May 2000 arXiv papers — page 8

Adi Armoni

We study the U(N) non-commutative Yang-Mills theory at the one-loop approximation. We check renormalizability and gauge invariance of the model and calculate the one-loop beta function. The interaction of the SU(N) gauge bosons with the U(1) gauge boson plays an important role in the consistency check. In particular, the SU(N) theory by itself is not consist

T. W. Allen, G. L. Payne, Wayne N. Polyzou

We investigate the difference between those relativistic models based on interpreting a realistic nucleon-nucleon interaction as a perturbation of the square of a relativistic mass operator and those models that use the method of Kamada and Glöckle to construct an equivalent interaction to add to the relativistic mass operator. Although both models reproduce

Yuichi Chikira, Yukihiro Mimura

It is studied that `no-scale' model makes hierarchy between scalar top mass and Z boson mass naturally. The supersymmetry breaking parameters are constrained by flavor changing neutral currents in minimal supersymmetric standard model. One of the solution of the problem is that gaugino mass is the only source of the supersymmetry breaking parameters at P

D. Grumiller, D. Hofmann, W. Kummer

Dimensional reduction of generalized gravity theories or string theories generically yields dilaton fields in the lower-dimensional effective theory. Thus at the level of D=4 theories, and cosmology many models contain more than just one scalar field (e.g. inflaton, Higgs, quintessence). Our present work is restricted to two-dimensional gravity theories with

Roderick C. Dewar

Jaynes' information theory formalism of statistical mechanics is applied to the stationary states of open, non-equilibrium systems. The key result is the construction of the probability distribution for the underlying microscopic phase space trajectories. Three consequences of this result are then derived : the fluctuation theorem, the principle of maxim

Andrew F. Nelson

We show that planet formation via both gravitational collapse and core accretion is unlikely to occur in equal mass binary systems with moderate (~ 50 AU) semi-major axes. Internal thermal energy generation in the disks is sufficient to heat the gas everywhere so that spiral structures quickly decay rather than grow or fragment. This same heating will inhibi

Jerome Martin, Robert H. Brandenberger

In most current models of inflation based on a weakly self-coupled scalar matter field minimally coupled to gravity, the period of inflation lasts so long that, at the beginning of the inflationary period, the physical wavelengths of comoving scales which correspond to the present large-scale structure of the Universe were smaller than the Planck length. Thu

Konrad Schmuedgen

Suppose q is a complex number of modulus one and different from 1,-1. Let O(R^2_q) be the *-algebra with two hermitean generators x and y satisfying the relation xy=qyx. Using operator representations of the *-algebra O(R^2_q) on Hilbert space and the Weyl calculus of pseudodifferential operators we construct *-algebras of ``functions'' on the quantu

J. Kallunki, J. Krug

We study a recently proposed nonlinear evolution equation describing the collective step meander on a vicinal surface subject to the Bales-Zangwill growth instability [O. Pierre-Louis et al., Phys. Rev. Lett. (80), 4221 (1998)]. A careful numerical analysis shows that the dynamically selected step profile consists of sloped segments, given by an inverse erro

D. K. Park, H. J. W. Müller-Kirsten, J. -Q. Liang, A. V. Shurgaia

The transition from the instanton-dominated quantum regime to the sphaleron-dominated classical regime is studied in the $d=2$ abelian-Higgs model when the spatial coordinate is compactified to $S^1$. Contrary to the noncompactified case, this model allows both sharp first-order and smooth second-order transitions depending on the size of the circle. This fi

Tae-Suk Kim, S. R. Eric Yang, A. H. MacDonald

We report on Hartree-Fock theory results for stripe states of two-dimensional hole systems in quantum wells grown on GaAs (311)A substrates. We find that the stripe orientation energy has a rich dependence on hole density, and on in-plane field magnitude and orientation. Unlike the electron case, the orientation energy is non-zero for zero in-plane field, an

Sang Pyo Kim, Chul H. Lee

We use the so-called Liouville-von Neumann (LvN) approach to study the nonequilibrium quantum dynamics of time-dependent second order phase transitions. The LvN approach is a canonical method that unifies the functional Schrödinger equation for the quantum evolution of pure states and the LvN equation for the quantum description of mixed states of either equ

A. Ino, C. Kim, M. Nakamura, T. Yoshida

The electronic structure of the La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) system has been studied by angle-resolved photoemission spectroscopy (ARPES). We report on the evolution of the Fermi surface, the superconducting gap and the band dispersion around the extended saddle point $k=(π,0)$ with hole doping in the superconducting and metallic phases. As hole concentrat

Chao-Shang Huang, Wu-Jun Huo, Yue-Liang Wu

We investigate the $ε^{\prime} /ε$ for $K\to ππ$ in a sequential fourth generation model. By giving the basic formulae for $ε^{\prime}/ε$ in this model, we analyze the numerical results which are dependent of $m_{t^{\prime}}$ and imaginary part of the fourth CKM factor, ${Im}V^{*}_{t^{'}s}V_{t^{'}d}$ (or $V^{*}_{t^{'}s}V_{t^{'}d}$ and the fou

Y. S. Myung, G. Kang

We discuss the compatibility between the weaker energy condition and the stability of Gregory, Rubakov and Sibiryakov (GRS) model. Because the GRS spacetime violates the weak energy condition, it may cause the instability. In the GRS model, the four dimensional gravity can be described by the massive KK modes with the resonance. Hence, instead of considering

Po Dong, A. K. Popov, Tang Sing Hai, Jin-Yue Gao

We propose a four-level model where sub-Doppler resolution as well as enhanced absorption of a weak probe field are realized by using two coherently driving fields. We show that spectral resolution can be improved by modifying the coherent fields intensity and frequencies.

A. Lezama, G. C. Cardoso, J. W. R. Tabosa

Nearly degenerate four-wave mixing (NDFWM) within a closed degenerate two-level atomic transition is theoretically and experimentally examined. Using the model presented by A. Lezama et al [Phys. Rev. A 61, 013801 (2000)] the NDFWM spectra corresponding to different pump and probe polarization cases are calculated and discussed. The calculated spectra are co

Helmut Fink, Hajo Leschke

In order to relate the probabilistic predictions of quantum theory uniquely to measurement results, one has to conceive of an ensemble of identically prepared copies of the quantum system under study. Since the universe is the total domain of physical experience, it cannot be copied, not even in a thought experiment. Therefore, a quantum state of the whole u

T. Ya. Popova, A. K. Popov, S. G. Rautian, R. I. Sokolovskii

Nonlinear effects in emission and absorption spectra of gaseous systems are considered. It is shown that level splitting can be detected spectroscopically even if it is below the Doppler width. Conditions for distinguishing interference effects from those due to nonequilibrium velocity distribution are determined. In the case of large Doppler broadening the

G. S. Agarwal

We demonstrate how the anisotropy of the vacuum of the electromagnetic field can lead to quantum interferences among the decay channels of close lying states. Our key result is that interferences are given by the {\em scalar} formed from the antinormally ordered electric field correlation tensor for the anisotropic vacuum and the dipole matirx elements for t

Balasubramanya T. Nadiga

An inviscid two-dimensional fluid model with nonlinear dispersion that arises simultaneously in coarse-grained descriptions of the dynamics of the Euler equation and in the description of non-Newtonian fluids of second grade is considered. The scaling of the equilibrium states of this model for conserved energy and enstrophy retains the corresponding scaling

Qiong Gao, Ming Li, Paul Vitanyi

The Minimum Description Length (MDL) principle is solidly based on a provably ideal method of inference using Kolmogorov complexity. We test how the theory behaves in practice on a general problem in model selection: that of learning the best model granularity. The performance of a model depends critically on the granularity, for example the choice of precis

Mala Das, B. K. Chatterjee, B. Roy, S. C. Roy

Superheated drops are known to detect neutrons through the nucleation caused by the recoil nuclei produced by the interactions of neutrons with the atoms constituting the superheated liquid molecule. A novel method of finding the neutron energy from the temperature dependence response of SDD has been developed. From the equivalence between the dependence of

David H. Wolpert

In the first of this pair of papers, it was proven that that no physical computer can correctly carry out all computational tasks that can be posed to it. The generality of this result follows from its use of a novel definition of computation, ``physical computation''. This second paper of the pair elaborates the mathematical structure and impossibil

David H. Wolpert

In this first of two papers, strong limits on the accuracy of physical computation are established. First it is proven that there cannot be a physical computer C to which one can pose any and all computational tasks concerning the physical universe. Next it is proven that no physical computer C can correctly carry out any computational task in the subset of

L. Tiator, D. Drechsel, S. S. Kamalov

Results of the recently developed unitary isobar model (MAID) are presented for the spin asymmetries, structure functions and relevant sum rules in the resonance region. The model describes the presently available data for single-pion photo- and electroproduction in the resonance region below Wcm = 2 GeV very well. It is based on Born terms and resonance con

Vitold V. Vecheslavov

Some results of numerical study of the canonical map with a sawtooth force are given and discovered new unexpected dynamical effects are described. In particular, it is shown that if the values of the system parameter K belong to the countable set determined by Ovsyannikov's theorem, separatrices of primary resonances are not splitted and chaotic layers

A. Peterman

A so-called Renormalization Group (RG) analysis is performed in order to shed some light on why the density of prime numbers in $\Bbb N^*$ decreases like the single power of the inverse neperian logarithm.

Paolo Piccione, Daniel V. Tausk

We study the local geometry of the space of horizontal curves with endpoints freely varying in two given submanifolds $\mathcal P$ and $\mathcal Q$ of a manifold $\mathcal M$ endowed with a distribution $\mathcal D\subset T\M$. We give a different proof, that holds in a more general context, of a result by Bismut (Large Deviations and the Malliavin Calculus,

Thomas Garrity

A generic compact real codimension two submanifold X of C^(n+2) will have a CR structure at all but a finite number of points (failing at the complex jump points J). The main theorem of this paper gives a method of extending the CR structure on the non-jump points X-J to the jump points. We examine a Gauss map from X-J to an appropriate flag manifold F and t

Alexander Ulyanov

A smooth compactification X<n> of the configuration space of n distinct labeled points in a smooth algebraic variety X is constructed by a natural sequence of blowups, with the full symmetry of the permutation group S_n manifest at each stage of the construction. The strata of the normal crossing divisor at infinity are labeled by trees with levels and their

Rimas Norvaisa

The paper discusses a path-wise approach to stock price modelling.

Luc Devroye, James Allen Fill, Ralph Neininger

The weak limit of the normalized number of comparisons needed by the Quicksort algorithm to sort n randomly permuted items is known to be determined implicitly by a distributional fixed-point equation. We give an algorithm for perfect random variate generation from this distribution.

James Allen Fill, Svante Janson

The limiting distribution μof the normalized number of key comparisons required by the Quicksort sorting algorithm is known to be the unique fixed point of a certain distributional transformation T -- unique, that is, subject to the constraints of zero mean and finite variance. We show that a distribution is a fixed point of T if and only if it is the convol

James Allen Fill, Svante Janson

Using Fourier analysis, we prove that the limiting distribution of the standardized random number of comparisons used by Quicksort to sort an array of n numbers has an everywhere positive and infinitely differentiable density f, and that each derivative f^{(k)} enjoys superpolynomial decay at plus and minus infinity. In particular, each f^{(k)} is bounded. O

Igor Rivin

The main result is that every complete finite area hyperbolic metric on a sphere with punctures can be uniquely realized as the induced metric on the surface of a convex ideal polyhedron in hyperbolic 3-space. A number of other observations are included.

Laurent Evain

Let HH_{ab}(H) be the equivariant Hilbert scheme parametrizing the zero dimensional subschemes of the affine plane k^2, fixed under the one dimensional torus T_{ab}={(t^{-b},t^a), t\in k^*} and whose Hilbert function is H. This Hilbert scheme admits a natural stratification in Schubert cells which extends the notion of Schubert cells on Grassmannians. Howeve

Stephen S. Y. Lu, Gregery T. Buzzard

An n-dimensional complex manifold M is said to be (holomorphically) dominable by $\CC^n$ if there is a map $F:\CC^n \ra M$ which is holomorphic such that the Jacobian determinant $\det(DF)$ is not identically zero. Such a map F is called a dominating map. In this paper, we attempt to classify algebraic surfaces X which are dominable by $\CC^2$ using a combin

Don Dawson, L. G. Gorostiza, A. Wakolbinger

We consider particle systems in locally compact Abelian groups with particles moving according to a process with symmetric stationary independent increments and undergoing one and two levels of critical branching. We obtain long time fluctuation limits for the occupation time process of the one-and two-level systems. We give complete results for the case of

Robert Brooks, Ruth Gornet, Peter Perry

The authors exhibit pairs of infinite-volume, hyperbolic three-manifolds that have the same scattering poles and conformally equivalent boundaries, but which are not isometric. The examples are constructed using Schottky groups and the Sunada construction.

Levent Tuncel, Masakazu Kojima

General Successive Convex Relaxation Methods (SRCMs) can be used to compute the convex hull of any compact set, in an Euclidean space, described by a system of quadratic inequalities and a compact convex set which is not very complicated. Linear Complementarity Problems (LCPs) make an interesting and rich class of structured nonconvex optimization problems.

Henrique Bursztyn, Stefan Waldmann

Motivated by deformation quantization, we introduced in an earlier work the notion of formal Morita equivalence in the category of $^*$-algebras over a ring $\ring C$ which is the quadratic extension by $\im$ of an ordered ring $\ring R$. The goal of the present paper is twofold. First, we clarify the relationship between formal Morita equivalence, Ara&#39;s

Leonardo Castellani

A brief review of bicovariant differential calculi on finite groups is given, with some new developments on diffeomorphisms and integration. We illustrate the general theory with the example of the nonabelian finite group S_3.

S. A. Merkulov

We introduce a category of extended complex manifolds, and prove that the functor describing deformations of a classical compact complex manifold $M$ within this category is versally representable by (an analytic subspace in) $H^*(M,T_M)$. By restricting the associated versal family of extended complex manifolds over $H^*(M,T_M)$ to the subspace $H^1(M,T_M)$

I. A. Taimanov

We show how to assign to any immersed torus in $\R^3$ or $S^3$ a Riemann surface such that the immersion is described by functions defined on this surface. We call this surface the spectrum or the spectral curve of the torus. The spectrum contains important information about conformally invariant properties of the torus and, in particular, relates to the Wil

Greg McShane, Igor Rivin

We define a norm on homology of punctured tori equipped with a complete hyperbolic metric of finite volume and use it to find asymptotics on the growth of the number of simple geodesics of bounded length.

E. V. Ferapontov

Some general properties of compatible Poisson brackets of hydrodynamic type are discussed, in particular: (1) an invariant differential-geometric criterion of the compatibility based on the Nijenhuis tensor; (2) the Lax pair with a spectral parameter governing compatible Poisson brackets in the diagonalizable case; (3) the connection of this problem with the

Greg McShane, Igor Rivin

We describe a new approach to the study of the set of all simple geodesics on a hyperbolic punctured torus. We introduce a valuation on the first integral homology group of the torus. This valuation associates to each homology class the length of the unique simple geodesic in it. We show that this valuation extends to a norm on the homology with real coeffic

Johan Kustermans, Stefaan Vaes

In this paper we complete in several aspects the picture of locally compact quantum groups. First of all we give a definition of a locally compact quantum group in the von Neumann algebraic setting and show how to deduce from it a C*-algebraic quantum group. Further we prove several results about locally compact quantum groups which are important for applica

Doug Bullock, Charles Frohman, Joanna Kania-Bartoszynska

For each closed, orientable surface F, we construct a local, diffeomorphism invariant trace on the Kauffman bracket skein module K_t(F x [0,1]). The trace is defined when |t| is neither 0 nor 1, and at certain roots of unity. At t = - 1, the trace is integration against the symplectic measure on the SU(2) character variety of the fundamental group of F.

Vassily Gorbounov, Fyodor Malikov, Vadim Schechtman

This note is a sequel to &#34;Gerbes of chiral differential operators. II&#34;, math.AG/0003170. We study gerbes of chiral differential operators acting on the exterior algebra $ΛE$ of a vector bundle over a smooth algebraic variety $X$. When $E=Ω^1_X$ this gerbe admits a canonical global section which coincides with the chiral de Rham complex of $X$.

Tathagata Dasgupta, Matthias R. Gaberdiel, Michael B. Green

The tree-level amplitude for the scattering of two gauge particles constrained to move on the two distinct boundaries of eleven-dimensional space-time in the Horava-Witten formulation of M-theory is constructed. At low momenta this reproduces the corresponding tree-level scattering amplitude of the E_8xE_8 heterotic string theory. After compactification to n

James M. Cline, Hassan Firouzjahi

We point out that the potential of Goldberger and Wise for stabilizing the distance between two 3-branes, separated from each other along an extra dimension with a warp factor, has a metastable minimum when the branes are infinitely separated. The classical evolution of the radion (brane separation) will place it in this false minimum for generic initial con

Achille Corsetti, Pran Nath

Several new effects have been investigated in recent analyses of supersymmetric dark matter. These include the effects of the uncertainties of wimp velocity distributions, of the uncertainties of quark densities, of large CP violating phases, of nonuniversalities of the soft SUSY breaking parameters at the unification scale and of coannihilation on supersymm

Stefano Catani

This contribution presents a selection of the topics (parton densities, fixed-order calculations, parton showers, soft-gluon resummation) discussed in my introductory lectures at the Workshop and includes a pedagogical overview of the corresponding theoretical tools.

T. Gehrmann, E. Remiddi

The calculation of exclusive observables beyond the one-loop level requires elaborate techniques for the computation of multi-leg two-loop integrals. We discuss how the large number of different integrals appearing in actual two-loop calculations can be reduced to a small number of master integrals. An efficient method to compute these master integrals is to

F. Arleo, P. -B. Gossiaux, T. Gousset, J. Aichelin

In addition to the final-state interactions, $J/ψ$ nuclear production might also be affected by parton energy loss. Using the upper limits from Drell-Yan data at SPS and Fermilab energies, we estimated energy loss contribution to $J/ψ$ production in p-A collisions. The results indicated that the effects might be sizeable at 200 GeV while remaining small at h

Masako Bando

I demonstrate that neutrino large mixing between $ν_μ$ and $ν_τ$ are naturally reproduced using a novel mechanism called `E-twisting&#39;in a supersymmetric $E_6$ grand unification model. This model explains all the characteristic features of the quark/lepton Dirac masses as well as the neutrino&#39;s Majorana masses despite the fact that all the members in

Gregory W. Carter, Sanjay Reddy

We calculate the neutrino mean free path in color superconducting quark matter, and employ it to study the cooling of matter via neutrino diffusion in the superconducting phase as compared to a free quark phase. The cooling process slows when quark matter undergoes a second order phase transition to a superconducting phase at the critical temperature $T_c$.

P. Pennanen

String breaking is a non-perturbative long-distance feature of QCD that is involved in for example meson decays. A mixing analysis of lattice operators at zero temperature gives the level splitting and mixing energy between the broken and unbroken string states.

L. Vacavant, I. Hinchliffe

The generic missing transverse energy signals at LHC for theories having large extra dimensions are discussed. Final states of jets plus missing energy and photons plus missing energy are simulated in the ATLAS detector. The discovery limit of LHC and the methods to determine the parameters of the underlying model are discussed.

M. N. Achasov, K. I. Beloborodov, A. V. Berdyugin, A. G. Bogdanchikov

The cross section of the $e^+e^-\toωπ^0\toπ^0π^0γ$ reaction was measured by the SND detector at VEPP-2M $e^+e^-$ collider in the energy range from threshold up to 1.4 GeV. Results of the cross section fitting by the sum of $ρ$, $ρ^{\prime}$ and $ρ^{\prime\prime}$ contributions are presented.

Paul R. Anderson, Wayne Eaker, Salman Habib, Carmen Molina-Paris

The renormalized expectation value of the energy-momentum tensor for a scalar field with any mass m and curvature coupling xi is studied for an arbitrary homogeneous and isotropic physical initial state in de Sitter spacetime. We prove quite generally that <T_{ab}> has a fixed point attractor behavior at late times, which depends only on m and xi, for any fo

N. Pinto-Neto, R. Rodrigues da Silva

A new prescription to calculate the total energies and angular momenta of asymptotically $(d+1)$-dimensional anti-de Sitter spacetimes is proposed. The method is based on an extension of the field theoretical approach to General Relativity to the case where there is an effective cosmological constant. A $(d-1)$-form $Ω$ is exhibited which, when integrated on

S. Antoci

It has been shown recently that the classical law of elasticity, expressed in terms of the displacement three-vector and of the symmetric deformation three-tensor, can be extended to the four dimensions of special and of general relativity with a physically meaningful outcome. In fact, the resulting stress- momentum-energy tensor can provide a unified accoun

Rainer E. Zimmermann

The relationship between modern philosophy and physics is discussed. It is shown that the latter develops some need for a modernized metaphysics which shows up as an ultima philosophia of considerable heuristic value, rather than as the prima philosophia in the Aristotelian sense as it had been intended, in the first place. It is shown then, that it is the p

Ke Xu, Wei Li

Phase transition is an important feature of SAT problem. For random k-SAT model, it is proved that as r (ratio of clauses to variables) increases, the structure of solutions will undergo a sudden change like satisfiability phase transition when r reaches a threshold point. This phenomenon shows that the satisfying truth assignments suddenly shift from being

Matthias Vojta, Chiranjeeb Buragohain, Subir Sachdev

We present the universal theory of arbitrary, localized impurities in a confining paramagnetic state of two-dimensional antiferromagnets with global SU(2) spin symmetry. The energy gap of the host antiferromagnet to spin-1 excitations, Δ, is assumed to be significantly smaller than a typical nearest neighbor exchange. In the absence of impurities, it was arg

A. Yu. Cherny, A. A. Shanenko

The thermodynamics of a homogeneous dilute Bose gas with an arbitrary strong repulsion between particles is investigated on the basis of the exact relation connecting the pair correlation function with the in-medium pair wave functions and occupation numbers. It is shown that the effective-interaction scheme which is reduced to the Bogoliubov model with the

N. Morozov, L. N. Bulaevskii, M. P. Maley, Yu. I. Latyshev

From measurements of the c-axis I-V characteristics of intrinsic Josephson junctions in Bi_2Sr_2CaCu_2O_{8+delta} (Bi-2212) mesas we obtain the field dependence (H || c) of the quasiparticle (QP) conductivity, sigma_q(H,T), and of the Josephson critical current density, J_c(H,T). The quasiparticle conductivity sigma_q(H) increases sharply with H and reaches

Liang-Xin Li, Sophia Sun, Yia-Chung Chang

A systematic theoretical study of the electronic and optical properties of Ga$_{1-x}$In$_x$As self-assembled quantum-wires (QWR&#39;s) made of short-period superlattices (SPS) with strain-induced lateral ordering is presented. The theory is based on the effective bond-orbital model (EBOM) combined with a valence-force field (VFF) model. Valence-band anisotro

M. Eschrig, M. R. Norman

Motivated by neutron scattering data, we develop a model of electrons interacting with a magnetic resonance and use it to analyze angle resolved photoemission (ARPES) and tunneling data in the superconducting state of Bi_2Sr_2CaCu_2O_{8+d}. We not only can explain the peak-dip-hump structure observed near the (pi,0) point, and its particle-hole asymmetry as

P. -A. Lemieux, D. J. Durian

Surface flows are excited by steadily adding spherical glass beads to the top of a heap. To simultaneously characterize the fast single-grain dynamics and the much slower collective intermittency of the flow, we extend photon-correlation spectroscopy via fourth-order temporal correlations in the scattered light intensity. We find that microscopic grain dynam

E. Arrigoni, W. Hanke

We consider the projected SO(5) bosonic model introduced in order to connect the SO(5) theory of high-T$_c$ superconductivity with the physics of the Mott-insulating gap, and derive the corresponding effective functional describing low-energy degrees of freedom. At the antiferromagnetic-superconducting transition, SO(5) symmetry-breaking effects due to the g

D. T. Dekadjevi, P. A. Ryan, B. J. Hickey, B. D. Fulthorpe

We present transport and structural data from epitaxial (100) and (111) Au/Fe multilayers grown by molecular beam epitaxy. From their analysis, we conclude that an electron channelling mechanism, due to strong specular reflection of the minority spin carrier at the Au/Fe interfaces, is responsible for the high conductivity in the (100) multilayers.

A. E. Allahverdyan, Th. M. Nieuwenhuizen

A pair of systems at different temperatures is a classic environment for a heat engine, which produces work during the relaxation to a common equilibrium. It is generally believed that a direct interaction between the two systems will always decrease the amount of the obtainable work, due to inevitable dissipation. Here a situation is reported where, in some

K. Ranjan, Sarbpreet Singh, K. Dharamvir, V. K. Jindal

The binding energy of A3C60, a conductor, is described well by an ionic solid type calculation. This succeeds because there is little overlap between molecular wave functions on neighbouring sites, so that electrons are practically localized on-shell. This leads one to believe that even in A4C60 and A6C60 systems such calculation may suffice. However, for la

V. Uski, B. Mehlig, R. A. Römer, M. Schreiber

We determine the statistical properties of wave functions in disordered quantum systems by exact diagonalization of one-, two- and quasi-one dimensional tight-binding Hamiltonians. In the quasi-one dimensional case we find that the tails of the distribution of wave-function amplitudes are described by the non-linear sigma-model. In two dimensions, the tails

R. Salazar, A. R. Plastino, R. Toral

We introduce a nonextensive entropic measure $S_χ$ that grows like $N^χ$, where $N$ is the size of the system under consideration. This kind of nonextensivity arises in a natural way in some $N$-body systems endowed with long-range interactions described by $r^{-α}$ interparticle potentials. The power law (weakly nonextensive) behavior exhibited by $S_χ$ is

D. Jaccard, H. Wilhelm, D. Jerome, J. Moser

The nature of the attractive electron-electron interaction, leading to the formation of Cooper-pairs in unconventional superconductors has still to be fully understood and is subject to intensive research. Here we show that the sequence spin-Peierls, antiferromagnetism, superconductivity observed in (TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagra

Ferenc Igloi, Robert Juhasz, Peter Lajko

The Ma-Dasgupta-Hu renormalization group (RG) scheme is used to study singular quantities in the Griffiths phase of random quantum spin chains. For the random transverse-field Ising spin chain we have extended Fisher&#39;s analytical solution to the off-critical region and calculated the dynamical exponent exactly. Concerning other random chains we argue by

Rong Lu, Jia-Lin Zhu, Zhi-Rong Liu, Lee Chang

The quantum tunneling of the magnetization vector are studied theoretically in single-domain ferromagnetic nanoparticles placed in an external magnetic field at an arbitrarily directed angle in the $ZX$ plane. We consider the magnetocrystalline anisotropy with trigonal and hexagonal crystal symmetry, respectively. By applying the instanton technique in the s

Srikanth Sastry

The liquid-gas spinodal and the glass transition define ultimate boundaries beyond which substances cannot exist as (stable or metastable) liquids. The relation between these limits is analyzed {\it via} computer simulations of a model liquid. The results obtained indicate that the liquid - gas spinodal and the glass transition lines intersect at a finite te

Shigeki Onoda, Masatoshi Imada

We analyze pseudogap phenomena widely observed in the underdoped cuprates. We assume the existence of a strong d-wave pairing force competing with antiferromagnetic(AFM) fluctuations and the formation of flat and damped dispersion around the $(π,0)$ and $(0,π)$ region as two important elements caused by the proximity from the Mott insulator. Using the mode-m

Masatoshi Imada, Shigeki Onoda

Aspects of electron critical differentiation are clarified in the proximity of the Mott insulator. The flattening of the quasiparticle dispersion appears around momenta $(π,0)$ and $(0,π)$ on square lattices and determines the criticality of the metal-insulator transition with the suppressed coherence in that momentum region of quasiparticles. Such coherence

B. P. Anderson, P. C. Haljan, C. E. Wieman, E. A. Cornell

We have observed and characterized the dynamics of singly quantized vortices in dilute-gas Bose-Einstein condensates. Our condensates are produced in a superposition of two internal states of 87Rb, with one state supporting a vortex and the other filling the vortex core. Subsequently, the state filling the core can be partially or completely removed, reducin

E. Amato, M. Salvati, R. Bandiera, F. Pacini

We extend Pacini & Salvati&#39;s model for the synchrotron emission from plerions to allow more realistic predictions of the surface brightness profiles of the Crab Nebula at radio, optical and X-ray frequencies. Abandoning the assumption of a uniform particle distribution, we assume that particles are injected into the synchrotron nebula only in the vicinit

R. W. Lessard, J. H. Buckley, V. Connaughton, S. Le Bohec

We present a method of atmospheric Cherenkov imaging which reconstructs the unique arrival direction of TeV gamma rays using a single telescope. The method is derived empirically and utilizes several features of gamma-ray induced air showers which determine, to a precision of 0.12 degrees, the arrival direction of photons, on an event-by-event basis. Data fr

Azita Valinia, Keith Arnaud, Michael Loewenstein, Richard Mushotzky

We report the results of hard X-ray observations of Abell 496 (A496), a nearby relaxed cluster, using the Rossi X-ray Timing Explorer (RXTE). The 3-20 keV spectrum of this cluster is well-modeled by a thermal component of kT ~ 4.1 keV plus a cooling flow with mass accretion rate of \dot{M} ~ 285 M_{\odot} yr^{-1}. The spectrum is equally well-modeled by a mu

P. Popowski, C. Alcock, R. A. Allsman, D. R. Alves

We present preliminary results of the analysis of 5 years of MACHO data on the Galactic bulge microlensing events with clump giants as sources. In particular, we discuss: 1) the selection of `giant&#39; events, 2) distribution of impact parameters, 3) distribution of event durations, 4) the concentration of long duration events in MACHO field 104 centered on

E. Berger, R. Sari, D. A. Frail, S. R. Kulkarni

We present broad-band radio observations of the afterglow of GRB000301C, spanning from 1.4 to 350 GHz for the period of 3 to 83 days after the burst. This radio data, in addition to measurements at the optical bands, suggest that the afterglow arises from a collimated outflow, i.e. a jet. To test this hypothesis in a self-consistent manner, we employ a globa

Takayoshi Sano, Shoken M. Miyama, Toyoharu Umebayashi, Takenori Nakano

We investigate where in protoplanetary disks magnetorotational instability operates, which can cause angular momentum transport in the disks. We investigate the spatial distribution of various charged particles and the unstable regions for a variety of models for protoplanetary disks taking into account the recombination of ions and electrons at grain surfac

Francesca Bacciotti, Reinhard Mundt, Thomas P. Ray, Jochen Eisloeffel

We have carried out a spatio-kinematic study of the outflow from the classical T Tauri star DG Tau using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). A series of seven spatially offset long-slit spectra spaced by 0.07&#39;&#39; were obtained along the axis of the outflow to build up a 3-D intensity-velocity ``cub

Michael Pivovaroff

(ABRIDGED) This dissertation concerns the use of CCDs for for X-ray astronomy. Part I of this thesis focuses on the calibration of the Advanced CCD Imaging Spectrometer (ACIS), one of the two primary focal plane instruments on the Chandra X-ray Observatory. I begin by presenting a series of measurements made using undispersed synchrotron radiation. I analyze

M. Uslenghi, P. Bergamini, S. Catalano, L. Tommasi

Time-resolved observations of a 6&#39; x 6&#39; field, containing the position error boxes of the X-ray source 1WGA J1958.2+3232, were performed in June 1999 with the 91 cm Catania telescope, equipped with a Photon Counting Intensified CCD. The star recently proposed as the optical counterpart of the 1WGA J1958.2+3232, exhibited a strong optical modulation w

S. D. Friedman, J. C. Howk, B-G Andersson, K. R. Sembach

We report on measurements of interstellar O VI, H2, P II, Si II, Ar I, and Fe II absorption along the line of sight to Sk -67 05, a B0 Ia star in a diffuse H II region in the western edge of the Large Magellanic Cloud (LMC). We find log N(O VI) = 14.40 +/- 0.04 in the Milky Way (MW) component and, using the C IV column density from previous IUE observations,

Maxim Lyutikov

We show that accretion disks with relativisticly hot electrons which are coupled to cold ions is subject to inertial-type instability in which kinematic drag between electrons and ions produces radial acceleration of electrons.

W. Sutantyo, X. -D. Li

We have carried out numerical evolutionary calculations of binary systems to investigate the formation of binary millisecond pulsars (pulsars with white dwarf companions). We apply the ``standard scenario&#39;&#39; in which the binary pulsars are formed from low-mass and intermediate-mass X-ray binaries as well the alternative scenario in which the neutron s

F. Herpin, A. Baudry

We have investigated the influence of several line overlaps between 28SiO, 29SiO and 30SiO on maser emission from the envelopes of late-type stars using the Large Velocity Gradient radiative transfer formalism modified to account for overlaps. Our model includes: (i) 40 rotational levels for each of the v=0 to 4 vibrational states and each isotopic species;

Bruce G. Elmegreen

Statistical sampling from the stellar initial mass function (IMF) for all star-forming regions in the Galaxy would lead to the prediction of ~1000 Msun stars unless there is a rapid turn-down in the IMF beyond several hundred solar masses. Such a turndown is not necessary for dense clusters because the number of stars sampled is always too small. Here we exp