June 1998 arXiv papers — page 8

A. S. Brun, S. Turck-Chieze, P. Morel

In this paper, we examine a new updated solar model taking advantage of recent reexamination of the nuclear reactions rates and of the microscopic diffusion of helium and heavy elements. Our best model fits the helioseismic data reasonably well: the base of the convective zone is at r=0.715 Ro, the photospheric helium in mass fraction is 0.243 and the sound

Victor Laliena

The effect of angular momentum conservation in microcanonical thermodynamics is considered. This is relevant in gravitating systems, where angular momentum is conserved and the collapsing nature of the forces makes the microcanonical ensemble the proper statistical description of the physical processes. The microcanonical distribution function with non-vanis

Paul Hoyer, Stephane Peigne

We propose a qualitatively new mechanism for quarkonium production, motivated by the global features of the experimental data and by the successes/failures of existing models. In QCD, heavy quarks are created in conjunction with a bremsstrahlung color field emitted by the colliding partons. We study the effects of perturbative gluon exchange between the quar

A. M. Rakhimov, F. C. Khanna, U. T. Yakhshiev, M. M. Musakhanov

Changes in the meson-nucleon coupling constant and the vertex form factor in nuclear matter are studied in a modified Skyrme Lagrangian including the sigma-meson field that satisfies the scale invariance. Renormalization of the axial-vector coupling constant, and the nucleon mass are studied in a consistent model. The results are consistent with the empirica

D. Lutz, H. W. W. Spoon, D. Rigopoulou, A. F. M. Moorwood

We report the first results of a low resolution mid-infrared spectroscopic survey of an unbiased, far-infrared selected sample of 60 ultraluminous infrared galaxies, using ISOPHOT-S on board ISO. We use the ratio of the 7.7um `PAH' emission feature to the local continuum as a discriminator between starburst and AGN activity. About 80% of all the ULIRGs a

G. V. Efimov, A. C. Kalloniatis, S. N. Nedelko

We examine in non-Abelian gauge theory the heavy quark limit in the presence of the (anti-)self-dual homogeneous background field and see that a confining potential emerges, consistent with the Wilson criterion, although the potential is quadratic and not linear in the quark separation. This builds upon the well-known feature that propagators in such a backg

Ting-Wai Chiu, Sergei V. Zenkin

We analyze general solutions of the Ginsparg-Wilson relation for lattice Dirac operators and formulate a necessary condition for such operators to have non-zero index in the topologically nontrivial background gauge fields.

Yosuke Imamura

We calculate the baryon mass in N=4 large $N$ gauge theory by means of AdS/CFT correspondence and show that it is a truly bound state, at least in some situations. We find that a phase transition occurs at a critical temperature. Furthermore, we find there are bound states of W-bosons in the Higgs phase, where the gauge group is broken to SU(N_1)xSU(N_2).

A. Keren, P. Mendels, A. Kratzer, A. Scuiller

In high spin molecules metal ions are coupled by ferro or antiferromagnetic short range interactions so that their magnetic moments are parallel or antiparallel to each other at temperatures (T) much smaller than the coupling constant J. This leads to a high spin (S) value in the ground state. In the crystal lattice, the molecules are well separated from eac

Hasan R. Karadayi, Meltem Gungormez

For a finite Lie algebra $G_N$ of rank N, the Weyl orbits $W(Λ^{++})$ of strictly dominant weights $Λ^{++}$ contain $dimW(G_N)$ number of weights where $dimW(G_N)$ is the dimension of its Weyl group $W(G_N)$. For any $W(Λ^{++})$, there is a very peculiar subset $\wp(Λ^{++})$ for which we always have $$ dim\wp(Λ^{++})=dimW(G_N)/dimW(A_{N-1}) . $$ For any domi

C. N. Likos, M. Watzlawek, H. Loewen

We consider a system of spherical particles interacting by means of a pair potential equal to a finite constant for interparticle distances smaller than the sphere diameter and zero outside. The model may be a prototype for the interaction between micelles in a solvent [C. Marquest and T. A. Witten, J. Phys. France 50, 1267 (1989)]. The phase diagram of thes

Osamu Tsuchiya, Ikuo Ichinose, Yasuyuki Kayama

We introduce an integrable impurity model in which both electrons and impurity have spin and flavour degrees of freedom. This model is a generalization of the multi-channel Kondo model and closely related with resonant tunneling through quantum dot. The Hamiltonian is exactly diagonalized by means of the Bethe ansatz.

Howard Barnum

I introduce rate-distortion theory for quantum coding, and derive a lower bound, involving the coherent information, on the rate at which qubits must be used to encode a quantum source with a given maximum level of distortion per source emission. The convexity of the "information rate-distortion function" which defines this bound is also derived.

Alan Edelman, T. A. Arias, Steven T. Smith

In this paper we develop new Newton and conjugate gradient algorithms on the Grassmann and Stiefel manifolds. These manifolds represent the constraints that arise in such areas as the symmetric eigenvalue problem, nonlinear eigenvalue problems, electronic structures computations, and signal processing. In addition to the new algorithms, we show how the geome

David McComb, Alistair Young

In this paper we consider the properties of the internal partitions of the nonlinear term, obtained when a filter with a sharp cutoff is introduced in wavenumber space. We see what appears to be some degree of independence of the choice of the position of the cutoff wavenumber for both instantaneous and time-integrated partitioned nonlinearities. We also inv

David McComb, Jaek-Jin Yang, Alistair Young, Luc Machiels

Renormalization group has enjoyed successes in other areas of statistical physics. However, its application to turbulence faces several technical difficulties, which have had to be circumvented by uncontrolled approximations. Indeed, in view of the deterministic nature of the Navier-Stokes equations, it is clear that the operation of averaging out the high-w

S. Setayeshgar, M. C. Cross

We present numerical solution of the chlorine dioxide-iodine-malonic acid reaction-diffusion system in two dimensions in a boundary-fed system using a realistic model. The bifurcation diagram for the transition from non-symmetry breaking structures along boundary feed gradients to transverse symmetry breaking patterns in a single layer is numerically determi

S. Setayeshgar, M. C. Cross

The formation of localized structures in the chlorine dioxide-idodine-malonic acid (CDIMA) reaction-diffusion system is investigated numerically using a realistic model of this system. We analyze the one-dimensional patterns formed along the gradients imposed by boundary feeds, and study their linear stability to symmetry-breaking perturbations (Turing insta

L. Canton

It is found that the coupled piNNN-NNN system breaks into fragments in a nontrivial way. Assuming the particles as distinguishable, there are indeed four modes of fragmentation into two clusters, while in the standard three-body problem there are three possible two-cluster partitions and conversely the four-body problem has seven different possibilities. It

Piotr A. Zolnierczuk

We propose to measure the two--photon capture mode of pionic hydrogen using the RMC pair spectrometer at the TRIUMF cyclotron. Currently, only an experimental upper limit of B.R.<= 5.5E-4 is available for the two-gamma capture mode. Our new data will critically test the theoretical calculations and the intriguing predicted dominance of the pi pi --> gamma ga

Boris Tsirelson

Brownian motions in the infinite-dimensional group of all unitary operators are studied under strong continuity assumption rather than norm continuity. Every such motion can be described in terms of a countable collection of independent one-dimensional Brownian motions. The proof involves continuous tensor products and continuous quantum measurements. A by-p

Masoud Khalkhali

In this note we extend the cyclic homology functor, and in particular the periodic cyclic homology, to the category of DG (= differential graded) coalgebras. We are partly motivated by the question of products and coproducts in the cyclic homology of algebras, pioneered by A.Connes. As an application we show how one can start from the classical shuffle map i

Alain Connes, Henri Moscovici

We present the solution of a longstanding internal problem of noncommutative geometry, namely the computation of the index of a transversally elliptic operator on an arbitrary foliation. The new and crucial ingredient is a certain Hopf algebra associated to the transverse frame bundle. Its cyclic cohomology is defined and shown to be canonically isomorphic t

Charles Frohman, Razvan Gelca

We show that the Kauffman bracket skein module of a cylinder over the torus embeds as a subalgebra of the noncommutative torus. Using this we derive nice formulas for the Jones-Wenzl idempotents and analyze the structure of the Kauffman bracket skein module of the unknot as a module over the Kauffman bracket skein module of a cylinder over the torus.

Iosif Polterovich, Alexander Shnirelman

Asymptotic subcone of an unbounded metric space is another metric space, capturing the structure of the original space at infinity. In this paper we define a functional metric space S which is an asymptotic subcone of the hyperbolic plane. This space is a real tree branching at every its point. Moreover, it is a homogeneous metric space such that any real tr

Arne Meurman, Mirko Primc

We show that a set of local admissible fields generates a vertex algebra. For an affine Lie algebra $\tilde\goth g$ we construct the corresponding level $k$ vertex operator algebra and we show that level $k$ highest weight $\tilde\goth g$-modules are modules for this vertex operator algebra. We determine the set of annihilating fields of level $k$ standard m

P. P. Kulish

The recently proposed jordanian quantization of the Lie superalgebra $osp(1|2)$ due to the embedding $sl(2) \subset osp(1|2)$, is extended including odd generators into the twisting element $\cal F$. This deformation is obtained as a contraction of the quantum superalgebra ${\cal U}_{q}(osp(1|2))$.

Lajos Molnar, Borut Zalar

We show that with few exceptions every local isometric automorphism of the group algebra $L^p(G)$ of a compact group $G$ is an isometric automorphism.

Tomohide Terasoma

We give a formula for the spectral pairs (after Steenbrink) for composite singularities of several variables. (Note that for two variable case is studyed by Nemethi-Steenbrink.) Here composite singularity is given by the equation f(g_1, ..., g_n) = 0. For technical reason, we assume that f is non-degenerated with respect to the Newton boundary.

Marco Spaans

A thought experiment is formulated to unify quantum mechanics and general relativity in a topological manner. An analysis of the interactions in Nature is then presented. The universal ground state of the constructed theory derives from the cyclic properties ($S^1$ homotopy) of the topological manifold $Q=2T^3\oplus 3S^1\times S^2$ which has 23 intrinsic deg

Hirosi Ooguri, Harlan Robins, Jonathan Tannenhauser

Spectra of glueball masses in non-supersymmetric Yang-Mills theory in three and four dimensions have recently been computed using the conjectured duality between superstring theory and large N gauge theory. The Kaluza-Klein states of supergravity do not correspond to any states in the Yang-Mills theory and therefore should decouple in the continuum limit. On

J. S. Dowker, K. Kirsten

We present a method for the calculation of the $a_{3/2}$ heat kernel coefficient of the heat operator trace for a partial differential operator of Laplace type on a compact Riemannian manifold with oblique boundary conditions. Using special case evaluations, restrictions are put on the general form of the coefficients, which, supplemented by conformal transf

A. Feinstein, M. A. Vazquez-Mozo

We look at the possibility of superinflationary behavior in a class of anisotropic Type-IIB superstring cosmologies in the context of Pre-big Bang scenario and find that there exists a rather narrow range of parameters for which these models inflate. We then show that, although in general this behavior is left untouched by the introduction of a Ramond-Ramond

Marco Fabbrichesi, Gabriele Ferretti, Roberto Iengo

It is briefly explained why recent claims about the vanishing of the one-loop effective potential in Matrix theory, thus invalidating the possible agreement with supergravity, do not hold.

Michele Morara, Roberto Soldati

A new light-front formulation of Q.E.D. is developed, within the framework of standard perturbation theory, in which $x^+$ plays the role of the evolution parameter and the gauge choice is $A_+=0$ (light-front &#34;temporal&#34; gauge). It is shown that this formulation leads to the Mandelstam-Leibbrandt causal prescription for the non-covariant singularitie

Yuji Igarashi, Katsumi Itoh, Kiyoshi Kamimura

We establish self-duality of super D3-brane theory as an exact symmetry of the action both in the Lagrangian and Hamiltonian formalism. In the Lagrangian formalism, the action is shown to satisfy the Gaillard-Zumino condition. This algebraic relation is recognized in our previous paper to be a necessary and sufficient condition for generic action of U(1) gau

Yuji Igarashi, Katsumi Itoh, Kiyoshi Kamimura

For D=4 theories of a single U(1) gauge field strength coupled to gravity and matters, we show that the electric-magnetic duality can be formulated as an invariance of the actions. The symmetry is associated with duality rotation acting directly on the gauge field. The rotation is constructed in flat space, and an extension to curved spaces is also given. It

Francois Gelis

Modifications of the $π^o\to 2γ$ decay amplitude by thermal effects have already been considered by several authors, leading to quite different results. I consider in this paper the triangle diagram connecting a neutral pion to two photons in a constituent quark model, within the real-time formulation of thermal field theory and study the zero external momen

Kurt Langfeld

The notion induced symmetry breaking (ISB) is introduced as a generalization of the spontaneous symmetry breaking mechanism and is illustrated in a simple two flavor spin model. In the case of QCD at finite baryon density, I argue that the quark interaction induced by zero sound satisfies the prerequisites which are necessary for a ISB scenario. In this scen

D. Ebert, A. S. Vshivtsev

We study the relativistic van Alphen--de Haas effect in cold dense quark matter in a homogeneous magnetic field which arises from oscillations in the effective potential of an underlying extended NJL-model. Finally, we discuss the phase structure of the model in the parameter plane $(μ,H)$ and the solution of the mass gap equation.

K. A. Oganessyan

We estimate the size of the azimuthal asymmetry of the semi-inclusive pion production in the deep-inelastic scattering of a polarized lepton beam off an unpolarized nucleon target for the produced hadron, arising due to both nonperturbative and perturbative effects.

Bijoy Kundu, Hsiang-nan Li, Jim Samuelsson, Pankaj Jain

We recalculate the proton Dirac form factor based on the perturbative QCD factorization theorem which includes Sudakov suppression. The evolution scale of the proton wave functions and the infrared cutoffs for the Sudakov resummation are carefully chosen, such that the soft divergences from large coupling constants are diminished and perturbative QCD predict

B. V. Geshkenbein

The problem of determining the pion electromagnetic formfactor $F(q^2)$ in the space-like region from the value of its modulus in the time-like region is solved by the formfactor analyticity. If $F(q^2)$has no zeroes in the complex plane then the formfactor in the space-like region is determined uniquely. If $F(q^2)$has zeroes in the complex plane $q^2$ it c

Walter Dittrich, Holger Gies

Table of Contents 1. One-loop effective Lagrangian in spinor QED. 2. Dispersion effects for low-frequency photons. 3. Vacuum birefringence in magnetic fields. 4. Light cone condition, effective Lagrangian approach.

A. Dobado, J. R. Pelaez

In this work we study the thermodynamic properties of the pion gas starting from the realistic elastic scattering phase-shifts obtained from Chiral Perturbation Theory and using the virial expansion. In particular we study the state equation and the behavior of the quark condensate as a function of the temperature and the density.

Frieder Kleefeld, Manfred Dillig

In the following short paper we list some useful results concerning determinants and inverses of matrices. First we show, how to calculate determinants of $d \times d$ matrices, if their traces are known. As a next step $4 \times 4$ matrices are expressed in terms of Dirac covariants. The third step is the calculation of the corresponding inverse matrices in

A. Duncan, E. Eichten, H. Thacker

A new approach to the inclusion of virtual quark effects in lattice QCD simulations is presented. Infrared modes which build in the chiral physics in the light quark mass limit are included exactly and in a gauge invariant way. At fixed physical volume the number of relevant infrared modes does not increase as the continuum limit is approached. The acceptanc

A. Bornheim

Measurements of the total cross section for real and virtual photons on protons at center-of-mass energies in the range from 20 GeV to 270 GeV with photon virtualities up to 5000 GeV^2 are presented. For real photons this cross section can be described by Regge-motivated models while for virtual photons perturbative QCD can be applied. The measurements of th

J. A. Crittenden

Recent measurements of diffractive vector-meson production with the general-purpose detectors H1 and ZEUS in electron-proton interactions with 300 GeV center-of-mass energy at the HERA accelerator complex have stimulated great interest in the question of whether perturbative QCD (pQCD) can provide an accurate description of such diffractive processes. The hi

ZEUS Collaboration

We have searched for the production of a selectron and a squark in $e^+p$ collisions at a center-of-mass energy of 300 GeV using the ZEUS detector at HERA. The selectron and squark are sought in the direct decay into the lightest neutralino in the framework of supersymmetric extensions to the Standard Model which conserve R-parity. No evidence for the produc

F. Kokubun

In this work we analyze the emission of gravitational waves from a gravitational system described by a Newtonian term plus a Hénon-Heiles term. The main concern is to analyze how the inclusion of the Newtonian term changes the emission of gravitational waves, considering its emission in the chaotic and regular regime.

Adam D. Helfer

Although negative energy densities are predicted by relativistic quantum field theories, I present an argument that an &#34;operational&#34; positivity still holds: the energy in a region, plus the energy of an isolated device which traps or measures that energy, must be positive. If we assume Einstein&#39;s field equation, this means the local geometry of a

Sergiu I. Vacaru

In this Report we outline some basic results on generalized Finsler--Kaluza--Klein gravity and locally anisotropic strings. There are investigated exact solutions for locally anisotropic Friedmann--Robertson--Walker universes and three dimensional and string black holes with generic anisotropy.

Carlo Rovelli, Peush Upadhya

We present a straightforward and self-contained introduction to the basics of the loop approach to quantum gravity, and a derivation of what is arguably its key result, namely the spectral analysis of the area operator. We also discuss the arguments supporting the physical prediction following this result: that physical geometrical quantities are quantized i

Jong Hyuk Yoon

The quasi-local energy conservation law is derived from the vacuum Einstein&#39;s equations on the timelike boundary surface in the canonical (2,2)-formalism of general relativity. The quasi-local energy and energy flux integral agree with the standard results in the asymptotically flat limit and in spherically symmetric spacetimes.

Serge Droz

We present further evidence that the second post-Newtonian (pN) approximation to the gravitational waves emitted by inspiraling compact binaries is sufficient for the detection of these systems. This is established by comparing the 2-pN wave forms to signals calculated from black hole perturbation theory. Results are presented for different detector noise cu

I. I. Mazin

Recent reports about observations of superconductivity in PrBa2Cu3O7 raise a number of questions: (i) of various theories striving to explain the Tc suppression in PrxY{1-x}Ba2Cu3O7, are there any compatible with possible superconductivity in stoichiometric PrBa2Cu3O7? (ii) if this superconductivity is not an experimental artifact, are the superconducting ca

K. J. Thomas, J. T. Nicholls, N. J. Appleyard, M. Pepper

We have investigated the transport properties of one-dimensional (1D) constrictions defined by split-gates in high quality GaAs/AlGaAs heterostructures. In addition to the usual quantized conductance plateaus, the equilibrium conductance shows a structure close to $0.7(2e^2/h)$, and in consolidating our previous work [K.~J. Thomas et al., Phys. Rev. Lett. 77

Luca Peliti

A model for the evolution of a finite population in a rugged fitness landscape is introduced and solved. The population is trapped in an evolutionary loop, alternating periods of stasis to periods in which it performs adaptive walks. The dependence of the average rarity of the population (a quantity related to the fitness of the most adapted individual) and

F. Corberi, G. Gonnella, A. Lamura

Results are presented for the phase separation process of a binary mixture subject to an uniform shear flow quenched from a disordered to a homogeneous ordered phase. The kinetics of the process is described in the context of the time-dependent Ginzburg-Landau equation with an external velocity term. The one-loop approximation is used to study the evolution

A. Cappelli, C. Mendez, J. M. Simonin, G. R. Zemba

We present a detailed analysis of the exact numerical spectrum of up to ten interacting electrons in the first Landau level on the disk geometry. We study the edge excitations of the hierarchical plateaus and check the predictions of two relevant conformal field theories: the multi-component Abelian theory and the W-infinity minimal theory of the incompressi

A. Lamura, G. Gonnella, J. M. Yeomans

A lattice Boltzmann model is introduced which simulates oil-water-surfactant mixtures. The model is based on a Ginzburg-Landau free energy with two scalar order parameters. Diffusive and hydrodynamic transport is included. Results are presented showing how the surfactant diffuses to the oil-water interfaces thus lowering the surface tension and leading to sp

X. Jehl, D. Braithwaite, P. Payet-Burin, R. Calemczuk

We present measurements obtained on a bulk cylinder of lead with a SQUID picovoltmeter. A distinctive hysteretic step structure is observed. It is washed out on increasing the current and reinforced in higher field. Classical models for the dissipation mechanisms in the intermediate state are briefly reviewed and used to give a first interpretation of these

Matteo Campellone, Giorgio Parisi, Paola Ranieri

In this work we discuss a short range version of the $p$-spin model. The model is provided with a parameter that allows to control the crossover with the mean field behaviour. We detect a discrepancy between the perturbative approach and numerical simulation. We attribute it to non-perturbative effects due to the finite probability that each particular reali

Robert Metzke, Wolfgang Nolting

A model Hamiltonian is introduced which considers the main features of the experimental spin filter situation as s-f interaction, planar geometry and the strong external electric field. The proposed many-body model can be solved analytically and exactly using Green functions. The spin polarization of the field-emitted electrons is expressed in terms of spin-

N. Schopohl, O. V. Dolgov

We reply to the criticism raised by Volovik in his Comment (cond-mat/9805159) and by Hirschfeld et al. in their Comment (cond-mat/9806085).

M. Micoulaut, G. G. Naumis

We give in this letter a set of general rules which allow the prediction of the value of the glass transition temperature $T_g$ in network glasses. Starting from the Gibbs-Di Marzio law which gives a very general relationship between this temperature and the average coordination number of a system, we explain how to compute from the valencies of the atoms of

Joao D. Correia

Inspired by previous work on the constraints that duality imposes on beta functions of spin models, we propose a consistency condition between those functions and RG flows at different points in coupling constant space. We show that this consistency holds for a non self-dual model which admits an exact RG flow, but that it is violated when the RG flow is onl

Judith Hochberg, Clint Scovel, Timothy Thomas, Sam Hall

This paper describes a method for asking statistical questions about a large text corpus. We exemplify the method by addressing the question, &#34;What percentage of Federal Register documents are real documents, of possible interest to a text researcher or analyst?&#34; We estimate an answer to this question by evaluating 200 documents selected from a corpu

Stefan Thurner, Markus C. Feurstein, Malvin C. Teich

We have carried out a pilot study on a standard collection of electrocardiograms from patients who suffer from congestive heart failure, and subjects without cardiac pathology, using receiver-operating-characteristic (ROC) analysis. The scale-dependent wavelet-coefficient standard deviation σ_{wav}(m), a multiresolution-based analysis measure, is found to be

Tod R. Lauer, S. M. Faber, Edward A. Ajhar, Carl J. Grillmair

WFPC-2 images are used to study the central structure of M31, M32, and M33. The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to 0.1&#34;, implying that it is the dynamical center of M31. P2 contains a compact source discovered by King et al. (1995) at 1700 A. This source is resolved, with r_{1/2} approx0.2 pc. It dominates the nucleus

G. Fritz Benedict, Barbara McArthur, E. Nelan, D. Story

We have observed Proxima Centauri and Barnard&#39;s Star with Hubble Space Telescope Fine Guidance Sensor 3. Proxima Centauri exhibits small-amplitude, periodic photometric variations. Once several sources of systematic photometric error are corrected, we obtain 2 milli-magnitude internal photometric precision. We identify two distinct behavior modes over th

Jonathan F. Schachter, Fabrizio Fiore, Martin Elvis, Smita Mathur

NGC 7582 is a candidate prototype of the Narrow Line X-ray Galaxies (NLXGs) found in deep X-ray surveys. An ASCA observation shows the hard (> 3 keV) X-ray continuum of NGC 7582 drops 40% in ~6 ks, implying an AGN, while the soft band (< 3 keV) does not drop in concert with the hard continuum, requiring a separate component. The X-ray spectrum of NGC 7582 al

Mario G. Abadi, Diego G. Lambas, Hernán Muriel

We compute the cluster auto-correlation function $ξ_{cc}(r)$ of an X-ray flux limited sample of Abell clusters (XBACs, \cite{ebe}). For the total XBACs sample we find a power-law fit $ξ_{cc}=(r/r_0)^γ$ with $r_0=21.1$ Mpc h$^{-1}$and $γ=-1.9$ consistent with the results of $R \ge 1 $ Abell clusters. We also analyze $ξ_{cc}(r)$ for subsamples defined by diffe

Philippe Fischer, David Schade, Felipe Barientos

Gravitational lensing is an important tool for probing the mass distribution of galaxies. In this letter we report the discovery of a new quadruple lens HST 1411+5211 found in archived WFPC2 images of the galaxy cluster CL140933+5226. If the galaxy is a cluster member then its redshift is $z=0.46$. The images of the source appear unresolved in the WFC implyi

F. P. Israel, P. P. van der Werf, R. P. J. Tilanus

Broadband continuum images of the edge-on galaxy NGC 891 at 850 and 450 microns are presented. These images are qualitatively very similar to the 1300 micron and CO images obtained by others. With respect to the 850 micron continuum, CO is strongest in the socalled `molecular ring&#39;, and weakest at the largest radii sampled. Inside the molecular ring, the

M. R. Burleigh, M. A. Barstow, J. B. Holberg

We report the results of our final search for hot white dwarfs in unresolved, Sirius-type, binary systems with IUE. One new system, RE J0500-364 (DA+F6/7V), has been identified. This star appears to lie at a distance of between 500-1000pc, making it one of the most distant white dwarfs, if not the most distant, to be detected in the EUV surveys. The very low

D. W. Koerner, M. E. Ressler, M. W. Werner, D. E. Backman

We report the discovery of a circumstellar disk around the young A0 star, HR 4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By fitting a model of the emission from a flat dusty disk to an image at lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face on, with the long axis of emission at PA 28 +/-6 deg. Th

J. M. Stil, F. P. Israel

High-sensitivity maps of the large-scale structure of atomic hydrogen in the starburst dwarf galaxy NGC 1569 show evidence for an HI cloud with a mass of 7*10**6 M_sun, at a projected distance of 5 kpc from the parent galaxy. This cloud may be a condensation in a low-column-density HI halo or a companion galaxy/HI-cloud. NGC 1569 and its companion are connec

Monica Tosi

The state-of-the-art of chemical evolution models for Irregular and Blue Compact galaxies is reviewed. The resulting scenarios for the initial mass function, the regime of star formation and the efficiency of gas outflows are described: The IMF appears to be roughly the same everywhere; the SF has possibly followed a bursting regime in BCGs and a more contin

G. Battistoni, M. Carboni, A. Ferrari, V. Patera

A detailed simulation of vertical showers in atmosphere produced by primary gammas and protons, in the energy range 1-100 TeV, has been performed by means of the FLUKA Monte Carlo code, with the aim of studying the time structure of the shower front at different detector heights. It turns out that the time delay distribution can be fitted using few parameter

Pasquale Blasi, Angela V. Olinto

A sufficiently magnetized Local Supercluster can explain the spectrum and angular distribution of ultra-high energy cosmic rays. We show that the spectrum of extragalactic cosmic rays with energies below $\sim 10^{20}$ eV may be due to the diffusive propagation in the Local Supercluster with fields of $\sim 10^{-8} - 10^{-7}$ Gauss. Above $\sim 10^{20}$ eV,

Joel R. Primack, Rachel S. Somerville, S. M Faber, Risa H. Wechsler

Using semi-analytic models of galaxy formation, we investigate the properties of $z\sim3$ galaxies and compare them with the observed population of Lyman-break galaxies (LBGs). In addition to the usual quiescent mode of star formation, we introduce a physical model for starbursts triggered by galaxy-galaxy interactions. We find that with the merger rate that

Bing Zhang, G. J. Qiao

The importance of the photon-photon pair production process ($γ+ γ^{\prime}\to e^{+}+e^{-}$) to form pair production cascades in pulsar polar caps is investigated within the framework of the Ruderman-Sutherland vacuum gap model. It is found that this process is unimportant if the polar caps are not hot enough, but will play a non-negligible role in the pair

Gerhardt R. Meurer, Lister Staveley-Smith, N. E. B. Killeen

We present 21cm HI line observations of the blue compact dwarf galaxy NGC1705. Previous optical observations show a strong outflow powered by an ongoing starburst dominating the HII morphology and kinematics. In contrast, most of the HI lies in a rotating disk. An extraplanar HI spur accounts for ~ 8% of the total HI mass, and is possibly associated with the

F. Kleefeld

A systematic field theoretic formalism for treating Fermionic resonances with non zero width is given. The implication of unitarity to coupling constants of non local interactions is shown. The extension of the formalism to Bosonic resonance field operators is straight forward.

Ofer Aharony, Ansar Fayyazuddin, Juan Maldacena

We consider field theories arising from a large number of D3-branes near singularities in F-theory. We study the theories at various conformal points, and compute, using their conjectured string theory duals, their large $N$ spectrum of chiral primary operators. This includes, as expected, operators of fractional conformal dimensions for the theory at Argyre

William H. Kinney

Observations of the polarization of the cosmic microwave backround (CMB) have the potential to place much tighter constraints on cosmological parameters than observations of the fluctuations in temperature alone. We discuss using CMB polarization to constrain parameters relevant for distinguishing among popular models for cosmological inflation, using the MA

Toby Falk, Andrew Ferstl, Keith A. Olive

We compute the four-Fermi neutralino-quark interaction Lagrangian including contributions from the CP violating phases in the MSSM. We find that neutralino-nucleus scattering cross-sections relevant for direct detection experiments show a strong dependence on the value of the CP-violating phase associated with the $μ$ parameter, $θ_μ$. In some cases, for a b

Dirk Hundertmark, Elliott H. Lieb, Lawrence E. Thomas

We give a proof of the Lieb-Thirring inequality in the critical case $d=1$, $γ= 1/2$, which yields the best possible constant.

Igor A. Shovkovy

The one-loop finite temperature effective potential of QED in an external electromagnetic field is obtained using the worldline method. The general structure of the temperature dependent part of the effective action in an arbitrary external inhomogeneous magnetic field is established. The two-derivative effective action of spinor and scalar QED in a static m

MILC Collaboration, C. Bernard, T. DeGrand, C. DeTar

We report on the MILC collaboration's calculation of $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$, and their ratios. Our central values come from the quenched approximation, but the quenching error is estimated from $N_F=2$ dynamical staggered lattices. We use Wilson light valence quarks and Wilson and static heavy quarks. We find, for example, $f_B=157 \pm 11 {}^{+25

Mary K. Gaillard, David H. Lyth, Hitoshi Murayama

The potential during inflation must be very flat in, at least, the direction of the inflaton. In renormalizable global supersymmetry, flat directions are ubiquitous, but they are not preserved in a generic supergravity theory. It is known that at least some of them are preserved in no-scale supergravity, and simple generalizations of it. We here study a more

Luis Bento

If the lepton numbers are associated with global symmetries spontaneously broken at a scale below 1 TeV, neutrino oscillations in supernovae produce classic Majoron fields that perturb the neutrino propagation itself and may change the oscillation patterns in the periods of largest $ν$ fluxes. The impact of the Majoron fields on the same transitions as $ν_{e

Christian D. Lorenz, Robert M. Ziff

Extensive Monte-Carlo simulations were performed to evaluate the excess number of clusters and the crossing probability function for three-dimensional percolation on the simple cubic (s.c.), face-centered cubic (f.c.c.), and body-centered cubic (b.c.c.) lattices. Systems L x L x L&#39; with L&#39; >> L were studied for both bond (s.c., f.c.c., b.c.c.) and si

M. Anwar Mughal, H. Athar

We study the effects of neutrino spin-flip in the magnetic field, B_{AGN}, of active galactic nuclei (AGN) for high-energy neutrinos (E > 10^{6} GeV) originating from AGN induced by an interplay of the violation of equivalence principle parameterized by $Δf$ and the twist in B_{AGN}. We point out that a conversion effect may exist for $Δf \sim 10^{-34} (δm^{

Alfredo Herrera-Aguilar, Oleg Kechkin

We present a simple algorithm to obtain solutions that generalize the Israel--Wilson--Perjés class for the low-energy limit of heterotic string theory toroidally compactified from D=d+3 to three dimensions. A remarkable map existing between the Einstein--Maxwell (EM) theory and the theory under consideration allows us to solve directly the equations of motio

Michael C. Ogilvie

Analytic methods for Abelian projection are developed. A number of results are obtained related to string tension measurements. It is proven that even without gauge fixing, abelian projection yields string tensions of the underlying non-Abelian theory. Strong arguments are given for similar results in the case where gauge fixing is employed. The methods used

James V. Steele, Volker Koch

The lifetime of a disoriented chiral condensate formed within a heat bath of pions is calculated assuming temperatures and densities attainable at present and future heavy-ion colliders. A generalization of the reduction formula to include coherent states allows us to derive a formula for the decay rate. We predict the half-life to be between 4 and 7 fm/c, d

A. Atalmi, M. Baldo, G. F. Burgio, A. Rapisarda

In the framework of a 2D Vlasov model, we study the time evolution of the &#34;coarse-grained&#34; Generalized Entropy (GE) in a nuclear system which undergoes a multifragmentation (MF) phase transition. We investigate the GE both for the gas and the fragments (surface and bulk part respectively). We find that the formation of the surface causes the growth o