October 1997 arXiv papers — page 15

Claudio Gheller, Ornella Pantano, Lauro Moscardini

We study the properties of X-ray galaxy clusters in four cold dark matter models with different baryon fraction $Ω_{BM}$ ranging from 5 to 20 per cent. By using an original three-dimensional hydrodynamic code based on the piecewise parabolic method, we run simulations on a box with size $64 h^{-1}$ Mpc and we identify the clusters by selecting the peaks in t

M W Sincell, M Gehmeyr, D Mihalas

We solve the equations of radiation hydrodynamics in the two-temperature fluid approximation on an adaptive grid. The temperature structure depends upon the electron-ion energy exchange length, $l_{ei}$, and the electron conduction length, $l_{ec}$. Three types of radiating shock structure are observed: subcritical, where preheating of the unshocked gas is n

V. G. Gurzadyan, A. Mazure

The S-tree method is used to estimate the redshift of the core of Coma cluster - $cz = 6953$ km s$^{-1}$ and dispersion $σ=949$ km s$^{-1}$. The existence of three subgroups of galaxies is revealed, one of them is associated with the cD galaxy NGC 4874, another - with NGC 4889. It is argued that these subgroups are 'galaxy associations', i.e. galacti

I. Sakelliou, M. R. Merrifield

In this paper we report on the analysis of a deep ROSAT HRI image of the moderately-rich cluster, Abell 2634, by which we have been able to detect the X-ray emission from the galaxies in the cluster. The ICM of Abell 2634 is an order of magnitude denser than that of the Virgo cluster, and so this analysis allows us to explore the X-ray properties of individu

A. Udalski, M. Kubiak, M. Szymanski

We describe a new 1.3 m Warsaw telescope located at Las Campanas Observatory and new instruments of the second phase of the Optical Gravitational Lensing Experiment - OGLE-2. Results of first observations are also presented.

J. K. Webb, R. F. Carswell, K. M. Lanzetta, R. Ferlet

Recent HST/GHRS observations of the z = 0.7010 absorber toward the QSO 1718+4807 (selected because of apparently ideal characteristics for measuring D/H) yield a D/H significantly higher D/H than some recent high-redshift measurements. Our analysis indicates D/H}= 1.8 - 2.5 x 10^{-4}. This may indicate a cosmological inhomogeneity in the deuterium abundance

Dante Minniti, Markus Kissler-Patig, Paul Goudfrooij, Georges Meylan

We report on the radial velocity measurements of 18 globular clusters and one dE galaxy in the field of the giant elliptical galaxy NGC 1399, the dominant galaxy of the Fornax cluster. We present also the radial velocity measurements of some candidates for young and super metal-rich globular clusters, which turn out to be foreground or background objects, vi

W. Yu, S. N. Zhang, B . A. Harmon, W. S. Paciesas

We report RXTE/PCA observations of 4U 1608-52 on March 15, 18 and 22 immediately after the outburst in early 1996. The persistent count rates ranged from 190 to 450 cps (1-60 keV). During this period of time, 4U 1608-52 was in the island state. We detected QPO features in the power density spectra (PDS) at 567-800 Hz on March 15 and 22, with source fractiona

Jiannis Pachos, Antonios Tsapalis

Within the Schroedinger Electric Representation we analytically calculate the complete wave functional obeying Gauss' law with static SU(2) sources in (1+1)-dimensions. The effective potential is found to be linear in the distance between the sources as expected.

B. Pioline, E. Kiritsis

We investigate D-brane instanton contributions to R^4 couplings in any toroidal compactification of type II theories. Starting from the 11D supergravity one-loop four-graviton amplitude computed by Green, Gutperle and Vanhove, we derive the non-perturbative O(e^{-1/λ}) corrections to R^4 couplings by a sequence of T-dualities, and interpret them as precise c

Mary Silber, Michael R. E. Proctor

Recent experiments by Kudrolli, Pier and Gollub on surface waves, parametrically excited by two-frequency forcing, show a transition from a small hexagonal standing wave pattern to a triangular ``superlattice'' pattern. We show that generically the hexagons and the superlattice wave patterns bifurcate simultaneously from the flat surface state as the

H. Pierre Noyes, E. D. Jones

Starting from a relativistic s-wave scattering length model for the two particle input we construct an unambiguous, unitary solution of the relativistic three body problem given only the masses $m_a,m_b,m_c$ and the masses of the two body bound states $μ_{bc},μ_{ca},μ_{ab}$.

Julien Lesgourgues, David Polarski

We consider a double-inflationary model with two massive scalar fields interacting only gravitationally in the context of a flat cold dark matter (CDM) Universe. The cosmic microwave background (CMB) temperature anisotropies produced in this theory are investigated in great details for a window of parameters where the density fluctuation power spectrum P(k)

K. Saygili

We apply the long-wavelength approximation to the low energy effective string action in the context of Hamilton-Jacobi theory. The Hamilton-Jacobi equation for the effective string action is explicitly invariant under scale factor duality. We present the leading order, general solution of the Hamilton-Jacobi equation. The Hamilton-Jacobi approach yields a so

I. V. Kanatchikov

A few generalizations of a Poisson algebra to field theory canonically formulated in terms of the polymomentum variables are discussed. A graded Poisson bracket on differential forms and an $(n+1)$-ary bracket on functions are considered. The Poisson bracket on differential forms gives rise to various generalizations of a Gerstenhaber algebra: the noncommuta

Diego F Torres, Andrew R Liddle, Franz E Schunck

`Gravitational memory' refers to the possibility that, in cosmologies with a time-varying gravitational `constant', objects such as black holes may retain a memory of conditions at the time of their birth. We consider this phenomenon in a different physical scenario, where the objects under consideration are boson stars. We construct boson star solut

Frank Waeckerle

The total hadronic cross-section for the interaction of real photons is extracted from a measurement of the cross-section of the process e+e->e+e- + hadrons using a luminosity function for the photon flux and form factors for extrapolating to Q**2=0. The data was taken with the OPAL detector at LEP at e+e- centre-of-mass energies of 161 GeV and 172 GeV. In t

H. Vedel, F. D. A. Hartwick

We construct models describing the velocity field in the infall regions of clusters. The velocity field is the superposition of a systematic component and a "noise" component accounting for the effects of small scale substructure and observational errors. This procedure results in models which resemble the observations (redshifts and angular separati

I. Bars, C. Deliduman

We formulate new gauge principles for n supersymmetric particles in a worldline formalism with N supersymmetries. The models provide realizations of the more general supersymmetries that are encountered in sectors of S-theory or Matrix theory, with a superalgebra that involves products of momenta. Due to local gauge and kappa symmetries the n superparticle m

John R. Klauder

Quantum mechanical phase space path integrals are re-examined with regard to the physical interpretation of the phase space variables involved. It is demonstrated that the traditional phase space path integral implies a meaning for the variables involved that is manifestly inconsistent. On the other hand, a phase space path integral based on coherent states

D. Cocolicchio, M. Viggiano

In this paper, we propose a complex approach to evaluate a function sum of two noncommuting non Hermitian operators. Then, it is proposed an explicit expansion of the evolution operator in the case of the neutral K-meson system under the influence of an external interaction. Then, the importance of the procedure is pointed out to consider the algebraic expan

Gerhard C. Hegerfeldt

Modern techniques allow experiments on a single atom or system, with new phenomena and new challenges for the theoretician. We discuss what quantum mechanics has to say about a single system. The quantum jump approach as well as the role of quantum trajectories are outlined and a rather sophisticated example is given.

Gerhard C. Hegerfeldt, Thorsten Koehler

Atomic diffraction through double slits and transmission gratings is well described in terms of the associated de Broglie waves and classical wave optics. However, for weakly bound and relatively large systems, such as the He_2 dimer, this might no longer hold true due to the possibility of break-up processes and finite-size effects. We therefore study the d

Waldemar Puszkarz

The idea of equivalence of the free electromagnetic phase and quantum-mechanical one is investigated in an attempt to seek modifications of Schrödinger's equation that could realize it. It is assumed that physically valid realizations are compatibile with the U(1)-gauge and Galilean invariance. It is shown that such extensions of the Schrödinger equation

R. Guillermo Moreno

In this paper we describe algebraically the zero divirsors of the Cayley- Dickson algebras $\a_{n}=\erre^{2^n}$ for $n \ge 4$ over the real numbers.

T. Tikkanen, K. Hamalainen, S. Huotari

Cathode electrodes of the Si(Li) detector elements of the SIXA X-ray spectrometer array are formed by gold-palladium alloy contact layers. The equivalent thickness of gold in one element was measured by observing the characteristic L-shell X-rays of gold excited by monochromatised synchrotron radiation with photon energies above the L3 absorption edge of gol

Ralf Schindler

It is shown that if every projective set of reals is Lebesgue measurable and has the property of Baire, if every projective set in the plane has a projective uniformization, and if Steel's K exists, then J^K_{ω_1} \models "there are infinitely many strong cardinals." This is best possible, by a recent result of Steel.

Carl M. Bender, Kimball A. Milton

Recently, it was observed that self-interacting scalar quantum field theories having a non-Hermitian interaction term of the form $g(iϕ)^{2+δ}$, where $δ$ is a real positive parameter, are physically acceptable in the sense that the energy spectrum is real and bounded below. Such theories possess PT invariance, but they are not symmetric under parity reflect

Steven Corley

We present a method for computing the spectrum of black hole radiation of a scalar field satisfying a wave equation with high frequency dispersion. The method involves a combination of Laplace transform and WKB techniques for finding approximate solutions to ordinary differential equations. The modified wave equation is obtained by adding a higher order deri

Timothy J. Hollowood

A complete definition of the cycles, on the auxiliary Riemann surface defined by Martinec and Warner for describing pure N=2 gauge theories with arbitrary group, is provided. The strong coupling monodromies around the vanishing cycles are shown to arise from a set of dyons which becomes massless at the singularities. It is shown how the correct weak coupling

P. S. Howe, A. Opfermann, G. Papadopoulos

We find that the target space of two-dimensional (4,0) supersymmetric sigma models with torsion coupled to (4,0) supergravity is a QKT manifold, that is, a quaternionic Kähler manifold with torsion. We give four examples of geodesically complete QKT manifolds one of which is a generalisation of the LeBrun geometry. We then construct the twistor space associa

Andrea Cappelli, Filippo Colomo

We analyse the Spherical Model with frustration induced by an external gauge field. In infinite dimensions, this has been recently mapped onto a problem of q-deformed oscillators, whose real parameter q measures the frustration. We find the analytic solution of this model by suitably representing the q-oscillator algebra with q-Hermite polynomials. We also p

A. M. Ghezelbash

We obtain the periods and one-instanton coefficient of the N=2 superrsymmetric Yang-Mills theory with the exceptional gauge group E_6. These calculations are based on the E_6 spectral curve and the obtained one-instanton coefficient is in agreement with the microscopic results.

Christian Schubert

An ambiguity inherent in the partial integration procedure leading to the Bern-Kosower rules is fixed in a way which preserves the complete permutation symmetry in the scattering states. This leads to a canonical version of the Bern-Kosower representation for the one-loop N - photon/gluon amplitudes, and to a natural decomposition of those amplitudes into pe

L. D. Faddeev, A. Yu. Volkov

Just like decent classical difference-difference systems define symplectic maps on suitable phase spaces, their counterparts with properly ordered noncommutative entries come as Heisenberg equations of motion for corresponding quantum discrete-discrete models. We observe how this idea applies to a difference-difference counterpart of the Liouville equation.

Xiangdong Ji

To investigate the internal structure of the nucleon, it is useful to introduce quantities that do not transform properly under Lorentz symmetry, such as the four-momentum of the quarks in the nucleon, the amount of the nucleon spin contributed by quark spin, etc. In this paper, we discuss to what extent these quantities do provide Lorentz-invariant descript

Ken Kiers, Nathan Weiss

We study the oscillations of neutrinos in a model in which the neutrino is coupled to a localized, idealized source and detector. By varying the spatial and temporal resolution of the source and detector we are able to model the full range of source and detector types ranging from coherent to incoherent. We find that this approach is useful in understanding

T. Mannel, S. Recksiegel

We investigate the rare decay $Λ_b \to Λγ$ which receives both short and long distance contributions. We estimate the long distance contributions and find them very small. The form factors are obtained from $Λ_c \to Λ\ell \barν_\ell$ using heavy quark symmetry and a pole model. The short distance piece opens a window to new physics and we discuss the sensiti

A. Bartl, H. Eberl, K. Hidaka, S. Kraml

We calculate the supersymmetric ${\cal O}(α_s)$ QCD corrections to stop and sbottom decays into vector bosons within the Minimal Supersymmetric Standard Model. We give analytic formulae and perform a numerical analysis of these decays. We find that SUSY-QCD corrections to the decay widths are typically -5% to -10% depending on the squark masses, squark mixin

A. K. Giri, L. Maharana, R. Mohanta

The two body non-leptonic $Λ_b$ decays are analyzed in the HQET with factorization approximation and large $N_c$ limit. In this limit, $Λ_b$ and $Λ_c$ baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes out in a straight forward manner. The results obtained remain well below their previ

Subhendra Mohanty

When neutrinos are produced from long lived particles the life-time of the source particle affects the flavour conversion probability formula. Due to this source dependence experiments (like LSND) which use muon decay neutrinos are two orders of magnitude more sensitive to lower values of mass square difference compared to other experiments where the sources

G. G. Devidze, G. R. Jibuti

In the present paper the two and three point functions which occur at the study of the various physical processes are considered. The investigation has dan in the framework of the perturbative theory at the one loop level. The general and asymptotic expressions for these functions are obtained.

Alessandro Ballestrero, Roberto Chierici

We analyze from a theoretical point of view the impact of various approximations on W mass distributions. This is done both at parton level and after a simulated W mass reconstruction using constrained fits. The results may help to understand the origin of various shifts and the broadening of the peak in direct reconstruction mass measurements.

Stephan Narison

This is a review of the estimate of the gluonia masses, decay and mixings from QCD spectral sum rules and low-energy theorems. Some phenomenological maximal gluonium-quarkonium mixing shemes in the scalar sector are presented. This talk is a compact version of the work in Ref.[1] (hep-ph/9612457) having the same title.

Sarka Todorova-Nova, Jiri Rames

The experimentally observed enhancement of number of close boson pairs in e+e- collisions is reproduced by local weighting according to the quantum mechanical prescriptions for production of identical bosons. The space-time picture of the process, inherently present in the Lund fragmentation model, is explicitly used. The model is used to check systematic er

J. Hisano, Yasunori Nomura, T. Yanagida

Dimension-five operators for nucleon decays are suppressed in the modified missing doublet (MMD) model in the supersymmetric SU(5) grand unification. We show that nonrenormalizable interactions decrease the unification scale in the MMD model which increases the nucleon decay rate of dimension-six operators by a significant amount. We find that the theoretica

T. Babutsidze, T. Kopaleishvili, A. Rusetsky

Bound q\bar q -systems are considered in the framework of three different versions of the 3-dimensional reduction of the Bethe-Salpeter equation, all having the correct one-body limit when one of the constituent quark masses tends to infinity, and in the framework of the Salpeter equation. The spin structure of confining qq interaction potential is taken in

Glennys R. Farrar

I summarize recent devlopments in supersymmetry scenarios which leave some or all gauginos light. The emphasis is on experimental and phenomenological progress in the past year.

S. Capitani, M. Goeckeler, R. Horsley, H. Oelrich

The Alpha Collaboration has proposed an optimal value for c_SW in the Sheikholeslami-Wohlert action, chosen to remove O(a) effects. To measure hadronic matrix elements to the same accuracy we need a method of finding O(a) improved operators, and their renormalization constants. We determine the Z factors by a non-perturbative method, measuring the matrix ele

U. M. Heller, F. Karsch, J. Rank

We study the gluon propagator and the singlet potential in Landau gauge in the deconfined phase of SU(2) lattice gauge theory, using both the standard Wilson action and a tree-level Symanzik improved action. From the long-distance behavior of correlation functions of temporal and spatial components of the gauge fields we extract electric (m_e) and magnetic (

P. Butera, M. Comi

High temperature expansions for the free energy, the susceptibility and the second correlation moment of the classical N-vector model [also denoted as the O(N) symmetric classical spin Heisenberg model or as the lattice O(N) nonlinear sigma model] have been extended to order beta^{21} on the simple cubic and the body centered cubic lattices, for arbitrary N.

S. Aoki, Y. Iwasaki, K. Kanaya, S. Kaya

We investigate the finite-temperature phase structure and the scaling of the chiral condensate in lattice QCD with two degenerate light quarks, using a renormalization group improved gauge action and the Wilson quark action. We obtain a phase diagram which is consistent with that from the parity-flavor breaking scenario. The scaling relation for the chiral c

F. Vendrell, M. E. Ortiz

The thermal nature of the propagator in a collapsed black-hole spacetime is shown to follow from the non-trivial topology of the configuration space in tortoise coordinates by using the path integral formalism.

J Podolsky, J B Griffiths

We describe a class of impulsive gravitational waves which propagate either in a de Sitter or an anti-de Sitter background. They are conformal to impulsive waves of Kundt's class. In a background with positive cosmological constant they are spherical (but non-expanding) waves generated by pairs of particles with arbitrary multipole structure propagating

B. Kleihaus, J. Kunz

We discuss the recently discovered new class of globally regular and black hole solutions in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These asymptotically flat solutions are static and possess only axial symmetry. The black hole solutions possess a regular event horizon.

Abha Sood, Burkhard Kleihaus, Jutta Kunz

Static spherically symmetric solutions in SU(N)-EYM and EYMD theories are classified by the node numbers of their non-trivial gauge field functions. With increasing node numbers, the solutions form sequences, tending to limiting solutions. The limiting solutions are based on subalgebras of $su(N)$, consisting of a neutral non-abelian part and a charged abeli

C. Barrabès, G. F Bressange, P. A. Hogan

Recently a simple solution of the vacuum Einstein-Maxwell field equations was given describing a plane electromagnetic shock wave sharing its wave front with a plane gravitational impulse wave. We present here an exact solution of the vacuum Einstein-Maxwell field equations describing the head-on collision of such a wave with a plane gravitational impulse wa

Lior M. Burko

We study the Cauchy horizon (CH) singularity of a spherical charged black hole perturbed nonlinearly by a self-gravitating massless scalar field. We show numerically that the singularity is weak both at the early and at the late sections of the CH, where the focusing of the area coordinate $r$ is strong. In the early section the metric perturbations vanish,

Lior M. Burko

We study numerically the fully nonlinear spherically-symmetric collapse of a self-gravitating, minimally-coupled, massless scalar field. Our numerical code is based on double-null coordinates and on free evolution of the metric functions and the scalar field. The numerical code is stable and second-order accurate. We use this code to study the late-time asym

Waldemar Puszkarz

A model of the gravitational dipole is proposed in a close analogy to that of the global monopole. The physical properties and the range of validity of the model are examined as is the motion of test particles in the dipole background. It is found that the metric of the gravitational dipole describes a curved space-time, so one would expect it to have a more

A. Vazquez, O. Sotolongo-Costa

The self-organized critical state is characterized by a power law distribution of cluster sizes and other properties. However experiments with sand and rice piles reveal distributions of avalanche sizes which are not power law distributed. In the present letter a one-dimensional rice-pile model which demonstrate that this is only an apparent contradiction is

Franck Celestini, Daniele Passerone, Furio Ercolessi, Erio Tosatti

Most realistic, off-lattice surface simulations are done canonically--- conserving particles. For some applications, however, such as studying the thermal behavior of rare gas solid surfaces, these constitute bad working conditions. Surface layer occupancies are believed to change with temperature, particularly at preroughening, and naturally call for a gran

Dmitrii S. Golubev, Andrei D. Zaikin

We point out that the low temperature saturation of the electron phase decoherence time in a disordered conductor can be explained within the existing theory of weak localization provided the effect of quantum (high frequency) fluctuations is taken into account. Making use of the fluctuation-dissipation theorem we evaluate the quantum decoherence time, the c

S. J. Phillipson, M. A. Moore, T. Blum

We examine nonlocal conductivity in high-temperature superconductors from a phenomenological point of view. One wants to deduce the properties of the conductivity, especially its inherent length scales, from the transport data. Although this is a challenging inverse problem, complicated further by the experimental data not being completely self-consistent, w

Th. M. Nieuwenhuizen

In the marriage problem, a variant of the bi-parted matching problem, each member has a `wish-list' expressing his/her preference for all possible partners; this list consists of random, positive real numbers drawn from a certain distribution. One searches the lowest cost for the society, at the risk of breaking up pairs in the course of time. Minimizati

Kurt Stokbro, Ulrich Quaade, Francois Grey

We present a high voltage extension of the Tersoff-Hamann theory of STM images, which includes the effect of the electric field between the tip and the sample. The theoretical model is based on first principles electronic structure calculations and has no adjustable parameters. We use the method to calculate theoretical STM images of the monohydrate Si(100)-

P. L. de Andres, J. A. Vergés

Intensities of LEED and PED are analyzed from a statistical point of view. The probability distribution is compared with a Porter-Thomas law, characteristic of a chaotic quantum system. The agreement obtained is understood in terms of analogies between simple models and Berry's conjecture for a typical wavefunction of a chaotic system. The consequences o

B. Schottky, U. Krey

We extend our study of phase transitions in the generalization behaviour of multilayer perceptrons with non-overlapping receptive fields to the problem of the influence of noise, concerning e.g. the input units and/or the couplings between the input units and the hidden units of the second layer (='input noise'), or the final output unit (='outpu

R. Gallego, M. San Miguel, Raul Toral

We present a study of dynamical scaling and domain growth in a non potential system that models Rayleigh-Benard convection in a rotating cell. In d=1, dynamical scaling holds, but the non potential terms modify the characteristic growth law with a crossover from logarithmic to linear in time. In d=2 the non potential terms prevent coarsening for any value of

J. P. Dekker, A. Lodder, J. van Ek

A multiple scattering formulation for the electromigration wind force on atoms in dilute alloys is developed. The theory describes electromigration via a vacancy mechanism. The method is used to calculate the wind valence for electromigration in various host metals having a close-packed lattice structure, namely aluminum, the noble metals copper, silver and

U. Ebert, L. Schäfer, A. Baumgärtner

We analyze the motion of individual beads of a polymer chain using a discrete version of De Gennes' reptation model that describes the motion of a polymer through an ordered lattice of obstacles. The motion within the tube can be evaluated rigorously, tube renewal is taken into account in an approximation motivated by random walk theory. We find microstr

G. Khaliullin, V. Oudovenko

We discuss spin and orbital ordering in the twofold orbital degenerate superexchange model in three dimensions relevant to perovskite transition metal oxides. We focus on the particular point on the classical phase diagram where orbital degeneracy is lifted by quantum effects exclusively. Dispersion and damping of the spin and orbital excitations are calcula

A. Barrat

Numerical simulations of various domain growth systems are reported, in order to compute the parameter describing the violation of fluctuation dissipation theorem (FDT) in aging phenomena. We compute two-times correlation and response functions and find that, as expected from the exact solution of a certain mean-field model (equivalent to the O(N) model in t

Jan Brinckmann, Patrick A. Lee

The dynamical spin susceptibility chi'' at wave vector (pi, pi) and the spectrum pi'' of the spin-triplet particle--particle excitation with center of mass momentum (pi, pi) (pi-excitation) are considered in the slave-boson formulation of the t--J-model. Propagators are calculated in a diagrammatic t-matrix approximation in the d-wave superco

Pabitra Mitra

In this brief, an algorithm for controlling chaotic systems using small, continuous time perturbations is presented. Stabilisation is achieved by self controlling feedback using low order LTI filters. The algorithm alleviates the need of complex calculati ons or costly delay elements, and can be implemented in a wide variety of systems using simple circuit e

Brian Keating, Peter Timbie, Alexander Polnarev, Julia Steinberger

In addition to its spectrum and temperature anisotropy, the 2.7K Cosmic Microwave Background is also expected to exhibit a low level of polarization. The spatial power spectrum of the polarization can provide details about the formation of structure in the universe as well as its ionization history. Here we calculate the magnitude of the CMB polarization in

Bohdan Paczynski

The optical afterglow of the gamma-ray burst GRB 970508 (z = 0.835) was a few hundred times more luminous than any supernova. Therefore, a name `hypernova' is proposed for the whole GRB/afterglow event. There is tentative evidence that the GRBs: 970228, 970508, and 970828 were close to star forming regions. If this case is strengthened with future afterglows

Pierluigi Monaco

This thesis aims to review the cosmological mass function problem, both from the theoretical and the observational point of view, and to present a new mass function theory, based on realistic approximations for the dynamics of gravitational collapse. Chapter 1 gives a general introduction on gravitational dynamics in cosmological models. Chapter 2 gives a co

A. Natta, M. R. Meyer, S. V. W. Beckwith

ISO observations will improve our understanding of disks around low-mass pre-main-sequence stars in various ways. In particular, ISO can measure simultaneously spectral energy distributions and low-resolution spectra from 2 to 12 \um of T Tauri stars with greater sensitivity, greater spectral coverage and finer spectral resolution than available in ground-ba

T. Appourchaux, L. Gizon, M. C. Rabello-Soares

In this article we present our state of the art of fitting helioseismic p-mode spectra. We give a step by step recipe for fitting the spectra: statistics of the spectra both for spatially unresolved and resolved data, the use of Maximum Likelihood estimates, the statistics of the p-mode parameters, the use of Monte-Carlo simulation and the significance of fi

F. Garzon, M. Lopez-Corredoira, P. Hammersley, T. J. Mahoney

We present an analysis of the optical spectroscopy of 58 stars in the Galactic plane at $l=27$\arcdeg, where a prominent excess in the flux distribution and star counts have been observed in several spectral regions, in particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were selected from the TMGS, to have a $K$ magnitude brighter than

S. Dodelson, C. Wiegert

A number of different mechanisms exist which can produce vector perturbations to the metric. One might think that such perturbations could deflect light rays from distant sources, producing observable effects. Indeed, this is expected to be the case for scalar perturbations. Here we show that the deflection from vector perturbations is very small, remaining

Eunwoo Choi, Dongsu Ryu

We report a study to constrain the fraction of baryonic matter in the cold plus hot dark matter (CHDM) universe by numerical simulations which include the hydrodynamics of baryonic matter as well as the particle dynamics of dark matter. Spatially flat, COBE-normalized CHDM models with the fraction of hot component $Ω_h\leq0.2$ are considered. We show that th

Walter Dehnen, James Binney

(shortened) From a kinematically unbiased subsample of the Hipparcos catalogue we have redetermined as a function of colour the kinematics of main-sequence stars. The stars' mean heliocentric velocity nicely follows the asymmetric drift relation, except for stars blueward of B-V=0.1. Extrapolating to zero dispersion yields for the velocity of the Sun w.r

J. Scalo, E. Vazquez-Semadeni, D. Chappell, T. Passot

We investigate the form of the one-point probability distribution function (pdf) for the density field of the interstellar medium using numerical simulations that successively reduce the number of physical processes included. Two-dimensional simulations of self-gravitating supersonic MHD and hydrodynamic turbulence, and of decaying Burgers turbulence, produc

Jolien D. E. Creighton, Robert B. Mann

We consider the thermodynamic properties of the constant curvature black hole solution recently found by Banados. We show that it is possible to compute the entropy and the quasilocal thermodynamics of the spacetime using the Einstein-Hilbert action of General Relativity. The constant curvature black hole has some unusual properties which have not been seen

Arlen Anderson, Yvonne Choquet-Bruhat, James W. York,

By employing the Bianchi identities for the Riemann tensor in conjunction with the Einstein equations, we construct a first order symmetric hyperbolic system for the evolution part of the Cauchy problem of general relativity. In this system, the metric evolves at zero speed with respect to observers at rest in a foliation of spacetime by spacelike hypersurfa

Edward Witten

More general constructions are given of six-dimensional theories that look at low energy like six-dimensional super Yang-Mills theory. The constructions start with either parallel fivebranes in Type IIB, or M-theory on $(\C^2\times§^1)/Γ$ for $Γ$ a suitable finite group. Via these constructions, one can obtain six-dimensional theories with any simple gauge g

L. Bonora, C. S. Chu, M. Rinaldi

We discuss several mechanisms to cancel the anomalies of a 5-brane embedded in M-theory. Two of them work, provided we impose suitable conditions either on the 11-dimensional manifold of M-theory or on the 4-form field strength of M-theory.

Subir Sarkar

Massive neutrinos were the first proposed, and remain the most natural, particle candidate for the dark matter. In the absence of firm laboratory evidence for neutrino mass, considerations of the formation of large scale structure in the universe provide a sensitive, albeit indirect, probe of this possibility. Observations of galaxy clustering and large angl

Ehud Cohen, Tsvi Piran, Ramesh Narayan

It is often stated that gamma-ray bursts (GRBs) have typical energies of several hundreds $\keV$, where the typical energy may be characterized by the hardness H, the photon energy corresponding to the peak of $νF_ν$. Among the 54 BATSE bursts analyzed by Band et al. (1993), and 136 analyzed by us, more then 60% have 50 keV < H < 300 keV. Is the narrow range

M. Goeckeler, R. Horsley, H. Perlt, P. Rakow

We have results from light hadron simulations in quenched QCD at beta=6.0 and 6.2 using non-perturbatively improved Sheikholeslami-Wohlert fermions in an effort to remove all order(a) effects. From looking at hadron masses and splittings and the RG-invariant quark masses (where we have one point at beta=5.7) we suggest this is plausible even with the limited

W. Yu, S. N. Zhang, B . A. Harmon, W. S. Paciesas

We present the results from RXTE/PCA observations of 4U 1608-52 in its island state on March 15, 18 and 22 of 1996. Three type I X-ray bursts were detected in one RXTE orbit on March 22. We observed QPO features peaking at 567-800 Hz on March 15 and 22, with source fractional rms amplitude of 13%-17% and widths of 78-180 Hz in the power density spectra avera

M. G. Zacher, E. Arrigoni, W. Hanke, J. R. Schrieffer

The problem of spin-charge separation is analyzed numerically in the metallic phase of the one-band Hubbard model in one dimension by studying the behavior of the single-particle Green&#39;s function and of the spin and charge susceptibilities. We first analyze the Quantum-Monte Carlo data for the imaginary-time Green&#39;s function within the Maximum Entrop

Gysbert Zwart

We construct the Matrix theory descriptions of M-theory on the Mobius strip and the Klein bottle. In a limit, these provide the matrix string theories for the CHL string and an orbifold of type IIA string theory.

Kazunori Takenaga

The effects of boundary conditions of the fields for the compactified space directions on the supersymmetric theories are discussed. The boundary conditions can be taken to be periodic up to the degrees of freedom of localized $U(1)_{R}$ transformations. The boundary condition breaks the supersymmery to yield universal soft supersymmetry breaking terms. The

J. N. Ginocchio, A. Leviatan

We show that the generators of pseudospin symmetry are the non - relativistic limit of the generators of an SU(2) symmetry which leaves invariant the Dirac Hamiltonian with scalar and vector potentials equal in magnitude but opposite in sign, $V_V = - V_S$. Furthermore, within this framework, we demonstrate that this symmetry may be approximately conserved f

Luc Blanchet

The tails of gravitational waves are caused by scattering of linear waves onto the space-time curvature generated by the total mass-energy of the source. Quite naturally, the tails of tails are caused by curvature scattering of the tails of waves themselves. The tails of tails are associated with the cubic non-linear interaction between two mass monopole mom

Mohamed Benarous

We analyze the Poisson structure of the time-dependent mean-field equations for bosons and construct the Lie-Poisson bracket associated to these equations. The latter follow from the time-dependent variational principle of Balian and Veneroni when a gaussian Ansatz is chosen for the density operator. We perform a stability analysis of both the full and the l

M. Kawasaki, N. Sugiyama, T. Yanagida

It has been recently pointed out that the initial value problem in new inflation models is naturally solved by supergravity effects if there exists a pre-inflation before the new inflation. We study this double inflation model in details and find that density fluctuations on small cosmological scales are much larger than those on large scales due to peculiar