December 1997 arXiv papers — page 4

Sergei A. Levshakov, Wilhelm H. Kegel, Fumio Takahara

Deuterium abundances measured recently from QSO absorption-line systems lie in the range from 3 10^{-5} to 3 10^{-4}, which shed some questions on standard big bang theory. We show that this discordance may simply be an artifact caused by inadequate analysis ignoring spatial correlations in the velocity field in turbulent media. The generalized procedure (ac

V. V. Usov

We show that the Coulomb barrier at the quark surface of a hot strange star may be a powerful source of $e^+e^-$ pairs which are created in an extremely strong electric field of the barrier and flow away from the star. The luminosity in the outflowing pair plasma depends on the surface temperature $T_{_S}$ and may be very high, up to $\sim 3\times 10^{51} er

E. E. Fenimore, E. Ramirez, M. C. Sumner

Two main types of models have been suggested to explain the long durations and multiple peaks of Gamma-Ray Bursts (GRBs). In one, there is a very quick release of energy at a central site resulting in a single relativistic shell that produces peaks in the time history through its interactions with the ambient material. In the other, the central site sporadic

M. C. Sumner, E. E. Fenimore

Many cosmological models of gamma-ray bursts (GRBs) assume that a single relativistic shell carries kinetic energy away from the source and later converts it into gamma rays, perhaps by interactions with the interstellar medium or by shocks within the shell. We investigate methods of achieving the observed variability using symmetry. Since our model emphasiz

Robert Savit, Radu Manuca, Rick Riolo

We analyze a simple model of adaptive competition which captures essential features of a variety of adaptive competitive systems in the social and biological sciences. Each of N agents, at each time step of a game, joins one of two groups. The agents in the minority group are awarded a point, while the agents in the majority group get nothing. Each agent has

A. Sedrakian, G. Roepke

A single-time quantum transport equation, which includes effects beyond the quasiparticle approximation, is derived for Fermi-systems in the framework of non-equilibrium real-time Green's functions theory. Ternary correlations are incorporated in the kinetic description via a cluster expansion for the self-energies (e.g., the transport vertex and the wid

Thomas R. Hemmert, Barry R. Holstein, Joachim Kambor

We demonstrate how heavy mass methods, previously applied to chiral perturbation theory calculations involving the interactions of nucleons and pions, can be generalized to include interactions with the $Δ(1232)$ in a systematic formalism which we call the "small scale expansion."

Adel Khoudeir

We show that the abelian topological mass mechanism in four dimensions, described by the Cremmer-Sherk action, can be obtained from dimensional reduction in five dimensions. Starting from a gauge invariant action in five dimensions, where the dual equivalence between a massless vector field and a massless second-rank antisymmetric field in five dimensions is

Loyal Durand, Phuoc Ha

We reexamine critically the chiral expansion for the baryon magnetic moments including the contributions from loops which involve intermediate octet and decuplet baryons. We find that, contrary to some claims, the nonanalytic loop contributions of orders $m_s^{1/2}$ and $m_s ln m_s$ are of the same general size because of large coupling factors for the latte

O. Bergman

We provide an explicit construction of 1/4 BPS states in four-dimensional N=4 Super-Yang-Mills theory with a gauge group SU(3). These states correspond to three-pronged strings connecting three D3-branes. We also find curves of marginal stability in the moduli space of the theory, at which the above states can decay into two 1/2 BPS states.

Pei-Ming Ho, Yi-Yen Wu, Yong-Shi Wu

In this paper we study generic M(atrix) theory compactifications that are specified by a set of quotient conditions. A procedure is proposed, which both associates an algebra to each compactification and leads deductively to general solutions for the matrix variables. The notion of noncommutative geometry on the dual space is central to this construction. As

Q. Y. Liu, A. Yu. Smirnov

We consider the ``standard'' spectrum of the active neutrinos (characterized by strong mass hierarchy and small mixing) with additional sterile neutrino, $ν_s$. The sterile neutrino mixes strongly with the muon neutrino, so that $ν_μ \leftrightarrow ν_s$ oscillations solve the atmospheric neutrino problem. We show that the parametric enhancement of t

M. J. Duff, P. Hoxha, H. Lu, R. R. Martinez-Acosta

A recent paper on the large-scale structure of the Universe presented evidence for a rectangular three-dimensional lattice of galaxy superclusters and voids, with lattice spacing ~120 Mpc and called for some ``hitherto unknown process'' to explain it. Here we report that a rectangular three-dimensional lattice of intersecting domain walls, with arbit

Rosario Fazio, F. W. J. Hekking, D. E. Khmelnitskii

We study thermal transport in a one-dimensional quantum wire, connected to reservoirs. Despite of the absence of electron backscattering, interactions in the wire strongly influence thermal transport. Electrons propagate with unitary transmission through the wire and electric conductance is not affected. Energy, however, is carried by bosonic excitations (pl

Carl H. Albright, S. M. Barr

It has recently been shown how to break SO(10) down to the Standard Model in a realistic way with only one adjoint Higgs. The expectation value of this adjoint must point in the B-L direction. This has consequences for the possible form of the quark and lepton mass matrices. These consequences are explored in this paper, and it is found that one is naturally

Shigeaki Wada, Hisao Hayakawa

Traffic jam in a fluid model of traffic flows proposed by Kerner and Konhäuser (B. S. Kerner and P. Konhäuser, Phys. Rev. E 52 (1995), 5574.) is analyzed. An analytic scaling solution is presented near the critical point of the hetero-clinic bifurcation. The validity of the solution has been confirmed from the comparison with the simulation of the model.

Christoph Richard, Moritz Hoeffe, Joachim Hermisson, Michael Baake

We introduce a concept for random tilings which, comprising the conventional one, is also applicable to tiling ensembles without height representation. In particular, we focus on the random tiling entropy as a function of the tile densities. In this context, and under rather mild assumptions, we prove a generalization of the first random tiling hypothesis wh

M. A. Diaz, M. A. Garcia-Jareno, D. A. Restrepo, J. W. F. Valle

In the simplest scheme for neutrino masses invoking a triplet of Higgs scalars there are two CP-even neutral Higgs bosons $H_i$ (i=1,2) and one massive pseudoscalar $A$. For some choices of parameters, the lightest $H_1$ may be lighter than the Standard Model Higgs boson. If the smallness of neutrino mass is due to the small value of the triplet expectation

D. Braun, G. Montambaux, M. Pascaud

It is shown that the universal behavior of the spacing distribution of nearest energy levels at the metal--insulator Anderson transition is indeed dependent on the boundary conditions. The spectral rigidity $Σ^2(E)$ also depends on the boundary conditions but this dependence vanishes at high energy $E$. This implies that the multifractal exponent $D_2$ of th

A. K. Nguyen, A. Sudbø

The statistical mechanics of the flux-line lattice in extreme type-II super- conductors is studied within the framework of the uniformly frustrated anisotropic 3D XY-model. A finite-field counterpart of an Onsager vortex-loop transition in extreme type-II superconductors renders the vortex liquid phase- incoherent when the Abrikosov vortex lattice undergoes

Nils A. Tornqvist

A novel, nonperturbative, way to generate chiral symmetry breaking within the linear sigma model for 3 flavours is discussed. After spontaneous chiral symmetry breaking in the vacuum at the tree level the scalar nonet obtains mass, while the pseudoscalars are massless. Then, including quantum loops in a nonperturbative, self-consistent way chiral symmetry is

M. A. Baranov, D. S. Petrov

We discuss a superfluid phase transition in a trapped neutral-atom Fermi gas. We consider the case where the critical temperature greatly exceeds the spacing between the trap levels and derive the corresponding Ginzburg-Landau equation. The latter turns out to be analogous to the equation for the condensate wave function in a trapped Bose gas. The analysis o

S. Falkenberg, B. Geyer, P. Moshin

The generating functionals of Green's functions with composite and external fields are considered in the framework of BV and BLT quantization methods for general gauge theories. The corresponding Ward identities are derived and the gauge dependence is investigated

Hideaki Hiro-Oka, Hisakazu Minakata

We discuss two-pion correlations as a possible experimental probe into disoriented chiral condensates. In particular, we point out that the iso-singlet squeezed states of the BCS type have peculiar two-particle correlations in the back-to-back and the identical momentum configurations which should be detectable experimentally. We motivate the examination of

M. Abolfath

In this article, we discuss the effect of the zero point quantum fluctuations to improve the results of the minimal field theory which has been applied to study %SMG the skyrmions in the quantum Hall systems. Our calculation which is based on the semiclassical treatment of the quantum fluctuations, shows that the one-loop quantum correction provides more acc

Naoki Itoh, Yasuharu Kohyama, Satoshi Nozawa

We study the generalized Kompaneets equation (kinetic equation for the photon distribution function taking into account the Compton scattering by electrons) using a relativistically covariant formalism. Using the generalized Kompaneets equation, we derive an analytic expression for the Sunyaev-Zel'dovich effect, which takes into account up to O(theta**5)

Yuri Ozhigov

Let a classical algorithm be determined by sequential applications of a black box performing one step of this algorithm. If we consider this black box as an oracle which gives a value F(a) for any query a, we can compute T sequential applications of F on a classical computer relative to this oracle in time T. It is proved that if T=O(2^{n/7}), where n is the

Alexander Molev, Grigori Olshanski

For each of the classical Lie algebras $g(n)=o(2n+1), sp(2n), o(2n)$ of type B, C, D we consider the centralizer of the subalgebra $g(n-m)$ in the universal enveloping algebra $U(g(n))$. We show that the $n$th centralizer algebra can be naturally projected onto the $(n-1)$th one, so that one can form the projective limit of the centralizer algebras as $n\to\

Anastass Anastasov

In the present report the author presents a simple and systematically defined formula for the fine structure constant based only on the number $π$. The difference between the suggested value and the currently known experimental one is about 60 times smaller than the uncertainty interval.

Nimai C. Mukhopadhyay, Vicente Vento

Relationships between mass intervals for free hadrons and in nuclei are studied in two theoretical approaches inspired by QCD: naive quark model and skyrmion model, taking one example each from mesons and baryons, that of pi-rho splitting in mesons, and nucleon-Delta splitting in baryons. Possible deconfinement effects in nuclei are examined.

M. Kirchbach

The pole positions of the various baryon resonances are known to reveal well-pronounced clustering, so-called Hoehler clusters. For nonstrange baryons the Hoehler clusters are shown to be identical to Lorentz multiplets of the type (j,j)*[(1/2,0)+(0,1/2)] with j being a half-integer. For the Lambda hyperons below 1800 MeV these clusters are shown to be of th

A. Acus, E. Norvaisas, D. O. Riska

A constructive realization of Skyrme's conjecture that an effective pion mass ``may arise as a self consistent quantal effect'' based on an ab initio quantum treatment of the Skyrme model is presented. In this quantum mechanical Skyrme model the spectrum of states with $I=J$, which appears in the collective quantization, terminates without any in

Alexander I. Titov, Yongseok Oh

We analyze the double polarization asymmetry of the omega-meson photoproduction in the vector-meson-dominance model of diffractive production and the one-pion exchange model. We find that the longitudinal beam-target asymmetry is very sensitive to the real part of the diffractive photoproduction amplitude and to the sign of the omega-pi-gamma coupling becaus

Robert Osserman

A number of classical results reflect the fact that if a holomorphic function maps the unit disk into itself taking the origin into the origin, and if some boundary point $b$ maps to the boundary, then the map is a magnification at $b$. We prove a sharp quantitative version of this result which also sharpens a classical result of Loewner, and which implies t

M. V. Manias, C. M. Naon, M. L. Trobo

We extend a recently proposed non-local and non-covariant version of the Thirring model to the finite-temperature case. We obtain a completely bosonized expression for the partition function, describing the thermodynamics of the collective modes which are the underlying excitations of this system. From this result we derive closed formulae for the free-energ

Dimitri Polyakov

We propose a string-theoretic ansatz describing the dynamics of SU(N) Yang-Mills theories in the limit of large N in D=4. The construction uses in a crucial way open-string vertex operators that describe non-perturbative brane dynamics. According to our proposal, various gauge theories are described by string theories with the same action, but with different

M. Daszkiewicz, Z. Hasiewicz, Z. Jaskolski

The paper containes a classification of consistent free string models in physical dimensions and a brief discussion of recent results concerning relations between various models.

Fedele Lizzi, Richard J. Szabo

We illustrate the various ways in which the algebraic framework of noncommutative geometry naturally captures the short-distance spacetime properties of string theory. We describe the noncommutative spacetime constructed from a vertex operator algebra and show that its algebraic properties bear a striking resemblence to some structures appearing in M Theory,

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

We review some basic notions on anomalies in field theories and superstring theories, with particular emphasis on the concept of locality. The aim is to prepare the ground for a discussion on anomalies in theories with branes. In this light we review the problem of chiral anomaly cancellation in M-theory with a 5-brane.

A. B. Bylev, H. J. Pirner

We derive and solve the Hamiltonian flow equations for a Dirac particle in an external static potential. The method shows a general procedure for the set up of continuous unitary transformations to reduce the Hamiltonian to a quasidiagonal form.

Michael Dine, Eva Silverstein

We propose examples, which involve orbifolds by elements of the U-duality group, with M-theory moduli fixed at the eleven-dimensional Planck scale. We begin by reviewing asymmetric orbifold constructions in perturbative string theory, which fix radial moduli at the string scale. Then we consider non-perturbative aspects of those backgrounds (brane probes and

M. Abou Zeid

We discuss an alternative form of the supersymmetric D-$p$-brane action which is quadratic in derivatives of $X$ and linear in $F_{μν}$. This action involves an auxiliary worldvolume tensor and generalises the simplification of the Nambu-Goto action for $p$-branes using a symmetric metric. When the worldvolume gauge field is abelian, it appears as a Lagrange

Alexey A. Petrov

We investigate the impact of the intrinsic heavy quark states on the predicted values of CP asymmetries in the decays of heavy mesons. It is shown that the intrinsic charm contribution, although dynamically suppressed in QCD, is favored by the weak interaction, and therefore it can significantly dilute the predicted values of CP-violating asymmetries. This i

V. Barger, T. J. Weiler, K. Whisnant

We present a four-neutrino model with three active neutrinos and one sterile neutrino which naturally has maximal $ν_μ\toν_τ$ oscillations of atmospheric neutrinos and can explain the solar neutrino and LSND results. The model predicts $ν_e \to ν_τ$ and $ν_e \to ν_μ$ oscillations in long-baseline experiments with $L/E \gg 1$ km/GeV with amplitudes that are d

Fredrick I. Olness, Randall J. Scalise, Wu-Ki Tung

Existing calculations of heavy quark hadroproduction in perturbative QCD are either based on the approximate conventional zero-mass perturbative QCD theory or on next-to-leading order (NLO) fixed-flavor-number (FFN) scheme which is inadequate at high energies. We formulate this problem in the general mass variable-flavor-number scheme which incorporates init

Joan Sola

We discuss the QCD and leading electroweak corrections to the hadronic width of the charged Higgs boson of the MSSM. In our renormalization framework, tan(beta) is defined through Gamma(H^+ -> tau^+ nu_{tau}). We show that a measurement of the hadronic width of H^\pm and/or of the branching ratio of its tau-decay mode with a modest precision of ~20% could be

Mark Hindmarsh

I report on some work in progress on the dynamics of extended objects in field theories after a rapid phase transition, as is relevant in the early Universe. An analytic technique, originally introduced to approximate the dynamics of topological defects in condensed matter systems, is extended to cover relativistic objects. An exact formula for the area dens

Manfred Lindner, Erhard Schnapka

We argue that a Standard Model decoupling limit is generically the necessary ingredient which makes scenarios of electro-weak symmetry breaking viable. This applies especially also to models of dynamical electro-weak symmetry breaking. Additional requirements are only that the mass predictions of a given model (e.g. predictions or theoretical limits on the H

M. S. Berger

Muon colliders are expected to naturally have a small spread in beam energy making them an ideal place to study the excitation curve. We present the parameter determinations that are possible from measuring the total cross section near threshold at a $μ^+μ^-$ collider.

C. Carimalo, N. Arteaga-Romero, S. Ong

We present predictions for the exclusive photoproduction of $Φ$-meson on Proton at large tranfer, where we use a quark-diquark structure model for the proton. Extrapolation from our results to lower tranfers is comparable in magnitude with available data in that range. This may support the diquark model in its ability to provide, for that process, an appropr

A. Bartl, F. de Campos, M. A. Garcia-Jareno, M. B. Magro

We study the pattern of gluino cascade decays in a class of supersymmetric models where R-parity is spontaneously broken. The multi-lepton and same-sign dilepton rates in these models are compared with those of the Minimal Supersymmetric Standard Model. We show that these rates can be substantially enhanced in models with broken R-parity.

S. J. Dong, K. F. Liu, A. G. Williams

We report on a lattice QCD calculation of the strangeness magnetic moment of the nucleon. Our result is $G_M^s(0) = - 0.36 \pm 0.20 $. The sea contributions from the u and d quarks are about 80% larger. However, they cancel to a large extent due to their electric charges, resulting in a smaller net sea contribution of $ - 0.097 \pm 0.037 \mu_N$ to the nucleo

J. Binnewies, B. A. Kniehl, G. Kramer

We present new sets of nonperturbative fragmentation functions for D^*+- mesons, both at leading and next-to-leading order in the MS-bar factorization scheme with five massless quark flavors. They are determined by fitting the latest OPAL and ALEPH data on inclusive D^*+- production in e^+e^- annihilation. We take the charm-quark fragmentation function to be

M. Beyer

In the framework of a relativistic covariant Bethe-Salpeter model for the quark-antiquark system we present a renewed determination of the Cabbibo-Kobayashi-Maskawa matrix element $|V_{cb}|$. Complementing an earlier analysis applied to the whole decay spectrum for $B\to D^* eν$ we now also employ the ``zero-recoil method'' that uses the end point of

D. Cocolicchio, M. Viggiano

We consider the covariant formulation of the kaon mixing in the context of the propagator method. It results important to check the possibility of a sizable effect in the vacuum regeneration of kaons. We discuss all those terms which may give relevant contributions to modify the exponential decay law of the Wigner-Weisskopf narrow width approximation. Moreov

Xiao-Gang He, Wei-Shu Hou, C. -S. Huang

The unexpectedly large branching ratios for $B\to η' K (η' X_s)$ decays could be of gluonic origin. We study the implications for $B\to ηK (ηX_s)$ and $P K (PX_s)$, where $P$ is the pseudoscalar glueball. In the mechanism proposed by Fritzsch, large branching ratios are predicted for these modes. The $B\to ηK$ rate is barely within the experimental l

A. V. Konychev

Using quantum electrodynamics as an example, a dependence of physical predictions of quantum field theory in a finite perturbation theory order on the choice of renormalization scheme is studied. It is shown that On-Mass-Shell renormalization scheme is distinguished in quantum electrodynamics not only due to the agreement of the theory predictions with exper

I. Bigi

CP violation has so far been observed in one system only, namely in the decays of neutral kaons, and it can still be described by a single real quantity corresponding to a superweak scenario. In these lectures I describe why limitations on CP invariance are a particularly fundamental phenomenon and what experimental information is available. The KM ansatz co

M. S. Berger

Precise determinations of the masses of the $W$ boson and of the top quark could stringently test the radiative structure of the Standard Model (SM) or provide evidence for new physics. We analyze the excellent prospects at a muon collider for measuring $M_W$ and $m_t$ in the $W^+W^-$ and $ZH$ threshold regions. With an integrated luminosity of 10 (100) fb$^

Chulwoo Jung

We study the three dimensional Georgi-Glashow model (which interpolates smoothly between pure U(1) and SU(2) limits) using a constrained cooling which preserves 't Hooft-Polyakov monopoles. We find that the monopole-antimonopole condensation gives an area law for the Wilson loops. The monopole contribution to the string tension is close to the Monte Carl

B. Abbott, M. Abolins, B. S. Acharya

We present a measurement of the W boson mass using data collected by the D0 experiment at the Fermilab Tevatron during 1994--1995. We identify W bosons by their decays to $eν$ final states. We extract the W mass, M(W), by fitting the transverse mass and transverse electron momentum spectra from a sample of 28,323 W to $eν$ decay candidates. We use a sample o

B. Abbott, M. Abolins, B. S. Acharya

We report a measurement of the W boson mass based on an integrated luminosity of 82 pb$^{-1}$ from \ppbar collisions at $\sqrt{s}=1.8$ TeV recorded in 1994--1995 by the \Dzero detector at the Fermilab Tevatron. We identify W bosons by their decays to $eν$ and extract the mass by fitting the transverse mass spectrum from 28,323 W boson candidates. A sample of

A. T. Doyle

Measurements of diffractive phenomena observed at HERA and the Tevatron are reviewed. A short introduction to the theoretical background is presented where colour singlet exchange reactions are discussed and the diffractive contribution and its interpretation via pomeron exchange outlined. The review focuses on the current experimental directions at HERA and

L. Crane, D. N. Yetter

The purpose of this note is to make several advances in the interpretation of the balanced state sum model by Barrett and Crane in gr-qc/9709028 as a quantum theory of gravity. First, we outline a shortcoming of the definition of the model in pointed out to us by Barrett and Baez in private communication, and explain how to correct it. Second, we show that t

Burkhard Kleihaus, Jutta Kunz

We discuss the new class of static axially symmetric black hole solutions obtained recently in Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole solutions are asymptotically flat and they possess a regular event horizon. The event horizon is almost spherically symmetric with a slight elongation along the symmetry axis. The energy d

F. Pretorius, D. Vollick, W. Israel

In this paper we calculate the entropy of a thin spherical shell that contracts reversibly from infinity down to its event horizon. We find that, for a broad class of equations of state, the entropy of a non-extremal shell is one-quarter of its area in the black hole limit. The considerations in this paper suggest the following operational definition for the

Hideki Nakamura

We show a noncommutative Rohlin type theorem for automorphisms of a certain class of purely infinite simple $C^{\ast}$-algebras. This class consists of the purely infinite unital simple $C^{\ast}$-algebras which are in the bootstrap category ${\cal N}$ and have trivial $K_{1}$-groups.

David Groisser, Lorenzo Sadun

We measure, in two distinct ways, the extent to which the boundary region of moduli space contributes to the ``simple type'' condition of Donaldson theory. Using a geometric representative of μ(pt), the boundary region of moduli space contributes 6/64 of the homology required for simple type, regardless of the topology or geometry of the underlying 4

Lorenzo Sadun

This is an expository article, explaining recent work by D. Groisser and myself [GS] on the extent to which the boundary region of moduli space contributes to the ``simple type'' condition of Donaldson theory. The presentation is intended to complement [GS], presenting the essential ideas rather than the analytical details. It is shown that the bound

Luis Guijarro, Lorenzo Sadun, Gerard Walschap

Let M be a simply connected Riemannian symmetric space, with at most one flat direction. We show that every Riemannian (or unitary) vector bundle with parallel curvature over M is an associated vector bundle of a canonical principal bundle, with the connection inherited from the principal bundle. The problem of finding Riemannian (or unitary) vector bundles

Kirill C. H. Mackenzie

We complete the construction of the double Lie algebroid of a double Lie groupoid begun in the first paper of this title. We show that the Lie algebroid structure of an LA--groupoid may be prolonged to the Lie algebroid of its Lie groupoid structure; in the case of a double groupoid this prolonged structure for either LA--groupoid is canonically isomorphic t

Kirill C. H. Mackenzie, Ping Xu

We prove that under certain mild assumptions a Lie bialgebroid integrates to a Poisson groupoid. This includes, in particular, a new proof of the existence of local symplectic groupoids for any Poisson manifold, a theorem of Karasev and of Weinstein.

Stefan Scheidl, Valerii M. Vinokur

The dynamic phase diagram of vortex lattices driven in disorder is calculated in two and three dimensions. A modified Lindemann criterion for the fluctuations of the distance of neighboring vortices is used, which unifies previous analytic approaches to the equilibrium and non-equilibrium phase transitions. The temperature shifts of the dynamic melting and d

W. Poirier, D. Mailly, M. Sanquer

We study the transport through gated GaAS:Si wires of 0.5 micrometer length in the insulating regime and observe transport via elastic tunneling at very low temperature. We describe the mean positive magnetoconductance and the mesoscopic fluctuations of the conductance (versus energy or magnetic field) purely within one electron model without introducing Cou

M. Nagelstraßer, H. Dröge, H. -P. Steinrück F. Fischer, T. Litz

Using angle-resolved synchrotron-radiation photoemission spectroscopy we have determined the dispersion of the valence bands of BeTe(100) along $ΓX$, i.e. the [100] direction. The measurements are analyzed with the aid of a first-principles calculation of the BeTe bulk band structure as well as of the photoemission peaks as given by the momentum conserving b

Elena Tareyeva, Valentin Ryzhov

A brief introduction to conventional DFT of 3D freezing is given and some recent results are reviewed. The conventional DFT, however, can not be used in the 2D case, particularly, because it can not describe the hexatic phase -- intermediate phase of 2D melting. We generalize DFT to describe 2D systems and two-stage melting scenario including intermediate he

V. N. Kotov, O. Sushkov, Zheng Weihong, J. Oitmaa

We consider quantum spin systems with dimerization, which at strong coupling have singlet ground states. To account for strong correlations, the excitations are described as dilute Bose gas of degenerate triplets with infinite on-site repulsion. This approach is applied to the two-layer Heisenberg model at zero temperature with general couplings. Our analyti

Barbara Coluzzi, Giorgio Parisi

In this note we apply some theoretical predictions that arise in the mean field framework for a large class of infinite range models to structural glasses and we present a first comparison of these predictions with numerical results.

WonMuk Hwang, Sungchul Kwon, Heungwon Park, Hyunggyu Park

We study nonequilibrium dynamical models with two absorbing states: interacting monomer-dimer models, probabilistic cellular automata models, nonequilibrium kinetic Ising models. These models exhibit a continuous phase transition from an active phase into an absorbing phase which belongs to the universality class of the models with the parity conservation. H

W. Zhang, K. Jahoda, R. L. Kelley, T. E. Strohmayer J. H. Swank

The Rossi X-Ray Timing Explorer observed the soft X-Ray transient Aql X-1 during its outburst in February and March 1997. We report the discovery of quasi-periodic oscillations (QPOs) in its persistent flux with frequencies in the range of 740 to 830 Hz, Q-value of over 100, and a fractional RMS amplitude of (6.8 +- 0.6)%, and nearly coherent oscillations (N

R. Hank Donnelly, M. Markevitch, W. Forman, C. Jones

We study the temperature structure of the rich cluster of galaxies Abell 1367 using two independent methods of correcting for the ASCA PSF. The results of the two methods are in excellent agreement and give solid evidence of a strong and localized shock in the intracluster medium (ICM). Our analysis suggests that we are observing the merger of two subcluster

Bruce G. Elmegreen, Eric Wilcots, D. J. Pisano

HI observations with the VLA of the late-type barred galaxy NGC 925 show clear streaming motions along four spiral arms close to the minor axis. A transition from inward streaming to outward streaming is found, presumably marking the corotation resonance. The realm of inward streaming extends to very large radii, corresponding to 1.3R25 and 1.7 bar radii dep

F. Frontera, L. Amati, E. Costa, M. Feroci

In about one year, five gamma-ray bursts were simultaneously observed with the Wide Field Cameras and Gamma Ray Burst Monitor aboard the BeppoSAX satellite. From some of them X-ray afterglow emission has been clearly detected with the same satellite. In order to understand how GRB emission is related to the X-ray afterglow, we are performing a systematic stu

I. H. Stairs, Z. Arzoumanian, F. Camilo, A. G. Lyne

We have made timing observations of binary pulsar PSR B1534+12 with radio telescopes at Arecibo, Green Bank, and Jodrell Bank. By combining our new observations with data collected up to seven years earlier, we obtain a significantly improved solution for the astrometric, spin, and orbital parameters of the system. For the first time in any binary pulsar sys

A. Cavaliere, V. Vittorini

The rise and the fall of the QS population are explained in terms of massive black holes forming/accreting during the assemblage of the host galaxies, and of accretion rekindled by interactions of the host with companions in a group. We compute the LFs out to z= 6. We also predict the masses of relict black holes to be found in many galaxies. We compare the

G. C. Anupama, Arati Chokshi

We present the first results from a pilot programme to monitor the short term optical variability in Broad Absorption Line system QSOs. Intra-night optical variations of ~5% were detected on time scales of ~ one hour in QSOs 0846+156 and 0856+172. Further, the mean magnitude level decreased in the two objects by ~0.05 and ~0.15 magnitude respectively during

Torsten A. Ensslin, Peter L. Biermann, Ulrich Klein, Sven Kohle

We present evidence for the existence of shock waves caused by the formation of the large-scale structure. In some clusters of galaxies peripherally located sources of extended diffuse radio emission exist, the so-called cluster radio relics. They have steep radio spectra but no apparent cutoff, as old remnants of radio galaxies usually have. Therefore parti

O. Vilhu, P. Muhli, J. Huovelin, P. Hakala

We observed AB Doradus, a young and active late type star (K0 - K2 IV-V, P= 0.514 d) with the Goddard High Resolution Spectrograph of the post-COSTAR Hubble Space Telescope with the time and spectral resolutions of 27 s and 15 km, respectively. The wavelength band (1531 - 1565 A) included the strong CIV doublet (1548.202 and 1550.774, formed in the transitio

G. M. Stirpe, B. J. Wilkes, A. Comastri, S. Mathur

We present the results of two observations of the bright Seyfert 1 galaxy NGC 3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is detected between 0.2 and 60 keV, allowing for the first time the simultaneous observation of all main spectral features. The source was brighter by a factor 2 at the second epoch of observation. Both spe

Milena Micono, Christopher J. Davis, Thomas P. Ray, Jochen Eislöffel

We report here on the first proper motion measurements of molecular hydrogen emission features in the Herbig-Haro 46/47 outflow. Assuming a distance of 350 pc to this flow, the inferred tangential velocities range from a few tens to almost 500 km/s . The highest velocities are observed for H2 knots either in, or close to, the jet/counterjet axes. Knots const

B. R. Espey, G. A. Kriss, J. H. Krolik, W. Zheng

We observed the Seyfert 1 galaxy NGC 4151 on eleven occasions at 1-2 day intervals using the Berkeley spectrometer during the ORFEUS-SPAS II mission in 1996 November. The mean spectrum covers 912-1220 A at ~0.3 A resolution with a total exposure of 15,658 seconds. The mean flux at 1000 A was 4.7e-13 erg/cm^2/s/A. We identify the neutral hydrogen absorption w

Y. Fujita, S. Inoue, T. Nakamura, T. Manmoto

Adopting the advection dominated accretion flow (ADAF) model, we have re-examined the radiation emitted by isolated stellar-mass black holes accreting from the interstellar medium of our Galaxy. Two distinct types of black holes are given consideration, 1) remnants of conventional massive star evolution (RBHs, mass $\sim 10 M_{\sun}$), and 2) low-mass object

Carme Gallart

The huge photometric databases that are being created for stars in the Magellanic Clouds and in Local Group galaxies not only allow detailed study of the star formation history of these systems, but also provide important information on stellar evolutionary theory. Two low-level features above the red-clump in the LMC color-magnitude diagram (CMD) have been

Yujiro Kawamata

We prove that small deformations of canonical singularities are canonical.

Vladimir D. Tonchev

This paper has been withdrawn since a Gilbert-Varshamov bound for general quantum codes has already appeared in Ekert and Macchiavello, Prys. Rev. Lett. 77, p. 2585, and a Gilbert-Varshamov bound for stabilizer codes connected with orthogonal geometry, or equivalently, with symmetric matrices as in this paper, has been proved by Calredbank, Rains, Shor and S

Hai-Yang Cheng

Since the x dependence of the axial-anomaly effect in inclusive polarized deep inelastic scattering is fixed, the transformation from the $\bar{MS}$ scheme to different factorization schemes are not arbitrary. If the quark spin distribution is demanded to be anomaly-free so that it does not evolve with $Q^2$ and hard gluons contribute to the first moment of

Carsten Gundlach

As first discovered by Choptuik, the black hole threshold in the space of initial data for general relativity shows both surprising structure and surprising simplicity. Universality, power-law scaling of the black hole mass, and scale echoing have given rise to the term "critical phenomena". They are explained by the existence of exact solutions whic

C. Ernst, S. A. Bass, M. Belkacem, H. Stöcker

Dielectron mass spectra are examined for various nuclear reactions recently measured by the DLS collaboration. A detailed description is given of all dilepton channels included in the transport model UrQMD 1.0, i.e. Dalitz decays of $π^0,η,ω,η'$ mesons and of the $Δ(1232)$ resonance, direct decays of vector mesons and $pn$ bremsstrahlung. The microscopic

Antonio Dobado, Antonio L. Maroto

In this work we calculate the low-energy effective action for gravity with torsion, obtained after the integration of scalar and fermionic matter fields, using the local momentum representation based on the Riemann normal coordinates expansion. By considering this expansion around different space-time points, we also compute the nonlocal terms together with

Y. J. Kim, M. Greven, U. -J. Wiese, R. J. Birgeneau

Antiferromagnetic Heisenberg spin chains with various spin values ($S=1/2,1,3/2,2,5/2$) are studied numerically with the quantum Monte Carlo method. Effective spin $S$ chains are realized by ferromagnetically coupling $n=2S$ antiferromagnetic spin chains with $S=1/2$. The temperature dependence of the uniform susceptibility, the staggered susceptibility, and