February 1998 arXiv papers — page 4

Rosario N. Mantegna

I find a topological arrangement of stocks traded in a financial market which has associated a meaningful economic taxonomy. The topological space is a graph connecting the stocks of the portfolio analyzed. The graph is obtained starting from the matrix of correlation coefficient computed between all pairs of stocks of the portfolio by considering the synchr

M. R. Evans, Y. Kafri, H. M. Koduvely, D. Mukamel

A driven system of three species of particle diffusing on a ring is studied in detail. The dynamics is local and conserves the three densities. A simple argument suggesting that the model should phase separate and break the translational symmetry is given. We show that for the special case where the three densities are equal the model obeys detailed balance

X. G. Qiu, V. V. Moshchalkov, Y. Bruynseraede, G. Jakob

Two-dimensional(2D) vortex dynamics was studied in an YBa_2Cu_3O_7/ PrBa_2Cu_3O_7 superlattice by measuring the I-V characteristics. In the high current limit, 2D collective creep was observed with an activation energy characterized by U(j)=a j^u. A dislocation mediated vortex melting happened when the temperature increased. In the low current limit, the exp

X. G. Qiu, V. V. Moshchalkov, Y. Bruynseraede, J. Karpinski

A sharp resistance drop associated with vortex lattice melting was observed in high quality YBa_2Cu_4O_8 single crystals. The melting line is well described well by the anisotropic GL theory. Two thermally activated flux flow regions, which were separated by a crossover line B_cr=1406.5(1-T/T_c)/T (T_c=79.0 K, B_cr in T), were observed in the vortex liquid p

Zhigang Zheng, Bambi Hu, Gang Hu

Kink dynamics of the damped Frenkel-Kontorova (discrete sine-Gordon) chain driven by a constant external force are investigated. Resonant steplike transitions of the average velocity occur due to the competitions between the moving kinks and their radiated phasonlike modes. A mean-field consideration is introduced to give a precise prediction of the resonant

Bumsoo Kyung

We present strong numerical evidence for the band Kondo effect in the doped 2D Hubbard model by showing the systematic change of the density of states, imaginary part of the self-energy, effective magnetic moment and quasiparticle residue upon decreasing the temperature. Quadratically vanishing (in frequency) scattering rates near the Fermi energy and a line

D. Gordon, C. M. Savage

We numerically calculate the density profile and excitation spectrum of a two-species Bose-Einstein condensate for the parameters of recent experiments. We find that the ground state density profile of this system becomes unstable in certain parameter regimes, which leads to a phase transition to a new stable state. This state displays spontaneously broken c

R. Benzi, L. Biferale, S. Succi, F. Toschi

The dependence of intermittent inertial properties on ultraviolet eddy viscosity closures is examined within the framework of shell-models of turbulent flows. Inertial intermittent exponents turn out to be fairly independent on the way energy is dissipated at small scales.

R. E. Prange, R. Narevich, Oleg Zaitsev

Perturbation theory, the quasiclassical approximation and the quantum surface of section method are combined for the first time. This solves the long standing problem of quantizing the resonances and chaotic regions generically appearing in classical perturbation theory. The result is achieved by expanding the `phase' of the wavefunction in powers of the

G. Steigman, N. Hata, J. E. Felten

Since the baryon-to-photon ratio "eta" is in some doubt at present, we ignore the constraints on eta from big bang nucleosynthesis (BBN) and fit the three key cosmological parameters (h, Omega_M, eta) to four other observational constraints: Hubble parameter, age of the universe, cluster gas (baryon) fraction, and effective shape parameter "Gamma

K. Otterbein, T. P. Krichbaum, A. Kraus, A. P. Lobanov

Broad-band (gamma to radio) variations of the flux density were observed in the first half of 1992 in the luminous high redshift (z = 2.172) quasar S5 0836+710. VLBI monitoring observations during 1993 -- 1996 performed at 86 GHz, 22 GHz, 15 GHz, and 8 GHz show the ejection of a new jet component, which most probably is directly related to a quasi simultaneo

Sylvie Vauclair, Corinne Charbonnel

Observational constraints on the primordial lithium abundance are important for the evaluation of the baryonic density of the universe. Its precise determination however suffers from uncertainties due to the possible depletion of this element inside the stars. Here we present and discuss new results on the lithium abundances in pop II stars obtained with mos

F. Bertola, E. M. Corsini

The phenomenon of counterrotation is observed when two galaxy components have their angular momenta projected antiparallel onto the sky. It follows that if the two components rotate around the same axis, the counterrotation is intrinsic. On the contrary the counterrotation is only apparent if the rotation axes are misaligned and the line-of-sight lies in bet

D. Raboud

The study of the very young open cluster NGC 6231 clearly shows the presence of a mass segregation for the most massive stars. These observations, combined with those concerning other young objects and very recent numerical simulations, strongly support the hypothesis of an initial origin for the mass segregation of the most massive stars. These results led

S. Reddy, J. Pons, M. Prakash, J. M. Lattimer

The early evolution of a protoneutron star depends both on the equation of state and neutrino interactions at high density. We identify the important sources of neutrino opacity and through model calculations show that in-medium effects play an important role in determining the neutrino mean free paths. The effects due to Pauli-blocking and many-body correla

M. L. Weil, V. R. Eke, G. Efstathiou

We investigate the influence of the cooling epoch on the formation of galaxies in a cold dark matter dominated universe. Isolated haloes, with circular speeds typical of spiral galaxies, have been selected from a low resolution numerical simulation for re-simulation at higher resolution with dark matter and gas components. The initial conditions are evolved

S. Reddy, J. Pons, M. Prakash, J. M. Lattimer

We study the diffusive transport of neutrinos in a newly born neutron star to explore its sensitivity to dense matter properties. Energy and lepton number which are trapped during the catastrophic implosion diffuse out on the time scale of a few tens of seconds. Results for different dense matter models are presented.

J. C. Vega Beltran, W. W. Zeilinger, P. Amico, M. Schultheis

Rotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components along five different position angles (P.A.=5, 50, 95, 125 and 155 degrees) of the nearby barred spiral NGC 6221. The observed kinematics extends out to about 80" from the nucleus. Narrow and broad-band imaging is also presented. The radial profiles

B. Funk, N. Magnussen, H. Meyer, W. Rhode

The energy spectrum of Mkn501 in the TeV energy regime, as measured by the HEGRA (High Energy Gamma Ray Astronomy) Cerenkov telescopes during its low state in 1995/96 and during a fraction of the 1997 outburst in the TeV energy regime, is shown to place stringent upper limits on the still unknown infrared photon density in the energy region between 3 x 10**(

K. Z. Stanek

Recently Schlegel, Finkbeiner & Davis published an all-sky reddening map based on the COBE/DIRBE and IRAS/ISSA infrared sky surveys. Using the reddening map of Baade&#39;s Window and sample of 19 low-latitude ($|b|<5°$) Galactic globular clusters I find that the DIRBE/IRAS reddening map overestimates $E(B-V)$ at low galactic latitudes by a factor of $\sim 1.

Ian Bonnell, Pavel Kroupa

This chapter reviews the dynamical processes in young stellar clusters. The accretion of gas by individual stars affects the dynamics of the cluster, and the masses of the stars. Dynamical mass segregation cannot explain the degree of mass segregation observed in clusters such as the Trapezium Cluster in Orion, implying that the location of the massive stars

J. W. Sulentic, P. Marziani, M. Calvani

Recent observations have shown that the Fe Kalpha line profile of the Seyfert~1 galaxy MCG-06-30-15 is strongly variable. We attempt accretion disk model fits to the Fa Kalpha line profiles in a high, low and medium continuum luminosity phase of this source. During the monitoring by Iwasawa et al. (1996) a broad red-shifted component remained reasonably cons

J. J. M. in &#39;t Zand, J. Heise, J. M. Muller, A. Bazzano

We report the discovery with BeppoSAX-WFC of two new X-ray sources that were only seen during bursts: SAX J1753.5-2349 and SAX J1806.5-2215. For both sources, no steady emission was detected above an upper limit of 5 mCrab (2 to 8 keV) for 3 10**5 s around the burst events. The single burst detected from SAX J1753.5-2349 shows spectral softening and a black

S. Kubis, M. Kutschera, S. Stachniewicz

We study the equation of state of beta-stable dense matter and models of neutron stars in the relativistic mean field theory with the isovector scalar mean field corresponding to the delta-meson [a_0(980)]. A range of values of the delta-meson coupling compatible with the Bonn potentials is explored. Parameters of the model in the isovector sector are constr

R. Valdarnini, S. Ghizzardi, S. Bonometto

We compare the evolution of morphology in X-ray cluster data and in clusters obtained in a simulation of flat CDM, normalized to the observed cluster abundance. We find that the evolution rate in model clusters is significantly higher than in data clusters. The results is stricking, as our cluster data are all just for $z \simlt 0.2$, but is not contrary to

C. Motch, F. Haberl

Deep optical B band images of the ROSAT HRI error region of RX J0720.4-3125 reveal the presence of two faint stellar-like objects with B = 26.1 +/- 0.25 and B = 26.5 +/- 0.30. Exposures obtained through U, V and I filters are not sensitive enough to detect the two candidates and provide upper limits of U = 24.9, V = 23.2 and I = 21.9. These new observations

Jihn E. Kim

I review the axionic solution of the strong CP problem and current status of the cosmic axion search.

I. Ya. Aref&#39;eva, M. G. Ivanov, O. A. Rytchkov, I. V. Volovich

Non-extremal overlapping p-brane supergravity solutions localised in their relative transverse coordinates are constructed. The construction uses an algebraic method of solving the bosonic equations of motion. It is shown that these non-extremal solutions can be obtained from the extremal solutions by means of the superposition of two deformation functions d

Martin White

The distance-redshift relation depends on the amount of matter of each type in the universe. Measurements at different redshifts constrain differing combinations of these matter densities and thus may be used in combination to constrain each separately. The combination of Omega_0 and Omega_Lambda measured in supernovae at z<1 is almost orthogonal to the comb

Z. Bern, L. Dixon, D. C. Dunbar, M. Perelstein

String theory implies that field theories containing gravity are in a certain sense `products&#39; of gauge theories. We make this product structure explicit up to two loops for the relatively simple case of N=8 supergravity four-point amplitudes, demonstrating that they are `squares&#39; of N=4 super-Yang-Mills amplitudes. This is accomplished by obtaining

Anne Schilling, S. Ole Warnaar

Inhomogeneous lattice paths are introduced as ordered sequences of rectangular Young tableaux thereby generalizing recent work on the Kostka polynomials by Nakayashiki and Yamada and by Lascoux, Leclerc and Thibon. Motivated by these works and by Kashiwara&#39;s theory of crystal bases we define a statistic on paths yielding two novel classes of polynomials.

Jorg P. Rachen, P. Meszaros

We investigate the spectrum of photohadronically produced neutrinos at very high energies (VHE, >10^14 eV) in astrophysical sources whose physical properties are constrained by their variability, in particular jets in Active Galactic Nuclei (blazars) and Gamma-Ray Bursts (GRBs). We discuss in detail the various competing cooling processes for energetic proto

Patricia Ball

I calculate the form factors describing semileptonic and penguin-induced decays of B mesons into light pseudoscalar mesons. The form factors are calculated from QCD sum rules on the light-cone including contributions up to twist 4, radiative corrections to the leading twist contribution and SU(3)-breaking effects. The theoretical uncertainty is estimated to

D. Bauer, P. Mulser

Numerically determined ionization rates for the field ionization of atomic hydrogen in strong and short laser pulses are presented. The laser pulse intensity reaches the so-called &#34;barrier suppression ionization&#34; regime where field ionization occurs within a few half laser cycles. Comparison of our numerical results with analytical theories frequentl

I. L. Buchbinder, B. A. Ovrut

This paper is a brief review of background field method and some of its applications in N=2 super Yang-Mills theories with a matter within harmonic superspace approach. A general structure of effective action is discussed, an absence of two-loop quantum corrections to first non-leading term in effective action is proved and N=2 non-renormalization theorem in

W. Barford, R. J. Bursill, M. Yu. Lavrentiev

The two state molecular orbital (2-MO) model of the phenyl based semiconductors is used to calculate the low-lying spectra of the Ag and Bu states of poly(para-phenylene) (PPP). The model parameters are determined by fitting its predictions to exact Pariser-Parr-Pople model calculations of benzene and biphenyl, and it is solved using the density matrix renor

Marek Czachor, Li You

We discuss a simple example demonstrating that spontaneous emission from &#34;space-time-superposed&#34; atomic center-of-mass wave packets is nontrivially and time-dependent modified with respect to the standard dipole-pattern typical of &#34;space-superposed&#34; wave packets. Our approach provides an approximate description of a nonsimultaneous interactio

D. Stevens, J. Brochard, A. M. Steane

Two techniques are described that simplify the experimental requirements for measuring and manipulating quantum information stored in trapped ions. The first is a new technique using electron shelving to measure the populations of the Zeeman sublevels of the ground state, in an ion for which no cycling transition exists from any of these sublevels. The secon

S. S. Safonov

The quadrature distribution for the quantum damped oscillator is introduced in the framework of the formulation of quantum mechanics based on the tomography scheme. The probability distribution for the coherent and Fock states of the damped oscillator is expressed explicitly in terms of Gaussian and Hermite polynomials, correspondingly.

Marek Czachor

Recenty Abrams and Lloyd have proposed a fast algorithm that is based on a nonlinear evolution of a state of a quantum computer. They have explicitly used the fact that nonlinear evolutions in Hilbert spaces do not conserve scalar products of states, and applied a description of separated systems taken from Weinberg&#39;s nonlinear quantum mechanics. On the

Chung-sik Song, George Fai

The effect of in-medium vector and axial-vector meson masses on photon production is studied. We assume that the effective mass of a vector meson in hot nuclear matter decreases according to a universal scaling law, while that of an axial-vector meson is given by Weinberg&#39;s mass formula. We find that the thermal production rate of photons increases with

D. R. Phillips, S. J. Wallace, N. K. Devine

The electromagnetic interactions of a relativistic two-body bound state are formulated in three dimensions using an equal-time (ET) formalism. This involves a systematic reduction of four-dimensional dynamics to a three-dimensional form by integrating out the time components of relative momenta. A conserved electromagnetic current is developed for the ET for

C. W. Johnson, G. F. Bertsch, D. J. Dean

We investigate the low-lying spectra of many-body systems with random two-body interactions, specifying that the ensemble be invariant under particle-hole conjugation.Surprisingly we find patterns reminiscent of more orderly interactions, such as a predominance of J=0 ground states separated by a gap from the excited states, and evidence of phonon vibrations

K. Yoshida, M. Matsuo

Damping of rotational motion in superdeformed Hg and Dy-region nuclei is studied by means of cranked shell model diagonalization. It is shown that a shell oscillation in single-particle alignments affects significantly properties of rotational damping. Onset properties of damping and damping width for Hg are quite different from those for Dy-region superdefo

Michael Röckner, Alexander Schied

We consider an $L^2$-Wasserstein type distance $ρ$ on the configuration space $Γ_X$ over a Riemannian manifold $X$, and we prove that $ρ$-Lipschitz functions are contained in a Dirichlet space associated with a measure on $Γ_X$ satisfying some general assumptions. These assumptions are in particular fulfilled by a large class of tempered grandcanonical Gibbs

Alexander Schied

We extend the class of $(ξ,ψ,K)$-superprocesses known so far by applying a simple transformation induced by a \lq\lq weight function\rq\rq\ for the one-particle motion. These transformed superprocesses may exist under weak conditions on the branching parameters, and their state space automatically extends to a certain space of possibly infinite Radon measure

A. Cossidente, J. W. P. Hirschfeld, G. Korchmaros, F. Torres

The genus of a maximal curve over a finite field with r^2 elements is either g_0=r(r-1)/2 or less than or equal to g_1=(r-1)^2/4. Maximal curves with genus g_0 or g_1 have been characterized up to isomorphism. A natural genus to be studied is g_2=(r-1)(r-3)/8, and for this genus there are two non-isomorphism maximal curves known when r \equiv 3 (mod 4). Here

D. V. Osipov

For a projective morphism of an smooth algebraic surface $X$ onto a smooth algebraic curve $S$, both given over a perfect field $k$, we construct the direct image morphism in two cases: from $H^i(X,Ω^2_X)$ to $H^{i-1}(S,Ω^1_S)$ and when $char k =0$ from $H^i(X,K_2(X))$ to $H^{i-1}(S,K_1(S))$. (If i=2, then the last map is the Gysin map from $CH^2(X)$ to $CH^

Aleksander Strasburger

With the aim of completing the previous study by A. Orłowski and the author concerning intertwining maps between induced representations and conjugation representation, termed here weighted class operators, we compute the latter explicitely for the conjugation representation arising from the regular representation in the group algebra of a compact group. To

Michael Neumann, Hans Schneider

Motivated by the theory of inhomogeneous Markov chains, we determine a sufficient condition for the convergence to 0 of a general product formed from a sequence of real or complex matrices. When the matrices have a common invariant subspace $H$, we give a sufficient condition for the convergence to 0 on $H$ of a general product. Our result is applied to obta

N. A. Sveshnikov, E. G. Timoshenko

We analyse dependence of the partition function on the boundary condition for the longitudinal component of the electric field strength in gauge field theories. In a physical gauge the Gauss law constraint may be resolved explicitly expressing this component via an integral of the physical transversal variables. In particular, we study quantum electrodynamic

Shin&#39;ichi Nojiri, Sergei D. Odintsov

We study the one-loop effective action for $N$ 4D conformally invariant scalars on the spherically symmetric background. The main part of effective action is given by integration of 4D conformal anomaly. This effective action (in large $N$ approximation and partial curvature expansion) is applied to investigate the quantum evolution of Schwarzschild-de Sitte

Z. Nemeth

The large distance behavior of the Maxwell- Chern-Simons (MCS) equations is analyzed, and it is found that the pure Chern-Simons limit, (when the Maxwell term is dropped from the equations), does not describe the large distance limit of the MCS model. This necessitates the solution of the original problem. The MCS gauge theory coupled to a nonrelativistic ma

Marco Cavaglia, Vittorio de Alfaro, Alexandre T. Filippov

We develop a simple scheme of quantization for the dilaton CGHS model without scalar fields, that uses the Gupta-Bleuler approach for the string fields. This is possible because the constraints can be linearized classically, due to positivity conditions that are present in the model (and not in the general string case). There is no ambiguity nor anomalies in

She-Sheng Xue

In the possible scaling region for lattice chiral fermions advocated in hep-lat/9609037, no hard spontaneous symmetry breaking occurs and doublers are gauge-invariantly decoupled via mixing with composite three-fermion-states. However the strong coupling expansion breaks down due to no ``static limit&#39;&#39; for the low-energy limit ($p\sim 0$). We further

Piljin Yi

We consider test strings and test branes ending on D$p$-branes ($p\le 6$) and NS5-branes in the background, for a heuristic understanding of the dynamics. Whenever some supersymmetry is preserved, a simple BPS bound appears, but the central charge in question is measured by certain isotropic coordinate system, rather than by the actual spacetime geometry. Th

S. Rai Choudhury, York-Peng Yao

We consider non-perturbative QCD effects on the energy spectrum of either one of the photons in B -> X_s gamma gamma. These are due to the subprocesses in which a charm quark loop interacts with a self-consistently produced background static QCD field. The magnitude is estimated to be a few percents in B -> X_s gamma gamma, but can be quite substantial in B_

Ariel Zhitnitsky

We discuss few, apparently different, but actually tightly related problems: a)Strangeness in the nucleon; b) B --> eta&#39; decays; c)Intrinsic charm in the proton spin problem. We argue that all these problems have a common origin and related to the OZI rule violation in 0^{\pm} vacuum channels . It leads to a noticeable role of a nonvalence component with

Thomas G. Rizzo

In the Standard Model and many of its extensions, it is well known that all of the observables associated with the rare decays $b\to sγ$ and $b\to s\ell^+\ell^-$ can be expressed in terms of the three Wilson coefficients, $C_{7L,9L,10L}(μ\sim m_b)$, together with several universal kinematic functions. In particular it has been shown that the numerical values

Frank Wilczek

These are the essence of two lectures given at the Ettore Majorana Summer School, 1997, and the discussion sections which followed them. The title indicates their content: some reasoned expectations for physics beyond the Standard Model, and an annotated list of major open questions.

C. Muñoz

Following Dyson&#39;s analogy between the quantum field theory and the 19th-century chemistry-both explain how but not why-one could also establish an analogy between atomic physics and string theory. Atomic physics was needed to answer the question why in chemistry, string theory is trying to answer the question why in the standard model. This attempt is ve

Per Elmfors

The anomaly equation can be derived from the ultraviolet properties of quantum field theory and should, therefore, not depend on infrared properties, such as the presence of a thermal heat bath. There is also an infrared explanation of anomalies which is related to fermionic zero modes. I show how the anomaly equation can be satisfied in a high temperature p

Per Elmfors, Bo-Sture Skagerstam

We calculate thermal corrections to the non-linear QED effective action for low-energy photon interactions in a background electromagnetic field. The high-temperature expansion shows that at $T \gg m$ the vacuum contribution is exactly cancelled to all orders in the external field except for a non-trivial two-point function contribution. The high-temperature

I. G. Alekseev, P. E. Budkovsky, V. P. Kanavets, L. I. Koroleva

We present the results of the experimental study of the reaction of dipion production by the beam of the negative pions with momentum 1.78 GeV/c on the polarized proton and liquid hydrogen targets. The experiment covers the region of dipion masses near the mass of rho-meson and small momenta transferred |t|<0.2(GeV/c)^2. The whole set of spin density matrix

M. Axenides, L. Perivolaropoulos

Vortices in superfluid 3He-B have been observed to undergo a core transition. We discuss the analog phenomenon in relativistic field theories which admit embedded global domain walls, vortices and monopoles with a core phase structure. They are present in scalar field theories with approximate global symmetries which are broken both spontaneously and in part

As. Abada, O. Pène, J. Rodriguez-Quintero

The effect of multibody massless neutrino exchanges between neutrons inside a finite-size neutron star is studied. We use an effective Lagrangian, which incorporates the effect of the neutrons on the neutrinos. Following Schwinger, it is shown that the total interaction energy density is computed by comparing the zero point energy of the neutrino sea with an

F. Borzumati, C. Greub

The decay $B \to X_s γ$ is studied at the Next to Leading Order in QCD in a class of models containing at least two Higgs doublets and with only one charged Higgs boson non-decoupled at low-energy. The two-loop matching condition is calculated and it is found to agree with existing results. The complete dependence of the Wilson coefficients on the matching s

Nils Andersson, Pablo Laguna, Philippos Papadopoulos

We analyze the amplification due to so-called superradiance from the scattering of pulses off rotating black holes as a numerical time evolution problem. We consider the &#34;worst possible case&#34; of scalar field pulses for which superradiance effects yield amplifications $< 1%$. We show that this small effect can be isolated by numerically evolving quasi

Daniel S. Fisher, A. P. Young

A previously introduced real space renormalization-group treatment of the random transverse-field Ising spin chain is extended to provide detailed information on the distribution of the energy gap and the end-to-end correlation function for long chains with free boundary conditions. Numerical data, using the mapping of the problem to free fermions, are found

D. Foerster, Y. Meurdesoif, B. Malet

We compute the magnetic profile of spin Peierls solitons in a simple Heisenberg model with magneto elastic couplings, using independently the DMRG method and the Hartree Fock approximation. Our results agree qualitatively with published NMR data provided we average over the spin profiles. We conclude that he dynamics of the spin plus lattice system must be i

Ganpathy Murthy, R. Shankar

We provide details of a shorter letter and cond-mat/9702098 and some new results. We describe a Chern-Simons theory for the fractional quantum Hall states in which magnetoplasmon degrees of freedom enter. We derive correlated wavefunctions, operators for creating quasiholes and composite fermions and bosons (which are electrons bound to zeros). We show how t

Y. Tanuma, Y. Tanaka, M. Ogata, S. Kashiwaya

Spatial dependencies of the pair potential and the local density of states near the surfaces of $d_{x^{2}-y^{2}}$-wave superconductors are studied theoretically. The calculation is based on the t-J model within a mean-field theory with Gutzwiller approximation. Various types of surface geometries are considered. Similar to our result in the extended Hubbard

J. Maucourt, D. R. Grempel

We investigate numerically the finite-size scaling properties of the domain wall energies in the three-dimensional gauge glass model. From the analysis of results obtained for systems of linear sizes $3\le L\le 8$ we conclude that the stiffness exponent of the model is positive. This implies the existence of a stable ordered phase at low but finite temperatu

Joerg P. Kottmann, Adriaan M. J. Schakel

A quantum field theory, consisting of the effective action of sound waves linearly coupled to a Chern-Simons term, is proposed to describe the dynamics of vortices in a superfluid film at the absolute zero of temperature.

N. M. R. Peres

This work deals with the one-dimensional Hubbard model. It has seven chapters: 1. Introduction; 2. The Hubbard Model; 3. Algebraic Representation for the Hilbert Space of the 1D Hubbard Model; 4. Pseudoparticle Perturbation Theory; 5. Excitations and Finite-Size Effects; 6. Zero-Temperature Transport; 7. Conclusions.

Bumsoo Kyung, E. G. Klepfish, P. E. Kornilovitch

A conserving T-matrix approximation is applied to the two-dimensional attractive Hubbard model in the low-density regime. A set of self-consistent equations is solved in the real-frequency domain to avoid the analytic continuation procedure. By tuning the chemical potential the particle density was varied in the limits 0.01 < n < 0.18. For the value of the a

C. Thessieu, K. Kamishima, T. Goto, G. Lapertot

The magnetization M(H) has been measured in the weakly helimagnetic itinerant compound MnSi under high pressure up to 10.2 kbar and high magnetic field up to 9 Tesla. We interpret the simultaneous decrease under pressure of the saturated magnetization, $p_s$, and the Curie temperature, $% T_c$ in the frame of the self-consistent renormalization theory (SCR)

Mahn-Soo Choi

Two chains of ultrasmall Josephson junctions, coupled capacitively with each other in the two different ways, straight and slanted coupling, are considered. As the coupling capacitance increases, regardless of the coupling scheme, the transport of particle-hole pairs in the system is found to drive the quantum-phase transition at zero temperature, which is a

C. Thessieu, K. Ishida, Y. Kitaoka, K. Asayama

The magnetic phase diagram $T_c(P)$ of the weak itinerant helimagnetic compound MnSi is reviewed upon a Nuclear Magnetic Resonance (NMR) experiment. We present a systematic study on the evolution of the NMR spin echo signal at $T=1.4$ K of the non-magnetic silicone sites, $^{29}$Si, up to 17.8 kbar. The pressure effect is interpreted as a weak variation of t

B. M. Roehner, D. Sornette

We find empirically a characteristic sharp peak-flat trough pattern in a large set of commodity prices. We argue that the sharp peak structure reflects an endogenous inter-market organization, and that peaks may be seen as local ``singularities&#39;&#39; resulting from imitation and herding. These findings impose a novel stringent constraint on the construct

H. v. Löhneysen, A. Neubert, A. Schröder, O. Stockert

We report on extensive elastic neutron scattering to determine the wave vector of the magnetic order in CeCu_{6-x}Au_x single crystals for x > 0.1. For all values of x investigated (0.2, 0.3, 0.5, 1.0) we find long-range incommensurate antiferromagnetic order with an ordering vector Q $\approx$ (0.625 0 0.275) for x=0.2, nearly unchanged for x=0.3, and Q $\a

Kedar Damle, Subir Sachdev

We present the theory of nonzero temperature ($T$) spin dynamics and transport in one-dimensional Heisenberg antiferromagnets with an energy gap $Δ$. For $T << Δ$, we develop a semiclassical picture of thermally excited particles. Multiple inelastic collisions between the particles are crucial, and are described by a two-particle S-matrix which has a super-u

B. R. Oppenheimer, S. R. Kulkarni, K. Matthews, M. H. van Kerkwijk

We present a spectrum of the cool (T_eff = 900 K) brown dwarf Gliese 229B. This spectrum, with a relatively high signal-to-noise ratio per spectral resolution element (> 30), spans the wavelength range from 0.837 microns to 5.0 microns. We identify a total of four different major methane absorption features, including the fundamental band at 3.3 microns, at

A. Bracco, A. Provenzale, E. A. Spiegel, P. Yecko

Rotating, turbulent cosmic fluids are generally pervaded by coherent structures such as vortices and magnetic flux tubes. The formation of such structures is a robust property of rotating turbulence as has been confirmed in computer simulations and laboratory experiments. We defend here the notion that accretion disks share this feature of rotating cosmic bo

Geraint F. Lewis, Rodrigo A. Ibata

Gravitational microlensing of quasars by stars in external galaxies can introduce fluctuations in the centroid of the ``point-like&#39;&#39; macro--images. The induced shifts are extremely small, on micro--arcsecond scales, below the limits of current optical observations. However, such shifts will become measurable with the proposed ``Space Interferometry&#

Marcos J. Montes, Schuyler D. Van Dyk, Kurt W. Weiler, Richard A. Sramek

New observations of SN 1980K made with the VLA at 20 and 6 cm from 1994 April through 1996 October show that the supernova (SN) has undergone a significant change in its radio emission evolution, dropping by a factor of ~2 below the flux density S \propto t^{-0.73} power-law decline with time t observed earlier. However, although S at all observed frequencie

Shigeru Yoshida, Hongyue Dai

Experimental results from Haverah Park, Yakutsk, AGASA and Fly&#39;s Eye are reviewed. All these experiments work in the energy range above 0.1 EeV. The &#39;dip&#39; structure around 3 EeV in the energy spectrum is well established by all the experiments, though the exact position differs slightly. Fly&#39;s Eye and Yakutsk results on the chemical compositi

Jens Hjorth, Jamila Oukbir, Eelco van Kampen

A tight mass-temperature relation, M(r)/r ~ T_X, is expected in most cosmological models if clusters of galaxies are homologous and the intracluster gas is in global equilibrium with the dark matter. We here calibrate this relation using 8 clusters with well-defined global temperatures measured with ASCA and masses inferred from weak and strong gravitational

Leif Festin

The brown dwarf population in the Pleiades cluster has been probed in a deep 850 arcmin2 RIJK survey. The survey is complete to I=21.4 in 76% of the area and to I=20.2 in the remaining 24%. Photometry of 32 previously known members is presented together with 8 new candidates, four of which are below the brown dwarf limit. The faintest one is the lowest mass

S. Cristiani, F. La Franca, P. Andreani

Recent results have questioned the description of the QSO luminosity function in terms of a pure luminosity evolution and call for a luminosity dependent luminosity evolution. Measurements of the QSO clustering amplitude and evolution allow further distinguishing among the various physical scenarios proposed to interpret the QSO phenomenon. The general prope

G. Tormen

We study the merging history of dark matter haloes that end up in rich clusters, using N-body simulations of a scale-free universe. We compare the predictions of the extended Press & Schechter (PS) formalism (Bond et al. 1991; Bower 1991; Lacey & Cole 1993) with several conditional statistics of the proto-cluster matter: the mass distribution and relative ab

L. B. F. M. Waters, D. A. Beintema, A. A. Zijlstra, A. de Koter

We present ISO-SWS spectroscopy of the cool dusty envelopes surrounding two Planetary Nebulae with [WC] central stars, BD+30~3639 and He~2-113. The lambda < 15micron region is dominated by a rising continuum with prominent emission from C-rich dust (PAHs), while the long wavelength part shows narrow solid state features from crystalline silicates. This demon

W. Bednarek, R. J. Protheroe

We discuss the consequences of almost rectilinear acceleration of protons to extremely high energies in a reconnection region on the surface of an accretion disk which surrounds a central black hole in an active galaxy. The protons produce $γ$-rays and neutrinos in interactions with the disk radiation as considered in several previous papers. However, in thi

Edouard Audit, Romain Teyssier, Jean-Michel Alimi

We compare the mass functions obtained analytically, in the framework of an extended Press & Schechter (PS) formalism, in a previous paper to the numerical mass functions obtained in N -- body simulations, using different algorithms to define objects in the density field. After discussing the properties of the algorithms, we show that the mass function obtai

P. North

The old question of rotational braking of Ap Si stars is revisited on the empirical side, taking advantage of the recent Hipparcos results. Field stars with various evolutionary states are considered, and it is shown that the loose correlation between their rotational period and their surface gravity is entirely compatible with conservation of angular moment

Roger Coziol, Thierry Contini, Emmanuel Davoust, Suzanne Considere

We discuss the implications of the recent discovery that Starburst Nucleus Galaxies (SBNGs) have lower oxygen abundances than &#34;normal galaxies&#34; of the same morphological type. Our interpretation of this result is that SBNGs are young galaxies, still in the process of formation. We consider several alternatives, but none of them provides a viable expl

Martin Schaden

An equivariant BRST-construction is used to define the continuum SU(3) gauge theory on a finite torus. I corroborate previous results using renormalization group techniques by explicitly computing the measure on the moduli-space of the model with 3 quark flavors to two loops. I find that the correction to the maximum of the one-loop effective action is indee

Rathin Adhikari, Gordana Omanovic

With only three flavors it is possible to account for various neutrino oscillation experiments. The masses and mixing angles for three neutrinos can be determined from the available experimental data on neutrino oscillation and from the astrophysical arguments. We have shown here that such masses and mixing angles which can explain atmospheric neutrino anoma

W. Hofstetter, D. Vollhardt

The perfect-nesting instability towards antiferromagnetism of the Hubbard model is suppressed by next-nearest neighbor hopping t&#39;. The exact asymptotic behavior of the critical coupling U_c(t&#39;) at small t&#39; is calculated in dimensions d=2,3 and infinity using Hartree theory, and the order of the transition is determined. A region of stability of a

Bo-yu Hou, Wen-Li Yang

From the dynamical twisting of the classical r-matrix, we obtain a new Lax operator for the elliptic Ruijsenaars-Schneider model (cf. Ruijsenaars&#39;). The corresponding r-matrix is shown to be the classical $Z_n$-symmetric elliptic r-matrix, which is the same as that obtained in the study of the nonrelativistic version---the $A_{n-1}$ Calogero-Moser model.