July 2004 arXiv papers — page 13

Kazuhiro Hikami

We reveal a relationship between the colored Jones polynomial and the A-polynomial for twist knots. We demonstrate that an asymptotics of the $N$-colored Jones polynomial in large $N$ gives the potential function, and that the A-polynomial can be computed. Also discussed is a case of torus knots.

Viswanath Ramakrishna, F. Costa

In this note explicit algorithms for calculating the exponentials of important structured 4 x 4 matrices are provided. These lead to closed form formulae for these exponentials. The techniques rely on one particular Clifford Algebra isomorphism and basic Lie theory. When used in conjunction with structure preserving similarities, such as Givens rotations, th

James Nolen, Jack Xin

We prove the existence of reaction-diffusion traveling fronts in mean zero space-time periodic shear flows for nonnegative reactions including the classical KPP (Kolmogorov-Petrovsky-Piskunov) nonlinearity. For the KPP nonlinearity, the minimal front speed is characterized by a variational principle involving the principal eigenvalue of a space-time periodic

Daniel Coutand, Steve Shkoller

The motion of an elastic solid inside of an incompressible viscous fluid is ubiquitous in nature. Mathematically, such motion is described by a PDE system that couples the parabolic and hyperbolic phases, the latter inducing a loss of regularity which has left the basic question of existence open until now. In this paper, we prove the existence and uniquenes

J. E. Palomar Tarancon

Consider a Hausdorff space (X,T) and a set C of converging nets in X. By virtue of the limit uniqueness, the relation Lim which assigns each member x of X to every net N lying in C that converges to x is a map. Of course, structuring C with some topology U, Lim can be a continuous map. If T is a topology induced by a uniformity, and F is a function space suc

Yuri Kondratiev, Eugene Lytvynov, Michael Röckner

We study properties of the semigroup $(e^{-tH})_{t\ge 0}$ on the space $L^ 2(Γ_X,π)$, where $Γ_X$ is the configuration space over a locally compact second countable Hausdorff topological space $X$, $π$ is a Poisson measure on $Γ_X$, and $H$ is the generator of the Glauber dynamics. We explicitly construct the corresponding Markov semigroup of kernels $(P_t)_

S. Hejazian, M. Mirzavaziri, M. S. Moslehian

Let ||.|| be a norm on the algebra M_n of all n-by-n matrices over the complex field C. An interesting problem in matrix theory is that "are there two norms ||.||_1 and ||.||_2 on C^n such that ||A||=max{||Ax||_2: ||x||_1=1} for all A in M_n. We will investigate this problem and its various aspects and will discuss under which conditions ||.||_1=||.||_2.

Andre Fonseca, Gerson Francisco

We study the existence of homoclic solutions for reversible Hamiltonian systems taking the family of differential equations u^4+au^2-u+f(u,b)=0 as a model. Here f is an analytic function and a, b real parameters. These equations are important in several physical situations such as solitons and in the existence of ``finite energy'' stationary states o

D. D. Porosniuc

We obtain a class of locally symetric Kaehler Einstein structures on the nonzero cotangent bundle of a Riemannian manifold of positive constant sectional curvature. The obtained class of Kaehler Einstein structures depends on one essential parameter and cannot have constant holomorphic sectional curvature.

D. A. Stepanov

Let $(X,o)$ be a 3-dimensional terminal singularity of type $cD$ or $cE$ defined in $\mathbb{C}^4$ by an equation non-degenerate with respect to its Newton diagram. We show that there is not more than 1 non-rational divisor $E$ over $(X,o)$ with discrepancy $a(E,X)=1$. We also describe all blowups $σ$ of $(X,o)$ such that $E=\Exc(σ)$ is non-rational and $a(E

Toru Ohmoto

We define the equivariant Chern-Schwartz-MacPherson class of a possibly singular algebraic variety with a group action over the complex number field (or a field of characteristic 0). In fact, we construct a natural transformation from the equivariant constructible function functor to the equivariant homology functor (in the sense of Totaro-Edidin-Graham), wh

Masaru Kada, Kazuo Tomoyasu, Yasuo Yoshinobu

It is known that the Stone-Čech compactification of a non-compact metrizable space $X$ is approximated by the collection of Smirnov compactifications of $X$ for all compatible metrics on $X$. We investigate the smallest cardinality of a set $D$ of compatible metrics on the countable discrete space $ω$ such that, the Stone-Čech compactification of $ω$ is appr

William Crawley-Boevey, Peter Shaw

We introduce a family of algebras which are multiplicative analogues of preprojective algebras, and their deformations, as introduced by M. P. Holland and the first author. We show that these algebras provide a natural setting for the 'middle convolution' operation introduced by N. M. Katz in his book 'Rigid local systems', and put in an alge

Richard P. Kent

Given a compact orientable 3-manifold M whose boundary is a hyperbolic surface and a simple closed curve C in its boundary, every knot in M is homotopic to one whose complement admits a complete hyperbolic structure with totally geodesic boundary in which the geodesic representative of C is as small as you like.

Roland Lehoucq, Jean-Philippe Uzan, Jeffrey Weeks

Cosmologists are taking a renewed interest in multiconnected spherical 3-manifolds (spherical spaceforms) as possible models for the physical universe. To understand the formation of large scale structures in such a universe, cosmologists express physical quantities, such as density fluctuations in the primordial plasma, as linear combinations of the eigenmo

Edward Shuryak

Although all interactions in the Standard Model generate nonzero shifts of the vacuum energy and pressure, gravity does not interact with them. Assuming (i) that the reason why it is so breaks down at some scale $M_g$ and that (ii) the instanton-induced shifts at such scale generate the observed cosmological constant, we found that it then should happen at a

Marija Dimitrijevic, Larisa Jonke, Lutz Moeller, Efrossini Tsouchnika

A general formalism is developed that allows the construction of field theory on quantum spaces which are deformations of ordinary spacetime. The symmetry group of spacetime is replaced by a quantum group. This formalism is demonstrated for the kappa-deformed Poincare algebra and its quantum space. The algebraic setting is mapped to the algebra of functions

G. Giachetta, L. Mangiarotti, G. Sardanashvily

Lagrangian contact supersymmetries (depending on derivatives of arbitrary order) are treated in very general setting. The cohomology of the variational bicomplex on an arbitrary graded manifold and the iterated cohomology of a generic nilpotent contact supersymmetry are computed. In particular, the first variational formula and conservation laws for Lagrangi

Sugumi Kanno, Jiro Soda

There are various different descriptions of Randall-Sundrum (RS) braneworlds. Here we present a unified view of the braneworld based on the gradient expansion approach. In the case of the single-brane model, we reveal the relation between the geometrical and the AdS/CFT approach. It turns out that the high energy and the Weyl term corrections found in the ge

Jian-Zu Zhang

Recent studies on non-perturbation aspects of noncommutative quantum mechanics explored a new type of boson commutation relations at the deformed level, described by deformed annihilation-creation operators in noncommutative space. This correlated boson commutator correlates different degrees of freedom, and shows an essential influence on dynamics. This pap

G. Moultaka, M. Rausch de Traubenberg, A. Tanasa

We investigate a non-trivial extension of the $D-$dimensional Poincaré algebra. Matrix representations are obtained. The bosonic multiplets contain antisymmetric tensor fields. It turns out that this symmetry acts in a natural geometric way on these $p-$forms. Some field theoretical aspects of this symmetry are studied and invariant Lagrangians are explicitl

Shin'ichi Nojiri

We review the several models of the dark energy, which may generate the accelerated expansion of the present universe. We also discuss the the Big Rip singularity, which may occur when the equation of the state parameter w is less than -1. We show that the quantum correction would be very important near the singularity.

Roberto Casadio, Cristiano Germani

This paper has been withdrawn by the authors because the Hawking radiation outside the core was just obtained for a specific (and somewhat unphysical) model of the tail. Interested readers should instead look at the more recent hep-th/0407191 where more general results are given for the formation and evolution of black-holes on the brane.

Yuval Grossman, Roni Harnik, Gilad Perez, Matthew D. Schwartz

The observed flavor structure of the standard model arises naturally in "split fermion" models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation

Mark Alford, Chris Kouvaris, Krishna Rajagopal

We recently argued that as the density of quark matter decreases, there is a continuous transition from the color-flavor-locked (CFL) phase to a gapless "gCFL" phase. The reason is the growing importance of the strange quark mass, and the constraint of electric/color neutrality. In this paper we discuss mixed phases that achieve neutrality by charge

Neil Russell

Clock-comparison experiments using a satellite platform can give Planck-scale sensitivity to many parameters for Lorentz and CPT violation that are difficult to measure on Earth. A discussion of the theoretical framework for such tests is given, with emphasis on comparisons of output frequencies of atomic clocks and of electromagnetic cavity oscillators.

Michele Gallinaro

The CDF Forward Detector upgrade project was designed to enhance the capabilities for diffractive physics at the Tevatron. It consists of a Roman Pot spectrometer to detect leading antiprotons, a set of counters near and around the beam-pipe to reject the non-diffractive event contamination to the data sample, and two Miniplug calorimeters to measure the eve

B. Field

The region of small transverse momentum in q-qbar- and gg-initiated processes must be studied in the framework of resummation to account for the large, logarithmically-enhanced contributions to physical observables. In this letter, we study resummed differential cross-sections for Higgs production via bottom-quark fusion. We find that the differential distri

Cosmin Macesanu, Satyanarayan Nandi, Marius Rujoiu

In the universal extra dimensions models, Kaluza Klein excitations of matter are generaly produced in pairs. However, if matter lives on a fat brane embedded in a larger space, gravity-matter interactions do not obey KK number conservation, thus making possible the production of single KK excitations at colliders. We evaluate the production rates for such ex

Quentin G. Bailey, Alan Kostelecky

The static limit of Lorentz-violating electrodynamics in vacuum and in media is investigated. Features of the general solutions include the need for unconventional boundary conditions and the mixing of electrostatic and magnetostatic effects. Explicit solutions are provided for some simple cases. Electromagnetostatics experiments show promise for improving e

Giuseppe Degrassi, Fabio Maltoni

We compute the two-loop electroweak corrections due to the top quark to the gluon fusion production cross section of an intermediate-mass Higgs boson. This result, together with the previously known contribution due to the light fermions, allows a complete determination of the two-loop electroweak corrections to this production cross section. For Higgs mass

J. -Alexis Rodriguez, Marc Sher

An interesting extension of the Standard Model is based on the electroweak gauge group SU(3)_L x U(1). It requires three generations to cancel anomalies, treats the third generation differently than the first two, and has a rich phenomenology. There are several models, distinguished by the embedding of the charge operator into the SU(3)_L group and by the ch

J. T. Londergan, A. W. Thomas

For the first time, charge symmetry breaking terms in parton distribution functions have been included in a global fit to high energy data. We review the results obtained for both valence and sea quark charge symmetry violation, and we compare these results with the most stringent experimental upper limits on charge symmetry violation for parton distribution

Steven D. Bass

Electroweak vacuum transition processes (sphalerons) in the early Universe provide a possible explanation of the baryon asymmetry. Anomaly theory suggests that these electroweak baryon number non-conserving processes are accompanied by the formation of a ``topological condensate'' which may remain in the Universe that we observe today.

S. Heinemeyer

Various aspects of the Higgs boson phenomenology of the Minimal Supersymmetric Standard Model (MSSM) are reviewed. Emphasis is put on the effects of higher-order corrections. The masses and couplings are discussed in the MSSM with real and complex parameters. Higher-order corrections to Higgs boson production channels at a prospective e+ e- linear collider a

Steven D. Bass

Neutrino proton elastic scattering and polarized deep inelastic spin sum rules provide complementary information about the spin structure of the proton. We outline the two approaches and what they may teach us about the transition from current to constituent quarks in QCD.

Piotr H. Chankowski, Adam Falkowski, Stefan Pokorski, Jakub Wagner

We propose a novel mechanism of electroweak symmetry breaking in supersymmetric models, as the one recently discussed by Birkedal, Chacko and Gaillard, in which the Standard Model Higgs doublet is a pseudo-Goldstone boson of some global symmetry. The Higgs mass parameter is generated at one loop level by two different, moderately fine-tuned sources of the gl

D. de Florian, M. Grazzini

We consider the back-to-back region in the energy--energy correlation in e^+e^- collisions. We present the explicit expression of the O(as^2) logarithmically enhanced contributions up to next-to-next-to-leading logarithmic accuracy. We study the impact of the results in a detailed comparison with precise LEP and SLC data. We find that, when hadronization eff

I. Rosell, J. J. Sanz-Cillero, A. Pich

We present a calculation of the Vector Form Factor at the next-to-leading order in the 1/N_C expansion, within the framework of Resonance Chiral Theory. The calculation is performed in the chiral limit, and with two dynamical quark flavours. The ultraviolet behaviour of quantum loops involving virtual resonance propagators is analyzed, together with the kind

D. Djukanovic, M. R. Schindler, J. Gegelia, G. Japaridze

It is shown that both the universal coupling of the rho-meson and the Kawarabayashi-Suzuki-Riadzuddin-Fayyazuddin expression for the magnitude of its coupling constant follow from the requirement that chiral perturbation theory of pions, nucleons, and rho-mesons is a consistent effective field theory. The prerequisite of the derivation is that all ultraviole

R. E. Browne, J. A. Gracey

We compute the one loop corrections to the pole mass of the gluon in the MSbar scheme in the Landau gauge in both the Curci-Ferrari model and the local composite operator formalism with Nf flavours of massless quarks. For the latter we determine an estimate for the gluon mass using the effective potential of a local dimension two composite operator and find,

L. Bibrzycki, L. Lesniak, A. P. Szczepaniak

We have analyzed the K+K- photoproduction on hydrogen in the effective mass region around the mass of the phi(1020) meson. The interference of the S-wave contribution with the P-wave has been studied. Both scalar resonances f0(980) and a0(980) have been taken into account. We have obtained a good description of the available experimental data, in particular

Ernest Ma, Myriam Mondragon, G. Zoupanos

We consider N=1 supersymmetric gauge theories based on the group SU(N)_1 x SU(N)_2 x ... x SU(N)_k with matter content (N,N*,1,...,1) + (1,N,N*,...,1) + >... + (N*,1,1,...,N) as candidates for the unification symmetry of all particles. In particular we examine to which extent such theories can become finite and we find that a necessary condition is that ther

H. Perez Rojas, E. Rodriguez Querts

We study the electron-positron vacuum in a strong magnetic field $B$ in parallel with Casimir effect. Use is made of the energy-momentum tensor, taken as the zero temperature and zero density limit of the relativistic quantum statistical tensor. In both magnetic field and Casimir cases it is shown the arising of anisotropic pressures. In the first case the p

Iorwerth Owain Thomas, Simon Hands

QED in 2+1 dimensions has long been studied as a model field theory which exhibits both asymptotic freedom and non-trivial IR behaviour. There is also a trend towards viewing it as a candidate low energy effective theory for the pseudogap phase of high temperature superconductors. One feature of these theories is their lack of isotropy in the x and y directi

Salvatore Mele

The high-energy and high-luminosity data-taking campaigns of the LEP e^+e^- collider provided the four collaborations, ALEPH, DELPHI, L3 and OPAL, with about 50000 W-boson pairs and about a thousand singly-produced W bosons. This unique data sample has an unprecedented reach in probing some aspects of the Standard Model of the electroweak interactions, and t

J. Przerwa, H. -H. Adam, A. Budzanowski, R. Czyzykiewicz

Due to the high sensitivity of the N N --> N N gamma reaction to the nucleon-nucleon potential, Bremsstrahlung radiation is used as a tool to investigate details of the nucleon-nucleon interaction. Such investigations can be performed at the cooler synchrotron COSY in the Research Centre Juelich, by dint of the COSY-11 detection system. The results of the id

J. H. Field

A method is proposed to calculate the confidence level for agreement of data with the Standard Model (SM) by combining information from direct and indirect Higgs Boson searches. Good agreement with the SM is found for $m_H \simeq 120$ GeV using the observables most sensitive to $m_H$: $A_l$ and $m_W$. In particular, quantum corrections, as predicted by the S

B. Aubert, BABAR Collaboration

We present a search for the decay $B^{-} \to τ^{-} \barν_τ$ in a sample of $88.9 \times 10^{6}$ $B\bar{B}$ pairs recorded with the BaBar detector at the SLAC $B$-Factory. One of the two $B$ mesons from the $Υ(4S)$ is reconstructed in a hadronic or a semileptonic final state and the decay products of the other $B$ in the event are analyzed for consistency wit

Salvatore Orlando, Raffaele Perego, Fabrizio Silvestri

This paper describes the architecture of MOSE (My Own Search Engine), a scalable parallel and distributed engine for searching the web. MOSE was specifically designed to efficiently exploit affordable parallel architectures, such as clusters of workstations. Its modular and scalable architecture can easily be tuned to fulfill the bandwidth requirements of th

D. S. Petrov, C. Salomon, G. V. Shlyapnikov

We consider weakly bound diatomic molecules (dimers) formed in a two-component atomic Fermi gas with a large positive scattering length for the interspecies interaction. We develop a theoretical approach for calculating atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic collisional relaxation of the molecules into deep bound states

W. Pan, J. L. Reno, J. A. Simmons

We present in this paper experimental results on the transport hysteresis in electron double quantum well structures. Exploring the measurement technique of fixing the magnetic field and sweeping a front gate voltage (Vg), we are able to study the hysteresis by varying the top layer Landau level fillings while maintaining a relatively constant filling factor

A. J. Zambano, W. P. Pratt

We present a versatile method for detecting the presence and motion of a trapped domain wall in a narrow ferromagnetic layer using current-perpendicular-to-plane (CPP) giant magnetoresistance (MR). The CPP-MR response to small motions of the trapped domain wall is enhanced because the CPP current is restricted to the region of wall trapping. We use a Permall

H. Ustunel, D. Roundy, T. A. Arias

This letter introduces ab initio study of the full activation-volume tensor of crystalline defects as a means to make contact with mechanical response experiments. We present a theoretical framework for prediction of the internal friction associated with divacancy defects and give the first ab initio value for this quantity in silicon. Finally, making connec

Klara Elteto, Eduard G. Antonyan, T. T. Nguyen, Heinrich M. Jaeger

We present a model supported by simulation to explain the effect of temperature on the conduction threshold in disordered systems. Arrays with randomly distributed local thresholds for conduction occur in systems ranging from superconductors to metal nanocrystal arrays. Thermal fluctuations provide the energy to overcome some of the local thresholds, effecti

C. Didraga, J. Knoester

We study the linear optical properties of helical cylindrical molecular aggregates accounting for the effects of static diagonal disorder. Absorption, linear dichroism, and circular dichroism spectra are presented, calculated using brute force numerical simulations and a modified version of the coherent potential approximation that accounts for finite size e

Jiang Xiao, A. Zangwill, M. D. Stiles

We use a matrix Boltzmann equation formalism to test the accuracy of Slonczewski's theory of spin-transfer torque in thin-film heterostructures where a non-magnetic spacer layer separates two non-collinear ferromagnetic layers connected to non-magnetic leads. When applicable, the model predictions for the torque as a function of the angle between the two

Stefano Zapperi, Phani Kumar V. V. Nukala, Srdan Simunovic

We analyze the scaling of the crack roughness and of avalanche precursors in the two dimensional random fuse model by numerical simulations, employing large system sizes and extensive sample averaging. We find that the crack roughness exhibits anomalous scaling, as recently observed in experiments. The roughness exponents ($ζ$, $ζ_{loc}$) and the global widt

S. N. Evangelou

The parametric motion of energy levels for non-interacting electrons at the Anderson localization critical point is studied by computing the energy level-curvatures for a quasiperiodic ring with twisted boundary conditions. We find a critical distribution which has the universal random matrix theory form ${\bar P}(K)\sim |K|^{-3}$ for large level-curvatures

V. L. Gurevich, D. A. Parshin, H. R. Schober

The inelastic scattering intensities of glasses and amorphous materials has a maximum at a low frequency, the so called Boson peak. Under applied hydrostatic pressure, $P$, the Boson peak frequency, $ω_{\rm b}$, is shifted upwards. We have shown previously that the Boson peak is created as a result of a vibrational instability due to the interaction of harmo

J. I. Pascual, G. Bihlmayer, Yu. M. Koroteev, H. -P. Rust

Quasiparticle interference patterns measured by scanning tunneling microscopy (STM) can be used to study the local electronic structure of metal surfaces and high temperature superconductors. Here, we show that even in non-magnetic systems the spin of the quasiparticles can have a profound effect on the interference patterns. On Bi(110), where the surface st

I. Galanakis

Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are almost completely quenched and they are negligible with respect to the spin moments. The change in the atomic-resolved orbital moments can be easily explained in terms of the spin-orbit strength and hybrid

H. Zenia, G. Banach, W. M. Temmerman, G. A. Gehring

The electronic and magnetic properties of ferromagnetic doped manganites are investigated by means of model tight-binding and \textit{ab initio} self-interaction corrected local spin density approximation calculations. It is found that the surface alone by breaking the cubic symmetry induces a difference in the occupation of the two $e_{g}$ orbitals at the s

G. -H. Gweon, T. Sasagawa, S. Y. Zhou, J. Graf

In conventional superconductors, the electron pairing that allows superconductivity is caused by exchange of virtual phonons, which are quanta of lattice vibration. For high-transition-temperature (high-Tc) superconductors, it is far from clear that phonons are involved in the pairing at all. For example, the negligible change in Tc of optimally doped Bi2Sr2

A. Bansil, M. Lindroos, S. Sahrakorpi, R. S. Markiewicz

Angle-resolved photoemission spectroscopy (ARPES) presents significant simplications in analyzing strictly two-dimensional (2D) materials, but even the most anisotropic physical systems display some residual three-dimensionality. Here we demonstrate how this third dimension manifests itself in ARPES spectra of quasi-2D materials by considering the example of

V. Sofonea, A. Lamura, G. Gonnella, A. Cristea

In this paper we apply a finite difference lattice Boltzmann model to study the phase separation in a two-dimensional liquid-vapor system. Spurious numerical effects in macroscopic equations are discussed and an appropriate numerical scheme involving flux limiter techniques is proposed to minimize them and guarantee a better numerical stability at very low v

A. Baas, J. -Ph. Karr, M. Romanelli, A. Bramati

We report the observation of optical bistability in a microcavity pumped at the "magic angle". Experimental evidence is given in the form of a hysteresis cycle of the nonlinear emission as a function of the pump intensity or the position of the excitation spot. The results can be well understood with simple theoretical considerations that underline t

Raphael Lefevere, Hal Tasaki

We develop a controlled high-temperature expansion for nonequilibrium steady states of the driven lattice gas. We represent the steady state as $P(η)\propto e^{-H(η)-Ψ(η)}$, and evaluate the lowest order contribution to the nonequilibrium effective interaction $Ψ(η)$. We see that, in dimensions $d\ge2$, all models with nonsingular transition rates have the s

N. M. Plakida

A microscopic theory of superconductivity is formulated within an effective $p$-$d$ Hubbard model for a CuO2 plane. By applying the Mori-type projection technique, the Dyson equation is derived for the Green functions in terms of Hubbard operators. The antiferromagnetic exchange caused by interband hopping results in pairing of all carries in the conduction

T. Matsumura, H. Ishida, T. J. Satoh, K. Katoh

Inelastic neutron scattering experiment has been performed on a new heavy fermion compound YbAgGe for a polycrystalline sample at zero magnetic field. A quasielastic scattering and a crystal field excitation at 12 meV was observed. Both of them are broadened with an intrinsic width of 0.9 meV at 1.5 K which increases to about 3 meV at 300 K. The temperature

Daniel B. Murray, S. Dhara, T. R. Ravindran, K. G. M. Nair

Spherical gold nanoclusters are grown by 1.8 MeV Au++ ion implantation into an amorphous silica matrix and subsequent air annealing at 873 K. Ultraviolet and visible light absorption confirms the presence of a dipolar surface plasmon peak at the expected location for a gold sphere in silica. Grazing incidence X-ray diffraction shows peaks corresponding to fc

Yunong Qi, Zhi-Gang Yu, Michael E. Flatté

We predict that the flow of unpolarized current in electron-doped GaAs and InP at room temperature is unstable at high electric fields to the dynamic formation of spin-polarized current pulses. Spin-polarized current is spontaneously generated because the conductivity of a spin-polarized electron gas differs from that of an unpolarized electron gas, even in

T. Naka, L. A. Ponomarenko, A. de Visser, A. Matsushita

We report magnetic susceptibility and electrical resistivity measurements on single-crystalline PrCu2 under hydrostatic pressure, up to 2 GPa, which pressure range covers the pressure-induced Van Vleck paramagnet-to-antiferromagnet transition at 1.2 GPa. The measured anisotropy in the susceptibility shows that in the pressure-induced magnetic state the order

Masashi Torikai, Mamoru Yamashita

Phase behaviours of liquid crystals under external fields, conjugate to the nematic order and smectic order, are studied within the framework of mean field approximation developed by McMillan. It is found that phase diagrams, of temperature vs interaction parameter of smectic A order, show several topologically different types caused by the external fields.

U. Gavish, B. Yurke, Y. Imry

Heisenberg uncertainty relations for current components impose constraints on the performance of linear amplifiers. Here we derive such constraints for amplifiers in which the input signal modulates a bias current in order to produce an amplified output. These amplifiers include transistors, macroscopic, mesoscopic, or molecular, operated as linear amplifier

M. A. Avila, M. Sera, T. Takabatake

We report on the structural, thermodynamic and transport properties of high-quality single crystals of YbNiSi3 grown by the flux method. This compound crystallizes in the SmNiGe3 layered structure type of the Cmmm space group. The general physical behavior is that of a Kondo lattice showing an antiferromagnetic ground state below T_N = 5.1 K. This is among t

Fusayoshi J. Ohkawa

A theory of Kondo lattices is applied to the crossover between local-moment magnetism and itinerant-electron magnetism in the t-J model on a quasi-two dimensional lattice. The Kondo temperature T_K is defined as a characteristic temperature or energy scale of local quantum spin fluctuations. Magnetism with T_N >> T_K, where T_N is the N\eel temperature, is c

O. Tchernyshyov

Vanadium spinels (ZnV_2O_4, MgV_2O_4, and CdV_2O_4) exhibit a sequence of structural and magnetic phase transitions, reflecting the interplay of lattice, orbital, and spin degrees of freedom. We offer a theoretical model taking into account the relativistic spin-orbit interaction, collective Jahn-Teller effect, and spin frustration. Below the structural tran

Rosa A. Gonzalez, Benne Holwerda, Laurent Loinard, Ronald J. Allen

Recently, we have developed and calibrated the Synthetic Field Method to derive total extinction through disk galaxies. The method is based on the number counts and colors of distant background field galaxies that can be seen through the foreground object. Here, we investigate how large (10-m) and very large (20 to 30-m), diffraction-limited, optical and inf

S. Starrfield, F. X. Timmes, W. R. Hix, E. M. Sion

Nova explosions occur on the white dwarf (WD) component of a Cataclysmic Variable stellar system which is accreting matter lost by a companion. A Type Ia supernova explosion is thought to result when a WD, in a similar binary configuration, grows in mass to the Chandrasekhar Limit. Here, we present calculations of accretion of Solar matter, at a variety of m

Stephan R. McCandliss, Kevin France, Paul D. Feldman, Karl Glazebrook

Shull et al. (1999) have asserted that the contribution of stars, relative to quasars, to the metagalactic background radiation that ionizes most of the baryons in the universe remains almost completely unknown at all epochs. The potential to directly quantify this contribution at low redshift has recently become possible with the identification by GALEX of

Christopher Conselice

There exists a gradual, but persistent, evolutionary effect in the galaxy population such that galaxy structure and morphology change with redshift. This galaxy structure-redshift relationship is such that an increasingly large fraction of all bright and massive galaxies at redshifts 2 < z < 3 are morphologically peculiar at wavelengths from rest-frame ultra

Tsvi Piran

Gamma ray bursts (GRBs) are short and intense pulses of $γ$-rays arriving from random directions in the sky. Several years ago Amelino-Camelia et al. pointed out that a comparison of time of arrival of photons at different energies from a GRB could be used to measure (or obtain a limit on) possible deviations from a constant speed of light at high photons en

Gustavo E. Romero

Microquasars are X-ray binary systems with non-thermal radio emission originated in jet-like features. They are attractive sites for gamma-ray production, since relativistic particles in the jet should traverse locally strong both photon and matter fields. In this review we discuss whether some of the unidentified gamma-ray sources detected by the EGRET inst

Rupali Chandar, Bradley Whitmore, Myung Gyoon Lee

We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of five (M81, M83, NGC 6946, M101, and M51) low inclination, nearby spiral galaxies to study ancient star cluster populations. M81 globular clusters (GC) have an intrinsic color distribution which is very similar to those in the Milky Way and M31, with ~40% of the clusters having colors

Mounib F. El Eid, Bradley S. Meyer, Lih-Sin The

We present a detailed study of the evolution of massive stars of masses 15, 20, 25 and 30 $\msun$ assuming solar-like initial chemical composition. The stellar sequences were evolved through the advanced burning phases up to the end of core oxygen burning. We present a careful analysis of the physical characteristics of the stellar models. In particular, we

T. P. Li, J. L. Qu, H. Feng, L. M. Song

A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and $γ$-ray bursts. The results indicate tha

Gerald K. Skinner

Achromatic combinations of a diffractive Phase Fresnel Lens and a refractive correcting element have been proposed for X-ray and gamma-ray astronomy and for microlithography, but considerations of absorption often dictate that the refractive component be given a stepped profile, resulting in a double Fresnel lens. The imaging performance of corrected Fresnel

L. Balaguer-Nunez, C. Jordi, D. Galadi-Enriquez, E. Masana

We have investigated the area of two NGC entries, NGC 1817 and NGC 1807, with deep CCD photometry in the uvby-Hbeta intermediate-band system. The photometric analysis of a selected sample of stars of the open cluster NGC 1817 yields a reddening value of E(b-y)= 0.19$\pm$0.05, a distance modulus of V0-MV= 10.9$\pm$0.6, a metallicity of [Fe/H]= -0.34$\pm$0.26

L. Balaguer-Nunez, C. Jordi, D. Galadi-Enriquez, J. L. Zhao

We have calculated proper motions and re-evaluated the membership probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC 1807. We have obtained absolute proper motions from 25 plates in the reference system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of 81 years; and they were taken with the double astrograph at

J. M. Paredes, J. Marti, D. F. Torres, G. E. Romero

We present preliminary results of a campaign undertaken with different radio interferometers to observe a sample of the most variable unidentified EGRET sources. We expect to detect which of the possible counterparts of the gamma-ray sources (any of the radio emitters in the field) varies in time with similar timescales as the gamma-ray variation. If the gam

D. R. Ballantyne, A. C. Fabian, K. Iwasawa

We present the results of a 127 ks XMM-Newton observation of the broad-line radio galaxy 3C 120 performed simultaneously with RXTE. The time-averaged spectrum is Seyfert-like, with a reflection amplitude R ~ 0.5, and a neutral Fe K line with equivalent width ~53 eV. The line is slightly broadened with a FWHM$\approx 10^4$ km s$^{-1}$. This is consistent with

J. -M. Virey, A. Ealet, C. Tao, A. Tilquin

We present a revised interpretation of recent analysis of supernovae data. We evaluate the effect of the priors on the extraction of the dark energy equation of state. We find that the conclusions depend strongly on the $Ω_M$ prior value and on its uncertainty, and show that a biased fitting procedure applied on non concordant simulated data can converge to

E. P. J. van den Heuvel

An important recent discovery by Pfahl et al. (2002) is that there are two classes of Be X-ray binaries: one with orbits of small eccentricity (<0.25), in which the neutron stars received hardly any kick velocity at birth and a class with substantial orbital eccentricities, in which the neutron stars received a kick velocity of order 100 km/s at birth. Also

Mariana Orellana, Gustavo E. Romero

Be/X-ray binaries are systems formed by a massive Be star and a magnetized neutron star, usually in an eccentric orbit. The Be star has strong equatorial winds occasionally forming a circumstellar disk. When the neutron star intersects the disk the accretion rate dramatically increases and a transient accretion disk can be formed around the compact object. T

Terry J. Jones, Charles E. Woodward, Michael S. Kelley

e present Near Infrared imaging polarimetry of three regions of massive star formation, G$192.16 - 3.82$, Cepheus A, and W42. In W42 we have discovered a new bipolar nebula located at the far side of the HII region behind the visible cluster of exciting stars. The axis of this new nebula is aligned with the magnetic field threading the entire cluster region.

M. Kutschera, J. Jalocha

Physical mechanisms that can influence rotation curves of spiral galaxies are discussed. For dark matter studies, possible contributions due to magnetic fields and non-Newtonian gravitational accelerations should be carefully accounted for. We point out that magnetic fields are particularly important in outermost parts of the disk. In the framework of genera

Anna Wolter, Ginevra Trinchieri

We present the results from the high resolution Chandra observation of the Cartwheel galaxy. Many individual sources are resolved in the image, mostly associated with the outer ring. All detected sources have a very high X-ray luminosity ($\geq 10^{39}$ erg s$^{-1}$)that classifies them as Ultra Luminous X-ray sources (ULX). The brightest of them is possibly

Anthony G A Brown, Enrico Fedrigo, Paul van der Werf

The SINFONI instrument for ESO&#39;s VLT combines integral field spectroscopy and adaptive optics (AO). We discuss detailed simulations of the adaptive optics module. These simulations are aimed at assessing the AO module performance, specifically for operations with extended sources and a laser guide star. Simulated point spread function (PSF) images will b

M. Bellazzini, N. Gennari, F. R. Ferraro, A. Sollima

We present V and I photometry of a 9.4 arcmin X 9.4 arcmin field centered on the dwarf spheroidal galaxy Leo I. The I magnitude of the tip of the Red Giant Branch is robustly estimated from two different datasets (I^{TRGB}=17.97 +0.05/-0.03). From this estimate, adopting [M/H]=-1.2 from the comparison of RGB stars with Galactic templates, we obtain a distanc