Polleri, I. N Mishustin, J. P. Bondorf

We discuss the interplay between collective flow and density profiles, describing light cluster production in heavy ion collisions at very high energies. Calculations are performed within the coalescence model. We show how collective flow can explain some qualitative features of the measured deuteron spectra, provided a proper parametrization of the spatial

H. Müther, S. Ulrych, H. Toki

A key point of Dirac Brueckner Hartree Fock calculations for nuclear matter is to decompose the self energy of the nucleons into Lorentz scalar and vector components. A new method is introduced for this decomposition. It is based on the dependence of the single-particle energy on the small component in the Dirac spinors used to calculate the matrix elements

A. Gil, J. Nieves, E. Oset

We have performed a many body calculation of the inclusive (e,e') cross section which runs over the three traditional regions at intermediate energies: the quasielastic peak, the dip region and the delta region. The longitudinal and transverse response functions in the quasielastic peak have also been evaluated. Traditional effects like polarization, mes

Renat Zhdanov

A symmetry reduction of the Dirac equation is shown to yield the system of ordinary differential equations whose integrability by quadratures is closely connected to the stationary mKdV hierarchy.

John H. Schwarz

There have been many remarkable developments in our understanding of superstring theory in the past few years, a period that has been described as ``the second superstring revolution.'' Several of them are discussed here. The presentation is intended primarily for the benefit of nonexperts.

N. Dragon, U. Theis

We gauge the central charge of the N=2 supersymmetry algebra in rigid superspace. The Fayet Sohnius hypermultiplet with gauged central charge coincides on-shell with N=2 supersymmetric electrodynamics. The gauge couplings of the vector-tensor multiplet turn out to be nonpolynomial.

Christopher D. Carone, Marc Sher

We present a supersymmetric model of fermion masses, based on a non-Abelian family symmetry and the Froggatt-Nielsen mechanism, that can account for the solar and atmospheric neutrino problems via quasi-degenerate neutrinos. The model predicts that the ratio of neutrino mass squared splittings Δm^2_{12} / Δm^2_{23} is of order m_s^2/m_b^2, and the angles θ_{

Daniel Boyanovsky, Hector J. de Vega, Richard Holman, S. Prem Kumar

We propose to study the non-equilibrium features of heavy-ion collisions by following the evolution of an initial state with a large number of quanta with a distribution around a momentum |\vec k_0| corresponding to a thin spherical shell in momentum space, a `tsunami'. An O(N); ({\vec Φ}^2)^2 model field theory in the large N limit is used as a framewor

Eugene Golowich, Joachim Kambor

We reconsider the DMO sum rule in light of our recent two-loop calculations of isospin and hypercharge vector and axialvector current propagators in chiral perturbation theory. A modified derivation valid to second order in the light quark masses is presented, and a phenomenological analysis yields determination of a combination of finite counterterms occurr

Sergio Lupia, Wolfgang Ochs

A complete numerical solution of the evolution equation for parton multiplicities in quark and gluon jets with initial conditions at threshold is presented. Data on both hadron and jet multiplicities in e+e- annihilation are well described with a common normalization, giving further support to the picture of Local Parton Hadron Duality. Predictions for LEP-I

G. Weiglein

A summary of recent results obtained for higher-order corrections to precision observables in the Standard Model and the Minimal Supersymmetric Standard Model is given. In the Standard Model electroweak two-loop results valid for arbitrary values of the masses of the top quark, the Higgs boson and the gauge bosons are discussed. For the example of two specif

E. Boos, A. Pukhov, M. Sachwitz, H. J. Schreiber

Results of complete tree level calculation of the single top and light Higgs production in the reaction $γe \to νb \bar{b} W$ at the Next Linear Collider are presented. In addition, the contributions of anomalous operators to the $Wtb$ and $WWH$ couplings are included into the complete 4-body consideration. The sensitivity for probing the structure of the co

I. L. Solovtsov, D. V. Shirkov

We further develop the approach recently used to construct an analytic ghost-free model for the QCD running coupling based on the requirement of the $Q^2$-analyticity and apply it to the process of $e^+e^-$ annihilation into hadrons to study the renormalization scheme dependence of the $R(s)$ cross-section ratio. \par By transforming the relevant QCD correct

J. M. Butterworth, N. Goodman, M. Stratmann, W. Vogelsang

We study various conceivable photoproduction reactions in a polarized ep collider mode of HERA with respect to their sensitivity to the proton's polarized gluon distribution. A special emphasis is put on the `resolved' part of the cross sections which in principle opens the possibility to determine for the first time also the completely unknown parto

S. Hannestad

We investigate the non-radiative decay during nucleosynthesis of a massive tau neutrino with mass 0.1 - 1 MeV into an electron neutrino and a scalar or pseudoscalar particle, $ϕ$. The full Boltzmann equation is used and shown to give markedly different results than the usual non-relativistic formalism for relativistic or semi-relativistic neutrino decays. In

A. V. Samsonov

Forward scattering amplitude of the virtual longitudinal photon at zero energy on electron in QED in the limit of small photon virtualities is calculated. The first radiation corrections are taken into account. Two terms in the expansion over photon virtualities are obtained.

M. Teper

Lectures given at the Isaac Newton Institute, NATO-ASI School on "Confinement, Duality and Non-Perturbative Aspects of QCD", 23 June - 4 July, 1997.

N. Yamada, S. Hashimoto, K-I. Ishikawa, H. Matsufuru

We investigate higher order effects in the nonrelativistic expansion of lattice QCD on the heavy-light meson decay constants and some other quantities in order to understand the truncation error of NRQCD. While our numerical results have large $O(a)$ and $O(α_s)$ errors due to the use of Wilson light quark action and the tree-level matching, we find that the

Tamas G. Kovacs, E. T. Tomboulis

We discuss the physical picture of thick vortices as the mechanism responsible for confinement at arbitrarily weak coupling in SU(2) gauge theory. By introducing appropriate variables on the lattice we distinguish between thin, thick and `hybrid' vortices, the latter involving Z(2) monopole loop boundaries. We present numerical lattice simulation results

K-I. Ishikawa, S. Aoki, S. Hashimoto, H. Matsufuru

We study the heavy quark mass dependence of the perturbative renormalization factors for the heavy-light currents involving Wilson, Clover, and NRQCD heavy quarks. We find that the one-loop Z-factor for the axial-vector current depends significantly on the heavy quark mass commonly for all actions we study, while that for the vector current has smaller depen

M. J. Reboucas, R. K. Tavakol, A. F. F. Teixeira

We introduce the notion of topological fragility and briefly discuss some examples from the literature. An important example of this type of fragility is the way globally anisotropic Bianchi V generalisations of the FLRW $k=-1$ model result in a radical restriction on the allowed topology of spatial sections, thereby excluding compact cosmological models wit

G. A. Monerat, H. P. de Oliveira, I. Damiao Soares

We show that homogeneous and isotropic cosmological models with radiation and scalar field have, in general, two possible chaotic exits to inflation. These models may describe the early stages of inflation. The central point of our analysis is based on the possible existence of one or two saddle-centers points in the phase space of the models.

Roberto De Pietri

The recent developments of the ``connection'' and ``loop'' representations have given the possibility to show that the two representation are equivalent and that it is possible to transform any result from one representation into the other. The glue between the two representations is the loop transform. Its use, combined with the techincs Pen

G"unter Scharf

It is shown that a quantized Schwarzschild black hole, if described by a square root energy spectrum with exponential multiplicity, can be treated as a microcanonical ensemble without problem leading to the expected thermodynamical properties.

Mattias Marklund, Gyula Fodor, Zoltán Perjés

Rigidly rotating stationary matter in general relativity has been investigated by Kramer by the Ernst coordinate method. A weakness of this approach is that the Ernst potential does not exist for differential rotation. We now generalize the techniques by the use of a nonholonomic and nonrigid frame. We apply these techniques for differentially rotating perfe

S. R. Brandt, P. Walker, P. Anninos

We describe a numerical grid generating procedure to construct new classes of orthogonal coordinate systems that are specially adapted to binary black hole spacetimes. The new coordinates offer an alternative approach to the conventional Čadež coordinates, in addition to providing a potentially more stable and flexible platform to extend previous calculation

S. R. Brandt, J. A. Font

We present preliminary results in our long-term project of studying the evolution of matter in a dynamical spacetime. To achieve this, we have developed a new code to evolve axisymmetric initial data sets corresponding to a black hole surrounded by matter fields. The code is based on the coupling of two previously existing codes. The matter fields are evolve

Robert M. Wald

We review the status of the weak cosmic censorship conjecture, which asserts, in essence, that all singularities of gravitational collapse are hidden within black holes. Although little progress has been made toward a general proof (or disproof) of this conjecture, there has been some notable recent progress in the study of some examples and special cases re

Gabriel Tellez

We revisit the model of the two-component plasma in a gravitational field, which mimics charged colloidal suspensions. We concentrate on the computation of the grand potential of the system. Also, a special sum rule for this model is presented.

Heiko Feldmann, Robert Shrock, Shan-Ho Tsai

We calculate complex-temperature (CT) zeros of the partition function for the $q$-state Potts model on the honeycomb and kagomé lattices for several values of $q$. These give information on the CT phase diagrams. A comparison of results obtained for different boundary conditions and a discussion of some CT singularities are given. Among other results, our fi

David S. Dean, Giorgio Parisi

We analyse the statistical physics of a two dimensional lattice based gas with long range interactions. The particles interact in a way analogous to Queens on a chess board. The long range nature of the interaction gives the mathematics of the problem a simple geometric structure which simplifies both the analytic and numerical study of the system. We presen

Andrzej Klejnberg, Jozef Spalek

A simple slave-boson representation combined with the Hartree-Fock approximation for the Hund's rule coupling is introduced for a doubly degenerate narrow band, which bears a direct relation to that introduced previously in the nondegenerate case. Namely, one keeps the fermion representation of the spin operator to recover properly the energy of fermioni

Heiner Kohler, Andreas Mielke

We consider a particle in the over-damped regime at zero temperature under the influence of a sawtooth potential and of a noisy force, which is correlated in time. A current occurs, even if the mean of the noisy force vanishes. We calculate the stationary probability distribution and the stationary current. We discuss, how these items depend on the character

Hang-Sheng Wu, Xian-Xiang Huang, Qi-Ming Weng

By choosing an electron gas resting instead of drifting in the laboratory coordinate system as the initial state, the first order perturbation calculation of the previous paper (Phys. Stat. Sol. (b) 198, 785(1996)) is revised and extended to include the high order field corrections in the expression for the frictional forces and the energy transfer rates. Th

Roger S Eccleston, Masatomo Uehara, Jun Akimitsu, Hiroshi Eisaki

We have performed inelastic neutron scattering on a single crystal sample of Sr14Cu24O41 to study the spin dynamics of the Cu2O3 spin ladder layers, and CuO2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV and 500 meV are best fitted with a dispersion with a spin gap of 32.5+/-0.1 meV and a maximum of 193.52.4 meV, consistent with a

M. N. Popova, A. B. Sushkov, A. N. Vasil'ev, M. Isobe

We report the first observation of new lines in the infrared spectrum of a crystal due to unit-cell doubling at the spin-Peierls transition (in NaV_2O_5). The change in the shape of the spectral lines at the spin-Peierls transition is recorded for the first time. A contour characteristic of a Fano resonance is observed above the transition temperature Tsp an

D. Bensimon, D. Dohmi, M. Mezard

We study the influence of some quenched disorder in the sequence of monomers on the entropic elasticity of long polymeric chains. Starting from the Kratky-Porod model, we show numerically that some randomness in the favoured angles between successive segments induces a change in the elongation versus force characteristics, and this change can be well describ

P. Di Francesco, B. Eynard, E. Guitter

We introduce and solve a two-matrix model for the tri-coloring problem of the vertices of a random triangulation. We present three different solutions: (i) by orthogonal polynomial techniques (ii) by use of a discrete Hirota bilinear equation (iii) by direct expansion. The model is found to lie in the universality class of pure two-dimensional quantum gravit

Colin Denniston, Chao Tang

We study a Josephson junction ladder in a magnetic field in the absence of charging effects via a transfer matrix formalism. The eigenvalues of the transfer matrix are found numerically, giving a determination of the different phases of the ladder. The spatial periodicity of the ground state exhibits a devil's staircase as a function of the magnetic flux

S. A. Golubchik, M. Isobe, A. N. Ivlev, B. N. Mavrin

We have measured polarized spectra of Raman scattering, infrared and optical transmission of NaV_2O_5 single crystals above the temperature of the spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines are strongly asymmetric, due to the spin-phonon interaction. In addition to the phonon lines, a broad band was observed in the c(aa)c R

G. Els, P. H. M. van Loosdrecht, P. Lemmens, H. Vonberg

Temperature and magnetic field dependent polarized Brillouin spectra of CuGeO_3 are reported. In addition to a bound singlet state at 30 cm^{-1}, a new feature has been observed at 18 cm^{-1}. This feature is interpreted in terms of a novel three-magnon light scattering process between excited triplet states.

Mahn-Soo Choi, J. Yi, M. Y. Choi, J. Choi

We investigate the quantum phase transition in a one-dimensional chain of ultra-small superconducting grains, considering both the self- and junction capacitances. At zero temperature, the system is transformed into a two-dimensional system of classical vortices, where the junction capacitance introduces anisotropy in the interaction between vortices. This l

Gen Tatara, Macoto Kikuchi, Satoshi Yukawa, Hiroshi Matsukawa

Quantum mechanical motion of a particle in a periodic asymmetric potential is studied theoretically at zero temperature. It is shown based on semi-classical approximation that the tunneling probability from one local minimum to the next becomes asymmetric in the presence of weak oscillating field, even though there is no macroscopic field gradient in average

Richard P. Sear

The correlations between the segments of a semidilute polymer solution are found to induce correlations in the positions of small particles added to the solution. Small means a diameter much less than the polymer's correlation length. In the presence of polymer the particles behave as if they attracted each other. It is shown how the polymer's correl

Satarou Yamaguchi, Hiroaki Nakamura, Kazuaki Ikeda, Tokushi Sakurai

Peltier current lead was proposed to reduce heat leak from the current lead. The temperature of the hot side of semiconductors was kept to be room temperature and the liquid nitrogen was used to cool the system in the experiment. The experiment confirmed the principle of the Peltier current lead, and the reduction of the heat leak is calculated to be 30 % fo

Yu. I. Latishev, B. Pannetier, P. Monceau

We demonstrate for the first time that a periodic array of submicrometer holes (antidots) can be patterned into thin single NbSe3 crystals. We report on the study of charge density wave (CDW) transport of the network of mesoscopic units between antidots. Size of the elementary unit can be as small as 0.5 micron along the chain axis and (0.2 micron) x (0.3 mi

Jayme De Luca

We show that an extra complex constant of motion with an analytic form can exist in the neighborhood of some discrete Wannier orbits of helium, when one includes retardation and self-interaction effects. The energies of these discrete Wannier orbits are in the correct atomic magnitude. The highest frequency in the stable manifold of one such orbit agrees wit

Guenter Sigl, Martin Lemoine

We present a detailed Monte Carlo study coupled to a likelihood analysis of the potential of next generation ultra-high energy cosmic ray experiments to reconstruct properties of the sources and the extra-galactic magnetic field. Such characteristics are encoded in the distributions of arrival time, direction, and energy of clusters of charged cosmic rays ab

G. A. Drukier, S. D. Slavin, H. N. Cohn, P. M. Lugger

We present velocities for 230 stars in the outer parts of the globular cluster M15 measured with the Hydra multi-object spectrograph on the WIYN telescope. A new Bayesian technique is used for analyzing the data. The mean velocity of the cluster is -106.9+/- 0.3 km/s. Rotation with an amplitude of 1.5+/- 0.4 km/s and a position angle of 125+/-19 degrees is o

M. Stiavelli, N. Panagia, C. M. Carollo, M. Romaniello

We present WFPC2 images in the F450W, F606W and F814W filters of the interacting pair of galaxies NGC 454. Our data indicate that the system is in the early stages of interaction. A population of young star-clusters has formed around the late component, and substantial amounts of gas have sunk into the center of the earlier component, where it has not yet pr

Changbom Park, Wesley N. Colley, J. Richard Gott, Bharat Ratra

We have simulated cosmic microwave background (CMB) anisotropy maps for several COBE-DMR-normalized cold dark matter (CDM) cosmogonies, to make predictions for the upcoming MAP experiment. We have studied the sensitivity of the simulated MAP data to cosmology, sky coverage, and instrumental noise. With accurate knowledge of instrumental noise, MAP data will

Paul C. Hewett, Craig B. Foltz, Margaret E. Harding, Geraint F. Lewis

We present photometric and spectroscopic observations of two close quasar-quasar pairs found in the Large Bright Quasar Survey (LBQS) (Hewett et al. 1995, AJ, 109, 1498). The two components of the 2153-2056 pair ($z=1.845$, $Δθ=7\farcs8$, $B=17.9$ and 21.3) have the same redshifts within the relatively large uncertainty, $Δv_{A-B} =-1100\pm1500 km s^{-1}$, o

S. I. Blinnikov, R. Eastman, O. S. Bartunov, V. A. Popolitov

The light curve of Supernova (SN) 1993J is calculated using two approaches to radiation transport as exemplified by the two computer codes, STELLA and EDDINGTON. Particular attention is paid to shock breakout and the photometry in the U, B, and V bands during the first 120 days. The hydrodynamical model, the explosion of a 13 Msun star which had lost most of

E. Oliva, A. Marconi, A. Cimatti, S. di Serego Alighieri

High quality 4500-6800 A spectropolarimetric observations of the Circinus galaxy are reported. These show polarized and relatively broad (FWHM~3300 km/s) Halpha (as well as marginal Hbeta) arising from a <3&#34; (<60 pc) region centered on the nucleus and coincident with the the peak of the narrow line region. Broad Halpha might also be present ~8&#34; (160

Matthew A. Bershady, Dario Trevese, Richard G. Kron

We have isolated a sample of 14 candidate variable objects with extended image structure to Bj = 22.5 in 0.284 deg^2 of Selected Area 57. The majority of candidates are blue (U-B<0) and relatively compact. At fainter magnitudes, there is a steep rise in the number of variable objects. These objects are also compact and blue, and some of them are likely to be

Klaas S. de Boer, Jochen M. Braun, Antonella Vallenari, Ulrich Mebold

The structure of supergiant shells, in particular of LMC 4, is hard to explain with stochastic self-propagating star formation. A series of supergiant structures lies along the outer edge of the LMC and form a sequence increasing clockwise in age. We have considered the rotation of the LMC and its motion through the halo of the Milky Way and propose that the

Paolo Padoan, Mika Juvela, John Bally, AAke Nordlund

The dynamics of molecular clouds is characterized by supersonic random motions in the presence of a magnetic field. We study this situation using numerical solutions of the three-dimensional compressible magneto-hydrodynamic (MHD) equations in a regime of highly supersonic random motions. The non-LTE radiative transfer calculations are performed through the

Daniel A. Dale, Riccardo Giovanelli, Martha P. Haynes, Marco Scodeggio

We present Tully-Fisher (TF) observations for nine rich Abell clusters of galaxies. This is the second such data installment of an all-sky survey of 50 clusters in the redshift range 0.02 < z < 0.06. The data extends the TF study of nearby clusters of Giovanelli et al.; they will be used jointly to determine an accurate I band TF template and to establish a

R. Capuzzo-Dolcetta, P. Miocchi

According to the hypothesis that AGNs are massive black holes and the mass which feeds them is made of stars belonging to globular clusters frictionally decayed and tidally destroyed by the field of the central object, it is possible to give an estimate of the number and spectral characteristics of detectable gravitational wave impulses generated by the fall

Fabio La Franca, Paola Andreani, Stefano Cristiani

The evolution of quasar clustering is investigated with a new sample of 388 quasars with 0.3<z<=2.2, B<=20.5 and Mb<-23, selected over an area of 24.6 sq. deg. in the South Galactic Pole. Assuming a two-point correlation function of the form xi(r) = (r/r_o)^-1.8, we detect clustering with r_0=6.2 +/- 1.6 h^-1 comoving Mpc at an average redshift of z=1.3. We

Amri Wandel, Thomas Boller

Recent ROSAT studies of narrow-line Seyfert 1 galaxies revealed these objects (with FWHM $H_β \le 2000 km s^{-1}$) generally show steeper soft X-ray spectra than broad line Seyfert 1&#39;s and that there are no AGN with broad lines and steep X-ray spectra. We derive a simple theoretical model which explains the observed correlation between the line width and

U. Lindner, J. Einasto, M. Einasto, K. J. Fricke

The Northern Local Void is a huge underdense region of the nearby Universe situated between the Hercules, Coma and Local Superclusters. We present an investigation of the galaxy distribution in the Northern Local Void using void statistics. In particular galaxies of different morphological type and luminosity have been studied separately and void catalogues

Stephen D. Landy, Alexander S. Szalay, Thomas J. Broadhurst

We present a novel measurement of the pairwise peculiar velocity distribution function of galaxies on scales $r<3200$ \kmsec in the Las Campanas Redshift Survey. The distribution is well described by a scale-independent exponential with a width $τ$ where $\sig =\sqrt{2}τ=363$ \kmsec. The signal is very stable. Results from the Northern and Southern sets of s

C. D. Fassnacht, J. G. Cohen

We present spectra of three gravitational lens systems taken with the Low Resolution Imaging Spectrograph on the W. M. Keck Telescopes. All of the systems were discovered in the JVAS and CLASS radio surveys, which were designed to find lenses suitable for measuring $H_0$. Previous spectra of these systems had low signal-to-noise ratios, and only one of the s

Robin Hartshorne, Mireille Martin-Deschamps, Daniel Perrin

Let $A$ be a local noetherian ring and $N$ be a locally sheaf on the projective space $P^3_A$ : one proves easily that there exists a family $C$ of (smooth connected) curves contained in $P^3_A$, flat over $A$, and an integer $h$ such that the ideal sheaf $J$ of $C$ has a resolution $0\to P\to N\to J\to 0$ where $P$ is a direct sum of invertible sheaves $O_P

Simeon Hellerman, Joseph Polchinski

We study field theories in the limit that a compactified dimension becomes lightlike. In almost all cases the amplitudes at each order of perturbation theory diverge in the limit, due to strong interactions among the longitudinal zero modes. The lightlike limit generally exists nonperturbatively, but is more complicated than might have been assumed. Some imp

T. Emonet, F. Moreno-Insertis

The physics of a twisted magnetic flux tube rising in a stratified medium is studied using a numerical MHD code. The problem considered is fully compressible (no Boussinesq approximation), includes ohmic resistivity, and is two dimensional, i.e., there is no variation of the variables in the direction of the tube axis. We study a high plasma beta case with s

A. Knutson, E. Sharpe

In this paper we give an inherently toric description of a special class of sheaves (known as equivariant sheaves) over toric varieties, due in part to A. A. Klyachko. We apply this technology to heterotic compactifications, in particular to the (0,2) models of Distler, Kachru, and also discuss how knowledge of equivariant sheaves can be used to reconstruct

Alon E. Faraggi, Marco Matone

Recently we showed that the postulated diffeomorphic equivalence of states implies quantum mechanics. This approach takes the canonical variables to be dependent by the relation p=\partial_q S_0 and exploits a basic GL(2,C)-symmetry which underlies the canonical formalism. In particular, we looked for the special transformations leading to the free system wi

R. G. Edwards, U. M. Heller, T. R. Klassen

Accurate determinations of the physical scale of a lattice action are required to check scaling and take the continuum limit. We present a high statistics study of the static potential for the SU(3) Wilson gauge action on coarse lattices ($5.54 \leq β\leq 6.0$). Using an improved analysis procedure we determine the string tension and the Sommer scale $r_0$ (

T. P. Devereaux, A. P. Kampf

A theory of electronic Raman scattering in nearly antiferromagnetic Fermi liquids is constructed using the phenomenological electron-electron interaction introduced by Millis, Monien, and Pines. The role of &#34;hot spots&#34; and their resulting signatures in the channel dependent Raman spectra is highlighted, and different scaling regimes are addressed. Th

Andrei Smilga

We consider the N=1 supersymmetric QCD with SU(N_c) gauge group involving N_f = N_c - 1 pairs of chiral matter multiplets in fundamental and antifundamental color representations. For this theory in the framework of the effective lagrangian approach, we solve the BPS equations for the domain walls interpolating between different vacua. The equations always h

Marco Serone

By scaling arguments we show that the presence of a $R^4$-term in the eleven dimensional supergravity effective lagrangian, if it is visible in (M)atrix theory, should produce a correction to the five-loops effective lagrangian of two moving D0-branes.