November 1997 arXiv papers — page 9

Jean Letessier, Johann Rafelski, Ahmed Tounsi

We demonstrate that both quark-gluon plasma (QGP) and hadronic gas (HG) models of the central fireball created in S -> W collisions at 200 GeV A are possible sources of the recently observed strange (anti-) baryons. From the theoretical point of view, the HG interpretation we attempt remains more obscure because of the high fireball temperature required. The

J. Liu, X. Q. Luo, X. Fang, S. Guo

We describe a nonperturbative method for calculating the QCD vacuum and glueball wave functions, based on an eigenvalue equation approach to Hamiltonian lattice gauge theory. Therefore, one can obtain more physical information than the conventional simulation methods. For simplicity, we take the 2+1 dimensional U(1) model as an example. The generalization of

Xiang-Qian Luo

The vacuum properties of lattice QCD with staggered quarks are investigated by an efficient simulation method. I present data for the quark condensate with flavor number $N_f=0, ~ 1, ~ 2, ~ 3, ~ 4$ and many quark masses, including the vacuum energy in the chiral limit. Obvious sea quark effects are observed in some parameter space. I also describe a mechanis

A. Borici, R. Rosenfelder

We test various improved gauge actions which are made of linear combinations of Wilson loops. We observe the restoration of rotational symmetry in the static interquark potential already on coarse lattices as small as 6^3x12. Furthermore, we study scaling and asymptotic scaling of the string tension with a MCRG-improved action on 12^3x24 lattices. Preliminar

A. Di Giacomo

The status of topology on the lattice is reviewed. Recent results show that the topological susceptibility chi can be unambigously determined. Different methods, if properly implemented, give results consistent with each other. For SU(3) the Witten-Veneziano prediction is confirmed. Preliminary results for full QCD are presented. The problem there is that th

Bo Feng, Jianming Li, Xingchang Song

A new approach to formulate the fermion field on lattice is introduced by proposing a new Dirac operator on lattice.This approach can eliminate the Fermion doubling problem, preserve the chiral symmetry and get the same dispersion relation for both Fermion and Boson fields.Then the Weinberg-Salam model on lattice may be formulated in this approach.

CLEO Collaboration, R. Godang et al

We have studied two-body charmless hadronic decays of B mesons into the final states $ππ$, $K π$, and $KK$. Using 3.3 million $B\bar{B}$ pairs collected with the CLEO-II detector, we have made the first observation of the decays $B^0\to K^+π^-$, $B^+\to K^0π^+$, and the sum of $B^+ \to π^+π^0$ and $B^+ \to K^+π^0$ decays (an average over charge-conjugate sta

Steven Weinstein

The quantization of time-reparametrization invariant systems such as general relativity is plagued by an ambiguity relating to the role of time in the theory. If one parametrizes observables by the (unobservable) time, and then relies on the existence of an approximate "clock" degree of freedom to give physical meaning to the observables, one finds m

V. A. Rubakov

We consider whether local and causal non-conservation of energy may occur in generally covariant theories with long-ranged fields (analogs of Newton's gravity) whose source is energy--momentum. We find that such a possibility exists in (1+1) dimensions.

Nikolaos A. Batakis

The theory of general relativity is reformed to a genuine Yang-Mills gauge theory of the Poincaré group for gravity. Several pathologies of the conventional theory are thus removed, but not every GR vacuum satisfies the Y-M equations. The sector of GR solutions which survive is fully classified and it is found to include the Schwarzschild black hole. Two oth

G. 't Hooft

A discussion is presented of the principle of black hole com- plementarity. It is argued that this principle could be viewed as a breakdown of general relativity, or alternatively, as the introduction of a time variable with multiple `sheets' or `branches' A consequence of the theory is that the stress-energy tensor as viewed by an outside observer i

Fritz Gesztesy, Konstantin A. Makarov, Eduard Tsekanovskii

We provide additional results in connection with Krein's formula, which describes the resolvent difference of two self-adjoint extensions A_1 and A_2 of a densely defined closed symmetric linear operator A with (possibly infinite) equal deficiency indices. In particular, we explicitly derive the linear fractional transformation relating the operator-valu

Theodore Voronov

We prove that an analog of the exterior differential acts on the space of arbitrary Lagrangians of multidimensional paths on any manifold or supermanifold, thus making this space into a cochain complex. An analog of the Stokes' formula holds. The construction and the proofs are purely geometrical, in terms of the variation of corresponding actions.

V. Ozolins, C. Wolverton, Alex Zunger

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%).

F. Igloi, P. Lajko, W. Selke, F. Szalma

Using Monte Carlo techniques and a star-triangle transformation, Ising models with random, 'strong' and 'weak', nearest-neighbour ferromagnetic couplings on a square lattice with a (1,1) surface are studied near the phase transition. Both surface and bulk critical properties are investigated. In particular, the critical exponents of the surfa

Rodrigo Arias, Fernando Lund

We study the excitation of harmonic waves in thin elastic samples by a single dislocation in arbitrary motion. We consider both screw and edge dislocations that move perpendicularly to the surfaces of the layer. In Fourier space the displacement velocity and dynamic stress fields generated by the motion of the dislocations are factored as the product of two

D. S. Fisher

In these lectures, a variety of non-equilibrium transport phenomena are introduced that all involve, in some way, elastic manifolds being driven through random media. A simple class of models is studied focussing on the behavior near to the critical ``depinning'' force above which persistent motion occurs in these systems. A simple mean field theory

H. Monien, M. Linn, N. Elstner

The low-energy fluctuations of a trapped, interacting quasi one-dimensional Bose gas are studied. Our considerations apply to experiments with highly anisotropic traps. We show that under suitable experimental conditions the system can be described as a Luttinger liquid. This implies that the correlation function of the bosons decays algebraically preventing

Hae-Young Kee, Yong Baek Kim, Elihu Abrahams, R. N. Bhatt

We obtain a ``mean field'' scaling flow of the longitudinal and the Hall conductivities in the fractional quantum Hall regime. Using the composite fermion picture and assuming that the composite fermions follow the Khmelnitskii-Pruisken scaling flow for the integer quantum Hall effect, the unstable fixed points which govern the transitions between di

Leonid A. Openov

The combined effect of nonmagnetic and magnetic defects and impurities on critical temperatures of superconductors with different gap anisotropy is studied theoretically within the weak coupling limit of the BCS model. An expression is derived which relates the critical temperature to relaxation rates of charge carriers by nonmagnetic and magnetic scatterers

I. Luk'yanchuk, A. Jorio, M. A. Pimenta

An Ising model with competing interaction is used to study the appearance of incommensurate phases in the basal plane of an hexagonal closed-packed structure. The calculated mean-field phase diagram reveals various 1q-incommensurate and lock-in phases. The results are applied to explain the basal-plane incommensurate phase in some compounds of the A'A&#3

P. Degiovanni, Ch. Chaubet, R. Melin

We present a comprehensive study of the effective Conformal Field Theory (CFT) describing the low energy excitations of a gas of spinless interacting fermions on a circle in the gapless regime (Luttinger liquid). Functional techniques and modular transformation properties are used to compute all correlation functions in a finite size and at finite temperatur

F. F. Assaad, M. Imada

We show numerically that the nature of the doping induced metal-insulator transition in the two-dimensional Hubbard model is radically altered by the inclusion of a term, $W$, which depends upon a square of a single-particle nearest-neighbor hopping. This result is reached by computing the localization length, $ξ_l$, in the insulating state. At finite values

Yves Noat, Helene Bouchiat, Bertrand Reulet, Dominique Mailly

We have measured the electromagnetic response of micron-size isolated mesoscopic GaAs/GaAlAs square dots down to temperature T=16mK, by coupling them to an electromagnetic micro-resonator. Both dissipative and non dissipative responses exhibit a large magnetic field dependent quantum correction, with a characteristic flux scale which corresponds to a flux qu

Anders Kristoffersen, Stefan Mashkevich, Jan Myrheim, Kaare Olaussen

We have computed by a Monte Carlo method the fourth virial coefficient of free anyons, as a function of the statistics angle theta. It can be fitted by a four term Fourier series, in which two coefficients are fixed by the known perturbative results at the boson and fermion points. We compute partition functions by means of path integrals, which we represent

E. I. Kats, V. V. Lebedev, S. V. Malinin

Dynamics of double membrane films is investigated in the long-wavelength limit including the overdamped squeezing mode. We demonstrate that thermal fluctuations essentially modify the character of the mode due to its nonlinear coupling to the transversal shear hydrodynamic mode. The corresponding Green function acquires as a function of the frequency a cut a

K. P. Yuen, M. F. Law, K. W. Yu, Ping Sheng

We investigate the polarization dependence of optical nonlinearity enhancement for a uniaxial anisotropic composite of metal nanocrystals in a dielectric host. Three cases are distinguished depending on whether the polarization is parallel, perpendicular or unpolarized with respect to the axis of anisotropy. For the parallel polarization, the results show th

S. P. Strong, J. C. Talstra

We propose an order parameter for the one dimensional Mott-Hubbard transition and provide numerical evidence and general theoretical arguments for the correctness of our proposal. In addition, we discuss some of the implications of this picture of the one dimensional Mott-Hubbard transition and speculate about possible higher dimensional analogs.

Torsten Fischer, Hans Henrik Rugh

We consider analytic coupled map lattices over $\Z^d$ with exponentially decaying interaction. We introduce Banach spaces for the infinite-dimensional system that include measures with analytic, exponentially bounded finite dimensional marginals. Using residue calculus and `cluster expansion'-like techniques we define transfer operators on these Banach s

Matthew G. Baring, Alice K. Harding

The complete absence of radio pulsars with periods exceeding a few seconds has lead to the popular notion of the existence of a high $P$ death line. In the standard picture, beyond this boundary, pulsars with low spin rates cannot accelerate particles above the stellar surface to high enough energies to initiated pair cascades through curvature radiation, an

Gregory A. Shields, Lance Wobus, Dirk Husfeld

HST observations of some QSOs show a strong, abrupt increase in polarization at rest wavelength about 750 A, suggestive of a connection with the Lyman edge of hydrogen. Blaes and Agol (1996) have proposed an explanation in terms of stellar atmosphere effects in an accretion disk around a supermassive black hole. We have computed the polarized spectrum of a s

Michael S. Vogeley

(Abridged) Statistical analysis of the unresolved light in the Hubble Deep Field (HDF) strongly constrains possible sources of the optical Extragalactic Background Light (EBL). To test for the statistical signature of previously undetected sources, we estimate the auto, cross, and color correlations of the ``sky'' in the HDF that remains after maskin

John J. Feldmeier, Robin Ciardullo, Roger Bartlett, George H. Jacoby

Planetary nebulae can be useful dynamical probes of elliptical galaxy halos, but progress thus far has been hampered by the small data samples available for study. In order to obtain a large sample of planetary nebulae for dynamical analysis, we have re-observed the giant elliptical galaxy M87 in the center of the Virgo Cluster. Surprisingly, we find that th

J. Greiner

I summarize the use of the ROSAT satellite over the last months for the investigation of well localized GRB error boxes. In particular, I report about the attempts for and results of quick follow-up observations (including the GRBs localized with BeppoSAX and RXTE) with ROSAT with its capability to achieve 10 arcsec locations of X-ray afterglow sources.

Luigi Guzzo

I critically discuss in a pedagogical and phenomenological way a few crucial tests challenging the claims by Pietronero and collaborators that there is no evidence from available galaxy catalogues that the Universe is actually homogeneous above a certain scale. In a series of papers, these authors assert that observations are consistent with a fractal distri

Z. Kuncic, G. V. Bicknell, M. A. Dopita

We revisit the shocked shell model for the class of Active Galactic Nuclei known as Gigahertz Peak Spectrum sources, incorporating new observational data on the radiation brightness temperatures. We argue that in addition to free-free absorption, induced Compton scattering will also have an important effect in forming the ~GHz peak and in shaping the radio s

H. J. Volk

A number of nearby Northern Hemisphere shell-type Supernova Remnants (SNRs) has been observed in TeV gamma rays, but none of them could be detected so far. This failure calls for a critical reevaluation of the theoretical arguments for gamma-ray emission of SNRs. The present paper discusses diffusive shock acceleration in shell-type SNRs in full kinetic theo

John P. Hughes, Mark Birkinshaw

We report optical spectroscopic observations of RX J0018.8+1602, a ROSAT X-ray source proposed to be an intermediate redshift cluster of galaxies. Our observations confirm the identification of RX J0018.8+1602 and provide measurements of its mean radial velocity (z=0.5406 +/- 0.0006) and velocity dispersion (sigma_p = 200 [+110, -80] km/s). This is the secon

A. D. Dolgov, B. E. J. Pagel

We try to explain the spatial variation of primordial deuterium suggested by some observations by varying leptonic chemical potentials. The variation of the latter may take place in some scenarios of leptogenesis. The model predicts a large mass fraction of $^4 He$ (35-60%) and $^7 Li$ (up to $10^{-9}$) in deuterium-rich regions. Because of lepton family sym

Lev R. Yungelson, Mario Livio

We examine the possibility that supernovae type Ia (SN Ia) are produced by white dwarfs accreting from Roche-lobe filling evolved companions, under the assumption that a strong optically thick stellar wind from accretor is able to stabilize the mass transfer. We show that if a mass transfer phase on a thermal timescale precedes a nuclear burning driven phase

K. I. Uchida, K. Sellgren, M. W. Werner

We present the results of imaging spectroscopy of the reflection nebula vdB 133, obtained with the infrared camera and circular variable filter wheel on the Infrared Space Observatory (ISO). Our observations reveal the infrared emission features (IEFs), at 6.2, 7.7, 8.6, 11.3, and 12.7 micron, and associated 5 -- 15 micron continuum emission. The stellar sys

Andrew Ulmer, Bohdan Paczynski, Jeremy Goodman

Optically-thick envelopes may form following the tidal disruption of a star by a massive black hole. Such envelopes would reprocess hard radiation from accretion close to the black hole into the UV and optical bands producing AGN-luminosity flares with duration ~1 year. We show that due to relativistic effects, the envelopes are convective. If convection is

W. Collmar, K. Bennett, H. Bloemen, J. J. Blom

The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have been analyzed. During the first two years PKS 0528+134 was most significantly detected at energies above 3 MeV. During the last year there is only evidence for the quasar at energies below 3 MeV indicat

Ene Ergma, Lev R. Yungelson

By means of population synthesis we find that the expected Galactic number of black holes with massive helium star companions is \sim 100 and depends on an assumed threshold for M_{pre-BH}. The overwhelming majority of these systems has orbital periods in excess of 10 hr, with a maximum at \sim 100 hr, while under the Illarionov & Sunyaev (1975) disk formati

A. Kopf, G. Raffelt

While the photon forward-scattering amplitude on free magnetic dipoles (e.g. free neutrons) vanishes, the nucleon magnetic moments still contribute significantly to the photon dispersion relation in a supernova (SN) core where the nucleon spins are not free due to their interaction. We study the frequency dependence of the relevant spin susceptibility in a t

Michel Boër, J. L. Atteia, M. Bringer, A. Klotz

TAROT-1 is an automatic, autonomous ground based observatory whose primary goal is the rapid detection of the optical counterparts of cosmic gamma-ray burst sources. It will be able to begin imaging any GRB localization 8 seconds after receipt of an alert from CGRO/BATSE or HETE-2. TAROT-1 will reach the 17th V magnitude in 10 seconds, at a 10$σ$ confidence

M. B. Green, M. Gutperle

A connection is made between the Witten index of relevance to threshold bound states of D-particles in the type IIA superstring theory and the measure that enters D-instanton sums for processes dominated by single multiply-charged D-instantons in the type IIB theory.

Maarten Golterman, Ka Chun Leung

Partially quenched theories are theories in which the valence- and sea-quark masses are different. In this paper we calculate the nonanalytic one-loop corrections of some physical quantities: the chiral condensate, weak decay constants, Goldstone boson masses, B_K and the K+ to pi+ pi0 decay amplitude, using partially quenched chiral perturbation theory. Our

H. Barnum, J. A. Smolin, B. M. Terhal

We show that no source encoding is needed in the definition of the capacity of a quantum channel for carrying quantum information. This allows us to use the coherent information maximized over all sources and and block sizes, but not encodings, to bound the quantum capacity. We perform an explicit calculation of this maximum coherent information for the quan

A. G. Bytsko, A. Fring

Employing factorized versions of characters as products of quantum dilogarithms corresponding to irreducible representations of the Virasoro algebra, we obtain character formulae which admit an anyonic quasi-particle interpretation in the context of minimal models in conformal field theories. We propose anyonic thermodynamic Bethe ansatz equations, together

I. Rudychev, E. Sezgin

A model for $n$ superparticles in $(d-n,n)$ dimensions is studied. The target space supersymmetry involves a product of $n$ momentum generators, and the action has $n(n+1)/2$ local bosonic symmetries and $n$ local fermionic symmetries. The precise relation between the symmetries presented here and those existing in the literature is explained. A new model is

E. Cuatle, G. Herrera, J. Magnin

We use a two-component model to describe the production mechanism of D mesons in pi-p collisions. The model combines the usual QCD processes plus fragmentation and recombination of charm that has been produced by nonperturbative QCD mechanisms. A hard charm component in the pion must be responsible of the particle anti-particle production asymmetries observe

P. H. Damgaard

Based on the relation to random matrix theory, exact expressions for all microscopic spectral correlators of the Dirac operator can be computed from finite-volume partition functions. This is illustrated for the case of $SU(N_c)$ gauge theories with $N_c\geq 3$ and $N_f$ fermions in the fundamental representation.

Noboru Fukushima, Yoshio Kuramoto

Effects of magnetic field on the quadrupolar ordering are investigated with inclusion of fluctuation of order parameters. For the simplest model with the nearest-neighbor quadrupolar interaction, the transition temperature and the specific heat are derived by the use of the recently proposed effective medium theory. It is shown that magnetic field H has two

Alfredo M. Ozorio de Almeida, Caio H. Lewenkopf, Eduardo R. Mucciolo

Reviewing the semiclassical theory for the parametric level density fluctuations, we show that for large parametric changes the density correlation function, after rescaling, becomes universal and coincides with the leading asymptotic term obtained from Random Matrix Theory. The advantage of the semiclassical approach is to provide a simple recipe for the ca

Jean Letessier, Johann Rafelski, Ahmed Tounsi

We study the cooling (heating) of a glue-parton gas due to production (destruction) of particles and determine the associated production of entropy. We incorporate sharing of the system energy among a changing number of particles. We find that the entropy of an evolving glue-parton gas changes in an insignificant range once the initial high temperature state

Toshio Nakatsu, Kazutoshi Ohta, Takashi Yokono, Yuhsuke Yoshida

We study configurations of a single $M$ fivebrane in the geometry ${\bf R}^7 \times Q$ where $Q$ is the Taub-NUT space. Taking the IIA limit at each value of their modulus, two possibilities of the IIA configuration are revealed. One consists of a NS fivebrane and a D sixbrane while the other consists of a NS fivebrane, a D sixbrane and a D fourbrane. In the

Jean Letessier, Jan Rafelski, Ahmed Tounsi

We reconsider thermal conditions of the central fireball presumed to be the source of abundantly produced strange (anti-)baryons in S -> W collisions at 200 GeV A. We show that it is possible to completely fix the freeze-out temperature of strange particles in terms of the central rapidity kaon to Lambda particle abundance ratio at fixed, high transverse mas

Saburo Higuchi

A Hamiltonian cycle of a graph is a closed path that visits each site once and only once. I study a field theoretic representation for the number of Hamiltonian cycles for arbitrary graphs. By integrating out quadratic fluctuations around the saddle point, one obtains an estimate for the number which reflects characteristics of graphs well. The accuracy of t

S. Hashimoto, K-I. Ishikawa, H. Matsufuru, T. Onogi

We present an exploratory lattice study of $B\toπ$ semileptonic decay form factors using the nonrelativistic lattice QCD for heavy quark with Wilson light quark on a $16^3 \times 32$ quenched lattice at $β=5.8$. The matrix elements are calculated at eight values of heavy quark mass in a range of $1.5-8$ GeV and with three values of light quark mass. The $1/m

F. Farchioni, A. Papa

We construct instanton-like classical solutions of the fixed point action of a suitable renormalization group transformation for the SU(3) lattice gauge theory. The problem of the non-existence of one-instantons on a lattice with periodic boundary conditions is circumvented by working on open lattices. We consider instanton solutions for values of the size (

G. Esirgen, N. E. Bickers

The fluctuation exchange, or FLEX, approximation for interacting electrons is applied to study instabilities in the standard three-band model for CuO2 layers in the high-temperature superconductors. Both intra-orbital and near-neigbor Coulomb interactions are retained. The filling dependence of the d(x2-y2) transition temperature is studied in both the "

C. J. Isham, N. Linden, K. Savvidou, S. Schreckenberg

We discuss the use of histories labelled by a continuous time in the approach to consistent-histories quantum theory in which propositions about the history of the system are represented by projection operators on a Hilbert space. This extends earlier work by two of us \cite{IL95} where we showed how a continuous time parameter leads to a history algebra tha

Keiji matsumoto

Two important classes of the quantum statistical model, the locally quasi-classical model and the quasi-classical model, are introduced from the estimation theoretical viewpoint, and they are characterized geometrically by the vanishing conditions of the relative phase factor (RPF), implying the close tie between Uhlmann parallel transport and the quantum es

H. C. Rosu

We discuss the proposal of Bell and Leinaas (BL) to measure the circular Unruh effect in storage rings. The ideal concept `circular Unruh effect' has a more realistic correspondent such as `circular vacuum noise' used by Shin Takagi [Prog. Theor. Phys. Suppl. 88, 1 (1986)] The BL resonance behavior does not fit to the SPEAR first order betatron reson

I. A. Pshenichnov, I. N. Mishustin, J. P. Bondorf, A. S. Botvina

We study the disintegration of nuclei by strong electromagnetic fields induced by ultrarelativistic heavy ions. The proposed multi-step model includes 1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of produced hadrons and 3) statistical decay of the excited residual nucleus. The combined model describes well existing data on pro

K. N. Barish

In this contribution I concentrate on the recent results from experiment E864 at the BNL-AGS. E864's recent analysis have achieved sensitivities of approximately $3\times 10^{-8}$ per 10% central interaction for the production of charged strangelets and the first analysis for neutral strangelets is near completion. I put the results in the context of coa

Sl. Cavallaro, ; R. Dayras, ; C. Beck, ; S. J. Sanders

Compound-nucleus fusion and binary-reaction mechanisms have been investigated for the $^{35}$Cl+$^{24}$Mg system at an incident beam energy of E$_{Lab}$= 282 MeV. Charge distributions, inclusive energy spectra, and angular distributions have been obtained for the evaporation residues and the binary fragments. Angle-integrated cross sections have been determi

I. Rudychev, E. Sezgin, P. Sundell

Spacetime superalgebras with 64 or less number of real supercharges, containing the type IIB Poincare superalgebra in (9,1) dimensions and the N=1 Poincare superalgebra in (10,1) are considered. The restriction D<14, and two distinct possibilities arise: The N=(1,0) superalgebra in (11,3) dimensions, and the N=(2,0) superalgebra in (10,2) dimensions. Emphasi

D. -S. Lee, C. N. Leung, Y. J. Ng

Chiral symmetry is dynamically broken in quenched, ladder QED at weak gauge couplings when an external magnetic field is present. In this paper, we show that chiral symmetry is restored above a critical chemical potential and the corresponding phase transition is of first order. In contrast, the chiral symmetry restoration at high temperatures (and at zero c

V. P. Nair, S. Randjbar-Daemi

In this letter we study a coupled system of six-dimensional N=1 tensor and super Yang-Mills multiplets. We identify some of the solitonic states of this system which exhibit stringy behaviour in six dimensions. A discussion of the supercharges and energy for the tensor multiplet as well as zero modes is also given. We speculate about the possible relationshi

Brian R. Greene

We study D-branes on three-dimensional orbifold backgrounds that admit topologically distinct resolutions differing by flop transitions. We show that these distinct phases are part of the vacuum moduli space of the super Yang-Mills gauge theory describing the D-brane dynamics. In this way we establish that D-branes --- like fundamental strings --- allow for

D. H. Tchrakian, T. N. Tomaras

A non-relativistic version of the 2+1 dimensional gauged Chern-Simons O(3) sigma model, augmented by a Maxwell term, is presented and shown to support topologically stable static self-dual vortices. Exactly like their counterparts of the ungauged model, these vortices are shown to exhibit Hall behaviour in their dynamics.

M. I. Caicedo, I. Martin, A. Restuccia

The geometry of antisymmetric fields with nontrivial transitions over a base manifold is described in terms of exact sequences of cohomology groups. This formulation leads naturally to the appearance of nontrivial topological charges associated to the periods of the curvature of the antisymmetric fields. The relation between the partition functions of dual t

C. Grosche

In this Letter I present an alternative solution of the path integral for the radial Coulomb problem which is based on a two-dimensional singular version of the Levi-Civita transformation.

C. Grosche

In this contribution I summarize the achievements of separation of variables in integrable quantum systems from the point of view of path integrals. This includes the free motion on homogeneous spaces, and motion subject to a potential force, and I would like to propose systematic investigations of parametric coordinate systems on homogeneous spaces.

K. Selivanov

A generating function for the Parke-Taylor amplitudes with any number of positive helicity gravitons in addition to the positive helicity gluons is obtained using the recently constructed self-dual classical solution of the type of perturbiner in Yang-Mills theory interacting with gravity.

D. Denegri, W. Majerotto, L. Rurua

We analyse the events with two same-flavour, opposite-sign leptons + $E_T^{miss}$ + (jets) as expected in pp collisions at LHC within the framework of the minimal Supergravity Model. The objective is the determination of the parameters m_0 and m_{1/2} of this model (for a given value of $\tanβ$). The signature $l^+ l^- + E_T^{miss}$ + (jets) selects the lept

Christophe Le Mouel, Gilbert Moultaka

We present, in the context of the Minimal Supersymmetric Standard Model, a detailed one-loop analytic study of the minimization conditions of the effective potential in the Higgs sector. Special emphasis is put on the role played by $Str M^4$ in the determination of the electroweak symmetry breaking conditions, where first and second order derivatives of the

H. Abramowicz, E. Gurvich, A. Levy

Leading order parton distributions in the photon are extracted from the existing $F_2^γ$ measurements and the low-$x$ proton structure function. The latter is related to the photon structure function by assuming Gribov factorization to hold at low $x$. The resulting parton distributions in the photon are found to be consistent with the Frankfurt-Gurvich sum

D. de Florian, G. M. Shore, G. Veneziano

Topological charge screening has been proposed as the mechanism responsible for the anomalous suppression in the first moment of the polarized proton structure function -- the `proton spin&#39; effect. An immediate consequence is that this suppression should be target-independent, since the screening is a fundamental property of the QCD vacuum. Here, we stud

R. Rueckl, H. Spiesberger

The excess of high-Q2 events recently observed in deep-inelastic positron-proton scattering at HERA has refuelled speculations on physics beyond the standard model, in particular on low-mass leptoquark-type particles. We review the theoretical framework for leptoquark interactions, and their production and decay at HERA. Bounds on leptoquark masses and coupl

J. Letessier, A. Tounsi, U. Heinz, J. Sollfrank

We determine the entropy per baryon content of the central reaction region in terms of the charged particle multiplicity. We study the consistency of our findings with recent data on strange anti-baryon production at 200 GeV A in S -> A collisions (A=200) assuming formation of a central fireball. Hadron gas models which do not invoke strong medium modificati

J. Hisano, Daisuke Nomura, T. Yanagida

The atmospheric neutrino anomaly reported by the super-Kamiokande collaboration suggests existence of a large flavour violating Yukawa coupling in the lepton sector. We discuss lepton-flavour violation at low energies in the framework of the supersymmetric SU(5)_{GUT} model with right-handed neutrinos. We find that for a wide range of parameter space suggest

Jean Letessier, Jan Rafelski, Ahmed Tounsi

We investigate here the relative abundance of strange particles produced in nuclear collisions at the SPS energies (9 GeV A in CM frame) assuming that the central reaction fireball consists of quark-gluon plasma. We show that the total strangeness yield in S-S, S-Ag and S-W reactions is compatible with this picture.

Thomas DeGrand, Anna Hasenfratz, Tamas G. Kovacs

In this paper we derive a simple parametrization of the cycling method developed by us in our earlier work. The new method, called renormalization group (RG) mapping, consists of a series of carefully tuned APE-smearing steps. We study the relation between cycling and RG mapping. We also investigate in detail how smooth instantons and instanton-anti-instanto

Michael P. Reisenberger

A lattice model for four dimensional Euclidean quantum general relativity is proposed for a simplicial spacetime. It is shown how this model can be expressed in terms of a sum over worldsheets of spin networks, and an interpretation of these worldsheets as spacetime geometries is given, based on the geometry defined by spin networks in canonical loop quantiz

M. Heller, W. Sasin

In the groupoid approach to noncommutative quantization of gravity, gravitational field is quantized in terms of a C*-algebra A of complex valued funcions on a groupoid G (with convolution as multiplication). In the noncommutative quantum gravitational regime the concepts of space and time are meaningless. We study the &#34;emergence of time&#34; in the tran

S. L. Shapiro, S. Zane

We construct analytic models of incompressible, rigidly rotating stars in PN gravity and study their stability against nonaxisymmetric Jacobi-like bar modes. PN configurations are modeled by homogeneous triaxial ellipsoids and the metric is obtained as a solution of Einstein&#39;s equations in 3+1 ADM form. We use an approximate subset of the equations well-

T. P. Singh

We derive an expression for the expansion of outgoing null geodesics in spherical dust collapse and compute the limiting value of the expansion in the approach to singularity formation. An analogous expression is derived for the spherical collapse of a general form of matter. We argue on the basis of these results that the covered as well as the naked singul

Fabio Podesta, Luigi Verdiani

We study cohomogeneity one Riemannian manifolds and we establish some simple criterium to test when a singular orbit is totally geodesic. As an application, we classify compact, positively curved Riemannian manifolds which are acted on isometrically by a non semisimple Lie group with an hypersurface orbit.

F. Babalievski

Recently S.Galam and A.Mauger [Phys.Rev.E 56, 322 (1997); cond-mat/9706304 ] proposed an approximant which relates the bond and the site percolation threshold for a particular lattice. Their formula is based on a fit to exact and simulation results obtained earlier for different periodic and aperiodic lattices. However, the numerical result for an aperiodic

Nicholas J. Ramer, Andrew M. Rappe

A new pseudopotential generation method is presented which significantly improves transferability. The method exploits the flexibility contained in the separable Kleinman-Bylander form of the nonlocal pseudopotential [Phys. Rev. Lett. 48, 1425 (1982)]. By adjusting the functional form of the local potential, we are able to improve the agreement with all-elec

Ping Ao, Xiao-Mei Zhu

We outline a path integral derivation of both the transverse force, the Berry phase, and friction for a vortex from the microscopic fermionic superfluid theory. The derivation manifests transparently the mutual independence of the Berry phase and dissipative terms in the effective vortex action.

C. Steinebach, T. Kurth, D. Heitmann, V. Gudmundsson

We have investigated experimentally and theoretically the far-infrared (FIR) absorption of gated, deep-mesa-etched GaAs/Al$_x$Ga$_{1-x}$As quantum wires. To overcome Kohn&#39;s theorem we have in particular prepared double-layered wires and studied the acoustic magnetoplasmon branch. We find oscillations in the magnetic-field dispersion of the acoustic plasm

Tapash Chakraborty

We present a many-body approach to calculate the ground state properties of a system of electrons in a half-filled Landau level. Our starting point is a simplified version of the recently proposed trial wave function where one includes the antisymmetrization operator to the bosonic Laughlin state. Using the classical plasma analogy, we calculate the pair-cor

Tapash Chakraborty, K. Niemelä, P. Pietiläinen

The temperature dependence of electron spin polarization for a narrow quantum Hall system shows behavior analogous to that of a two-dimensional system at major filling factors. At the lowest half-filled quantum Hall state for which no two-dimensional analog exists, we find a stable spin partially-polarized system. Periodic Gaussian repulsive impurities (anti

Daniel F. Agterberg, M. Sigrist

We examine the magnetic interference patterns of Josephson junctions with a region of 0- and of pi-phase shift. Such junctions have recently been realized as c-axis YBCO-Pb junctions with a single twin boundary in YBCO. We show that in general the junction generates self-fields which introduces an asymmetry in the critical current under reversal of the magne

R. Hayn, V. N. Plechko

We discuss some aspects of a new noncombinatorial fermionic approach to the two-dimensional dimer problem in statistical mechanics based on the integration over anticommuting Grassmann variables and factorization ideas for dimer density matrix. The dimer partition function can be expressed as a Gaussian fermionic integral. For regular lattices, the analytic

Rodrigo Arias, Fernando Lund

Integral expressions are determined for the elastic displacement and stress fields due to stationary or moving dislocation loops in three dimensional, not necessarily isotropic, finite samples. A line integral representation is found for the stress field, thus satisfying the expectation that stresses should depend on the location of the dislocation loop, but