July 2001 arXiv papers — page 17

Tetsuo Deguchi

For the one-dimensional XXX model under the periodic boundary conditions, we discuss two types of eigenvectors, regular eigenvectors which have finite-valued rapidities satisfying the Bethe ansatz equations, and non-regular eigenvectors which are descendants of some regular eigenvectors under the action of the SU(2) spin-lowering operator. It was pointed out

Youngjai Kiem, Soo-Jong Rey, Haru-Tada Sato, Jung-Tay Yee

One-loop effective action of noncommutative scalar field theory with cubic self-interaction is studied. Utilizing worldline formulation, both planar and nonplanar part of the effective action are computed explicitly. We find complete agreement of the result with Seiberg-Witten limit of string worldsheet computation and standard Feynman diagrammatics. We prov

P. Colangelo, F. De Fazio

We consider the semileptonic and nonleptonic $D_s$ decay modes to final states with $η$ and $η^\prime$. We use QCD sum rules to determine the $D_s \to η$ form factor $f_+^η$, and a generalized factorization ansatz to compute nonleptonic decays. We propose a parameterization of possible OZI suppressed contributions producing the $η^\prime$ in the final state,

R. H. Hadfield, G. Burnell, P. K. Grimes, D. -J. Kang

We explore novel junction configurations as an extension of our established Focused Ion Beam-based low TC SNS Junction fabrication technique. By milling a circular trench (diameter 1 micron, width 50 nm) in a 125 nm Nb 75 nm Cu bilayer we define a superconducting island connected to the bulk of the film by a normal metal barrier and entirely enclosed in-plan

D. Moss, A. Shukurov, D. Sokoloff, R. Beck

We study the generation and maintenance of large-scale magnetic fields in barred galaxies. We take a velocity field (with strong noncircular components) from a published gas dynamical simulation of Athanassoula (1992), and use this as input to a galactic dynamo calculation. Our work is largely motivated by recent high quality VLA radio observations of the ba

Xiao-yan Tang, Sen-yue Lou, Ying Zhang

After extending the Clarkson-Kruskal's direct similarity reduction ansatz to a more general form, one may obtain various new types of reduction equations. Especially, some lower dimensional turbulence systems or chaotic systems may be obtained from the general type of similarity reductions of a higher dimensional Lax integrable model. Especially, the Kur

M. Hayakawa, N. Ishibashi

We study the world-volume theory of a bosonic membrane perturbatively and discuss if one can obtain any conditions on the number of space-time dimensions from the consistency of the theory. We construct an action which is suitable for such a study. In order to study the theory perturbatively we should specify a classical background around which perturbative

TOF collaboration

The cross section for the production of $ω$ mesons in proton-proton collisions has been measured in a previously unexplored region of incident energies. Cross sections were extracted at 92 MeV and 173 MeV excess energy, respectively. The angular distribution of the $ω$ at $ε$=173 MeV is strongly anisotropic, demonstrating the importance of partial waves beyo

Hiroki Saito, Masahito Ueda

The dynamics of collapsing and exploding trapped Bose-Einstein condensat es caused by a sudden switch of interactions from repulsive to attractive a re studied by numerically integrating the Gross-Pitaevskii equation with atomic loss for an axially symmetric trap. We investigate the decay rate of condensates and the phenomena of bursts and jets of atoms, and

Kazuyuki Furuuchi, Kazumi Okuyama

We study the matter part of the algebra of open string fields using the 3-string vertex over the sliver state, which we call ``comma vertex''. By generalizing this comma vertex to the $N$-string overlap, we obtain a closed form of the Neumann coefficients in the $N$-string vertex and discuss its relation to the oscillator representation of wedge stat

Gagik Yu. Kryuchkyan

The problems of cavity atom optics in the presence of an external strong coherent field are formulated as the problems of potential scattering of doubly-dressed atomic wave packets. Two types of potentials produced by various multiphoton Raman processes in a high-finesse cavity are examined. As an application the deflection of dressed atomic wave by a cavity

Gagik Yu. Kryuchkyan, Suren B. Manvelyan

A quantum manifestation of chaotic classical dynamics is found in the framework of oscillatory numbers statistics for the model of nonlinear dissipative oscillator. It is shown by numerical simulation of an ensemble of quantum trajectories that the probability distributions and variances of oscillatory number states are strongly transformed in the order-to-c

Kiyoshi Higashijima, Tetsuji Kimura, Muneto Nitta

We present the Ricci-flat metric and its Kahler potential on the conifold with the O(N) isometry, whose conical singularity is repaired by the complex quadric surface Q^{N-2} = SO(N)/SO(N-2)xU(1).

A. P. Balachandran, Brian P. Dolan, J. Lee, X. Martin

We derive an explicit expression for an associative *-product on fuzzy complex projective spaces. This generalises previous results for the fuzzy 2-sphere and gives a discrete non-commutative algebra of functions on fuzzy complex projective spaces, represented by matrix multiplication. The matrices are restricted to ones whose dimension is that of the totall

R. Foot

Mirror matter is predicted to exist if parity (i.e. left-right symmetry) is a symmetry of nature. Remarkably mirror matter is capable of simply explaining a large number of contemporary puzzles in astrophysics and particle physics including: Explanation of the MACHO gravitational microlensing events, the existence of close-in extrasolar gas giant planets, ap

Krzysztof Sacha, Bruno Eckhardt

We consider the final stage of triple ionization of atoms in a strong linearly polarized laser field. We propose that for intensities below the saturation value for triple ionization the process is dominated by the simultaneous escape of three electrons from a highly excited intermediate complex. We identify within a classical model two pathways to triple io

Xiaoying Li, Qing Pan, Jietai Jing, Jing Zhang

Highly efficient quantum dense coding for continuous variables has been experimentally accomplished by means of exploiting bright EPR beam with anticorrelation of amplitude quadratures and correlation of phase quadratures, which is generated from a nondegenerate optical parametric amplifier operating in the state of deamplification. Two bits of classical inf

Hoi-Kwong Lo

We prove the unconditional security of the standard six-state scheme for quantum key distribution (QKD). We demonstrate its unconditional security up to a bit error rate of 12.7 percents, by allowing only one-way classical communications in the error correction/privacy amplification procedure between Alice and Bob. This shows a clear advantage of the six-sta

A. B. van Oosten

Attempts to quantize light in a manifestly Lorentz covariant manner fail because of the indefinite metric problem. Here an error in the interpretation is uncovered that is at the root of this problem.

J. S. Kole, M. T. Figge, H. De Raedt

Based on the Suzuki product-formula approach, we construct a family of unconditionally stable algorithms to solve the time-dependent Maxwell equations. We describe a practical implementation of these algorithms for one-, two-, and three-dimensional systems with spatially varying permittivity and permeability. The salient features of the algorithms are illust

Paramel P. Rajeev, Arvinder S. Sandhu, G. Ravindra Kumar

K x-ray emission from copper plasmas produced by 100 fs, 806 nm laser pulses at intensities in the range of 10^15-10^16 W cm^-2 is studied with respect to input laser polarization and target surface conditions. We demonstrate that even moderate surface roughness enhances the characteristic x-ray yield by as much as 70 %. We further show that surface roughnes

W. L. Qian, Ru-Keng Su, H. Q. Song

By means of the Furnstahl, Serot and Tang's model, the effects of surface tension and Coulomb interaction on the liquid-gas phase transition for finite nuclei are investigated. A limit pressure p-lim above which the liquid-gas phase transition cannot take place has been found. It is found that comparing to the Coulomb interaction, the contribution of sur

Sen-yue Lou

In this letter, a definition of the higher dimensional Lax pair for a lower dimensional system which may be a chaotic system is given. A special concrete (2+1)-dimensional Lax pair for a general (1+1)-dimensional three order autonomous partial differential equation is studied. The result shows that any (1+1)-dimensional three order semi-linear autonomous sys

Y. Takahashi, N. Kataoka, K. Kaneko, T. Namiki

We show mathematical structure of the function dynamics, i.e., the dynamics of interval maps $f_{n+1} = (1-\e)f_n + \e f_n\circ f_n$ and clarify the types of fixed points, the self-referential structure and the hierarchical structure.

Debabrata Biswas

Polygonalization of any smooth billiard boundary can be carried out in several ways. We show here that the semiclassical description depends on the polygonalization process and the results can be inequivalent. We also establish that generalized tangent-polygons are closest to the corresponding smooth billiard and for de Broglie wavelengths larger than the av

Debabrata Biswas

The arbitrary trajectory quantization method (ATQM) is a time dependent approach to quasiclassical quantization based on the approximate dual relationship that exists between the quantum energy spectra and classical periodic orbits. It has recently been shown however, that, for polygonal billiards, the periodicity criterion must be relaxed to include closed

G. Gallavotti, G. Gentile

We consider a class of a priori stable quasi-integrable analytic Hamiltonian systems and study the regularity of low-dimensional hyperbolic invariant tori as functions of the perturbation parameter. We show that, under natural nonresonance conditions, such tori exist and can be identified through the maxima or minima of a suitable potential. They are analyti

Peter A. Linnell

A. H. Rhemtulla proved that if a group is a residually finite p-group for infinitely many primes p, then it is two-sided orderable. In problem 10.30 of the Kourovka notebook 14th. edition, N. Ya. Medvedev asked if there is a non-right-orderable group which is a residually finite p-group for at least two different primes p. Using a result of Dave Witte, we wi

Claudio Gorodski

We show that a totally geodesic submanifold of a symmetric space satisfying certain conditions admits an extension to a minimal submanifold of dimension one higher, and we apply this result to construct new examples of complete embedded minimal submanifolds in simply connected noncompact globally symmetric spaces.

Scott Baldridge

The main result of this paper is a formula for calculating the Seiberg-Witten invariants of 4-manifolds with fixed-point free circle actions. This is done by showing under suitable conditions the existence of a diffeomorphism between the moduli space of the 4-manifold and the moduli space of the quotient 3-orbifold. Two corollaries include b_+>1 4-manifolds

Claude Schochet

In this paper we identify QD(A,B), the quasidiagonal classes in KK_1(A,B), in terms of K_*(A) and K_*(B), and we use these results in various applications. Here is our central result. Theorem: Suppose that A is in the category of separable nuclear C^*-algebras which satisfy the UCT and A is quasidiagonal relative to B. Then there is a natural isomorphism QD(

M. Kapranov

We develop a theory of measures, differential forms and Fourier tramsforms on some infinite-dimensional real vector spaces by generalizing the following two constructions: (a) The construction of the semiinfinite wedge power of a Tate vector space V. Recall that it is obtained as a certain double inductive limit of the exterior algebras of finite-dimensional

C. Mason

We begin by studying semigroup estimates that are more singular than those implied by a Sobolev embedding theorem but which are equivalent to certain logarithmic Sobolev inequalities. We then give a method for showing such log--Sobolev inequalities hold for Euclidean regions that satisfy a certain Hardy-type inequality. Our main application is to show that d

J. Ginibre, G. Velo

We study the theory of scattering for the system consisting of a Schr"odinger equation and a wave equation with a Yukawa type coupling,in space dimension 3.We prove in particular the existence of modified wave operators for that system with no size restriction on the data and we determine the asymptotic behaviour in time of solutions in the range of the

A. P. Isaev, O. V. Ogievetsky

For a Hopf algebra A, we define the structures of differential complexes on two dual exterior Hopf algebras: 1) an exterior extension of A and 2) an exterior extension of the dual algebra A^*. The Heisenberg double of these two exterior Hopf algebras defines the differential algebra for the Cartan differential calculus on A. The first differential complex is

J. S. Milne

Define an arithmetic variety to be the quotient of a bounded symmetric domain by an arithmetic group. An arithmetic variety is algebraic, and the theorem in question states that when one applies an automorphism of the field of complex numbers to the coefficients of an arithmetic variety the resulting variety is again arithmetic. This article simplifies Kazhd

G. Hoermann, M. V. de Hoop

In global seismology Earth's properties of fractal nature occur. Zygmund classes appear as the most appropriate and systematic way to measure this local fractality. For the purpose of seismic wave propagation, we model the Earth's properties as Colombeau generalized functions. In one spatial dimension, we have a precise characterization of Zygmund re

Alejandro Adem, Jeff H. Smith

In this paper we show that the cohomology of a connected CW complex is periodic if and only if it is the base space of an orientable spherical fibration with total space that is homotopically finite dimensional. As applications we characterize those discrete groups that act freely and properly on a cartesian product of euclidean space and a sphere; we constr

M. D. Maia, V. B. Bezerra

Quaternion quantum mechanics is examined at the level of unbroken SU(2) gauge symmetry. A general quaternionic phase expression is derived from formal properties of the quaternion algebra.

Amitabha Lahiri

A novel inhomogeneous gauge transformation law is proposed for a non-Abelian adjoint two-form in four dimensions. Rules for constructing actions invariant under this are given. The auxiliary vector field which appears in some of these models transforms like a second connection in the theory. Another local symmetry leaves the compensated three-form field stre

Sergio M. Iguri, Francisco D. Mazzitelli

We derive a generalized Nielsen identity for the case of Yang-Mills theories that include some classical fields. We discuss under which circumstances the effective action of the classical fields (i.e., after integration of quantum fields) becomes gauge fixing independent. We conclude that classical test fields provide a physical insight into the problem of t

N. Mohammedi

A new T-duality transformation is found in two-dimensional non-linear sigma models. This is a straightforward generalisation of Abelian and non-Abelian T-dualities.

F. Finelli, S. Khlebnikov

We consider decay of the inflaton with a quartic potential coupled to other fields, including gravity, but restricted to spherical symmetry. We describe analytically an early, quasilinear regime, during which inflaton fluctuations and the metric functions are driven by nonlinear effects of the decay products. We present a detailed study of the leading nonlin

Sangyong Jeon

We study the production of $η'$ from hadronizing thermal gluons using recently proposed $η'-g-g$ effective vertex. The $η'$ yield is found to be sensitive to the initial condition. At RHIC and LHC, the enhancement is large enough to be easily detected.

M. Cacciari, S. Catani

We present a QCD study of fragmentation processes for light and heavy quarks in the semi-inclusive region of large x. Large logarithmic terms, due to soft-gluon radiation, are evaluated and resummed to all perturbative orders in the QCD coupling alpha_s. Complete analytical results to next-to-leading logarithmic accuracy are given for one-particle and two-pa

J. Dias de Deus, Yu. M. Shabelski

We present a short review of theoretical results (mainly for experimentalists) published in many different papers. The formulae are presented for the different integrated cross sections, the number of interacting nucleons, multiplicities of secondaries, the dispersions of multiplicity distributions. Two possible tests for the search of Quark-Gluon Plasma for

A. V. Kotikov, A. V. Lipatov, G. Parente, N. P. Zotov

We calculate the perturbative parts of the structure functions $F_2^c$ and $F_L^c$ for a gluon target having nonzero transverse momentum squared at order $α_s$. The results of the double convolution (with respect to the Bjorken variable $x_B$ and the transverse momentum) of the perturbative part and the unintegrated gluon densities are compared with HERA exp

Hiroaki Sugiyama

The critical and the tricritical exponents of the Gross-Neveu model are calculated in the large-$N_f$ limit. Our results indicate that these exponents are given by the mean-field values.

Jisuke Kubo, Daijiro Suematsu

The idea of Nelson and Strassler to obtain a power law suppression of parameters by a superconformal force is applied to understand the smallness of the $μ$ parameter and neutrino masses in R-parity violating supersymmetric standard models. We find that the low-energy sector should contain at least another pair of Higgs doublets, and that a suppression of $\

A. Belyaev, G. Buchalla, A. Ceccucci, M. Chizhov

We study opportunities for future high-precision experiments in kaon physics using a high-intensity proton driver, which could be part of the front-end of a muon storage ring complex. We discuss in particular the rare decays $K_L\toπ^0ν\barν$, $K^+\toπ^+ν\barν$, $K_L\toπ^0e^+e^-$, and lepton-flavour violating modes such as $K_L\toμe$ and $K\toπμe$. The outst

Nicolas Delerue

Searches for physics beyond the Standard Model have been performed in high-energy $e^{\pm}p$ collisions at HERA. No significant deviation from the Standard Model has been observed while searching for contact interactions, extra dimensions, leptoquarks, R-parity violating squarks and excited fermions. Exclusion limits have been inferred which extend or comple

H1 Collaboration, C. Adloff

A search for scalar and vector leptoquarks coupling to first generation fermions is performed in the H1 experiment at the ep collider HERA. The analysis uses e^- p data collected in 1998 and 1999 at a centre-of-mass energy of 320 GeV, corresponding to an integrated luminosity of 15 pb^-1. No evidence for the direct production of such particles is found in a

L. Gualtieri, E. Berti, J. A. Pons, G. Miniutti

We compute the energy spectra of the gravitational signals emitted when a pointlike mass moves on a closed orbit around a non rotating neutron star, inducing a perturbation of its gravitational field and its internal structure. The Einstein equations and the hydrodynamical equations are perturbed and numerically integrated in the frequency domain. The result

Jerome Novak

The collapse of spherical neutron stars is studied in General Relativity. The initial state is a stable neutron star to which an inward radial kinetic energy has been added through some velocity profile. For two different equations of state and two different shapes of velocity profiles, it is found that neutron stars can collapse to black holes for high enou

Krzysztof R. Apt

This is a tutorial on logic programming and Prolog appropriate for a course on programming languages for students familiar with imperative programming.

Timothy H. Keitt, Luis A. N. Amaral, Sergey V. Buldyrev, H. E. Stanley

We consider statistical patterns of variation in growth rates for over 400 species of breeding birds across North America surveyed from 1966 to 1998. We report two results. First, the standard deviation of population growth rates decays as a power-law function of total population size with an exponent $β= 0.36\pm0.02$. Second, the number of subpopulations, m

K. Levin, Qijin Chen, Ioan Kosztin, Boldizsar Janko

In the last few years evidence has been accumulating that there are a multiplicity of energy scales which characterize superconductivity in the underdoped cuprates. In contrast to the situation in BCS superconductors, the phase coherence temperature Tc is different from the energy gap onset temperature T*. In addition, thermodynamic and tunneling spectroscop

Ajay Gopinathan, Tong Zhou, S. N. Coppersmith, L. P. Kadanoff

We investigate the influence of geometric confinement on the free energy of an idealized model for charge-stabilized colloidal suspensions. The mean-field Poisson-Boltzmann formulation for this system predicts pure repulsion among macroionic colloidal spheres. Fluctuations in the simple ions' distribution provide a mechanism for the macroions to attract

V. Bouchiat, M. Faucher, C. Thirion, W. Wernsdorfer

We present a method for fabricating Josephson junctions and superconducting quantum interference devices (SQUIDs) which is based on the local anodization of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained either by partial or total oxidation of the niobium la

Claudio Chamon, Eduardo R. Mucciolo, Antonio H. Castro Neto

Based on recent experimental evidence for a spin polarized ground state in the insulating phase of the two-dimensional electron system, we propose that ferromagnetic spin fluctuations lead to an attractive interaction in the triplet channel and cause p-wave pairing in the conducting phase. We use the Landau Fermi liquid phenomenology to explain how the enhan

D. Sreedhar Babu, R. Shankar, M. Sivakumar

We study the current algebra of FQHE systems in the hydrodynamical limit of small amplitude, long-wavelength fluctuations. We show that the algebra simplifies considerably in this limit. The hamiltonian is expressed in a current-current form and the operators creating inter-Landau level and lowest Landau level collective excitations are identified.

Xavier Waintal, Piet W. Brouwer

A ferromagnet-normal-metal-ferromagnet trilayer does not conserve spin current and as a result, the conduction electrons can create a torque on the magnetic moments. When the trilayer is connected to a superconducting electrode, the spin torque created by a current flowing perpendicularly to the trilayer can drive the system to a configuration where the two

Paola Gori-Giorgi, John P. Perdew

We use the two-electron wavefunctions (geminals) and the simple screened Coulomb potential proposed by Overhauser [Can. J. Phys. 73, 683 (1995)] to compute the pair-distribution function for a uniform electron gas. We find excellent agreement with Quantum Monte Carlo simulations in the short-range region, for a wide range of electron densities. We are thus a

N. Klein, B. B. Jin, J. Schubert, M. Schuster

We have measured the temperature dependence of the microwave surface impedance Z_s = R_s + iΩμ_0 of a MgB2 film at a frequency Ω/2Πof 18 GHz employing a dielectric resonator technique. We found that the temperature dependence of the magnetic field penetration depth \Lamda can be fitted by \Lamda(T)= \Lamda(0) [1-(T/Tc)^2] ^(-1/2) with \Lamda(0)=(260 +/- 20)n

Xavier Waintal, Piet W. Brouwer

We show that a Josephson current flowing through a ferromagnet-normal-metal-ferromagnet trilayer connected to two superconducting electrodes induces an equilibrium exchange interaction between the magnetic moments of the ferromagnetic layers. The sign and magnitude of the interaction can be controlled by the phase difference between the order parameters of t

M. Potthoff

The basic theory of photoemission, inverse photoemission, Auger-electron and appearance-potential spectroscopy is developed within a unified framework starting from Fermi's golden rule. The spin-resolved and temperature-dependent appearance-potential spectroscopy of band-ferromagnetic transition metals is studied in detail. It is shown that the considera

Fabrizio Lillo, Rosario N. Mantegna

We study the price dynamics of stocks traded in the NASDAQ market by considering the statistical properties of an ensemble of stocks traded simultaneously. For each trading day of our database, we study the ensemble return distribution by extracting its first two central moments. According to previous results obtained for the NYSE market, we find that the se

W. Nolting, M. Potthoff, T. Herrmann, T. Wegner

We investigate the possibility and stability of bandferromagnetism in the single-band Hubbard model. This model poses a highly non-trivial many-body problem the general solution of which has not been found up to now. Approximations are still unavoidable. Starting from a simple two-pole ansatz for the spectral density our approach is systematically improved b

J. Vidal, D. Mouhanna, T. Giamarchi

We consider interacting spinless fermions in one dimension embedded in self-similar quasiperiodic potentials. We examine generalizations of the Fibonacci potential known as precious mean potentials. Using a bosonization technique and a renormalization group analysis, we study the low-energy physics of the system. We show that it undergoes a metal-insulator t

M. Zareyan, W. Belzig, Yu. V. Nazarov

We investigate superconducting proximity effect in clean ferromagnetic layers with rough boundaries. The subgap density of states is formed by Andreev bound states at energies which depend on trajectory length and the ferromagnetic exchange field. At energies above the gap, the spectrum is governed by resonant scattering states. The resulting density of stat

M. F. Menezes, R. M. Zorzenon dos Santos

In this paper we revisit the Mackey-Glass model for blood-forming process, which was proposed to describe the spontaneous fluctuations of the blood cell counts in normal individuals and the first stage of chronic myelocytic (or granylocytic) leukemia (CML). We obtain the bifurcation diagram as a function of the time delay parameter and show that the onset of

Daniel Huertas-Hernando, Gerrit E. W. Bauer, Yu. V. Nazarov

The resistance of CPP spin valve is a continuous function of the angle $θ$ between the magnetizations of both ferromagnets. We use the cicuit theory for non-collinear magnetoelectronics to compute the angular magnetoresistance of CPP spin valves taking the spin accumulation in the ferromagnetic layers into account.

Susanna C. Manrubia, Ugo Bastolla, Alexander S. Mikhailov

Systems of globally coupled logistic maps (GCLM) can display complex collective behaviour characterized by the formation of synchronous clusters. In the dynamical clustering regime, such systems possess a large number of coexisting attractors and might be viewed as dynamical glasses. Glass properties of GCLM in the thermodynamical limit of large system sizes

P. Prelovsek, X. Zotos

The zero-temperature Hall response within tight-binding models of correlated electrons is studied. Using the linear response theory and a linearization in the magnetic field B, a general relation for the reactive (zero frequency) Hall constant in the fast (transport) limit is derived, involving only matrix elements between the lowest excited states at B=0; f

Himanshu Agrawal, Deepak Dhar

We have studied the probability distribution of the perimeter and the area of the k-th largest erased-loop in loop-erased random walks in two-dimensions for k = 1 to 3. For a random walk of N steps, for large N, the average value of the k-th largest perimeter and area scales as N^{5/8} and N respectively. The behavior of the scaled distribution functions is

Atisdipankar Chakrabarti, Abhijit Mookerjee

Off-stoichiometric alloys exhibit partial disorder, in the sense that only some of the sublattices of the stoichiometric ordered alloy become disordered. This paper puts forward a generalization of the augmented space recursion (ASR) (introduced earlier by one of us (Mookerjee et al 1997(*))) for systems with many atoms per unit cell. In order to justify the

N. P. Armitage, D. H. Lu, C. Kim, A. Damascelli

We report a high-resolution angle-resolved photoemission spectroscopic (ARPES) study of the electron-doped (n-type) cuprate superconductor Nd_1.85Ce_0.15CuO_4. We observe regions along the Fermi surface where the near-E_F intensity is suppressed and the spectral features are broad in a manner reminiscent of the high-energy ``pseudogap'' in the underd

D. J. Huang, W. P. Wu, C. F. Chang, J. Chen

With on- and off- resonant excitation photons, spin-resolved Auger electron spectra of epitaxial CrO$_{2}$ thin films show an experimental evidence of the spin-selective KLL Auger decay. The on-resonance O KLL Auger electrons are found to be highly spin-polarized, while the off-resonance ones with almost zero spin polarization. These results lead to conclude

S. Reich, G. Leitus, I. Felner

The experimentally observed ferromagnetism in MgB2 in the normal state is attributed to micro phase separated inclusions of iron. This magnetic character is also observed when the iron content of the samples is reduced below 20 micro-g/g, however in these samples the diamagnetism of MgB2 is apparent and is measured. It is found experimentally that the diamag

R. C. Berrington, C. D. Dermer, S. J. Sturner

Subcluster interactions within clusters of galaxies produce shocks that accelerate nonthermal particles. We treat Fermi acceleration of nonthermal electrons and protons by injecting power-law distributions of particles during the merger event, subject to constraints on maximum particle energies. The broadband nonthermal spectrum emitted by accelerated electr

Moshe Gai

GeV beams of light ions and electrons are used for creating a high flux of real and virtual photons, with which some problems in Nuclear Astrophysics are studied. GeV 8B beams are used to study the Coulomb dissociation of 8B and thus the 7Be(p,gamma)8B reaction. This reaction is one of the major source of uncertainties in estimating the 8B solar neutrino flu

S. M. Kahn, A. Kinkhabwala, M. Sako, E. Behar

X-ray spectroscopy of Seyfert 2 galaxies provides an excellent probe of the circumnuclear environment in active galactic nuclei. The grating experiments on both Chandra and XMM-Newton have now provided the first high resolution spectra of several of the brightest Seyfert 2's. We present Chandra HETG data on Markarian 3 and XMM-Newton RGS data on NGC 1068

A. Kinkhabwala, M. Sako, E. Behar, F. Paerels

Soft X-ray spectroscopy of Seyfert 2 galaxies offers perhaps the best method to probe the possible connection between AGN activity and star formation. Obscuration of powerful radiation from the inferred nucleus allows for detailed study of circumnuclear emission regions. And soft X-ray spectroscopy of these regions allows for robust discrimination between wa

K. E. Saavik Ford, David A. Neufeld

We argue that the presence of water vapor in the circumstellar outflow of a carbon-rich AGB star is potentially a distinctive signature of extra-solar cometary systems. Detailed models show that at suitable distances from the star, water ice can survive well into the carbon-rich AGB phase; water vapor abundances as large as 10^-6 could result from the vapori

Gary Steigman

The primordial abundances of deuterium, helium, and lithium probe the baryon density of the universe only a few minutes after the Big Bang. Of these relics from the early universe, deuterium is the baryometer of choice. After reviewing the current observational status (a moving target!), the BBN baryon density is derived and compared to independent estimates

Elizabeth L. Blanton, Craig L. Sarazin, Brian R. McNamara, Michael W. Wise

We present a Chandra observation of Abell 2052, a cooling flow cluster with a central cD that hosts the complex radio source 3C 317. The data reveal ``holes'' in the X-ray emission that are coincident with the radio lobes. The holes are surrounded by bright ``shells'' of X-ray emission. The data are consistent with the radio source displacing

P. Coelho, B. Barbuy, M. -N. Perrin, T. Idiart

Low resolution spectra of 23 stars towards the bulge globular clusters NGC 6528 and NGC 6553 are analysed. Radial velocities and atmospheric parameters are derived in order to check their membership in the clusters. Effective temperatures were obtained from photometric data for stars with Teff > 3800 K, whereas for cooler stars, they were derived from equiva

John Kormendy, Karl Gebhardt, F. Duccio Macchetto, W. B. Sparks

Many ellipticals contain nuclear disks of dust and gas. Some ellipticals contain nuclear disks of stars that are distinct from the rest of the galaxy. We show that the dwarf E2 galaxy NGC 4486A contains both -- it is a "Rosetta stone" object that tells us how nuclear disks evolve. Its properties suggest that, as accreted gas dissipates and settles to

C. D. Dermer, M. Boettcher, E. P. Liang

Many classes of gamma-ray sources, such as gamma-ray bursts, blazars, Seyfert galaxies, and galactic black hole sources are surrounded by large amounts of gas and dust. X-rays and gamma-rays that traverse this material will be attenuated by Compton scattering and photoelectric absorption. One signature of an intervening scattering cloud is radiation-hardenin

C. D. Dermer, R. J. Murphy

Observations of annihilation radiation in the Galaxy are briefly reviewed. We summarize astrophysical mechanisms leading to positron production, and recent estimates for production rates from nova and supernova nucleosynthesis in the Galaxy. The physical processes involved in the production of annihilation radiation in the interstellar medium are described.

B. E. J. Pagel

An attempt is made to guess the overall cosmic abundance of `metals' and the contribution made by the energy released in their production to the total intensity of extragalactic background light (EBL). With a comparable or somewhat larger amount coming from white dwarfs, and a probably quite modest contribution from AGNs, one can fairly easily account fo

Andrew Cumming, Lars Bildsten

We show that burning of a small mass fraction of carbon in a neutron star ocean is thermally unstable at low accumulated masses when the ocean contains heavy ashes from the hydrogen burning rapid proton (rp) process. The key to early unstable ignition is the low thermal conductivity of a heavy element ocean. The instability requires accretion rates in excess

Gary J. Melnick, David A. Neufeld, K. E. Saavik Ford, David J. Hollenbach

Since 1995, astronomers have discovered planets with masses comparable to that of Jupiter (318 times Earth's mass) in orbit around approximately 60 stars. Although unseen directly, the presence of these planets is inferred by the small reflex motions that they gravitationally induce on the star they orbit; these result in small periodic wavelength shifts

P. A. M. van Hoof, J. C. Weingartner, P. G. Martin, K. Volk

Ever since the pioneering study of Spitzer, it has been widely recognized that grains play an important role in the heating and cooling of photo-ionized environments. This includes the diffuse ISM, as well as H II regions, planetary nebulae, and photo-dissociation regions. A detailed code is necessary to model grains in a photo-ionized medium since the inter

M. Doering, K. Bernloehr, G. Hermann, W. Hofmann

The HEGRA system of Imaging Atmospheric Cherenkov Telescopes (IACTs) detects Cherenkov light produced by air showers. The concept of stereoscopic observation with the five HEGRA telescopes allows the reconstruction of various shower parameters, for example the shower direction, the location of the shower core and the energy of cosmic rays. One of the telesco

David S. Graff

Based on a proper motion survey, Oppenheimer et al. claim the detection of a white dwarf component of the dark matter of the halo. I show that most of the white dwarfs in their sample are likely disk white dwarfs which have been previously detected, and represent no new population.

K. S. Viswanathan, Yi Yang

We use the BSFT method to study the unoriented open string field theory (type I). The partition function on the Mobius strip is calculated. We find that, at the one-loop level, the divergence coming from planar graph and unoriented graph cancel each other as expected.

Benson Farb, John Franks

This self-contained paper is part of a series \cite{FF2,FF3} on actions by diffeomorphisms of infinite groups on compact manifolds. The two main results presented here are: 1) Any homomorphism of (almost any) mapping class group or automorphism group of a free group into $\Diff_+^r(S^1), r\geq 2$ is trivial. For r=0 Nielsen showed that in many cases nontrivi

C. A. Bertulani, F. Navarra

The production of mesons in ultra-peripheral collisions of relativistic heavy ions is re-analyzed using a projection technique to calculate the amplitudes for the appropriate Feynman diagrams. The virtuality of the exchanged photons is fully accounted for in this approach. In the case of two-photon fusion, it is explicitly shown that the inclusion of nuclear

Frank Ferrari

The large Nc expansion of N=2 supersymmetric Yang-Mills theory with gauge group SU(Nc) has recently been shown to break down at singularities on the moduli space. We conjecture that by taking Nc to infinity and approaching the singularities in a correlated way, all the observables of the theory have a finite universal limit yielding amplitudes in string theo