June 2000 arXiv papers — page 13

K. Nakao, H. Iguchi, T. Harada

Spherical dust collapse generally forms a shell focusing naked singularity at the symmetric center. This naked singularity is massless. Further the Newtonian gravitational potential and speed of the dust fluid elements are everywhere much smaller than unity until the central shell focusing naked singularity formation if an appropriate initial condition is se

Stuart C. Shapiro, Frances L. Johnson

SNePS is a logic- and network- based knowledge representation, reasoning, and acting system, based on a monotonic, paraconsistent, first-order term logic, with compositional intensional semantics. It has an ATMS-style facility for belief contraction, and an acting component, including a well-defined syntax and semantics for primitive and composite acts, as w

S. G. Chung

The spontaneous symmetry breaking in the quantum sine-Gordon model is studied by a density matrix renormalization group. A phase diagram in the coupling constant - system size plane is obtained.

R. J. Radwanski, Z. Ropka

It is pointed out that it is the local symmetry that determines the realization of the low- and high-spin state of the Co3+ ion. We can rigorously prove it treating the Co3+ ion as the highly-correlated electron system 3d6, that fulfiles the Hund's rules with taking into account the spin-orbit coupling. As the function of the sign of the off-cubic crysta

J. B. Staunton, J. Poulter, B. Ginatempo, E. Bruno

We describe our theoretical formalism and computational scheme for making ab-initio calculations of the dynamic paramagnetic spin susceptibilities of metals and alloys at finite temperatures. Its basis is Time-Dependent Density Functional Theory within an electronic multiple scattering, imaginary time Green function formalism. Results receive a natural inter

Jon Machta, Mark Newman, Lincoln Chayes

The random field Ising model with Gaussian disorder is studied using a new Monte Carlo algorithm. The algorithm combines the advantanges of the replica exchange method and the two-replica cluster method and is much more efficient than the Metropolis algorithm for some disorder realizations. Three-dimensional sytems of size $24^3$ are studied. Each realizatio

A. W. C. Lau, Dov Levine, P. Pincus

In this Letter, we show that at low temperatures, zero-point fluctuations of the plasmon modes of two mutually coupled 2-D planar Wigner crystals give rise to a novel long-range attractive force. For the case where the distance $d$ between two planar surfaces is large, this attractive force has an unusual power-law decay, which scales as $d^{-7/2},$ unlike o

Y. Sidis, P. Bourges, B. Keimer, L. P. Regnault

Nonmagnetic Zn impurities are known to strongly suppress superconductivity. We review their effects on the spin excitation spectrum in $\rm YBa_2Cu_3O_{7}$, as investigated by inelastic neutron scattering measurements.

A. W. C. Lau, P. Pincus, Dov Levine, H. A. Fertig

In this paper, we present a unified physical picture for the electrostatic attraction between two coupled planar Wigner crystals at finite (but below their melting) temperature. At very low temperatures, we find a new regime where the attraction, arising from the long-wavelength excitation of the plasmon mode, scales with the interplanar distance $d$ as $d^{

L. Pricoupenko

The occurrence of a molecular Bose-Einstein condensate is studied for an atomic system near a zero energy resonance of the binary scattering process, with a large and positive scattering length. The interaction potential is modeled by a pseudo-potential having one bound state. Using a variational Gaussian ansatz for the $N$-body density operator, we discuss

M. Grousson, G. Tarjus, P. Viot

We present a theoretical study of the phase diagram of a frustrated Ising model with nearest-neighbor ferromagnetic interactions and long-range (Coulombic) antiferromagnetic interactions. For nonzero frustration, long-range ferromagnetic order is forbidden, and the ground-state of the system consists of phases characterized by periodically modulated structur

G. Santoro, S. Scandolo, E. Tosatti

We discuss the spectroscopic fingerprints that a surface Mott-Hubbard insulator should show at the intra-atomic level. The test case considered is that of the Si-terminated SiC(0001) sqrt{3}xsqrt{3} surface, which is known experimentally to be insulating. We argue that, due to the Mott-Hubbard phenomenon, spin unpaired electrons in the Si adatom dangling bon

Johannes Voit

We determine the distribution of size and growthrates of German business firms in 1987-1997. We find a log-normal size distribution. The distribution of growth rates has fat tails. It can be fitted to an exponential in a narrow central region and is dominated by finite-sample-size effects far in its wings. We study the dependence of the growth rate distribut

Paola Giacconi, Roberto Soldati

The problem of a non-relativistic electron in the presence of a uniform electromagnetic field and of one impurity, described by means of an Aharonov-Bohm point-like vortex, is studied. The exact solution is found and the quantum Hall's conductance turns out to be the same as in the impurity-free case. This exactly solvable model seems to give indications

Oleg N. Mryasov, Yu. N. Gornostyrev, A. J. Freeman

New aspects of a relation between lattice and dislocation structures are examined within a physically transparent theoretical scheme. Predicted features originating from the lattice discreteness include: (i) multiple core dislocation structures and (ii) their dependence on the position of the dislocation axis. These effects, which in principle can be observe

Wil van Breugel

At low redshifts powerful radio sources are uniquely associated with massive galaxies, and are thought to be powered by supermassive black holes. Modern 8m -- 10m telescopes may be used used to find their likely progenitors at very high redshifts to study their formation and evolution.

Slavek M. Rucinski, Carla Maceroni

Thirty eight long-period (P>10 days), apparently contact binary stars discovered by the OGLE-II project in the SMC appear to be Beta Lyrae-type systems with ellipsoidal variations of the cool components dominating over eclipse effects in the systemic light variations and in the total luminosity. A new period-luminosity- color (PLC) relation has been establis

R. G. Ohl, P. Chayer, H. W. Moos

We present an abundance analysis of the far-ultraviolet (905--1187 A) spectrum of the subdwarf B star PG0749+658, obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE). The data have a resolution of about R = lambda / Delta lambda = 12000--15000 (20--25 km/s). We determine C, N, Si, P, S, Cr, Mn, Fe, Co, and Ni abundances, and upper limits on the abu

P. Severgnini, R. Maiolino, M. Salvati, D. Axon

Obscured AGNs are thought to contribute a large fraction of the hard X-ray background (2-10 keV), and have also been proposed as the powerhouse of a fraction of the SCUBA sources which make most of the background at 850um, thus providing a link between the two spectral windows. We have tackled this issue by comparing data at 2-10 keV and at 850um for a sampl

Fred C. Adams

We construct a family of semi-analytic models for young open clusters, including a gaseous component and varying assumptions about the distribution function for the stellar component. The parameters of these models are informed by observed open clusters and general theoretical considerations regarding cluster formation. We use this framework to estimate the

David A. Golimowski, Todd J. Henry, John E. Krist, Daniel J. Schroeder

Multiple-epoch, multicolor images of the astrometric binary Gliese 105A and its very low mass companion Gliese 105C have been obtained using the Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). The optical and near-infrared colors of Gl 105C strongly suggest a spectral type of

G. Bono, M. Marconi, R. F. Stellingwerf

We present the results of an extensive theoretical investigation on the pulsation behavior of Bump Cepheids. We constructed several sequences of full amplitude, nonlinear, convective models by adopting a chemical composition typical of Large Magellanic Cloud (LMC) Cepheids (Y=0.25, Z=0.008) and stellar masses ranging from 6.55 to 7.45 solar masses. We find t

F. Caputo, M. Marconi, I. Musella, P. Santolamazza

We use theoretical Period-Luminosity and Period-Luminosity-Color relations in the VI passbands, as based on nonlinear, nonlocal and time-dependent convective pulsating models, to predict the reddening and true distance modulus of distant Cepheids observed with the Hubble Space Telescope. By relying on the pulsating models with metal content Z=0.008, we find

N. Y. Yamasaki, T. Ishikawa, T. Ohashi

X-ray observation of a famous Lyman-limit quasar PKS2145+067at z_em= 0.990 was carried with ASCA. The source showed a 2-10 keV flux of 1.3 E-11 erg cm^-2 sec^-1 (L_X = 2.5 E46 erg sec^-1 for H_0=50 km s^-1 Mpc^-1) described by a power-law spectrum with a photon index Gamma=1.63 +/- 0.04 . In the ASCA energy band, no excess absorption was detected implying th

Guo-Chin Liu, Kazuhiro Yamamoto, Naoshi Sugiyama, Hiroaki Nishioka

The evolution of baryon density perturbations on very small scales is investigated. In particular, the nonlinear growth induced by the radiation drag force from the shear velocity field on larger scales during the recombination epoch, which is originally proposed by Shaviv in 1998, is studied in detail. It is found that inclusion of the diffusion term which

Jean-Pierre Lasota

I argue that it is very unlikely that X-rays from quiescent black-hole low-mass X-ray binary transients are emitted by coronae of companion stars. I show that in a simple model in which these X-rays are emitted by an ADAF filling the inner part of an unsteady, dwarf-nova type disc, the X-ray luminosity is correlated with the orbital period. I predict what va

A. Różańska, B. Czerny

We investigate the model of the disc/corona accretion flow around the black hole. The model, parameterized by the total (i.e. disk plus corona) accretion rate, $\dot m$, mass of the black hole, $M$ and the viscosity parameter, $α$, uniquely determines the fraction of energy released in the corona as a function of radius and, in particular, the transition rad

Yusuf A. Kinkhabwala, Alexander N. Korotkov

The average current and the shot noise at correlated sequential tunneling via two localized sites are studied. At zero temperature the Fano factor averaged over the positions and energies of sites is shown to be 0.707. The noise dependence on temperature and frequency is analyzed numerically.

T. Plehn

We analyze the production of a single top squark at hadron colliders: ppbar/pp -> \tilde{t}_1 + X. The total cross sections and the transverse momentum distributions are presented in next-to-leading order QCD. The higher-order corrections render the predictions theoretically stable with respect to variations of the factorization and renormalization scales. T

C. M. Maekawa, J. S. Veiga, U. van Kolck

The anapole form factor of the nucleon is calculated in chiral perturbation theory to sub-leading order. This is the lowest order in which the isovector anapole form factor does not vanish. The anapole moment depends on counterterms that reflect short-range dynamics, but the momentum dependence or the form factor is determined by pion loops in terms of param

Ariel Megevand

We investigate the evolution of the electroweak phase transition, using a one-Higgs effective potential that can be regarded as an approximation for the Minimal Supersymmetric Standard Model. The phase transition occurs in a small interval around a temperature T_t below the critical one. We calculate this temperature as a function of the parameters of the po

Guang-Hong Chen, Yong-Shi Wu

In this paper we study the one-loop shift in the coupling constant in a noncommutative pure U(N) Chern-Simons gauge theory in three dimensions. The one-loop shift is shown to be a constant proportional to $N$, independent of noncommutativity parameters, and non-vanishing for U(1) theory. Possible physical and mathematical implications of this result are disc

Romualdo Pastor-Satorras, Alessandro Vespignani

We investigate the critical behavior of a reaction-diffusion system exhibiting a continuous absorbing-state phase transition. The reaction-diffusion system strictly conserves the total density of particles, represented as a non-diffusive conserved field, and allows an infinite number of absorbing configurations. Numerical results show that it belongs to a wi

Jose D. Edelstein, Marta Gomez-Reino, Marcos Marino

We investigate blowup formulae in Donaldson-Witten theory with gauge group SU(N), using the theory of hyperelliptic Kleinian functions. We find that the blowup function is a hyperelliptic sigma-function and we describe an explicit procedure to expand it in terms of the Casimirs of the gauge group up to arbitrary order. As a corollary, we obtain a new express

E. Bergshoeff, D. S. Berman, J. P. van der Schaar, P. Sundell

The M5-brane is investigated near critical field-strength. We show that this limit on the M5-brane reduces to the noncommutative open string limit on the D4-brane. The reduction on a two-torus leads to both the noncommutative open string limit and the noncommutative Yang-Mills limit on the D3-brane. The decoupled noncommutative five-brane is identified with

Uri Hershberg, Yoram Louzoun, Henri Atlan, Sorin Solomon

AIDS is the pandemic of our era. A disease that scares us not only because it is fatal but also because its insidious time course makes us all potential carriers long before it hands us our heads in a basket. The strange three stage dynamics of aids is also one of the major puzzles in describing the disease theoretically (1). Aids starts, like most diseases,

P. H. Damgaard, S. M. Nishigaki

Based on the exact relationship to Random Matrix Theory, we derive the probability distribution of the k-th smallest Dirac operator eigenvalue in the microscopic finite-volume scaling regime of QCD and related gauge theories.

T. A. Rector, J. T. Stocke, E. S. Perlman, S. L. Morris

We present updated and complete radio, optical and X-ray data for BL Lacs in the Einstein Medium Sensitivity Survey (EMSS). The complete "M91" sample first presented in Morris et al. is updated to include 26 BL Lacs in total and we define a new, virtually complete sample consisting of 41 EMSS BL Lacs (the "D40" sample). New high signal-to-noi

G. Ecker, G. Isidori, G. Mueller, H. Neufeld

We construct a low-energy effective field theory that permits the complete treatment of isospin-breaking effects in nonleptonic weak interactions to next-to-leading order. To this end, we enlarge the chiral Lagrangian describing strong and Delta S=1 weak interactions by including electromagnetic terms with the photon as additional dynamical degree of freedom

W. Melnitchouk

The internal structure of the nucleon is discussed within the context of QCD. Recent progress in understanding the distribution of flavor and spin in the nucleon is reviewed, and prospects for extending our knowledge of nucleon structure in electron scattering experiments at modern facilities such as Jefferson Lab are outlined.

Paola Goatin, Philippe G. LeFloch

In this paper, we introduce a generalization of Liu-Yang's weighted norm to linear and to nonlinear hyperbolic equations. Extending a result by Hu and LeFloch for piecewise constant solutions, we establish sharp L1 continuous dependence estimates for general solutions of bounded variation. Two different strategies are successfully investigated. On one ha

R. D'Auria, S. Ferrara, S. Vaulà

F(4) supergravity, the gauge theory of the exceptional six-dimensional Anti-de Sitter superalgebra, is coupled to an arbitrary number of vector multiplets whose scalar components parametrize the quaternionic manifold $SO(4,n)/SO(4)\times SO(n)$. By gauging the compact subgroup $SU(2)_d \otimes \cG$, where SU(2)_d is the diagonal subgroup of $SO(4)\simeq SU(2

W. Kummer, D. V. Vassilevich

Rederiving the one-loop divergences for the most general coupling of the open string sigma model by the heat kernel technique, we distinguish the classical background field from the mean field of the effective action. The latter is arbitrary, i.e. does not fulfil the boundary conditions. As a consequence a new divergent counter term strongly suggests the int

Wilfried Buchmuller, Laura Covi, David Delepine

We study the connection between inflation and supersymmetry breaking in the context of an O'Raifeartaigh model which can account for both hybrid inflation and a true vacuum where supersymmetry is spontaneously broken. For a weakly coupled inflaton field, the dynamics during the inflationary phase can be determined by the supersymmetry breaking scale $M_S

Peter Braun, Sven Gnutzmann, Fritz Haake, Marek Kus

The spectral fluctuations of quantum (or wave) systems with a chaotic classical (or ray) limit are mostly universal and faithful to random-matrix theory. Taking up ideas of Pechukas and Yukawa we show that equilibrium statistical mechanics for the fictitious gas of particles associated with the parametric motion of levels yields spectral fluctuations of the

Y. Aghababaie, C. P. Burgess

We extend earlier constructions of the effective action for neutrino-photon scattering, using the connection between low-energy neutrino-photon and photon-photon scattering together with the known effective Lagrangian describing low-energy photon scattering in QED. We use this effective action to calculate analytic expressions for the low-energy cross sectio

Tomonari Dotera, Yasuo Y. Suzuki

We consider quantum particle or Gaussian polymer confinement between two surfaces and in cylinders with sinusoidal undulations. In terms of the variational method, we show that the quantum mechanical wave equations have lower ground state energy in these geometries under long wavelength undulations, where bulges are formed and waves are localized in the bulg

Chia-Hung V. Chang, J. N. Ng

We embed the Standard Model in the Randall-Sundrum model of 5 dimensional brane localized gravity. The SM gauge and chiral fermion fields are restricted on the 4D visible brane whereas the Higgs and the right-handed neutrino are assumed to be 5D bulk fields. We calculate the effective couplings of the lowest mass Higgs field to the SM fermions and to the gau

Ralf Hofmann

Characterizing the vacuum of a thermalized SU(3) Yang-Mills theory in the dual Ginzburg-Landau description, the possibility of topologically nontrivial, classical monopole fields in the deconfining phase is explored. These fields are assumed to be Bogomoln'yi-Prasad-Sommerfield (BPS) saturated solutions along the compact, euclidean time dimension. A corr

Ying Chen, Bing He, Ji-Min Wu

It is shown that the application of the non-Abelian Stokes theorem to the computation of the operators constructed with Wilson loop will lead to ambiguity, if the gauge field under consideration is a non-trivial one. This point is illustrated by the specific examples of the computation of a non-local operator.

C. Contreras, J. C. Retamal, L. Vergara

We show how a method inspired in renormalization group techniques can be useful for deriving Hamiltonians in the adiabatic approximation in a systematic way.

D. L. Shepelyansky

The standard generic quantum computer model is studied analytically and numerically and the border for emergence of quantum chaos, induced by imperfections and residual inter-qubit couplings, is determined. This phenomenon appears in an isolated quantum computer without any external decoherence. The onset of quantum chaos leads to quantum computer hardware m

Adrian Alscher, Hermann Grabert

The semiclassical approximation of coherent state path integrals is employed to study the dynamics of the Jaynes-Cummings model. Decomposing the Hilbert space into subspaces of given excitation quanta above the ground state, the semiclassical propagator is shown to describe the exact quantum dynamics of the model. We also present a semiclassical approximatio

Michal Horodecki, Pawel Horodecki, Ryszard Horodecki

We provide necessary and sufficient conditions for separability of mixed states of n-particle systems. The conditions are formulated in terms of maps which are positive on product states of $n-1$ particles. The method of providing of the maps on the basis of unextendable product bases is provided. The three qubit state problem is reformulated in the form sug

G. Quznetsov

A gauge fields (and massive, too) arise from the production of the probability by the spinors.

R. Bijker, A. Frank

The anharmonic vibrator and rotor regions in nuclei are investigated in the framework of the interacting boson model using an ensemble of random one- and two-body interactions. Despite the randomness of the interactions (in sign and size) we find a predominance of L(P)=0(+) ground states and strong evidence for the occurrence of both vibrational and rotation

L. Canton, G. Pisent, W. Schadow, J. P. Svenne

We have calculated the proton analyzing power A_{y0} of the pion-production reaction from pd collisions for one energy close to threshold and for another in the region of the $Δ$-resonance. A fair reproduction of the experimental data could be obtained in both cases with a model which includes isoscalar and isovector $πN$ rescatterings in s waves, as well as

Peter Constantin, Alexander Kiselev, Leonid Ryzhik

We consider a simple scalar reaction-advection-diffusion equation with ignition-type nonlinearity and discuss the following question: What kinds of velocity profiles are capable of quenching any given flame, provided the velocity's amplitude is adequately large? Even for shear flows, the answer turns out to be surprisingly subtle. If the velocity profile

Boris Chirikov

Direct computation of the transition time between neighbor resonances in the standard map, as a function of the perturbation parameter $K$, allows for improving the accuracy of the critical perturbation value up to $K_{cr}-K_g < 2.5\times 10^{-4}$ that is by a factor of about 50 as compared to the previous result due to MacKay and Percival.

B. V. Chirikov, V. G. Davidovsky

The results of numerical experiments on the structure of chaotic attractors in the Khalatnikov - Kroyter model of two freedoms are presented. This model was developed for a qualitative description of the wave turbulence of the second sound in helium. The attractor dimension, size, and the maximal Lyapunov exponent in dependence on the single dimensionless pa

P. Zinn-Justin, J. -B. Zuber

The connection between matrix integrals and links is used to define matrix models which count alternating tangles in which each closed loop is weighted with a factor n, i.e. may be regarded as decorated with n possible colors. For n=2, the corresponding matrix integral is that recently solved in the study of the random lattice six-vertex model. The generatin

John B. Etnyre, Ko Honda

We classify Legendrian torus knots and figure eight knots in the tight contact structure on the 3-sphere up to Legendrian isotopy. As a corollary to this we also obtain the classification of transversal torus knots and figure eight knots up to transversal isotopy.

D. A. Shmel&#39;kin

Let $U(G)$ be a maximal unipotent subgroup of one of classical groups $G=GL(V),O(V),Sp(V)$. Let $W$ be a direct sum of copies of $V$ and its dual $V*$. For the natural action $U(G):W$, we describe a minimal system of homogeneous generators for the algebra of $U(G)$-invariant regular functions on $W$. For $G=GL(V)$, we also describe the syzygies among these g

Michael Farber

This paper continues math.DG/9903140. Here we construct a linking form on the torsion part of middle dimensional extended L^2 homology and cohomology of odd-dimensional manifolds. We give a geometric necessary condition when this linking form is hyperbolic. We compute this linking form in case when the manifold bounds. We introduce and study new numerical in

P. Maraner

The fermionic sector of the Standard Model of Elementary Particles emerges as the low energy limit of a single fermionic field freely propagating in a higher dimensional background. The local geometrical framework is obtained by enforcing at a space-time level the whole gauge group SO(1,3) x U(1) x SU(2) x SU(3) associated to fundamental interactions; equiva

C. P. Sun X. F. Liu, S. X. Yu

Most recently &#39;t Hooft has postulated (G &#39;t Hooft, Class. Quant. Grav. 16 (1999) 3263-3279) that quantum states at the ``atomic scale&#39;&#39;can be understood as equivalence classes of primordial states governed by a dissipative deterministic theory underlying quantum theory at the ``Planck scale&#39;&#39;. Defining invariant subspaces clearly for

James D. Bjorken

After a very brief review of twentieth century elementary particle physics, prospects for the next century are discussed. First and most important are technological limits of opportunities; next, the future experimental program, and finally the status of the theory, in particular its limitations as well as its opportunities.

D. V. Bugg, M. Peardon, B. S. Zou

Mass ratios of glueballs predicted by the latest Lattice QCD calculations in the quenched approximation agree well with four prime experimental candidates.

G. Valencia

I discuss CP violation in $Λ$ to p $π^-$ comparing the standard model expectations with what could happen in new physics scenarios. I point out that Fermilab experiment E871 is sensitive to some of these scenarios.

P. Nadolsky, D. R. Stump, C. -P. Yuan

We discuss resummation of large logarithmic terms that appear in the cross-section of semi-inclusive DIS in the case when the final-state hadron follows the direction of the incoming electroweak vector boson in the c.m. frame of the vector boson and the initial-state proton.

A. Ali, L. T. Handoko, D. London

We argue that one can search for physics beyond the standard model through measurements of the isospin-violating quantity $Δ^{-0} \equiv Γ(B^- \to ρ^- γ)/2Γ(B^0 \to ρ^0 γ)-1$, its charge conjugate $Δ^{+0}$, and direct CP violation in the partial decay rates of $B^\pm \to ρ^\pm γ$. We illustrate this by working out theoretical profiles of the charge-conjugate

Nir Polonsky, Shufang Su

Given its non-renormalization properties, low-energy supersymmetry provides an attractive framework for extending the Standard Model and for resolving the hierarchy problem. Models with softly broken N =1 supersymmetry were extensively studied and are phenomenologically successful. However, it could be that an extended N = 2 supersymmetry survives to low ene

Thomas Hambye, Ernest Ma, Utpal Sarkar

In supersymmetric models with lepton-number violation, hence also R-parity violation, it is easy to have realistic neutrino masses, but then leptogenesis becomes difficult to achieve. After explaining the general problems involved, we study the details of a model which escapes these constraints and generates a lepton asymmetry, which gets converted into the

Gautam Dutta, D. Indumathi, M. V. N. Murthy, G. Rajasekaran

We study the effect of non-vanishing masses and mixings among neutrino flavours on the detection of neutrinos from stellar collapse by a water Cerenkov detector. We consider a frame-work in which there are four neutrino flavours, including a sterile neutrino, whose mass squared differences and mixings are constrained by the present understanding of solar, at

A. Bonanno, D. Zappala&#39;

The Wegner-Houghton formulation of the exact renormalization group evolution equation is used in order to study the chiral symmetry breaking of the linear sigma model coupled to an isospin doublet of quarks. A numerical investigation for a particular truncation of the equation which includes the scalar field renormalization function is presented.

L. Favart

A new, very forward proton spectrometer (VFPS) with large acceptance is proposed to be installed in the proton beam of the H1 experiment after the luminosity upgrade in the year 2000. The spectrometer, located at 220 m downstream of the interaction point is based on the Roman Pot technique and consists of two stations situated in the cold section of the prot

Leif Lonnblad, Hannes Jung

We discuss three implementations of the CCFM evolution equations in event generator programs. We find that some of them are able to describe observables such as forward jet rates in DIS at HERA, but only if the so-called consistency constraint is removed. We also find that these results are sensitive to the treatment of non-singular terms in the gluon splitt

B. O. Kerbikov

Strangeness photoproduction of the deuteron is investigated theoretically making use of the covariant reaction formalism and the P-matrix approach the final state hyperon-nucleon interaction. Remarkably simple analytical expression for the amplitude is obtained. Pronounced effects due to final state interaction are predicted.

Martin Lüscher

In the framework of perturbation theory, it is possible to put chiral gauge theories on the lattice without violating the gauge symmetry or other fundamental principles, provided the fermion representation of the gauge group is anomaly-free. The basic elements of this construction (which starts from the Ginsparg-Wilson relation) are briefly recalled and the

O. Biebel

The effects of the hadronisation of partons on the distribution of event shape observables are associated with corrections which are suppressed by reciprocal powers of the energy scale of the process. The correction is determined by one non-calculable parameter α_0 for which an universal value of 0.5 +/- 20% is found from the investigation of the distributio

F. S. Guzman, T. Matos

In this manuscript the authors present a detailed answer to the comment in order to avoid misunderstandings in the future.

Tomas Dolezel, Jiri Bicak, Nathalie Deruelle

We consider a spacetime consisting of an empty void separated from an almost Friedmann-Lema\^ıtre-Robertson-Walker (FLRW) dust universe by a spherically symmetric, slowly rotating shell which is comoving with the cosmic dust. We treat in a unified manner all types of the FLRW universes. The metric is expressed in terms of a constant characterizing the angula

Ralph Werner, M. Hücker, B. Büchner

The Sr concentration dependence of the structural transition from the orthorhombic into the tetragonal low-temperature phase in rare-earth-doped (R = Nd, Eu) La_{2-x-y}Sr_xR_yCuO_4 has been studied in detail. Independently of the rare earth concentration the transition temperature is strongly reduced at x ~ 0.05. We give a qualitative argument that the effec

M. I. Katsnelson, M. Sigalas, A. V. Trefilov, K. Yu. Khromov

The simplest anharmonic characteristics of Ir and Rh are discussed in the framework of a previously developed simple pseudopotential model which describes the elastic moduli, phonon spectra and the lattice heat capacity in the harmonic approximation of these metals succesfully. The microscopic Gruneisen parameters, the dependences of the elastic moduli on pr

M. Nicolas, P. Duru, O. Pouliquen

In this paper we present experimental results concerning the compaction of a granular assembly of spheres under periodic shear deformation. The dynamic of the system is slow and continuous when the amplitude of the shear is constant, but exhibits rapid evolution of the volume fraction when a sudden change in shear amplitude is imposed. This rapid response is

K. Y. Michael Wong, S. Li, Peixun Luo

Using the cavity method and diagrammatic methods, we model the dynamics of batch learning of restricted sets of examples. Simulations of the Green&#39;s function and the cavity activation distributions support the theory well. The learning dynamics approaches a steady state in agreement with the static version of the cavity method. The picture of the rough e

Yvan Castin, Ralph Dum, Emmanuel Mandonnet, Anna Minguzzi

We investigate the coherence properties of an atomic beam evaporatively cooled in a magnetic guide, assuming thermal equilibrium in the quantum degenerate regime. The gas experiences two-dimensional, transverse Bose-Einstein condensation rather than a full three-dimensional condensation because of the very elongated geometry of the magnetic guide. First orde

Vladislav Popkov, Mario Salerno

We show the existence of quantum states of the Heisenberg XY chain which closely follow the motion of the corresponding semi-classical ones, and whose evolution resemble the propagation of a shock wave in a fluid. These states are exact solutions of the Schroedinger equation of the XY model and their classical counterpart are simply domain walls or soliton-l

Wolfgang Thimm, Christian Friedrich, Tobias Roths, Josef Honerkamp

In this paper, a model is proposed for the kernel in the generalized mixing rule recently formulated by Anderssen and Mead (1998). In order to derive such a model, it is necessary to take account of the rheological significance of the kernel in terms of the relaxation behaviour of the individual polymers involved. This leads naturally to consider a way how a

Paolo Carra, Robert Benoist

This paper discusses a theory of natural circular dichroism in the x-ray region. Integrated spectra are interpreted in terms of microscopic effective operators, which are derived in the framework of a localised (atomic) model. It is shown that the generators of a de Sitter group, such as that introduced by Goshen and Lipkin for nuclear structure, are suitabl

Bosiljka Tadic, Vyatcheslav Priezzhev

We simulate queues of activity in a directed sandpile automaton in 1+1 dimensions by adding grains at the top row with driving rate $0 < r \leq 1$. The duration of elementary avalanches is exactly described by the distribution $P_1(t) \sim t^{-3/2}\exp{(-1/L_c)}$, limited either by the system size or by dissipation at defects $L_c= \min (L,ξ)$. Recognizing t

Gerardo Aquino, Paolo Grigolini, Nicola Scafetta

In the case of fully chaotic systems the distribution of the Poincare&#39;recurrence times is an exponential whose decay rate is the Kolmogorov-Sinai(KS) entropy.We address the discussion of the same problem, the connection between dynamics and thermodynamics,in the case of sporadic randomness,using the Manneville map as a prototype of this class of processe

Debasis Dan, Mangal C. Mahato, A. M. Jayannavar

We present a detailed study of the transport and energetics of a Brownian particle moving in a periodic potential in the presence of an adiabatic external periodic drive. The particle is considered to move in a medium with periodic space dependent friction with the same periodicity as that of the potential but with a phase lag. We obtain several results, mos

Elihu Boldt, Michael Loewenstein

The quasar remnant cores of nearby giant elliptical galaxies NGC 4486 (M87), NGC 1399, NGC 4649 and NGC 4472 are the sites of supermassive (greater than one billion solar masses) black holes. These objects are investigated as to the viability of the conjecture that they could harbor compact dynamos capable of generating the highest energy cosmic rays. For an

D. C. Backer, T. Wong, J. Valanju

In 1997 October daily monitoring observations of the Crab pulsar at 327 MHz and 610 MHz with an 85ft telescope in Green Bank, WV showed a jump in the dispersion measure by 0.1 cm$^{-3}$ pc. Pulses were seen simultaneously at both old and new dispersions over the course of several days. During the dispersion jump the pulsed flux diminished by an order of magn

Karl E. Haisch, Elizabeth A. Lada, Charles J. Lada

We present the results of the first sensitive L band (3.4 micron) imaging study of the nearby young embedded cluster NGC 2024. Two separate surveys of the cluster were acquired in order to obtain a census of the circumstellar disk fraction in the cluster. From an analysis of the JHKL colors of all sources in our largest area, we find an infrared excess fract

Romeel Davé, David N. Spergel, Paul J. Steinhardt, Benjamin D. Wandelt

We present a comparison of halo properties in cosmological simulations of collisionless cold dark matter (CDM) and self-interacting dark matter (SIDM) for a range of dark matter cross sections. We find, in agreement with various authors, that CDM yields cuspy halos that are too centrally concentrated as compared to observations. Conversely, SIDM simulations

Andrew E. Dolphin

HSTphot, a photometry package designed to handle the undersampled PSFs found in WFPC2 images, is introduced and described, as well as some of the considerations that have to be made in order to obtain accurate PSF-fitting stellar photometry with WFPC2 data. Tests of HSTphot&#39;s internal reliability are made using multiple observations of the same field, an

Gijs Nelemans, Frank Verbunt, Lev R. Yungelson, Simon F. Portegies Zwart

The unique core-mass - radius relation for giants with degenerate helium cores enables us to reconstruct the evolution of three observed double helium white dwarfs with known masses of both components. The last mass transfer phase in their evolution must have been a spiral-in. In the formalism proposed by Webbink (1984), we can constrain the efficiency of th

Glen R. Petitpas, Christine D. Wilson

This paper presents 12CO J=3-2, 13CO J=3-2, C18O J=3-2, and 13CO J=2-1 spectra of the irregular starburst galaxy M82 taken with the 15 m James Clerk Maxwell Telescope. All maps exhibit a double peaked morphology, despite evidence that the higher J transitions are optically thick. This morphology suggests that the double peaked structure is not the result of