December 1998 arXiv papers — page 22

N. J. Watson

A brief account is given of the problems involved in extended the pinch technique beyond the one-loop level, and of investigations into one possible approach to solving them.

N. J. Watson

It is shown how the pinch technique algorithm may be consistently extended beyond the one-loop level to obtain the gauge-independent two-loop fermion self-energy -i\hatΣ^(2)(p) in QCD in the pinch technique approach. The starting point for the construction is the general diagrammatic representation of the two-loop quark self-energy in terms of renormalized o

G. Martinelli, C. T. Sachrajda

We compute the two-loop term in the perturbation series for the quark-mass in the lattice Heavy Quark Effective Theory. This is an ingredient in the matching factor required to obtain the $b$-quark mass from lattice simulations of the HQET. Combining our calculations with numerical results from the APE collaboration, we find, at two-loop order, $\bar m_b \eq

B. G. Sidharth

The early work of Lorentz, Abraham and others, evolved through the work of Fokker, Dirac and others to ultimately culminate in the Feynman- Wheeler direct action at a distance theory. However this theory has encountered certain conceptual difficulties like non-locality in time, self force of the electron, pre acceleration and the perfect absorption condition

C. Stephen Hellberg, Efstratios Manousakis

We investigate the two-dimensional t-J model at a hole doping of x = 1/8 and J/t = 0.35 with exact diagonalization. The low-energy states are uniform (not striped). We find numerous excited states with charge density wave structures, which may be interpreted as striped phases. Some of these are consistent with neutron scattering data on the cuprates and nick

S. Kondo, D. C. Johnston, L. L. Miller

The preparative method, characterization and magnetic susceptibility χmeasurements versus temperature T of the heavy fermion transition metal oxide LiV_{2}O_{4} are reported in detail. The intrinsic χ(T) shows a nearly T-independent behavior below ~ 30 K with a shallow broad maximum at about 16 K, whereas Curie-Weiss-like behavior is observed above 50-100 K.

M. Nideroest, A. Suter, P. Visani, A. C. Mota

Using a custom made dc-SQUID magnetometer, we have measured the time relaxation of the remanent magnetization M_rem of a Bi_2Sr_2CaCu_2O_{8+δ} single crystal from the fully critical state for temperatures 13 K < T < 83 K. The measurements cover a time window of seven decades 10^{-2} s < t < 10^5 s, so that the current density j can be studied from values ver

E. Del Giudice, G. Preparata

The remarkable recent experiments on ensembles of magnetically trapped ultracold alkali atoms have demonstrated the transition to a highly ordered phase, that has been attributed to the process of quantum-mechanical condensation, predicted long ago (1924) by Bose and Einstein. After having presented our argument against the above attribution, we show that th

A. B. Kuklov, B. V. Svistunov

We suggest measuring one-particle density matrix of a trapped ultracold atomic cloud by scattering fast atoms in a pure momentum state off the cloud. The lowest-order probability of the inelastic process, resulting in a pair of outcoming fast atoms for each incoming one, turns out to be given by a Fourier transform of the density matrix. Accordingly, importa

M. Opel, R. Hackl, T. P. Devereaux, A. Virosztek

It is shown theoretically that the buckling of the CuO$_{2}$ planes in certain cuprate systems can be explained in terms of an electric field across the planes which originates from different valences of atoms above and below the plane. This field results also in a strong coupling of the Raman-active out-of-phase vibration of the oxygen atoms ($B_{1g}$ mode)

K. Gorny, O. M. Vyaselev, J. A. Martindale, V. A. Nandor

We report, for magnetic fields of 0, 8.8, and 14.8 Tesla, measurements of the temperature dependent ^{63}Cu NMR spin lattice relaxation rate for near optimally doped YBa_2Cu_3O_{7-delta}, near and above T_c. In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required preci

Klaus Fabricius, Andreas Klümper, Barry M. McCoy

We study the correlation $<σ^z_0σ^z_n>$ for the XXZ chain in the massless attractive (ferromagnetic) region at positive temperatures by means of a numerical study of the quantum transfer matrix. We find that there is a range of temperature where the behavior of the correlation for large separations is oscillatory with an incommensurate period which depends o

E. Del Giudice, G. Preparata

The recent report of the observation of Bose-Einstein condensation in atomic Hydrogen, characterized by an &#34;anomalous&#34; density spectrum, is shown to be in agreement with the prediction of the existence of two condensates for temperatures lower than a well defined temperature (which for Hydrogen is $ 105~ μK $), based on the QED coherent interaction i

Xuekun Kou, M. A. Novotny, Per Arne Rikvold

The magnetization switching dynamics of biaxial single-domain homogeneous ferromagnetic particles, in which the two easy axes are perpendicular to each other, is simulated using a 4-state clock model. A zero-field mapping of the statics between the symmetric 4-state clock model and two decoupled Ising models is extended to non-zero field statics and to the d

Andreas Jaster

We investigate the short-time dynamic relaxation of the two-dimensional XY model in the high temperature phase. Starting from the ordered state, we measure the autocorrelation function and determine the autocorrelation time. It is shown that apart from a constant the equilibrium spatial correlation length can be calculated in this way.

W. D. Heiss, R. G. Nazmitdinov

It is found that various kind of shell structure which occurs at specific values of the magnetic field leads to the disappearance of the orbital magnetization for particular magic numbers of small quantum dots with an electron number $A < 30$.

A. R. Ruppenthal, J. R. Iglesias, M. A. Gusmão

The usual Kondo-lattice, including an antiferromagnetic exchange interaction between nearest-neighboring localized spins, is treated here in a mean-field scheme that introduces two mean-field parameters: one associated with the local Kondo effect, and the other related to the magnetic correlations between localized spins. Phases with short-range magnetic cor

S. Kronmueller, W. Dietsche, K. v. Klitzing, G. Denninger

Two dimensional electron gases in narrow GaAs quantum wells show huge longitudinal resistance (HLR) values at certain fractional filling factors. Applying an RF field with frequencies corresponding to the nuclear spin splittings of {69}Ga, {71}Ga and {75}As leads to a substantial decreases of the HLR establishing a novel type of resistively detected NMR. The

Stefan Rommer, Sebastian Eggert

We use the density matrix renormalization group (DMRG) for transfer matrices to numerically calculate impurity corrections to thermodynamic properties. The method is applied to two impurity models in the spin-1/2 chain, namely a weak link in the chain and an external impurity spin. The numerical analysis confirms the field theory calculations and gives new r

V. Polinger, D. Haskel, E. A. Stern

Polarized XAFS measurements on powder of LaSrCuO with aligned c-axes find that apical oxygens neighboring only the Sr dopants have a double-site distribution. This result requires that the doped holes reside in impurity states peaked on the CuO6 octahedron neighboring the dopant (denoted as Sr-octahedrons). A model of the double site is presented of two co-e

Paul N. Suding, Robert M. Ziff

The site percolation thresholds p_c are determined to high precision for eight Archimedean lattices, by the hull-walk gradient-percolation simulation technique, with the results p_c = 0.697043, honeycomb or (6^3), 0.807904 (3,12^{2}), 0.747806 (4,6,12), 0.729724 (4,8^{2}), 0.579498 (3^{4},6), 0.621819 (3,4,6,4), 0.550213 (3^{3},4^{2}), and 0.550806 (3^{2},4,

Tatsuo Shibata, Tsuyoshi Chawanya, Kunihiko Kaneko

We consider the effect of microscopic external noise on the collective motion of a globally coupled map in fully desynchronized states. Without the external noise a macroscopic variable shows high-dimensional chaos distinguishable from random motion. With the increase of external noise intensity, the collective motion is successively simplified. The number o

Taft E. Armandroff, Gary S. Da Costa

Our current knowledge of M31&#39;s dwarf spheroidal companions is reviewed. Two topics of recent interest constitute the bulk of this review. First, color-magnitude diagrams reaching below the horizontal branch have been constructed for two M31 dwarf spheroidals based on images from HST/WFPC2. The horizontal branches are predominantly red in both galaxies, r

F. Krennrich, S. D. Biller, I. H. Bond, P. J. Boyle

The close relation between ground-based TeV observations and satellite borne $γ$-ray measurements has been important for the understanding of blazars. The observations which involve the TeV component in blazar studies are reviewed.

M. J. Drinkwater, S. Phillipps, M. D. Gregg, Q. A. Parker

We describe a sample of thirteen bright (18.5<Bj<20.1) compact galaxies at low redshift (0.05<z<0.21) behind the Fornax Cluster. These galaxies are unresolved on UK Schmidt sky survey plates, so would be missing from most galaxy catalogs compiled from this material. The objects were found during initial observations of The Fornax Spectroscopic Survey. This p

Michael Rauch, Wallace L. W. Sargent, Thomas A. Barlow

We have obtained high resolution (FWHM = 4.4 km/s) Keck spectra of images A and C of the gravitationally lensed QSO Q1422+231. The images are separated by 1.3&#34; on the sky. In an absorption system at z = 3.538 gas column density variations by an order of magnitude and velocity shear on the order of 10 km/s are observed in the low ionization (SiII, CII) li

David O. Caldwell

Despite direct observations favoring a low mass density, a critical density universe with a neutrino component of dark matter provides the best existing model to explain the observed structure of the universe over more than three orders of magnitude in distance scale. In principle this hot dark matter could consist of one, two, or three species of active neu

K. Hurley, M. S. Briggs, R. M. Kippen, C. Kouveliotou

We present Interplanetary Network localization information for 147 gamma-ray bursts observed by the Burst and Transient Source Experiment between the end of the 3rd BATSE catalog and the end of the 4th BATSE catalog, obtained by analyzing the arrival times of these bursts at the Ulysses and Compton Gamma-Ray Observatory (CGRO) spacecraft. For any given burst

K. K. McLeod, G. H. Rieke, L. J. Storrie-Lombardi

We have detected the host galaxies of 16 nearby, radio-quiet quasars using images obtained with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). We confirm that these luminous quasars tend to live in luminous, early-type host galaxies, and we use the host-galaxy magnitudes to refine the luminosity/host-mass limit inferred from ground-based st

Joachim Wambsganss

Deflection of light by gravity was predicted by General Relativity and observationaly confirmed in 1919. In the following decades various aspects of the gravitational lens effect were explored theoretically, among them the possibility of multiple or ring-like images of background sources, the use of lensing as a gravitational telescope on very faint and dist

M. A. Bershady, A. Jangren, D. R. Andersen, M. P. Haynes

1) Rotation Curves and M/L Evolution for Galaxies to z=0.4, (Bershady, Haynes, Giovanelli, & Andersen) 2) Mass Estimates of Starbursting Galaxies: Line Widths versus Near-IR Luminosities (Jangren, Bershady, & Gronwall) 3) Galaxy Kinematics with Integral Field Spectroscopy (Andersen, Bershady)

Holly K. Nordquist, Robert J. Klinger, Pablo Laguna, Jane C. Charlton

One of the external fields that influences the population of globular clusters is that due to galactic bulges. In extreme situations, perigalactic distances $r_p \le 100$ pc, globular clusters could suffer total disruption in a single passage. A more common scenario is that for cluster orbits with $r_p \ge 200$ pc. We investigate the effects of tidal forces

L. I. Gurvits, K. I. Kellermann, S. Frey

We discuss the ``angular size - redshift&#39;&#39; relation for compact radio sources distributed over a wide range of redshifts 0.01 < z < 4.73. Our study is based on a sample of 330 5 GHz VLBI contour maps taken from the literature. Unlike extended source samples, the ``angular size - redshift&#39;&#39; relation for compact radio sources appears consistent

Thaisa Storchi-Bergmann, H. R. Schmitt, R. Cid Fernandes

The nature of the UV-Optical continuum in Seyfert 2 galaxies is a matter of current debate, fundamental to which is the issue of characterizing and quantifying the stellar population contribution to the nuclear spectra. Using high S/N long-slit spectroscopy of a sample of 20 Seyfert 2 galaxies, we have applied a novel approach to investigate the nuclear stel

Erik Kuulkers

The outbursts of WZ Sge stars (or TOADs), are compared to those seen in the (soft) X-ray transients. Both types of outbursts exhibit strong similarities: large amplitudes, long recurrence times, occurrence of superhumps, and of rebrightenings or reflares at the end or just after the main outburst. This suggests that the same kind of mechanism is at work to p

A. Bosma

In these notes I will briefly summarize our knowledge about the dark matter problem, and emphasize the corresponding dynamical aspects. This covers a wide area of research, so I have been selective, and have concentrated on the subject of dark matter in nearby galaxies, in particular spirals.

E. Athanassoula

Disc galaxies can be substantially modified by close encounters and mergers, since their discs are very responsive components. Close interactions can be held responsible for the formation of bridges and tails, as well as for the formation of some bars, asymmetries and grand design spirals. Bound clumps can form in the tails, due to self-gravity, and could ev

A. Bosma

Recent work on the mass distribution in spiral galaxies, using mainly HI observations, is reviewed. The principal problem is still to determine to what extent the dark matter is important in the inner parts of a galaxy, or in other words, how dominant is the self-gravitation of the disc. Studies of the shapes of rotation curves show that in detail there is s

N. Brynildsen, T. Leifsen, O. Kjeldseth-Moe, P. Maltby

Based on observations obtained with the Solar and Heliospheric Observatory - SOHO joint observing program for velocity fields in sunspot regions, we have detected 3 min transition region umbral oscillations in NOAA 8156. Simultaneous recordings of O V $λ$629 and N V $λ$1238, $λ$1242 with the SUMER instrument give the spatial distribution of power in the 3 mi

T. Beckert, W. J. Duschl

We present a modified description of advection-dominated accretion flows (ADAF) with a geometrical viscosity. A simplified treatment of the dynamics of the flow in the inner relativistic part is suggested and results are compared with the galactic center source Sgr A*.

Henri M. J. Boffin, Kei Haraguchi, Takuya Matsuda

We discuss some 3D numerical simulations of accretion discs using the SPH method and a polytropic equation of state. We show that discs exist even for as large value of the polytropic index as 1.2, and that these discs are always in hydrostatic balance. We also show that even without any inflow, spiral shocks appear in the discs.

X. Delfosse, T. Forveille, J. -L. Beuzit, S. Udry

We present preliminary results of a radial-velocity search for companions to a volume limited sample of M dwarfs. Typical accuracy range between 10m/s for the brighter stars and 70m/s at our limiting magnitude. We complement the radial velocity monitoring with adaptive optics imaging to identify close visual companions in a larger volume-limited sample. For

Michael A. Nowak, Dana E. Lehr

The study of stable accretion disc oscillations relevant to black hole candidate (BHC) systems dates back over twenty years. Prior work has focused on both unstable and (potentially) stable disc oscillations. The former has often been suspected of being the underlying cause for the observed broad-band variability in BHC, whereas the latter has had little obs

Amri Wandel

Assuming Active Galactic Nuclei are powered by accretion onto a massive black holes we suggest that the growth of the central black hole due to the matter accreted over the AGN lifetime causes an evolution of the luminosity and spectrum. We show that the effective temperature of the UV continuum spectrum is likely to be anti-correlated with the black-hole ma

Vijay K. Narayanan, Andreas Berlind, David H. Weinberg

We examine the influence of the morphology-density(MD) relation and a wide range of simple models for biased galaxy formation on statistical measures of large scale structure. We contrast the behavior of local biasing models, in which the efficiency of galaxy formation is determined by density, geometry, or velocity dispersion of the local mass distribution,

J. J. Bryant, R. W. Hunstead

We present J, H and K-band images and 0.9-2.5 micron spectra of the nuclear regions of Centaurus A obtained with IRIS on the AAT. While K band has a point source coincident with the nucleus, at H and J we identify diffuse structure extending to the NE as a possible ionisation cone. By considering the NIR colours we show that the point-like K-band emission or

Marco Lombardi, Giuseppe Bertin

Recently, it has been shown that it is possible to reconstruct the projected mass distribution of a cluster from weak lensing provided that both the geometry of the universe and the probability distribution of galaxy redshifts are known; actually, when additional photometric data are taken to be available, the galaxy redshift distribution could be determined

Florin Ambro

We prove the existence of Fano ladders on weak log Fano varieties of coindex less than 4, as an application of adjunction and nonvanishing.