May 2000 arXiv papers — page 7

Jonathan Pakianathan, Ergün Yalçin

In this paper we study various simplicial complexes associated to the commutative structure of a finite group G. We define NC(G) (resp. C(G)) as the complex associated to the poset of pairwise non-commuting (resp. commuting) sets in G. We observe that NC(G) has only one positive dimensional connected component, which we call BNC(G), and we prove that BNC(G)

William Arveson

A CP semigroup is a semigroup of normal unit-preserving completely positive maps acting on the algebra B(H) of all operators on a separable Hilbert space H. Such a semigroup has a natural generator L; since the individual maps of the semigroup need not be multiplicative, the domain Dom(L) of L is typically an operator system, but not an algebra. However, we

William Arveson

Let P and Q be the canonical operators acting on the Hilbert space of all L^2 functions on the real line, defined appropriately on a common dense domain. The derivations D_P(A) = i(PA - AP) and D_Q(A) = i(QA - AQ) act on the *-algebra of all integral operators having smooth kernels of compact support, for example, and one may consider the noncommutative &#34

Mark Andrea de Cataldo, Luca Migliorini

We compute the Chow motive and the Chow groups with rational coefficients of the Hilbert scheme of points on a smooth algebraic surface

Palle E. T. Jorgensen, Steen Pedersen

We consider the problem of finding commuting self-adjoint extensions of the partial derivatives {(1/i)(\partial/\partial x_j):j=1,...,d} with domain C_c^\infty(Ω) where the self-adjointness is defined relative to L^2(Ω), and Ωis a given open subset of R^d. The measure on Ωis Lebesgue measure on R^d restricted to Ω. The problem originates with I.E. Segal and

P. Zgliczynski, K. Mischaikow

We present a new topological method for the study of the dynamics of dissipative PDE's. The method is based on the concept of the self-consistent apriori bounds, which allows to justify rigorously the Galerkin projection. As a result we obtain a low-dimensional system of ODE's subject to rigorously controlled small perturbation from the neglected mod

Alexander I. Bobenko, Tim Hoffmann

From the geometric study of the elementary cell of hexagonal circle packings --- a flower of 7 circles --- the class of conformally symmetric circle packings is defined. Up to Moebius transformations, this class is a three parameter family, that contains the famous Doyle spirals as a special case. The solutions are given explicitly. It is shown, that these c

J-P. Monnier

The Witt group of a smooth curve over a real closed field is explicitely calculated. The method uses a comparison theorem between the graded Witt group and the etale cohomology groups. In the second part of the paper, the torsion Picard group of a smooth real curve is also computed. The calculation depends on a new invariant introduced here. We prove that se

Branko Saric

In the main part of the paper, on the basis of contour integration of complex meromorphic functions whose singularities lie onto an integration contour, in the first step, a concept of improper integrals absolute existence of meromorphic functions, as more general one with respect to the concept of improper integrals convergence (existence), is introduced in

Herbert Schroeder

In this largely expository paper we give a self-contained treatment of the Dirac operator. Emphasizing the algebraic point of view we first sketch the necessary prerequisites from Clifford algebras and their representations and then define (and characterize) spin structures and the corresponding Spin-Dirac operator purely in the spirit of irreducible represe

Noam D. Elkies

We give explicit equations for the simplest towers of Drinfeld modular curves over any finite field, and observe that they coincide with the asymptotically optimal towers of curves constructed by Garcia and Stichtenoth.

Shu-Cheng Chang, Jih-Hsin Cheng

We deform the contact form by the amount of the Tanaka-Webster curvature on a closed spherical $CR$ three-manifold. We show that if a contact form evolves with free torsion and positive Tanaka-Webster curvature as initial data, then a certain Harnack inequality for the Tanaka-Webster curvature holds.

Nordine Mir

Let f : (M,p)\to (M',p') be a formal biholomorphic mapping between two germs of real analytic hypersurfaces in \C^n, p'=f(p). Assuming the source manifold to be minimal at p, we prove the convergence of the so-called reflection function associated to f. As a consequence, we derive the convergence of formal biholomorphisms between real analytic mi

P. Binetruy, G. Girardi, R. Grimm

This report provides a pedagogical introduction to the description of the general Poincare supergravity/matter/Yang-Mills couplings using methods of Kahler superspace geometry. At a more advanced level this approach is generalized to include tensor field and Chern-Simons couplings in supersymmetry and supergravity, relevant in the context of weakly and stron

S. Penati, A. Santambrogio, D. Zanon

We compute two-point functions of chiral operators Tr(Φ^k) for any k, in {\cal N}=4 supersymmetric SU(N) Yang-Mills theory. We find that up to the order g^4 the perturbative corrections to the correlators vanish for all N. The cancellation occurs in a highly non trivial way, due to a complicated interplay between planar and non planar diagrams. In complete g

M. Billo`, D. Fabbri, P. Fre`, P. Merlatti

We discuss a general pairing that occurs in compactifications of M-theory on AdS_4 x X^7 backgrounds between massless ultra short multiplets and their massive shadows, namely certain universal long multiplets with fixed protected dimensions. In particular we consider the shadow of the short graviton multiplet in N=3 compactifications. It turns out to be a ma

M. Billo`, D. Fabbri, P. Fre`, P. Merlatti

In this paper we investigate three-dimensional superconformal gauge theories with N=3 supersymmetry. Independently from specific models, we derive the shortening conditions for unitary representations of the Osp(3|4) superalgebra and we express them in terms of differential constraints on three dimensional N=3 superfields. We find a ring structure underlying

G. S. Djordjevic, B. Dragovich, LJ. Nesic

We consider spectral problem for a free relativistic particle in p-adic and adelic quantum mechanics. In particular, we found p-adic and adelic eigenfunctions. Within adelic approach there exist quantum states that exhibit discrete structure of spacetime at the Planck scale.

Yu. V. Shtanov

In the study of three-brane cosmological models, an unusual law of cosmological expansion on the brane has been reported. According to this law, the energy density of matter on the brane quadratically enters the right-hand side of the new equations for the brane world, in contrast with the standard cosmology, where it enters the similar equations linearly. H

David London, Nita Sinha, Rahul Sinha

We describe a new method for extracting weak, CP-violating phase information, with no hadronic uncertainties, from an angular analysis of B -> V_1 V_2 decays, where V_1 and V_2 are vector mesons. The quantity $\sin^2 (2β+ γ)$ can be cleanly obtained from the study of decays such as B_d^0(t) -> D^{*\pm} ρ^\mp, D^{*\pm} a_1^{\mp}, D^{*0} K^{*0}, etc. Similarly

T. E. Clark, S. T. Love

The consequences of large radius extra space-time compactified dimensions on the four dimensional one loop effective potential are investigated for a model which includes scalar self interactions and Yukawa coupling to fermions. The Kaluza-Klein tower of states associated with the extra compact dimensions shifts the location of the effective potential minimu

S. I. Bityukov, N. V. Krasnikov

We investigate squark and gluino pair production at LHC (CMS) with subsequent decays into quarks, leptons and LSP in models with effective supersymmetry where third generation of squarks is relatively light while the first two generations of squarks are heavy. We consider the general case of nonuniversal gaugino masses. Visibility of signal by an excess over

A. A. Bykov, M. C. Gonzalez-Garcia, C. Peña-Garay, V. Yu. Popov

We study the effect of random matter density fluctuations in the sun on resonant neutrino conversion in matter by solving numerically the evolution equation for the neutrino system including the full effect of the random matter density fluctuations of given amplitude and correlation length. In order to establish the possible effect on the MSW solutions to th

J. Smith

We discuss how the operator product expansion (OPE) can be used to derive asymptotic expressions for certain integrals. This yields operator matrix elements (OME's) which determine the matching conditions for $\bar{\rm MS}$ parton densities across heavy flavour thresholds. Then we construct four and five-flavour densities from a three-flavour set via the

J. Smith

We discuss heavy quark production in deep inelastic scattering (DIS)

R. Mohanta

We have studied new CP violating effects in $Λ_b \to p π$ decay mode, that can arise in Minimal Supersymmetric Standard Model with R-parity violation. We have estimated how much R-parity violation modifies the Standard Model predictions for CP asymmetries within the present bounds. We found that in the R-parity violating model, the rate asymmetry ($a_{cp}$)

Isabella Masina

I introduce and sketch the main features of those see-saw models where a large atmospheric mixing can be achieved starting from nearly diagonal matrices for charged leptons, Dirac neutrinos and Majorana right-handed neutrinos. It turns out that these models can be realized in Grand Unified Theories and they are well compatible with the related phenomenology

A. V. Kopylov

The comparison of magnetic moments of neutron and proton reveals three possible states of a nucleon each composed of quark plus diquark. In this scheme for the quark content uds there should be three baryons with a different structure: ud+s, us+d, ds+u. So one can expect the existence of a third companion to the known baryons Lambda and Sigma0.

O. Yavas, A. K. Ciftci, S. Sultansoy

Main parameters of linac-ring type $phi$-factory proposed as the part of the Turkic Accelerator Complex (TAC) in the framework of ATAM Science Sity Project are discussed. Two sets of parameters, corresponding to E=130(260) MeV for electron linac and E=2000(1000) MeV positron ring, are considered. It is swoun that, in principle, L=10^(34)cm^(-2)s^(-1) can be

The D0 Collaboration

The result of a search for gaugino pair production with a trilepton signature is reinterpreted in the framework of minimal supergravity (mSUGRA) with R-parity violation via leptonic lambda Yukawa couplings. The search used 95 pb^{-1} of p-barp collisions at sqrt{s}=1.8 TeV recorded by the D0 detector at the Fermilab Tevatron. A large domain of the mSUGRA par

Don N. Page

Bekenstein&#39;s conjectured entropy bound for a system of linear size R and energy E, S < 2 pi E R, can be violated by an arbitrarily large factor, among other ways, by a scalar field having a symmetric potential allowing domain walls, and by the electromagnetic field modes between an arbitrarily large number of conducting plates.

Doug Singleton

The formation of singularities in certain situations, such as the collapse of massive stars, is one of the unresolved issues in classical general relativity. Although no complete theory of quantum gravity exists it is often suggested that quantum gravity effects may prevent the formation of these singularities. In this article we will present arguments that

Andrzej Krasinski

The Einstein equations for one of the hypersurface-homogeneous rotating dust models are investigated. It is a Bianchi type V model in which one of the Killing fields is spanned on velocity and rotation (case 1.2.2.2 in the classification scheme of the earlier papers). A first integral of the field equations is found, and with a special value of this integral

Adrian C. Ottewill, Elizabeth Winstanley

We present a simple proof, using the conservation equations, that any quantum stress tensor on Kerr space-time which is isotropic in a frame which rotates rigidly with the angular velocity of the event horizon must be divergent at the velocity of light surface. We comment on our result in the light of the absence of a `true Hartle-Hawking&#39; vacuum for Ker

Fran De Aquino

According to the weak form of Einstein&#39;s general relativity equivalence principle, the gravitational and inertial masses are equivalent. However recent calculations (gr-qc/9910036) have revealed that they are correlated by an adimensional factor, which is equal to one in absence of radiation only. We have built an experimental system to check this unexpe

S. Sonego, J. Almergren, M. Abramowicz

The notion of optical geometry, introduced more than twenty years ago as a formal tool in quantum field theory on a static background, has recently found several applications to the study of physical processes around compact objects. In this paper we define optical geometry for spherically symmetric gravitational collapse, with the purpose of extending the c

Branko Dragovich, Ljubisa Nesic

p-Adic and adelic generalization of ordinary quantum cosmology is considered. In [1], we have calculated p-adic wave functions for some minisuperspace cosmological models according to the &#34;no-boundary&#34; Hartle-Hawking proposal. In this article, applying p-adic and adelic quantum mechanics, we show existence of the corresponding vacuum eigenstates. Ade

Igor Sobrado

A one-time pad (OTP) based cipher to insure both data protection and integrity when mobile code arrives to a remote host is presented. Data protection is required when a mobile agent could retrieve confidential information that would be encrypted in untrusted nodes of the network; in this case, information management could not rely on carrying an encryption

Daniel Duque, Michael Schick

We apply self consistent field theory to twist grain boundaries of block copolymer melts. The distribution of monomers throughout the grain boundary is obtained as well as the grain boundary free energy per unit area as a function of twist angle. We define an intermaterial dividing surface in order to compare it with minimal surfaces which have been proposed

P. M. C. de Oliveira, A. Delfino, E. V. Costa, C. A. F. Leite

We performed an experiment on elementary hydrodynamics. The basic system is a cylindrical bottle from which water flows through a pin-hole located at the bottom of its lateral surface. We measured the speed of the water leaving the pin-hole, as a function of both the time and the current level of water still inside the bottle. The experimental results are co

J. Goldenberg, B. Libai, S. Solomon, N. Jan

A percolation model is presented, with computer simulations for illustrations, to show how the sales of a new product may penetrate the consumer market. We review the traditional approach in the marketing literature, which is based on differential or difference equations similar to the logistic equation (Bass 1969). This mean field approach is contrasted wit

A. A. Likhachev, K. Ullakko

Recently, several research groups have reported on the observation of super-large more than 5% magneto-strain effect in some non-stoichiometric Ni-Mn-Ga alloys close to 5.78% value expected from the tetragonality aspect ratio of the martensite crystal lattice. New Ni-Mn-Ga alloys showing giant magneto-strain effect display simultaneously few interesting phys

F. Gillet, O. Pierre-Louis, C. Misbah

Step meandering due to a deterministic morphological instability on vicinal surfaces during growth is studied. We investigate nonlinear dynamics of a step model with asymmetric step kinetics, terrace and line diffusion, by means of a multiscale analysis. We give the detailed derivation of the highly nonlinear evolution equation on which a brief account has b

R. M. Lewis, H. P. Wei, S. Y. Lin, J. F. Klem

We investigate the transport of holes through $AlAs/In_{.10}Ga_{.90}As$ resonant tunneling diodes which utilize $In_xGa_{1-x}As$ prewells in the emitter with $x=0,.10,$ and $.20$. The data show an increase in peak current and bias at resonance and a concurrent increase in the peak-to-valley ratio with increasing x. We explain this enhancement in tunneling as

P. Villain, P. Ohberg, L. Santos, A. Sanpera

We study the process of four-wave mixing (4WM) in ultracold degenerate atomic gases. In particular we address the problem of 4WM in boson-fermion mixtures. We develop an approximate description of such processes using asymptotic analysis of high order perturbation theory taking into account quantum statistics. We perform also numerical simulations of 4WM in

Sorin Solomon, Moshe Levy

The LLS stock market model is a model of heterogeneous quasi-rational investors operating in a complex environment about which they have incomplete information. We review the main features of this model and several of its extensions. We study the effects of investor heterogeneity and show that predation, competition, or symbiosis may occur between different

Peter Olsson, Petter Holme

Evidence for a Kosterlitz-Thouless transition in the 2D step model is obtained from Monte Carlo determinations of the helicity modulus. It is argued that the free energy of a single vortex at the center of the system depends logarithmically on the system size in spite of the fact that the spin interaction is not harmonic for small differences in the spin ang

Fabio Siringo

A recently proposed molecular model is discussed as a non-trivial extension of the Ising model. For d=2 the two models are shown to be equivalent, while for d>2 the molecular model describes a peculiar second order transition from an isotropic high temperature phase to a low-dimensional anisotropic low temperature state. The general mean field analysis is co

H. Meyer-Ortmanns, T. Reisz

Dynamical linked cluster expansions are linked cluster expansions with hopping parameter terms endowed with their own dynamics. This amounts to a generalization from 2-point to point-link-point interactions. An associated graph theory with a generalized notion of connectivity is reviewed. We discuss physical applications to disordered systems, in particular

V. Meregalli, M. Parrinello

We study via density functional-based molecular dynamics the structural and dynamical properties of the rare earth silicon amorphous alloy Y_xSi_{1-x} for x=0.093 and x=0.156. The Si network forms cavities in which a Y^{3+} cation is entrapped. Its electrons are transferred to the Si network and are located in the dangling bonds of the Si atoms that line the

P. Seba, P. Exner, K. N. Pichugin, P. Streda

Effect of the spin-involved interaction of electrons with impurity atoms or defects to the transport properties of a two-dimensional electron gas is described by using a simplifying two-component model. Components representing spin-up and spin-down states are supposed to be coupled at a discrete set of points within a conduction channel. The used limit of th

Ladislav Jankovic, D. K. Sunko

We investigate parametrizations required to reproduce observed Fermi surfaces of overdoped and slightly underdoped LSCO in two different models. One is the standard three-band saddle-point slave boson (SB). The other is a model of CuO4 `molecules&#39; randomly tiled in the plane, emphasizing the distinction between the local overlap, always the full (bare) o

Christian Beck

We apply non-extensive methods to the statistical analysis of fully developed turbulent flows. Probability density functions of velocity differences at distance r obtained by extremizing the Tsallis entropies coincide well with what is measured in turbulence experiments. We derive a set of relations between the hyperflatness factors F_m and the non-extensiti

A. Kormányos, J. Cserti, G. Vattay

The transmission poles of $N$ number of identical Dirac delta potentials placed periodically in one-dimension are examined in the complex-energy plane. The numerical results show that the imaginary part of the poles scales with 1/N. An approximate form of the poles is derived which supports the scaling behaviour of the poles found numerically. It is shown th

R. Michalski, Z. Ropka, R. J. Radwanski

Ferromagnetic compound PrRu2Si2 exhibits a giant magnetocrystalline anisotropy of about 400 T. Its ordered moment below Tc=14K reaches 2.7 mB and is parallel to [0 0 1] crystalline direction. We have attributed the magnetism of PrRu2S2 to the Pr ions and performed calculations of the fine electronic structure of the Pr ion in the tetragonal symmetry, relevan

E. Bacry, J. Delour, J. F. Muzy

We introduce a class of multifractal processes, referred to as Multifractal Random Walks (MRWs). To our knowledge, it is the first multifractal processes with continuous dilation invariance properties and stationary increments. MRWs are very attractive alternative processes to classical cascade-like multifractal models since they do not involve any particula

D. Poilblanc, O. Chiappa, J. Riera, S. R. White

The evolution of the spin gap of a 2-leg ladder upon doping depends upon the nature of the lowest triplet excitations in a ladder with two holes. Here we study this evolution using various numerical techniques for a t-t&#39;-J ladder as the next-near-neighbor hopping t&#39; is varied. We find that depending on the value of t&#39;, the spin gap can evolve con

Th. M. Nieuwenhuizen

A picture for thermodynamics of the glassy state is introduced. It assumes that one extra parameter, the effective temperature, is needed to describe the glassy state. This explains the classical paradoxes concerning the Ehrenfest relations and the Prigogine-Defay ratio. As a second part, the approach connects the response of macroscopic observables to a fie

M. Baenitz, C. Geibel, M. Dischner, G. Sparn

CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of CuSiO_3 using susceptibility, magnetization and specific heat measurements on powder samples. The magnetic susceptibility χ(T) is reprodu

J. F. Muzy, J. Delour, E. Bacry

In this paper, we provide a simple, ``generic&#39;&#39; interpretation of multifractal scaling laws and multiplicative cascade process paradigms in terms of volatility correlations. We show that in this context 1/f power spectra, as observed recently by Bonanno et al., naturally emerge. We then propose a simple solvable ``stochastic volatility&#39;&#39; mode

Meghmalhar Manekar, S. B. Roy, P. Chaddah

We present results of ac susceptibility measurements highlighting the presence of thermal hysteresis and phase coexistence across the ferro-to antiferromagnetic transition in various CeFe$_2$ based pseudobinary systems. These results indicate that the ferro-to antiferromagnetic transition in these systems is first order in nature.

Abhishek Dhar, B Sriram Shastry

We present a calculation of the lowest excited states of the Heisenberg ferromagnet in 1-d for any wave vector. These turn out to be string solutions of Bethe&#39;s equations with a macroscopic number of particles in them. These are identified as generalized quantum Bloch wall states, and a simple physical picture provided for the same.

A. Yu. Sivachenko, M. E. Raikh, Z. V. Vardeny

Light propagation in a photonic crystal infiltrated with polarizable molecules is considered. We demonstrate that the interplay between the spatial dispersion caused by Bragg diffraction and polaritonic frequency dispersion gives rise to novel propagating excitations, or braggoritons, with intragap frequencies. We derive the braggoriton dispersion relation a

Yukitoshi Motome, Gabriel Kotliar

We study the nonlinear feedback in a fermion-boson system using an extension of dynamical mean-field theory and the quantum Monte Carlo method. In the perturbative regimes (weak-coupling and atomic limits) the effective interaction among fermions increases as the width of the boson dispersion increases. In the strong coupling regime away from the anti-adiaba

D. Quirion, F. Lefloch, M. Sanquer

We measured the low temperature subgap resistance of titanium nitride (superconductor, Tc=4.6K)/highly doped silicon (degenerated semiconductor) SIN junctions, where I stands for the Schottky barrier. At low energies, the subgap conductance is enhanced due to coherent backscattering of the electrons towards the interface by disorder in the silicon (&#39;&#39

F. M. Rieger, K. Mannheim

We consider the centrifugal acceleration of charged test particles by rotating magnetospheres which are widely believed to be responsible for the relativistic jet phenomenon in active galactic nuclei (AGN). Based on an analysis of forces the equation for the radial accelerated motion is derived and an analytical solution presented under the assumption of an

F. De Paolis, G. Ingrosso, Ph. Jetzer, M. Roncadelli

A recent re-analysis of EGRET data by Dixon et al. has led to the discovery of a statistically significant diffuse $γ$-ray emission from the galactic halo. We show that this emission can naturally be accounted for within a previously-proposed model for baryonic dark matter, according to which dark clusters of brown dwarfs and cold self-gravitating $H_2$ clou

Renee C. Kraan-Korteweg, Ofer Lahav

Due to the foreground extinction of the Milky Way, galaxies appear increasingly fainter the closer they lie to the Galactic Equator, creating a &#34;zone of avoidance&#34; of about 25% in the distribution of optically visible galaxies. A &#34;whole-sky&#34; map of galaxies is essential, however, for understanding the dynamics in our local Universe, in partic

V. G. Kurt, V. N. Komarova, T. A. Fatkhullin, V. V. Sokolov

Fields of Geminga, PSR B0950+08, PSR J1908+0734 and PSR J0108-1431 have been observed within the program of optical investigation of nearby neutron stars carried out with the 6m telescope. Our multicolour BVR_cI_c photometry has yielded the following magnitudes of Geminga: V=25.3+/-0.4; R_c=25.4+/-0.3. The estimates of the 3σupper limits in the B and I_c ban

Jean H. Swank

Observations of Type I X-ray bursts have long been taken as evidence that the sources are neutron stars. Black body models approximate the spectral data and imply a suddenly heated neutron star cooling over characteristic times of seconds to minutes. The phenomena are convincingly explained in terms of nuclear burning of accreted gas on neutron stars with lo

P. F. Bloser, J. E. Grindlay, D. Barret, L. Boirin

We present the results of detailed spectral studies of the ultra-compact low mass X-ray binary (LMXB) 4U 1915-05 carried out with the Rossi X-ray Timing Explorer (RXTE) during 1996. 4U 1915-05 is an X-ray burster (XRB) known to exhibit a ~199-day modulation in its 2--12 keV flux. Observations were performed with the PCA and HEXTE instruments on RXTE at rough

P. F. Bloser, J. E. Grindlay, P. Kaaret, W. Zhang

We present the results of detailed spectral studies of the ultra-compact low mass X-ray binary (LMXB) 4U 1820-30 carried out with the Rossi X-ray Timing Explorer (RXTE) during 1996-7. 4U 1820-30 is an ``atoll&#39;&#39; source X-ray burster (XRB) located in the globular cluster NGC 6624. It is known to have an 11 minute binary period and a ~176 day modulation

Michael R. Corbin, Earl O&#39;Neil, Rodger I. Thompson, Marcia J. Rieke

We present a photometric analysis of all high Galactic lattitude (|b| > 20d) broad-band parallel images taken by the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument during its initial lifetime in HST Cycle 7. These images, taken through the F110W and F160W filters, reach a mean 3-sigma limiting magnitude of approximately 22 in both ban

Pinaki Chatterjee, Lars Hernquist

We consider the accretion model for anomalous X-ray pulsars proposed recently by Chatterjee, Hernquist and Narayan, in which the emission is powered by accretion from a fossil disk formed by the fallback of material from a supernova explosion. We demonstrate that this model is able to account for the spin period, luminosity and age distributions of the obser

R. Mukherjee, E. V. Gotthelf, J. Halpern, M. Tavani

We present a high-energy study of the intriguing COS-B gamma-ray field, 2CG 075+00, in order to search for possible counterparts. New EGRET data show that the COS-B emission probably corresponds to two localized gamma-ray sources, 3EG J2016+3657 and 3EG J2021+3716. Spectral fits to these EGRET sources, assuming a power-law model, yield photon indices of ~ 2

Ana B. Heller, Noah Brosch, Elchanan Almoznino, Liese van Zee

We quantify the amplitude of the lopsidedness, the azimuthal angular asymmetry index, and the concentration of star forming regions, as represented by the distribution of the H$α$ emission, in a sample of 78 late-type irregular galaxies. We bin the observed galaxies in two groups representing blue compact galaxies (BCDs) and low surface brightness dwarf gala

D. J. Fixsen, J. D. Offenberg, R. J. Hanisch, J. C. Mather

We present an algorithm to optimally process uniformly sampled array image data obtained with a nondestructive readout. The algorithm discards full wells, removes cosmic ray (particle) hits and other glitches, and makes a nearly optimum estimate of the signal on each pixel. The algorithm also compresses the data. The computer requirements are modest, and the

Antonaldo Diaferio, Guinevere Kauffmann, Michael L. Balogh, Simon D. M. White

We combine dissipationless N-body simulations and semi-analytic models of galaxy formation to study the spatial and kinematic distributions of cluster galaxies in a LCDM cosmology. We investigate how the star formation rates, colours and morphologies of galaxies vary as a function of distance from the cluster centre and compare our results with the CNOC1 sur

R. P. Olling, D. M. Peterson

Accurate distances to stars and galaxies allow for significant tests of stellar evolution, galaxy formation and evolution and cosmology. NASA&#39;s Space Interferometry Mission (SIM) will obtain precision [1-30 microarcsec] astrometry for 10-20k objects brighter than V=20 mag. In this paper we discuss a method to determine the distance of nearby spiral galax

Diego Harari, Silvia Mollerach, Esteban Roulet

We show that in the model of Galactic magnetic wind recently proposed to explain the extremely high energy (EHE) cosmic rays so far observed as originating from a single source (M87 in the Virgo cluster), the magnetic field strongly magnifies the fluxes and produces multiple images of the source. The apparent position on Earth of the principal image moves, f

P. Kahabka, T. H. Puzia, W. Pietsch

We established the catalog of X-ray point sources in the field of the Magellanic-type spiral galaxy NGC 3109 (DDO 236) from two ROSAT PSPC observations. Of the 91 X-ray sources 26 are contained within the HI extent of NGC 3109 as derived by Jobin & Carignan (1990) with the VLA. For 10 of these we can determine accurate hardness ratios delta HR2<=0.2. We find

Duncan A. Forbes, Juan C. Forte

A large number of early type galaxies are now known to possess blue and red subpopulations of globular clusters. We have compiled a database of 28 such galaxies exhibiting bimodal globular cluster colour distributions. After converting to a common V-I colour system, we investigate correlations between the mean colour of the blue and red subpopulations with g

H. Ritter, U. Kolb, Z. -Y. Zhang

We study the reaction of low-mass stars to anisotropic irradiation and its importance for the long-term evolution of compact binaries binaries. We show by means of a simple homology model that if the energy outflow through the surface layers of a low-mass main sequence star is blocked over a fraction s_eff < 1 of its surface it will inflate only modestly and

F. M. Rieger, J. G. Kirk, A. Mastichiadis

We consider particle acceleration to high energy via diffusive shock acceleration in a simple, self-consistent shock in jet model for blazars. Electrons are assumed to be accelerated at a shock front in relativistic jets and radiate synchrotron emission in a post-shock region. The full time, space and momentum dependence of the electron distribution function

F. J. Lu, B. Aschenbach, L. M. Song

We present in this paper analyses of the $ROSAT$ PSPC and $ASCA$ SIS and GIS observations of the Crab-like supernova remnant (SNR) G54.1+0.3. Its spectrum obtained by $ROSAT$ PSPC favors a power law model with a photon index of -0.8$^{+0.8}_{-2.0}$, absorbed energy flux in 0.1-2.4 keV of 1.0$\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$, and absorption column dens

Eric Gawiser

The claim that large-scale structure data independently prefers the Lambda Cold Dark Matter model is a myth. However, an updated compilation of large-scale structure observations cannot rule out Lambda CDM at 95% confidence. We explore the possibility of improving the model by adding Hot Dark Matter but the fit becomes worse; this allows us to set limits on

Eric Gawiser

Massive neutrinos have a detectable effect on cosmological structure formation, in particular on the large-scale distribution of galaxies. Adding Hot Dark Matter to the now-standard Lambda CDM model leads to a worse fit to large-scale structure and CMB anisotropy data. This results in a limit on the mass of the most massive neutrino of 4 eV, assuming a power

K. Hirotani

We study the structure of an outer-magnetospheric gap around a rotating neutron star. Migratory electrons and positrons are accelerated by the electric field exerted in the gap and radiate copious gamma-rays via curvature process. Some of the gamma-rays materialize by colliding with the X-rays illuminating the gap, leading to a pair production cascade. The r

W. J. G. de Blok, F. Walter

We present a wide-field, high spatial and velocity resolution map of the entire extended HI distribution of the Local Group dwarf galaxy NGC 6822. The observations were obtained with the Australia Telescope Compact Array in mosaicing mode. The interstellar medium of NGC 6822 is shaped by the presence of numerous H{\sc i} holes and shells, including a supergi

ROTSE Collaboration, C. Akerlof, R. Balsano, S. Barthelmy

In order to observe nearly simultaneous emission from Gamma-ray Bursts (GRBs), the Robotic Optical Transient Search Experiment (ROTSE) receives triggers via the GRB Coordinates Network (GCN). Since beginning operations in March, 1998, ROTSE has also taken useful data for 10 SGR events: 8 from SGR 1900+14 and 2 from SGR 1806-20. We have searched for new or va

Jason X. Prochaska, Andrew McWilliam

We investigate the impact of hyperfine splitting on stellar abundance analyses of Mn and Sc, and find that incorrect hfs treatment can lead to spurious abundance trends with metallicity. We estimate corrections to a recent study by Nissen et al. (2000), and find: (1) [Mn/Fe] is described by a bimodal distribution, with [Mn/Fe] ~ -0.3 for stars [Fe/H] < -0.7,

John S. Arabadjis, Joel N. Bregman

We have developed a technique to map the three-dimensional structure of the local interstellar medium using a maximum entropy reconstruction technique. A set of column densities N to stars of known distance can in principle be used to recover a three-dimensional density field n, since the two quantities are related by simple geometry through the equation N =

Roberto Grena, Simone Lelli, Michele Maggiore, Anna Rissone

Type 0B string theory has been proposed as the dual description of non-supersymmetric SU(N) Yang-Mills theory coupled to six scalars, in four dimensions. We study numerically and analytically the equations of motion of type 0B gravity and we find RG trajectories of the dual theory that flow from an asymptotically free UV regime to a confining IR regime. In t

S. Alexander, R. Brandenberger, D. Easson

Over the past decade it has become clear that fundamental strings are not the only fundamental degrees of freedom in string theory. D-branes are also part of the spectrum of fundamental states. In this paper we explore some possible effects of D-branes on early Universe string cosmology, starting with two key assumptions: firstly that the initial state of th

M. B. Hastings

We show that there exists a long-range RVB state for the kagome lattice spin-1/2 Heisenberg antiferromagnet for which the spinons have a massless Dirac spectrum. By considering various perturbations of the RVB state which give mass to the fermions by breaking a symmetry, we are able to describe a wide-ranging class of known states on the kagome lattice, incl

Branislav K. Nikolic, Philip B. Allen

We study the transport properties of a finite three dimensional disordered conductor, for both weak and strong scattering on impurities, employing the real-space Green function technique and related Landauer-type formula. The dirty metal is described by a nearest neighbor tight-binding Hamiltonian with a single s-orbital per site and random on-site potential

Christopher A. Metzler, Martin White, Chris Loken

In modern hierarchical theories of structure formation, rich clusters of galaxies form at the vertices of a weblike distribution of matter, with filaments emanating from them to large distances and with smaller objects forming and draining in along these filaments. The amount of mass contained in structure near the cluster can be comparable to the collapsed

E. V. Bezuglyi, E. N. Bratus&#39;, V. S. Shumeiko, G. Wendin

The incoherent regime of Multiple Andreev Reflections (MAR) is studied in long diffusive SNS junctions at applied voltages larger than the Thouless energy. Incoherent MAR is treated as a transport problem in energy space by means of a circuit theory for an equivalent electrical network. The current through NS interfaces is explained in terms of diffusion flo

Benedetta Ciardi, Andrea Ferrara

We calculate the expected Mid-IR molecular hydrogen line emission from the first objects in the universe. Due to their low masses, the stellar feedback from massive stars is able to blowaway their gas content and collect it into a cooling shell where H_2 rapidly forms and IR roto-vibrational (as for example the restframe 2.12 micron) lines carry away a large

Leonardo Castellani

This review is based on two lectures given at the 2000 TMR school in Torino. We discuss two main themes: i) Moyal-type deformations of gauge theories, as emerging from M-theory and open string theories, and ii) the noncommutative geometry of finite groups, with the explicit example of Z_2, and its application to Kaluza-Klein gauge theories on discrete intern