July 1997 arXiv papers — page 10

Th. M. Nieuwenhuizen

A directed polymer is considered on a flat substrate with randomly located parallel ridges. It prefers to lie inside wide regions between the ridges. When the transversel width $W=\exp(λL^{1/3})$ is exponential in the longitudinal length $L$, there can be a large number $\sim \exp L^{1/3}$ of available wide states. This ``complexity'' causes a phase

J. J. McGuire, T. Room, T. E. Mason, T. Timusk

We report on far infrared measurements on Zn and Si doped crystals of the spin-Peierls compound CuGeO3. Zn doping has the effect of introducing several new absorption lines, polarized in the ab-plane, between 5 and 55 cm-1. The intensity of the absorption grows with Zn concentration but saturates above 2% Zn. One line at 10 cm-1 loses intensity above 4K, and

Yuval Oreg, Alexander M. Finkel'stein

The problem of a single impurity in one dimensional Tomonaga-Luttinger liquids with a repulsive electron-electron interaction is discussed. We find that the renormalization group flow diagram for the parameters characterizing the impurity is rather complex. Apart from the fixed points corresponding to two weakly connected semi-infinite wires, the flow diagra

Yuval Oreg, Alexander M. Finkel'stein

In their comment Fabrizio and Gogolin dispute our result of the enhancement of the tunneling density of states in a Tomonaga-Luttinger liquid at the location of a backward scattering defect [Phys. Rev. Lett. 76, 4230(1996); cond-mat/9601020]. They state that the anticommutativity of the fermion operators of the left and right moving electrons was not conside

J. Oswald, G. Heigl, G. Span, A. Homer

We report on conductance fluctuations which are observed in local and non-local magnetotransport experiments. Although the Hall bar samples are of macroscopic size, the amplitude of the fluctuations from the local measurements is close to e^2/h. It is shown that the fluctuations have to be attributed to edge channel effects.

A. Kristoffersen, K. Olaussen

We consider a model for 2D electrons in a very strong magnetic field (i.e. projected onto a single Landau level) and a random potential $V$. The computation of the averaged Green function for this system reduces to calculating the averaged density of states. We have constructed a computer algebra program which automatically generates a perturbation expansion

J. Oswald, G. Heigl, M. Pippan, G. Span

The 3D- and 2D- behaviour of wide parabolic PbTe single quantum wells, which consist of PbTe p-n-p-structures, are studied theoretically and experimentally. A simple model combines the 2D- subband levels and the 3D-Landau levels in order to calculate the density of states in a magnetic field perpendicular to the 2D plane. It is shown that at a channel width

J. Oswald, M. Pippan, G. Heigl, G. Span

In this paper the 3D- and 2D- behavior of wide quantum wells which consist of one period of a PbTe nipi-structure is studied theoretically and experimentally. A simple model combines the 2D- subband levels and the 3D-Landau levels in order to calculate the density of states in a magnetic field perpendicular to the 2D plane. It is shown that at a channel widt

C. Coste, F. Lund

We study the scattering of first and second sound waves by quantum vorticity in superfluid Helium using two-fluid hydrodynamics. The vorticity of the superfluid component and the sound interact because of the nonlinear character of these equations. Explicit expressions for the scattered pressure and temperature are worked out in a first Born approximation, a

Megumi Kameyama

One of the necessary extensions to the centering model is a mechanism to handle pronouns with intrasentential antecedents. Existing centering models deal only with discourses consisting of simple sentences. It leaves unclear how to delimit center-updating utterance units and how to process complex utterances consisting of multiple clauses. In this paper, I w

Jan Jaspars, Megumi Kameyama

In order to enrich dynamic semantic theories with a `pragmatic' capacity, we combine dynamic and nonmonotonic (preferential) logics in a modal logic setting. We extend a fragment of Van Benthem and De Rijke's dynamic modal logic with additional preferential operators in the underlying static logic, which enables us to define defeasible (pragmatic) entailment

M. F. Bietenholz, N. Kassim, D. A. Frail, R. A. Perley

We present the results of a new, comprehensive investigation of the radio spectral index of the Crab Nebula supernova remnant. New data at 74 MHz are combined with data at 327 MHz, 1.5 GHz and 5 GHz. In contrast to previous claims, little spatial variation in the spectral index is seen. In particular, between 327 MHz and 5 GHz we see no evidence of spectral

M. Moles, J. W. Sulentic, I. Márquez

Multiwavelength data for Stephan's Quintet (SQ) are consistent with the following model for this compact galaxy group. (1) Discordant redshift NGC 7320 is an unrelated foreground galaxy. (2) In the past SQ was an accordant redshift quartet involving NGC 7317, 18A, 19 and 20C. NGC 7320C collided (probably not for the first time) with the group a few times

D. J. Fixsen, J. L. Weiland, S. Brodd, M. G. Hauser

We compare the independent FIRAS and DIRBE observations from the COBE in the wavelength range 100-300 microns. This cross calibration provides checks of both data sets. The results show that the data sets are consistent within the estimated gain and offset uncertainties of the two instruments. They show the possibility of improving the gain and offset determ

G. S. Bisnovatyi-Kogan

Selection effects, connected with stochastic errors in source flux and threshold value determination are analyzed. Normal and normal logarithmic distributions of stochastic deviations are considered. These two kind of distributions produce different effects on the source statistics. Applications to Gamma Ray Burst statistics are discussed. A physical test fo

G. S. Bisnovatyi-Kogan, S. V. Repin

Timing of Geminga gamma-ray pulsar is done using data of COS B and EGRET. It is shown, that errors in angular coordinates of sources similar to Geminga strongly influence a determination of $\ddot ν$, so that at angular precision less then $10^{-3}$ arc sec determination of the value of $\ddot ν$ by means of criterion gives error more then $100 %$. Attempt h

Martin D. Weinberg

This paper explores the dynamical interaction between extended halo and spheroid components of a disk galaxy and an environmental disturbance. One finds that resonant interaction between a galaxy and passing interlopers or satellite companions can carry the disturbance inward, deep inside the halo, where it can perturb the disk. Applied to the Milky Way for

G. S. Bisnovatyi-Kogan, S. A. Silich

Equations are derived which describe a propagation of strong shocks in the interstellar matter, without any demands for a symmetry, in a thin layer approximation (2.5 dimensions). Using these equations permits to calculate a propagation of shock waves from nonsymmetric supernovae explosions in the medium with arbitrary density distribuion, formation of super

Shude Mao, Peter Schneider

We discuss whether one should expect that multiply imaged QSOs can be understood with `simple' lens models which contain a handful of parameters. Whereas for many lens systems such simple mass models yield a remarkably good description of the observed properties, there are some systems which are notoriously difficult to understand quantitatively. We argu

S. J. Hatton, S. Cole

We use a set of large, high-resolution cosmological N-body simulations to examine the redshift-space distortions of galaxy clustering on scales of order 10-200h^{-1} Mpc. Galaxy redshift surveys currently in progress will, on completion, allow us to measure the quadrupole distortion in the 2-point correlation function, ξ(σ,π), or its Fourier transform, the p

Joseph J. Mohr, August E. Evrard

We show that galaxy clusters conform to a tight relation between X-ray isophotal size R_I and emission weighted intracluster medium (ICM) temperature T_X. The best fit relation for 41 members of an X-ray flux limited cluster sample is: $log{R_I}= (0.93\pm0.11) log{(<T_X>/6 keV)} -\ (0.08\pm0.01)$; intrinsic scatter in size about the relation is 15%, and for

R. T. Gangadhara, H. Lesch

We consider the role of centrifugal force on the energetics of electrons moving along the magnetic field lines of spinning active galactic nuclei. We find the energy gained by charged particles against inverse Compton scattering and/ synchrotron radiation losses, become quite significant in the region close to the light cylinder. The particles accelerated by

Edvige Corbelli, Daniele Galli, Francesco Palla

We show that gaseous \HI disks of primordial composition irradiated by an external radiation field can develop a multiphase medium with temperatures between 10^2 and 10^4 K due to the formation of molecular hydrogen. For a given \HI column density there is a critical value of the radiation field below which only the cold \HI phase can exist. Due to a time de

S. Cassisi, V. Castellani, S. Degl&#39;Innocenti, A. Weiss

In the first part of this paper we revisit the history of theoretical predictions for HB luminosities in old Population II stellar clusters, starting from the results of `old&#39; evolutionary computations to introduce in various steps all the available `new&#39; physics. We discuss the influence of physical ingredients on selected evolutionary parameters, f

M. Catanese, S. M. Bradbury, A. C. Breslin, J. H. Buckley

We present multiwavelength observations of the BL Lacertae object Markarian 501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray observations taken with the Whipple Observatory gamma-ray telescope, data from the Oriented Scintillation Spectrometer Experiment of the Com

Seunghun Lee, Cheongho Han

The most important uncertainty in the results of gravitational microlensing experiments comes from the difficulties of photometry caused by blending of source stars. Recently Nemiroff (1997) pointed out that the results of microlensing experiments can also be affected by the blending of light from the lens itself if a significant fraction of lenses are compo

Biman Nath, Neil Trentham

Observations of metal lines in $\lyal$ absorption systems of small H~I column density and their ubiquitous nature suggest that the intergalactic medium (IGM) was enriched to about $Z \sim 0.01 \> Z_{\odot}$ by a redshift $z \sim 3$. We investigate the role of winds from small star-forming galaxies at high $z$ in enriching the IGM. The existence of large numb

Scott Burles, David Tytler

The absorption system at $z=3.572$ towards Q1937--1009 provides the best extragalactic measurement of the atomic deuterium to hydrogen ratio, D/H. We have obtained a new low-resolution, high signal-to-noise ratio (SNR) Keck spectrum to re-measure the total neutral hydrogen column density N(H I) using the amount of Lyman continuum absorption. We develop a new

Kalvis M. Jansons, G. D. Lythe

For the dynamic pitchfork bifurcation in the presence of white noise, the statistics of the last time at zero are calculated as a function of the noise level and the rate of change of the parameter. The threshold crossing problem used, for example, to model the firing of a single cortical neuron is considered, concentrating on quantities that may be experime

Alexander L. Kagan, Alexey A. Petrov

Standard model factorization can account for the large rate for $B^\pm \to η&#39; K^\pm$. The large rate for $B \to η&#39; X_s$ is more problematic and requires a ``cocktail&#39;&#39; solution. Individual contributions from factorization, $b \to η&#39; s g$, and ``intrinsic charm&#39;&#39; fall significantly short of the observed rate. In contrast, the obser

A. F. Martini, M. J. Menon, D. S. Thober

Making use of the gluon gauge-invariant two-point correlation function, recently determined by numerical simulation on the lattice in the quenched approximation and the stochastic vacuum model, we calculate the elementary (parton-parton) amplitudes in both impact-parameter and momentum transfer spaces. The results are compared with those obtained from the Kr

P. S. Howe, N. D. Lambert, P. C. West

We consider the most general form for eleven dimensional supersymmetry compatible with on-shell superfields. This allows for the introduction of a conformal Spin(1,10) connection. In eleven dimensional Minkowski space this modification is trivial and can be removed by a field redefinition, however, upon compactification on S^1 it is possible to introduce a n

L. Gamberg, H. Reinhardt, H. Weigel

We study the frame dependence of nucleon structure functions obtained within a chiral soliton model for the nucleon. Employing light cone coordinates and introducing collective coordinates together with their conjugate momenta, translational invariance of the solitonic quark fields (which describe the nucleon as a localized object) is restored. This formulat

Roy Maartens, Daniel Tilley

Toy models for the Hubble rate or the scalar field potential have been used to analyze the amplification of scalar perturbations through a smooth transition from inflation to the radiation era. We use a Hubble rate that arises consistently from a decaying vacuum cosmology, which evolves smoothly from nearly de Sitter inflation to radiation domination. We fin

Justin R. David, Avinash Dhar, Gautam Mandal

We analyse the velocity-dependent potentials seen by D0 and D4-brane probes moving in Type I&#39; background for head-on scattering off the fixed planes. We find that at short distances (compared to string length) the D0-brane probe has a nontrivial moduli space metric, in agreement with the prediction of Type I&#39; matrix model; however, at large distances

C. R. Gattringer, I. Hip, C. B. Lang

We investigate the interplay between topological charge and the spectrum of the fermion matrix in lattice-QED_2 using analytic methods and Monte Carlo simulations with dynamical fermions. A new theorem on the spectral decomposition of the fermion matrix establishes that its real eigenvalues (and corresponding eigenvectors) play a role similar to the zero eig

M. Irac-Astaud, G. Rideau

Generalizing the case of the usual harmonic oscillator, we look for Bargmann representations corresponding to deformed harmonic oscillators. Deformed harmonic oscillator algebras are generated by four operators $a, a^\dagger, N$ and the unity 1 such as $[a,N] = a, [a^\dagger,N] = -a^\dagger$, $a^\dagger a = ψ(N)$ and $aa^\dagger =ψ(N+1)$. We discuss the cond

B. Enriquez

We express Hitchin&#39;s systems on curves in Schottky parametrization, and construct dynamical $r$-matrices attached to them.

H. Sorge

I discuss strangeness production in nucleus-nucleus reactions at ultrarelativistic energies (up to 200 AGeV). In these reactions matter may be created with densities and temperatures in the transition region between quark-gluon plasma (QGP) and hadron gas. Strange anti-baryon enhancement at 200 AGeV and probably even more so at 10 AGeV signals importance of

Josef Sollfrank

Thermal models are very useful in the understanding of particle production in general and especially in the case of strangeness. We summarize the assumptions which go into a thermal model calculation and which differ in the application of various groups. We compare the different results to each other. Using our own calculation we discuss the validity of the

Saharon Shelah, Andrés Villaveces

We provide here the first steps toward Classification Theory of Abstract Elementary Classes with no maximal models, plus some mild set theoretical assumptions, when the class is categorical in some lambda greater than its Lowenheim-Skolem number. We study the degree to which amalgamation may be recovered, the behaviour of non mu-splitting types. Most importa

Saharon Shelah

Affirming a conjecture of Erdős and Renyi we prove that for any (real number) c_1>0 for some c_2>0, if a graph G has no c_1(log n) nodes on which the graph is complete or edgeless (i.e. G exemplifies |G| not-> (c_1 log n)^2_2) then G has at least 2^{c_2n} non-isomorphic (induced) subgraphs.

Saharon Shelah

We deal with the problem of preserving various versions of completeness in (< kappa) --support iterations of forcing notions, generalizing the case ``S --complete proper is preserved by CS iterations for a stationary co-stationary S subseteq omega_1&#39;&#39;. We give applications to Uniformization and the Whitehead problem. In particular, for a strongly ina

Mikhail Lyubich

We prove uniform hyperbolicity of the renormalization operator for all possible real combinatorial types. We derive from it that the set of infinitely renormalizable parameter values in the real quadratic family $P_c: x\mapsto x^2+c$ has zero measure. This yields the statement in the title (where ``regular&#39;&#39; means to have an attracting cycle and ``st

Benjamin Hinkle

In this paper we give a combinatorial description of the renormlization limits of infinitely renormalizable unimodal maps with {\it essentially bounded} combinatorics admitting quadratic-like complex extensions. As an application we construct a natural analogue of the period-doubling fixed point. Dynamical hairiness is also proven for maps in this class. The

M. Kachkachi

We develop an electromagnetic symplectic structure on the space-time manifold by defining a Poisson bracket in terms of an invertible electromagnetic tensor F_{μν}. Moreover, we define electromagnetic symplectic diffeomorphisms by imposing a special condition on the electromagnetic tensor. This condition implies a special constraint on the Levi-Civita tensor

Giampiero Esposito, Alexander Yu. Kamenshchik

A crucial problem in quantum cosmology is a careful analysis of the one-loop semiclassical approximation for the wave function of the universe, after an appropriate choice of mixed boundary conditions. The results for Euclidean quantum gravity in four dimensions are here presented, when linear covariant gauges are implemented by means of the Faddeev-Popov fo

A. Bassetto, G. Nardelli, E. Vianello

The Schwinger model, defined in the space interval $-L \le x \le L$, with (anti)periodic boundary conditions, is canonically quantized in the light-cone gauge $A_-=0$ by means of equal-time (anti)commutation relations. The transformation diagonalizing the complete Hamiltonian is explicitly constructed, thereby giving spectrum, chiral anomaly and condensate.

S. A. Gogilidze, A. M. Khvedelidze, D. M. Mladenov, H. -P. Pavel

The SU(2) gauge invariant Dirac-Yang-Mills mechanics of spatially homogeneous isospinor and gauge fields is considered in the framework of the generalized Hamiltonian approach. The unconstrained Hamiltonian system equivalent to the model is obtained using the gaugeless method of Hamiltonian reduction. The latter includes the Abelianization of the first class

Alec Matusis

We find the potential per unit length between two non-intersecting D1-branes as a function of their relative angle.

D. T. Son

We derive, from first principle, the Fokker-Planck equation describing the non-perturbative real-time evolution of a gauge field at high temperatures on the spatial scale $(g^2T)^{-1}$ and the time scale $(g^4T)^{-1}$, where $g$ is the gauge coupling and $T$ is the temperature. The knowledge of the effective dynamics on such spatial and time scales is crucia

Yoshitaka Okumura

In the two loop approximation, a renormalization group analysis of the Higgs boson mass is performed based on the condition $g^2=(5/3)g&#39;^2=4λ$ for SU(2)_L, U(1)_Y gauge and the Higgs quartic coupling constants, respectively. This condition is introduced in the new scheme of our noncommutative differential geometry (NCG) for the reconstruction of the stan

Y. Kikukawa, H. Neuberger

In odd dimensions the lattice overlap formalism is simpler than in even dimensions. Masslessness of fermions can still be preserved without fine tuning and gauge invariance without gauge averaging can be maintained, although, sometimes, only at the expense of parity invariance. When parity invariance is enforced invariance under small gauge transformations c

P. Hernandez

I review our method to formulate chiral gauge theories on the lattice based on a two-cutoff lattice regularization, and discuss recent numerical results in a chiral U(1) gauge theory in 2D.

MILC Collaboration, Claude Bernard, Tom Blum, Carleton DeTar

We present the current status of our ongoing calculations of the light hadron spectrum with both Kogut-Susskind (KS) and Wilson quarks in the valence or quenched approximation. We discuss KS quarks first and find that the chiral extrapolation is potentially the biggest source of systematic error. For the Wilson case, we focus on finite volume and source size

MILC Collaboration, Claude Bernard, Tom Blum, Thomas A. DeGrand

We present the current status of our ongoing calculations of pseudoscalar meson decay constants for mesons that contain one light and one heavy quark (f_B, f_{B_s}, f_D, f_{D_s}). We are currently generating new gauge configurations that include dynamical quarks and calculating the decay constants. In addition, we have several new results for the static appr

Jochen Fingberg

We present a new method to study the properties of heavy quarks at finite temperature. It combines non-relativistic QCD with an improved gluonic action on anisotropic lattices. The efficiency of the approach is demonstrated by the first non-perturbative calculation of the temperature dependence of low-lying quarkonium &#34;pole&#34; masses. For ground state

A. Santoro

Preliminary results from the D0 experiment on jet production with rapidity gaps in $p\bar{p}$ collisions are presented. A class of dijet events with a forward rapidity gap is observed at center-of-mass energies $\sqrt{s}$ = 1800 GeV and 630 GeV. The number of events with rapidity gaps at both center-of-mass energies is significantly greater than the expectat

CLEO Collaboration, K. Edwards et al

We have searched for the decay of the tau lepton into seven charged particles and zero or one pi0. The data used in the search were collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) and correspond to an integrated luminosity of 4.61 fb^(-1). No evidence for a signal is found. Assuming all the charged particles are pions, we set

Stefan Aminneborg, Ingemar Bengtsson, Dieter Brill, Soren Holst

A large variety of spacetimes---including the BTZ black holes---can be obtained by identifying points in 2+1 dimensional anti-de Sitter space by means of a discrete group of isometries. We consider all such spacetimes that can be obtained under a restriction to time symmetric initial data and one asymptotic region only. The resulting spacetimes are non-etern

M. Gasperini

The general properties of the gravity wave backgrounds of cosmological origin are reviewed and briefly discussed, with emphasis on the relic background expected from an early pre-big bang phase typical of string cosmology models.

V. Moncrief, J. E. Nelson

Constants of motion are calculated for 2+1 dimensional gravity with topology R x T^2 and negative cosmological constant. Certain linear combinations of them satisfy the anti - de Sitter algebra so(2,2) in either ADM or holonomy variables. Quantisation is straightforward in terms of the holonomy parameters. On inclusion of the Hamiltonian three new global con

D. K. Shukla, Manohar Lal, Navdeep Goyal

The paper reports a possible application of AgInSe_2 for opto-electronic switching. Material has been studied over a wide range of frequencies (5Hz to 1MHz), through measurements of conductance and capacitance, at different temperatures and illumination levels. The results indicate that there is an increase in capacitance (C) as well as conductance (G), when

R. W. Nunes, J. Bennetto, David Vanderbilt

We investigate the physics of the core reconstruction and associated structural excitations (reconstruction defects and kinks) of dislocations in silicon, using a linear-scaling density-matrix technique. The two predominant dislocations (the 90-degree and 30-degree partials) are examined, focusing for the 90-degree case on the single-period core reconstructi

Bosiljka Tadić, Deepak Dhar

We introduce and study a new directed sandpile model with threshold dynamics and stochastic toppling rules. We show that particle conservation law and the directed percolation-like local evolution of avalanches lead to the formation of a spatial structure in the steady state, with the density developing a power law tail away from the top. We determine the sc

D. E. Katsanos, S. N. Evangelou, C. J. Lambert

We have studied the effect of a random superconducting order parameter on the localization of quasi-particles, by numerical finite size scaling of the Bogoliubov-de Gennes tight-binding Hamiltonian. Anderson localization is obtained in d=2 and a mobility edge where the states localize is observed in d=3. The critical behavior and localization exponent are un

T. Fukui, N. Kawakami

We investigate low-energy properties of the alternating spin chain model composed of spin $s_1$ and $s_2$ with a singlet ground state. After examining the spin-wave spectrum in detail, we map low-energy spin excitations to the O(3) non-linear sigma model in order to take into account quantum fluctuations. Analyzing the topological term in the resulting sigma

Piotr A. Popowski, David H. Weinberg, Barbara S. Ryden, Patrick S. Osmer

The non-Euclidean geometry of spacetime induces an anisotropy in the apparent correlation function of high-redshift quasars. This effect can constrain the cosmological constant Λindependent of any assumptions about evolution of luminosities, sizes, or clustering. We examine the prospects for distinguishing between low-density (Ω_0=0.1-0.4) cosmological model

Francois Roueff, Pierre Salati, Richard Taillet

Measurements of the surface brightness distribution and of the velocity dispersion profile have been so far used to infer the inner dynamics of globular clusters. We show that those observations do not trace back the dark matter potentially concealed in these systems in the form of low-mass compact objects. We have built Michie models of globular clusters wh

D. Reimers, S. Koehler, L. Wisotzki, D. Groote

We report on observations of redshifted HeII 304 A absorption in the QSO HE 2347-4342 (z=2.885, V=16.1) with the GHRS on board HST (FWHM=0.7 A). At the expected position of HeII 304 A absorption, HE 2347-4342 is the most UV-bright high redshift QSO discovered so far. We show that the HeII opacity as a function of redshift is patchy showing spectral regions w

G. S. Bisnovatyi-Kogan

Formation of a neutron star is accompanied by neutrino emission carring about 10% of the rest energy of the star. Toroidal field produced by twisting of a dipole field in differentially rotating star is antisymmetric. Its summation with antisymmetric toroidal field results in braking of mirror symmetry of the magnetic field . For large magnetic field the neu

S. D. Doty, D. A. Neufeld

We present a detailed model for the thermal balance, chemistry, and radiative transfer within quiescent dense molecular cloud cores that contain a central protostar. Large variations in the gas temperature are expected to affect the gas-phase chemistry dramatically; with the predicted H2O abundance varying by more than a factor of 1000 within cloud cores. Ba

Claudia Winge, D. J. Axon, F. D. Macchetto, A. Capetti

We present the first results of the Hubble Space Telescope/Faint Object Camera long-slit spectroscopy of the inner 8&#34; of the Narrow Line Region of NGC 4151 at a spatial resolution of 0&#34;.029. The emission gas is characterized by an underlying general orderly behaviour, consistent with galactic rotation, over which are superposed kinematically distinct

J. Bezecourt, R. Pello, G. Soucail

We present a detailed model of the absolute number counts, color and redshift distributions of gravitational arclets observed in clusters of galaxies. The framework adopted for galaxy evolution is chosen to fairly reproduce the observed number counts and redshift distribution of field galaxies. Then, the spectrophotometric evolutionary code is coupled with a

R. T. Gangadhara

We consider the polarization properties of radiation emitted by relativistic charged particles while moving along the curved magnetic field lines in a pulsar manetosphere. We propose that the radiation emitted by positrons and electrons while moving along the curved magnetic field lines is orthogonally polarized. The polarization angle of each orthogonal pol

Matthias Bartelmann, Andreas Huss, Joerg M. Colberg, Adrian Jenkins

We use numerical simulations of galaxy clusters in different cosmologies to study their ability to form large arcs. The cosmological models are: Standard CDM (SCDM; Omega_0=1, Omega_Lambda=0); tauCDM with reduced small-scale power (parameters as SCDM, but with a smaller shape parameter of the power spectrum); open CDM (OCDM; Omega_0=0.3, Omega_Lambda=0); and

Arjun Dey, Wil van Breugel, William Vacca, Robert Antonucci

Spectropolarimetric observations obtained with the W. M. Keck Telescope of the z=3.8 radio galaxy 4C41.17 show that the UV continuum emission from this galaxy, which is aligned with the radio axis, is unpolarized (P[2sigma] < 2.4%). This implies that scattered AGN light, which is generally the dominant contributor to the rest-frame UV emission in z~1 radio g

A. N. Lasenby, C. J. L. Doran, Y. Dabrowski, A. D. Challinor

We discuss three applications of a gauge theory of gravity to rotating astrophysical systems. The theory employs gauge fields in a flat Minkowski background spacetime to describe gravitational interactions. The iron fluorescence line observed in AGN is discussed, assuming that the line originates from matter in an accretion disk around a Kerr (rotating) blac

A. Guarnieri, C. Bartolini, N. Masetti, A. Piccioni

The optical counterpart of the Gamma-Ray Burst GRB 970228, discovered by Groot et al. (IAU Circ. 6584), is also detected in the B and R frames obtained about 4 hours earlier at the Bologna Observatory. Our observations indicate a very likely rise of the optical emission within these 4 hours. The R luminosity of the transient at maximum was about 15 times tha

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

After a quarter of a century of gamma-ray burst (GRB) astronomy, the Italian-Dutch satellite BeppoSAX on Feb 28th, 1997 detected a soft X-ray afterglow from GRB 970228 and positioned it accurately. This made possible the successful detection of an optical transient. Two public Hubble Space Telescope (HST) images of the GRB/optical transient region were taken

T. Beckert, W. J. Duschl

We investigate the spectrum of a quasi-monoenergetic ensemble of relativistic electrons, especially for the mildly relativistic case, and discuss the effect of inclination of the magnetic field on the emissivity. We apply the exact theoretical description to the spectrum of the radio source Sgr A* which is located at or very close to the dynamical center of

Robert W. Nelson, Scott Tremaine

We apply linear response theory to a general, inhomogeneous, stationary stellar system, with particular emphasis on dissipative processes analogous to Landau damping. Assuming only that the response is causal, we show that the irreversible work done by an external perturber is described by the anti-Hermitian part of a linear response operator, and damping of

Karen E. Smith, Joel Rosenberg

This is a detailed write-up of Kollár&#39;s course at the EMS summer school in Algebraic Geometry in Eger, Hungary, August 1996. The topics include definitions and examples of rational and unirational varieties, with special attention to varieties defined over non-algebraically closed fields, Segre&#39;s theorem on non-rationality of cubic surfaces of Picard

J. Russo, A. A. Tseytlin

We find explicit expression for the one-loop four-graviton amplitude in eleven-dimensional supergravity compactified on a circle. Represented in terms of the string coupling (related to the compactification radius) it takes the form of an infinite sum of perturbative string loop corrections. We also compute the amplitude in the case of compactification on a

Radoslav Derka, Vladimir Buzek, Artur Ekert

We present a universal algorithm for the optimal quantum state estimation of an arbitrary finite dimensional system. The algorithm specifies a physically realizable positive operator valued measurement (POVM) on a finite number of identically prepared systems. We illustrate the general formalism by applying it to different scenarios of the state estimation o

J. S. Bagla

Recent observations show a large concentration of galaxies at high redshift. At first sight strong clustering of galaxies at high redshifts seems to be in contradiction with the models of structure formation. In this paper we show that such structures are a manifestation of the strong clustering of rare peaks in the density field. We compute the frequency of

Christopher W. Churchill

First results from a study of high ionization absorption properties in roughly 30 Mg II absorption selected galaxies are presented. We have tested for correlations of Mg II, C IV, Si IV, N V, and O VI equivalent widths with the galaxy properties and Mg II gas kinematics. The results are suggestive of multi-phase halos with little to no global ionization grad

Christopher W. Churchill, Vincent Le Brun

We report the detection of Mg II absorption in two Lyman alpha forest clouds along the line of sight to PKS 0454+039. These clouds, at redshifts z=0.6248 and z=0.9315, respectively, also have strong Fe II absorption. We present results on the z=0.9315 cloud. The upper limit on log N(HI) is 16.5 cm^-2. Based upon UV background photoionization models, we infer

Michael H. Seymour

We discuss the phenomenology of jet physics at hadron colliders, concentrating on the internal structure of jets, which is studied using the jet shape distribution or subjet distributions.

Michael H. Seymour

The jet shape is a simple measure of how widely a jet's energy is spread. At present jet shape distributions have only been calculated to leading order in perturbative QCD. In this paper we consider how much these predictions should be affected by higher order perturbative corrections, by resummation of enhanced corrections to all orders, and by (power-suppr

Pavel Etingof, Israel Gelfand, Vladimir Retakh

We find explicit (multisoliton) solutions for nonabelian integrable systems such as periodic Toda field equations, Langmuir equations, and Schrodinger equations for functions with values in any associative algebra. The solution for nonabelian Toda field equations for root systems of types A, B, C was expressed by the authors in a previous paper (q-alg/970100

P. A. S. Carvalho, M. J. Menon

We present the results of fitting elastic $pp$ differential cross section data at 23.5 $\leq \sqrt{s} \leq$ 62.5 GeV with a novel analytic parametrization for the scattering amplitude. Making use of a fitting method, the errors from the free parameters are propagated to the imaginary part of the eikonal in the momentum transfer space. A novel systematic stud

T. Meissner, F. Myhrer, K. Kubodera

The first measurement of the radiative muon capture (RMC) rate on a proton was recently carried out at TRIUMF. The TRIUMF group analyzed the RMC rate in terms of the theoretical formula of Beder and Fearing, and found the surprising result that the pseudoscalar coupling g_P is 1.5 times the value expected from PCAC. To assess the reliability of the theoretic

Francesco Vissani

We compute the spectrum of $β$-decay, assuming that (Majorana or Dirac) neutrinos propagate in constant potentials. We study the modifications of the spectrum due to the effect of these potentials. Data on tritium decay and on ${}^3$H--${}^3$He mass difference allow us to infer bounds in the electronvolts range on the potentials.

E. Bergshoeff, M. de Roo, E. Eyras

We perform a generalised Scherk-Schwarz reduction of the effective action of the heterotic string on T^6 to obtain a massive N=4 supergravity theory in four dimensions. The local symmetry-group of the resulting d=4 theory includes a Heisenberg group, which is a subgroup of the global O(6,6+n) obtained in the standard reduction. We show explicitly that the sa

Eugene Golowich, Joachim Kambor

A new calculation of the isospin and hypercharge axialvector current propagators ($Δ_{A33}^{μν}(q^2)$ and $Δ_{A88}^{μν}(q^2)$) to two loops in SU(3) x SU(3) chiral perturbation theory is used to derive chiral spectral function sum rules valid to second order in the light quark masses. Explicit forms are given for the three-pion isospin axialvector spectral f

Ion V. Vancea

The set of constraints under which the eigenvalues of the Dirac operator can play the role of the dynamical variables for Euclidean supergravity is derived. These constraints arise when the gauge invariance of the eigenvalues of the Dirac operator is imposed. They impose conditions which restrict the eigenspinors of the Dirac operator.

Felix Finster

The perturbation of the Dirac sea to first order in the external potential is calculated in an expansion around the light cone. It is shown that the perturbation consists of a causal contribution, which describes the singular behavior of the Dirac sea on the light cone and contains bounded line integrals over the potential and its partial derivatives, and a

J. Alberto Lobo, M. Angeles Serrano

Motion sensing in a spherical GW detector requires a multiple set of transducers attached to its surface at suitable locations. If transducers are of the resonant type then their motion couples to that of the sphere and the joint dynamics of the system has to be properly understood before reliable conclusions can be drawn from its readout. In this paper we a

C. Bachas, C. Fabre, E. Kiritsis, N. A. Obers

We study heterotic/type I duality in d=8,9 uncompactified dimensions. We consider the special (``BPS saturated&#39;&#39;) F^4 and R^4 terms in the effective one-loop heterotic action, which are expected to be non-perturbatively exact. Under the standard duality map these translate to tree-level, perturbative and non-perturbative contributions on the type I s