April 2000 arXiv papers — page 20

Ruth Britto-Pacumio, Andrew Strominger, Anastasia Volovich

The quantum mechanics of $N$ slowly-moving BPS black holes in five dimensions is considered. A divergent continuum of states describing arbitrarily closely bound black holes with arbitrarily small excitation energies is found. A superconformal structure appears at low energies and can be used to define an index counting the weighted number of supersymmetric

John N. Bahcall, Peter Meszaros

A gamma-ray burst fireball is likely to contain an admixture of neutrons, in addition to protons, in essentially all progenitor scenarios. Inelastic collisions between differentially streaming protons and neutrons in the fireball produce muon neutrinos (antineutrinos) of ~ 10 GeV as well as electron neutrinos (antineutrinos) of ~ 5 GeV, which could produce ~

Dorit Aharonov, Amnon Ta-Shma, Umesh Vazirani, Andrew Yao

Unconditionally secure bit commitment and coin flipping are known to be impossible in the classical world. Bit commitment is known to be impossible also in the quantum world. We introduce a related new primitive - {\em quantum bit escrow}. In this primitive Alice commits to a bit $b$ to Bob. The commitment is {\em binding} in the sense that if Alice is asked

S. Bose, V. Vedral

We consider the apparatus in a quantum measurement process to be in a mixed state. We propose a simple upper bound on the probability of correctly distinguishing any number of mixed states. We use this to derive fundamental bounds on the efficiency of a measurement in terms of the temperature of the apparatus.

A. Ekert, M. Ericsson, P. Hayden, H. Inamori

We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus

Klaus Molmer, Anders Sorensen

Candidates for quantum computing which offer only restricted control, e.g., due to lack of access to individual qubits, are not useful for general purpose quantum computing. We present concrete proposals for the use of systems with such limitations as RISQ - reduced instruction set quantum computers and devices - for simulation of quantum dynamics, for multi

Spiridon Dumitru

In spite \smallskip of their popularity the \QTR{bf}{H}eisenberg's (``uncertainty'') \QTR{bf}{R}elations (HR) still generate controversies. The \QTR{bf}{T}raditional \QTR{bf}{I}nterpretation of HR (TIHR) dominate our days science, although over the years a lot of its defects were signaled. These facts justify a reinvestigation of the questions co

D. L. Zhou, X. X. Yi, G. R. Jin, Y. H. Su

We propose a natural expansion of the atomic field operator in studying elementary excitations in trapped Bose-Einstein Condensation (BEC) system near T=0K. Based on this expansion, a system of coupled equations for elementary excitations, which is equivalent to the standard linearized GP equation, is given to describe the collective excitation of BEC in a n

E. Ventura, A. M. Simas, D. Bazeia

We investigate the presence of topological twistons in crystalline polyethylene. We describe crystalline polyethylene with a model that couples the torsional and longitudinal degrees of freedom of the polymeric chain by means of a system of two real scalar fields. This model supports topological twistons, which are described by exact and stable topological s

G. Getz, E. Levine, E. Domany

We present a novel coupled two-way clustering approach to gene microarray data analysis. The main idea is to identify subsets of the genes and samples, such that when one of these is used to cluster the other, stable and significant partitions emerge. The search for such subsets is a computationally complex task: we present an algorithm, based on iterative c

J. T. Lenaghan, D. H. Rischke, J. Schaffner-Bielich

We study patterns of chiral symmetry breaking at zero temperature and its subsequent restoration at nonzero temperature within the $SU(3)_{r} \times SU(3)_{\ell}$ linear sigma model. Gap equations for the masses of the scalar and pseudoscalar mesons and the non-strange and strange quark condensates are systematically derived in the Hartree approximation via

A. Sibirtsev, V. Hejny, H. Ströher, W. Cassing

Within transport calculations we study the production and decay of $ω$-mesons in $pA$ reactions at COSY energies including elastic and inelastic $ωN$ rescattering, the $ω{\to}π^0γ$ Dalitz decay as well as $π^0 N$ rescattering. The resulting invariant $π^0 γ$ mass distributions indicate that in-medium modifications of the $ω$-meson may be observed experimenta

M. Rysavy, O. Dragoun

The internal conversion coefficients for the elements 104 <= Z <= 126 are presented.

R. Bijker, A. Frank

Low-lying collective states in nuclei are investigated in the framework of the interacting boson model using an ensemble of random many-body interactions. It is shown that whenever the number of bosons is sufficiently large compared to the rank of the interactions, the spectral properties are characterized by a dominance of L(P)=0(+) ground states and the oc

Kristi Pance, Wentao Lu, S. Sridhar

N-disk microwave billiards, which are representative of open quantum systems, are studied experimentally. The transmission spectrum yields the quantum resonances which are consistent with semiclassical calculations. The spectral autocorrelation of the quantum spectrum is shown to be determined by the classical Ruelle-Pollicot resonances, arising from the com

T. Michoel, A. Verbeure

We consider an exactly soluble model of two Bose-Einstein condensates with a Josephson-type of coupling. Its equilibrium states are explicitly found showing condensation and spontaneously broken gauge symmetry. It is proved that the total number and total phase fluctuation operators, as well as the relative number and relative current fluctuation operators f

Anna Dyubina, Iosif Polterovich

We present some explicit constructions of universal R-trees with applications to the asymptotic geometry of hyperbolic spaces. In particular, we show that any asymptotic cone of a complete simply connected manifold of negative curvature is a complete homogeneous R-tree with the valency $2^{\aleph_0}$ at every point. It implies that all these asymptotic cones

Viktor L. Ginzburg

Hamiltonian dynamical systems tend to have infinitely many periodic orbits. For example, for a broad class of symplectic manifolds almost all levels of a proper smooth Hamiltonian carry periodic orbits. The Hamiltonian Seifert conjecture is the existence problem for regular compact energy levels without periodic orbits. Very little is known about how large t

Jerrold E. Marsden, Sergey Pekarsky, Steve Shkoller

For a discrete mechanical system on a Lie group $G$ determined by a (reduced) Lagrangian $\ell$ we define a Poisson structure via the pull-back of the Lie-Poisson structure on the dual of the Lie algebra ${\mathfrak g}^*$ by the corresponding Legendre transform. The main result shown in this paper is that this structure coincides with the reduction under the

Yi Hu, Sean Keel

The main goal of this paper is to study varieties with the best possible Mori theoretic properties (measured by the existence of a certain decomposition of the cone of effective divisors). We call such a variety a Mori Dream Space. There turn out to be many examples, including quasi-smooth projective toric (or more generally, spherical) varieties, many GIT q

Michael Schröder

This paper adresses the valuation of the Paris barrier options proposed by Yor, Jeanblanc-Picque, and Chesnay (Advances in Applied Probability, 29(1997), 165-184) using the Laplace transform approach. Based on suggestions by Pliska the notion of Paris options is extended such that their valuation is possible at any point during their lifespan. The Laplace tr

Izabella Laba, Terence Tao

We use geometrical combinatorics arguments, including the ``hairbrush&#39;&#39; and x-ray arguments of Wolff and the sticky/plany/grainy analysis of Katz, Laba, and Tao, to show that Besicovitch sets in R^n have Minkowski dimension at least (n+2)/2 + \eps_n for all n > 3, where \eps_n > 0 is an absolute constant depending only on n. This complements the resu

Richard Dipper, Andrew Mathas

We prove that every Ariki-Koike algebra is Morita equivalent to a direct sum of tensor products of smaller Ariki-Koike algebras which have q-connected parameter sets. A similar result is proved for the cyclotomic q-Schur algebras. Combining our results with work of Ariki and Uglov, the decomposition numbers for the Ariki-Koike algebras defined over fields of

Stuart Dowker, Peter Gilkey, Klaus Kirsten

Let $P$ be an operator of Dirac type on a compact Riemannian manifold with smooth boundary. We impose spectral boundary conditions and study the asymptotics of the heat trace of the associated operator of Laplace type.

Carlos Castro

A straightforward two-line derivation of the Bekenstein-Hawking Area-Entropy relation for Black-Holes in {\bf any} dimension is shown based on Shannon&#39;s information theory and Clifford algebras required by the New Relativity Principle.

Robert H. Brandenberger

The presence of cosmological perturbations affects the background metric and matter configuration in which the perturbations propagate. This effect, studied a long time ago for gravitational waves, also is operational for scalar gravitational fluctuations, inhomogeneities which are believed to be more important in inflationary cosmology. The back-reaction of

Amer Iqbal, Asad Naqvi

We extend the recent computation of the tachyon potential by Berkovits, Sen and Zwiebach by including level two fields and keeping up to level four terms in the action. We find 90.5% of the expected result.

J. A. Harvey, D. Kutasov, E. J. Martinec

We study condensation of open string tachyons using renormalization group flow in the worldsheet field theory. This approach leads to a simple picture of the physics of the nontrivial condensate.

Marcello Ciafaloni, German Rodrigo

We further analyze the definition and the calculation of the heavy quark impact factor at next-to-leading (NL) log(s) level, and we provide its analytical expression in a previously proposed k-factorization scheme. Our results indicate that k-factorization holds at NL level with a properly chosen energy scale, and with the same gluonic Green&#39;s function p

A. D. Dolgov

Phenomenology of neutrino oscillations in vacuum and in cosmological plasma is considered. Neutrino oscillations in vacuum are usually described in plane wave approximation. In this formalism there is an ambiguity if one should assume $δp =0$ and correspondingly $δE\neq 0$ or vice versa $δE =0$ and $δp \neq 0$, or some other condition. We will use the standa

Charanjit S. Aulakh, Borut Bajc, Alejandra Melfo, Andrija Rasin

We study the Higgs sector of a SO(10) grand unified theory which predicts exact conservation of R-parity at all scales and incorporates the see-saw mechanism. We find possible intermediate scales and light states compatible with the constraints coming from the running of the gauge couplings. Such a pattern could lower the SO(10) breaking scale, allowing the

Francesco Caravaglios

Loop calculations involve the evaluation of divergent integrals. Usually [1] one computes them in a number of dimensions different than four where the integral is convergent and then one performs the analytical continuation and considers the Laurent expansion in powers of epsilon =n-4. In this paper we discuss a method to extract directly all coefficients of

Jochen Bartels, Carlo Ewerz, René Staritzbichler

We perform a numerical study of various improvements of the LO BFKL prediction for the gamma^* gamma^* total cross section in the kinematical region of the L3 detector at LEP. In particular, we study the effects of a massive charm quark and of different photon polarizations. The variation of the BFKL prediction under changes of alpha_s is investigated.

Takaaki Nagano

It was reported that the NNLO correction to the total cross section near the ttbar threshold in e+e- collisions is as large as the NLO correction to it. In the thesis, we improve the convergence of the perturbative series of the total cross section by choosing appropriate expansion parameters for both m_t and alpha_s. With these two prescriptions, the pertur

Ken-ichi Okumura

Lepton flavor violating processes $μ\to e γ$ and $μ\to 3e$ with polarized muons are studied in the supersymmetric grand unified theory (SUSY GUT). As a result of a detailed numerical calculation, it is shown that the P- and T-odd asymmetries defined with the help of the muon polarization and the ratio of two branching fractions make a good contrast between t

Gary Felder, Lev Kofman, Andrei Linde, Igor Tkachev

Preheating after inflation may lead to nonthermal phase transitions with symmetry restoration. These phase transitions may occur even if the total energy density of fluctuations produced during reheating is relatively small as compared with the vacuum energy in the state with restored symmetry. As a result, in some inflationary models one encounters a second

Aneesh V. Manohar, Iain W. Stewart

The velocity renormalization group is used to determine ln(alpha) contributions to QED bound state energies. The leading order anomalous dimension for the potential gives the alpha^5 ln(alpha) Bethe logarithm in the Lamb shift. The next-to-leading order anomalous dimension determines the alpha^6 ln(alpha), alpha^7 ln^2(alpha), and alpha^8 ln^3 (alpha) correc

A. Mondragon, R. E. Allen

A new theory yields unconventional results for the angular distribution of products like $b-\bar{b}$ jets in Higgs decays.

L3 Collaboration

The structure functions of real and virtual photons are derived from cross section measurements of the reaction e^+e^ -> e^+e^- + hadrons at LEP. The reaction is studied at \sqrt{s} ~ 91 GeV with the L3 detector. One of the final state electrons is detected at a large angle relative to the beam direction, leading to Q^2 values between 40 GeV^2 and 500 GeV^2.

D. C. Salisbury, J. M. Pons, L. C. Shepley

It might seem that a choice of a time coordinate in Hamiltonian formulations of general relativity breaks the full four-dimensional diffeomorphism covariance of the theory. This is not the case. We construct explicitly the complete set of gauge generators for Ashtekar&#39;s formulation of canonical gravity. The requirement of projectability of the Legendre m

Luc Blanchet

1 Introduction 2 Multipole Decomposition 3 Source Multipole Moments 4 Post-Minkowskian Approximation 5 Radiative Multipole Moments 6 Post-Newtonian Approximation 7 Point-Particles 8 Conclusion

E. I. Guendelman

The possibility of mass in the context of scale-invariant, generally covariant theories, is discussed. Scale invariance is considered in the context of a gravitational theory where the action, in the first order formalism, is of the form $S = \int L_{1} Φd^4x$ + $\int L_{2}\sqrt{-g}d^4x$ where $Φ$ is a density built out of degrees of freedom independent of t

E. I. Guendelman, J. Portnoy

The stability of our vacuum is analyzed and several aspects concerning this question are reviewed. 1) In the standard Glashow-Weinberg-Salam (GWS) model we review the instability towards the formation of a bubble of lower energy density and how the rate of such bubble formation process compares with the age of the Universe for the known values of the GWS mod

Marcos R. S. Tavares, S. Das Sarma, G-Q. Hai

We calculate the intersubband and intrasubband many-body inelastic Coulomb scattering rates due to electron-electron interaction in two-subband semiconductor quantum wire structures. We analyze our relaxation rates in terms of contributions from inter- and intrasubband charge-density excitations separately. We show that the intersubband (intrasubband) charge

C. J. Olson, G. T. Zimanyi, A. B. Kolton, N. Gronbech-Jensen

We use three-dimensional molecular dynamics simulations of magnetically interacting pancake vortices to study vortex matter in disordered, highly anisotropic materials such as BSCCO. We observe a sharp 2D-3D transition from vortex lines to decoupled pancakes as a function of relative interlayer coupling strength, with an accompanying large increase in the cr

Leonid Burakovsky, Dean L. Preston, Richard R. Silbar

The Bragg, Leibfried, and modified Leibfried numbers are defined in the context of a theory of dislocation-mediated melting, and their values are determined from the properties of the dislocation ensemble at the melting temperature. The approximate numerical coincidence of the Bragg and modified Leibfried numbers is explained. The parameter K in the definiti

R. Zeyher, E. Cappelluti

The phase diagram of the t-J-V model is discussed using a 1/N expansion in terms of X operators. It is shown that a flux phase of d-wave symmetry is stabilized by the Coulomb interaction V at intermediate dopings and competes with d-wave superconductivity. Since the flux wave instability is stronger than the superconducting one optimal doping is essentially

Kristen A. Fichthorn, Matthias Scheffler

We describe a theoretical study of the role of adsorbate interactions in island nucleation and growth, using Ag/Pt(111) heteroepitaxy as an example. From density-functional theory, we obtain the substrate-mediated Ag adatom pair interaction and we find that, past the short range, a repulsive ring is formed about the adatoms. The magnitude of the repulsion is

I. Loutsenko, D. Roubtsov

The extended version of our reply to Comment on ``Critical Velocities in Exciton Superfluidity&#39;&#39; by S. G. Tikhodeev (Phys. Rev. Lett., 84 (2000), 3502 or from http://prl.aps.org/) is presented here. The principal question is discussed: does the moving exciton-phonon packet contain the coherent `nucleus&#39;, or the exciton-phonon condensate?

H. Schomerus, K. J. H. van Bemmel, C. W. J. Beenakker

A dynamical effect of coherent backscattering is predicted theoretically and supported by computer simulations: The distribution of single-mode delay times of waves reflected by a disordered waveguide depends on whether the incident and detected modes are the same or not. The change amounts to a rescaling of the distribution by a factor close to $\sqrt{2}$.

Nestor Caticha, Evaldo Araujo de Oliveira

Relations between the off thermal equilibrium dynamical process of on-line learning and the thermally equilibrated off-line learning are studied for potential gradient descent learning. The approach of Opper to study on-line Bayesian algorithms is extended to potential based or maximum likelihood learning. We look at the on-line learning algorithm that best

F. C. Alcaraz, V. Rittenberg

The wave functions corresponding to the zero energy eigenvalue of a one-dimensional quantum chain Hamiltonian can be written in a simple way using quadratic algebras. Hamiltonians describing stochastic processes have stationary states given by such wave functions and various quadratic algebras were found and applied to several diffusions processes. We show t

J. Gonzalez

We study the role of electron correlations in the formation of the surface charge-density-wave state in the Sn/Ge(111) interface. The Fermi energy of the overlayer is treated as a dynamical variable, which undergoes a substantial renormalization by the interaction. We show that the Fermi level turns out to be pinned to a Van Hove singularity in the density o

Christopher Mudry, P. W. Brouwer, Akira Furusaki

The conductance of a quantum wire with off-diagonal disorder that preserves a sublattice symmetry (the random hopping problem with chiral symmetry) is considered. Transport at the band center is anomalous relative to the standard problem of Anderson localization both in the diffusive and localized regimes. In the diffusive regime, there is no weak-localizati

E. Lutz

Two models for quantum Brownian motion - the Oscillator Bath (OB) model and the Random-Band-Matrix (RBM) model - are compared and a relation between the spectral density function I(w) and the variance (Vab)^2 is established. The extension to a fractal environment is then considered and the microscopic origin of anomalous diffusion is discussed. In particular

D. O. Kharchenko

The behavior of the most probable values of the order parameter $x$ and the amplitude $ϕ$ of conjugate force fluctuations is studied for a stochastic system with a colored multiplicative noise with absorbing states. The phase diagrams introduced as dependencies the noise self-correlation time vs temperature and noise growth velocity are defined. It is shown

B. Pozzi, L. Salasnich, A. Parola, L. Reatto

We study the thermodynamics of the Bose-condensed atomic hydrogen confined in the Ioffe-Pritchard potential. Such a trapping potential, that models the magnetic trap used in recent experiments with hydrogen, is anharmonic and strongly anisotropic. We calculate the ground-state properties, the condensed and non-condensed fraction and the Bose-Einstein transit

K. W. Madison, F. Chevy, W. Wohlleben, J. Dalibard

We stir with a focused laser beam a Bose-Einstein condensate of $^{87}$Rb atoms confined in a magnetic trap. We observe the formation of a single vortex for a stirring frequency exceeding a critical value. At larger rotation frequencies we produce states of the condensate for which up to eleven vortices are simultaneously present. We present measurements of

K. V. Mitsen, O. M. Ivanenko

The mechanism of -U center formation in high-$T_{c}$ superconductors (HTS) with doping is considered. It is shown that the transition of HTS from insulator to metal passes through the particular dopant concentration range where the local transfer of singlet electron pairs from oxygen ions to pairs of neighboring cations (-U centers) are allowed while the sin

H. X. Han, G. H. Li, W. K. Ge, Z. P. Wang

ultiwalled carbon nanotubes, prepared by both electric arc discharge and chemical vapor deposition methods, show a strong visible light emission in photoluminescence experiments. All the samples employed in the experiments exhibit nearly same super-linear intensity dependence of the emission bands on the excitation intensity, and negligible temperature depen

Massimo G. Noro, Daan Frenkel

We propose an extension of the law of corresponding states that can be applied to systems - such as colloidal suspensions - that have widely different ranges of attractive interactions. We argue that, for such systems, the ``reduced&#39;&#39; second virial coefficient is a convenient parameter to quantify the effective range of attraction. This procedure all

J. -W. van der Horst, P. A. Bobbert, P. H. L. de Jong, M. A. J. Michels

We calculate the electronic and optical excitations of polythiophene using the GW approximation for the electronic self-energy, and include excitonic effects by solving the electron-hole Bethe-Salpeter equation. Two different situations are studied: excitations on isolated chains and excitations on chains in crystalline polythiophene. The dielectric tensor f

Aleksey D. Drozdov

Constitutive equations are derived for enthalpy recovery in polymeric glasses after thermal jumps. The model is based on the theory of cooperative relaxation in a version of the trapping concept. It is demonstrated that some critical temperature and some critical degree of crystallinity exist above which the energy landscape becomes homogeneous and structura

Zhi Fang Zhan, Lik Wee Lee, Jian-Sheng Wang

A new approach known as flat histogram method is used to study the +/-J Ising spin glass in two dimensions. Temperature dependence of the energy, the entropy, and other physical quantities can be easily calculated and we give the results for the zero-temperature limit. For the ground-state energy and entropy of an infinite system size, we estimate e0 = -1.40

Keiji Saito, Seiji Miyashita

The magnetization curves as a response of sweeping magnetic field in the thermal environment are investigated using the quantum master equation. In a slow velocity region where the system almost behaves adiabatically, the magnetic plateau appears which has been observed in the recent experiment of V$_{15}$ [ Phys. Rev. Lett. (2000)]. We investigate its mecha

G. Garberoglio, R. Vallauri

We present an Instantaneous Normal Modes analysis of liquid HF aimed to clarify the origin of peculiar dynamical properties which are supposed to stem from the arrangement of molecules in linear hydrogen-bonded network. The present study shows that this approach is an unique tool for the understanding of the spectral features revealed in the analysis of both

D. N. C. Lin, S. D. Murray

Within protogalaxies, thermal instability leads to the formation of a population of cool fragments, confined by the pressure of residual hot gas. The hot gas remains in quasi-hydrostatic equilibrium, at approximately the virial temperature of the dark matter halo. It is heated by compression and shock dissipation and is cooled by bremsstrahlung emission and

Robert E. Rutledge, Robert J. Brunner, Thomas A. Prince, Carol Lonsdale

We quantitatively cross-associate the 18811 ROSAT Bright Source Catalog (RASS/BSC) X-ray sources with optical sources in the USNO-A2 catalog, calculating the the probability of unique association (Pid) between each candidate within 75 arcsec of the X-ray source position, on the basis of optical magnitude and proximity. We present catalogs of RASS/BSC sources

Shai Kaspi, W. N. Brandt, Hagai Netzer, Rita Sambruna

We present the first grating-resolution X-ray spectra of the Seyfert 1 galaxy NGC 3783, obtained with the High Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory. These spectra reveal many narrow absorption lines from the H-like and He-like ions of O, Ne, Mg, Si, S and Ar, as well as FeXVII-FeXXI L-shell lines. We have also identified

Bo Milvang-Jensen, Inger Jorgensen

We describe galaxy surface photometry based on fitting ellipses to the isophotes of the galaxies. Example galaxies with different isophotal shapes are used to illustrate the process, including how the deviations from elliptical isophotes are quantified using Fourier expansions. We show how the definitions of the Fourier coefficients employed by different aut

L. K. Townsley, P. S. Broos, G. P. Garmire, J. A. Nousek

The ACIS front-illuminated CCDs onboard the Chandra X-ray Observatory were damaged in the extreme environment of the Earth&#39;s radiation belts, resulting in enhanced charge transfer inefficiency (CTI). This produces a row dependence in gain, event grade, and energy resolution. We model the CTI as a function of input photon energy, including the effects of

Joseph C. Shields, Hans-Walter Rix, Daniel H. McIntosh, Luis C. Ho

We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer-line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk, and is reminiscent of double-peaked transient Balmer emission observed in a handful of other LINER

R. N. Mohapatra, V. L. Teplitz

There appear to be three challenges that any theory of dark matter must face: (i) why is $Ω_{DM}$ of the same order as $Ω_{Baryons}$ ? (ii) what are the near solar mass objects ($\sim 0.5 M_{\odot}$) observed by the MACHO microlensing project ? and (iii) understanding the shallow core density profile of the halos of dwarf as well as low surface brightness ga

Wilhelm Kley

The orbital parameters of the observed extrasolar planets differ strongly from those of our own solar system. The differences include planets with high masses, small semi-major axis and large eccentricities. We performed numerical computations of embedded planets in disks and follow their mass growth and orbital evolution over several thousand periods. We fi

Wilhelm Kley, Andreas Burkert

The star formation process in molecular clouds usually leads to the formation of multiple stellar systems, mostly binaries. Remaining disks around those stars may be located around individual stars (circumstellar disks) or around the entire binary system (circumbinary disk). We shall briefly review the present observational evidence for both types of disks i

Andrew Gould

I present a somewhat selective review of microlensing theory, covering five major areas: 1) the derivation of the basic formulae, 2) the relation between the observables and the fundamental physical parameters, 3) binaries, 4) astrometric microlensing, and 5) femtolensing.

B. Mookerjea, S. K. Ghosh, T. N. Rengarajan, S. N. Tandon

High angular resolution far-infrared observations at 143 & 185 \micron, using the TIFR 1-m balloon borne telescope, are presented for two Galactic star forming complexes associated with IRAS 00494+5617 and 05327-0457. The latter map also reveals the cold dust in OMC-3. The HIRES processed IRAS maps at 12, 25, 60 & 100 micron have also been presented for comp

Renato Falomo, Marie-Helene Ulrich

We present optical images and spectroscopy for a dozen of BL Lac objects. Most of these objects were not previously studied and we give for the first time the properties of their host galaxies. The properties of the new host galaxies are generally consistent with those derived in previous optical studies. We found a case (1101-23) where the external isophote

Maria A. Chernyakova, Andrei F. Illarionov

PSR B1259-63 is the only known binary system with a radio pulsar from which the non-pulsed radio and X-ray emission was detected. The companion star in this system is a Be star SS 2883. A rapidly rotating radio pulsar is expected to produce a wind of relativistic particles. Be stars are known to produce highly asymmetric mass loss. Due to the interaction of

A. Caccianiga, T. Maccacaro, A. Wolter, R. Della Ceca

We present 71 Emission Line objects selected from the REX survey. Except for 3 of them, for which the presence of an active nucleus is dubious, all these sources are Active Galactic Nuclei (QSOs, Seyfert galaxies, emission line radiogalaxies). In addition, we present the spectra of other 19 AGNs included in a preliminary version of the REX catalog but not in

Geraint F. Lewis, Rodrigo A. Ibata

Recently it has been suggested that the majority of dark matter in the universe resides in the form of Jupiter mass black holes distributed cosmologically. This population makes itself apparent by microlensing high redshift quasars and introducing pronounced variability into their observed light curves. While several arguments dismissing this hypothesis have

Frank Verbunt, Helen M. Johnston

We detect stars from the Hipparcos and Tycho Catalogues in the field of view of observations with the ROSAT HRI of three globular clusters. We use the positions of these stars to reduce the systematic error in the positions of X-ray sources in the clusters to ~2&#39;&#39; for omega Cen and NGC6752, and 1&#39;&#39; for NGC6397. We detect three X-ray sources i

A. Melatos

Euler&#39;s equations of motion are derived exactly for a rigid, triaxial, internally frictionless neutron star spinning down electromagnetically in vacuo. It is shown that the star precesses, but not freely: its regular precession relative to the principal axes of inertia couples to the component of the radiation torque associated with the near-zone radiati

E. V. Mikheeva, V. N. Lukash, N. A. Arkhipova, A. M. Malinovsky

An analysis of cosmological models in spatially flat Friedmann Universe with cosmic gravitational wave background and zero $Λ$-term is presented. The number of free parameters is equal to 5, they are $σ_8$, $n$, $Ω_ν$, $Ω_b$, and $h$. The normalization of the spectrum of density perturbations on galaxy cluster abundance ($σ_8 = 0.52\pm 0.04$) has been used t

L. S. Pilyugin

The problem of the line intensities -- oxygen abundance calibration has been considered. We confirm the idea of McGaugh (1991) that the strong oxygen lines ([OII] 3727, 3729 and [OIII] 4959, 5007) contain the necessary information for determination of accurate abundances in low-metallicity (and may be also in high-metallicity) HII regions. It has been found

W. P. Abbett, G. H. Fisher, Y. Fan

We present three-dimensional numerical simulations of the rise and fragmentation of twisted, initially horizontal magnetic flux tubes which evolve into emerging Omega-loops. The flux tubes rise buoyantly through an adiabatically stratified plasma that represents the solar convection zone. The MHD equations are solved in the anelastic approximation, and the r

Philip Yock

Terrestrial planets may be detected using the gravitational microlensing technique. This was demonstrated in the high magnification event MACHO-98-BLG-35. Observing strategies aimed at measuring the abundance of terrestrial planets are discussed, using both existing telescopes and planned telescopes.

Jeremy S. Heyl, Lars Hernquist

Recent observations of 1E~161348-5055, the neutron-star candidate at the center of the supernova remnant RCW 103, show that a component of its emission varies sinusoidally with a period of approximately six hours. We argue that this period is what one would expect for a freely precessing neutron star with a spin period of about one second. We produce light c

David Wallace

This paper presents a simple model for repeated measurement of a quantum system: the evolution of a free particle, simulated by discretising the particle&#39;s position. This model is easily simulated by computer and provides a useful arena to investigate the effects of measurement upon dynamics, in particular the slowing of evolution due to measurement (the

M. Woods

At a future linear collider, a polarized electron beam will play an important role in interpreting new physics signals. Backgrounds to a new physics reaction can be reduced by choice of the electron polarization state. The origin of a new physics reaction can be clarified by measuring its polarization-dependence. This paper examines some options for polarime

Hong Liu, Jeremy Michelson

Motivated by recent discussions of IR/UV mixing in noncommutative field theories, we perform a detailed analysis of the non-planar amplitudes of the bosonic open string in the presence of an external B-field at the one-loop level. We carefully isolate, at the string theory level, the contribution which is responsible for the IR/UV behavior in the field theor

Tony Gherghetta, Mikhail Shaposhnikov

We present a metric solution in six dimensions where gravity is localized on a four-dimensional singular string-like defect. The corrections to four-dimensional gravity from the bulk continuum modes are suppressed by ${\cal O}(1/r^3)$. No tuning of the bulk cosmological constant to the brane tension is required in order to cancel the four-dimensional cosmolo

Luc Blanchet, Guillaume Faye

We investigate the dynamics of two point-like particles through the third post-Newtonian (3PN) approximation of general relativity. The infinite self-field of each point-mass is regularized by means of Hadamard&#39;s concept of ``partie finie&#39;&#39;. Distributional forms associated with the regularization are used systematically in the computation. We det

Luc Blanchet, Guillaume Faye

Motivated by the problem of the dynamics of point-particles in high post-Newtonian (e.g. 3PN) approximations of general relativity, we consider a certain class of functions which are smooth except at some isolated points around which they admit a power-like singular expansion. We review the concepts of (i) Hadamard ``partie finie&#39;&#39; of such functions

Travis R. Miller, Michael C. Ogilvie

After a rapid increase in temperature across the deconfinement temperature $% T_{d}$, pure gauge theories exhibit unstable long wavelength fluctuations in the approach to equilibrium. This phenomenon is analogous to spinodal decomposition observed in condensed matter physics, and also seen in models of disordered chiral condensate formation. At high temperat

Valerio Faraoni

The slow-roll approximation to inflation is ultimately justified by the presence of inflationary attractors for the orbits of the solutions of the dynamical equations in phase space. There are many indications that the inflaton field couples nonminimally to the spacetime curvature: the existence of attractor points for inflation with nonminimal coupling is d

Christian Baer, Alexander Strohmaier

Let M be a connected Riemannian manifold and let D be a Dirac type operator acting on smooth compactly supported sections in a Hermitian vector bundle over M. Suppose D has a self-adjoint extension A in the Hilbert space of square-integrable sections. We show that any $L^2$-section $ϕ$ contained in a closed A-invariant subspace onto which the restriction of

Mohsen Alishahiha, Harald Ita, Yaron Oz

We consider systems of D6 branes in the presence of a nonzero $B$ field of different ranks. We study the scattering of gravitons in the corresponding supergravity backgrounds. We show that the nonzero $B$ field does not modify the form of the scattering potential. The graviton scattering equation has two solutions one normalizable and one non-normalizable. T

Todor Mishonov, Evgeni Penev

A detailed theoretical analysis of the Gaussian fluctuations of the order parameter in layered superconductors is performed within the Ginzburg-Landau (GL) theory. The available results for the Gaussian fluctuations are systematized and a number of novel formulae for the fluctuation magnetization, nonlinear magnetic susceptibility, heat capacity and high-fre

Doron Cohen, Tsampikos Kottos

Consider a time-dependent Hamiltonian $H(Q,P;x(t))$ with periodic driving $x(t)=A\sin(Ωt)$. It is assumed that the classical dynamics is chaotic, and that its power-spectrum extends over some frequency range $|ω|<ω_{cl}$. Both classical and quantum-mechanical (QM) linear response theory (LRT) predict a relatively large response for $Ω<ω_{cl}$, and a relative