December 1996 arXiv papers — page 10

P. Osland, A. A. Pankov

We discuss the potential of present e^+e^- colliders to probe for a heavy Z^' boson via its interference effects, in a model-independent framework. The leptonic channel is unambiguous, and thus favourable over the hadronic ones. The effect on the leptonic cross section $σ_{μμ}$, induced by a heavy Z^' with arbitrary couplings, is uniquely determined

A. V. Kuznetsov, N. V. Mikheev

A process of the electron--positron pair production by neutrino propagating in a strong magnetic field is investigated in the framework of the Standard Model. The process probability and the mean values of the neutrino energy and momentum loss are calculated. Possible astrophysical manifestations of the process considered are briefly analysed.

J. C. Romao

We show that in the presence of sufficiently strong tau neutrino annihilations into majorons, the primordial nucleosynthesis constraints can not rule out tau neutrino masses in the MeV range.

S. Moretti

This paper follows hep-ph/9611397, where updated calculations of cross sections and branching ratios relevant for Standard Model Higgs phenomenology at the LHC were presented. Here, we complete that study by carrying out an updated signal-to-background analysis. We present results obtained by using exact matrix element computations at parton level for all pr

S. Hegyi

An iterative procedure is developed with the aim of constructing homogeneity rules for the distribution P(rho,delta) of the particle density rho at resolution scale delta. A single iteration step consists of a change in the normalization point of P(rho,delta) followed by a rescaling. Similar transformation rule is introduced for density fluctuations contamin

A. Pich

The pure leptonic or semileptonic character of tau decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interactions in very clean conditions; a well-known example is the pr

Gerhard Buchalla

The present status of CP violation in decays of neutral kaons is reviewed. In addition selected rare decays of both K and B mesons are discussed. The emphasis is in particular on observables that can be reliably calculated and thus offer the possibility of clean tests of standard model flavor physics.

Ramesh Anishetty, N. D. Hari Dass, H. S. Sharatchandra

Chiral perturbation theory has to be substantially modified for the problem of nuclear forces. Loop effects dominate over tree level effects. The dominant behaviours in the scalar isoscalar channel and multi-nucleon forces are obtained in the chiral limit and for a small explicit breaking.

The US-ATLAS, US-CMS Collaborations, edited by Ian Hinchliffe, John Womersley

This note summarizes the various physics studies done for the LHC. It concentrates on the processes involving the production of high mass states. Results are drawn from simulations performed by the CMS and ATLAS collaborations. The ability of the LHC to provide insight into the mechanism of electroweak symmetry breaking is exemplified.

I. H. Dwivedi, P. S. Joshi

We examine here the relevance of the initial state of a collapsing dust cloud towards determining it's final fate in the course of a continuing gravitational collapse. It is shown that given any arbitrary matter distribution $M(r)$ for the cloud at the initial epoch, there is always a freedom to choose rest of the initial data, namely the initial velocit

Alexandru Nica, Roland Speicher

Let A be a unital $C^*$-algebra, given together with a specified state $ϕ:A \to C$. Consider two selfadjoint elements a,b of A, which are free with respect to $ϕ$ (in the sense of the free probability theory of Voiculescu). Let us denote $c:=i(ab-ba)$, where the i in front of the commutator is introduced to make c selfadjoint. In this paper we show how the s

C. M. Newman, D. L. Stein

In realistic disordered systems, such as the Edwards-Anderson (EA) spin glass, no order parameter, such as the Parisi overlap distribution, can be both translation-invariant and non-self-averaging. The standard mean-field picture of the EA spin glass phase can therefore not be valid in any dimension and at any temperature. Further analysis shows that, in gen

Stefano Zapperi, Alessandro Vespignani, H. Eugene Stanley

It has been recently observed that synthetic materials subjected to an external elastic stress give rise to scaling phenomena in the acoustic emission signal. Motivated by this experimental finding we develop a mesoscopic model in order to clarify the nature of this phenomenon. We model the synthetic material by an array of resistors with random failure thre

Stefano Zapperi, Purusattam Ray, H. Eugene Stanley, Alessandro Vespignani

We study the approach to global breakdown in disordered media driven by increasing external forces. We first analyze the problem by mean-field theory, showing that the failure process can be described as a first-order phase transition, similarly to the case of thermally activated fracture in homogeneous media. Then we quantitatively confirm the predictions o

Stefano Zapperi, Purusattam Ray, H. Eugene Stanley, Alessandro Vespignani

We study the behavior of fracture in disordered systems close to the breakdown point. We simulate numerically both scalar (resistor network) and vectorial (spring network) models with threshold disorder, driven at constant current and stress rate respectively. We analyze the scaling of the susceptibility and the cluster size close to the breakdown. We observ

Carsten Wengel, Uwe Claus Täuber

We study the properties of the Bose glass phase of localized flux lines in irradiated superconductors near the matching field $B_Φ$. Repulsive vortex interactions destroy the Mott insulator phase predicted to occur at $B=B_Φ$. For ratios of the penetration depth to average defect distance $λ/ d \leq 1$ remnants of the Mott insulator singularities remain visi

R. Martonak, W. Paul, K. Binder

In this paper we present a classical Monte Carlo simulation of the orthorhombic phase of crystalline polyethylene, using an explicit atom force field with unconstrained bond lengths and angles and periodic boundary conditions. We used a recently developed algorithm which apart from standard Metropolis local moves employs also global moves consisting of displ

P. Fazekas

It is becoming widely recognized that, contrary to earlier expectations, the usual one-band Hubbard model does not give an explanation for itinerant ferromagnetism. After reviewing the status of magnetic ordering in the one-band model, we discuss the possibility of ferromagnetism in some recently introduced two-band Hubbard models, and in generalized Anderso

Michael Wilkinson, Paul N. Walker, Kaumba Chinyama

We investigate the distribution of oscillator strengths for the recombination of excitons in a two dimensional sample, trapped in local minima of the confinement potential: the results are derived from a statistical topographic model of the potential. The predicted distribution of oscillator strengths is very different from the Porter-Thomas disribution whic

David Clarke, Steven Strong

We comment on recent numerical studies concerning coupled 1D electron liquids (F. Mila and D. Poilblanc, Phys. Rev. Lett. 76, 287 (1996)). In particular, we point out that the importance of integrability observed in the results of these authors for the quantity $P(t)$ is really an indication of the importance of integrability for questions of ergodicity, rat

L. I. Plimak, M. J. Collett, D. F. Walls

Collisional damping of the excitations in a Bose-condensed gas is investigated over the wide range of energies and temperatures. Numerical results for the damping rate are presented and a number of asymptotic and interpolating expressions for it are derived.

C. B. Yang, X. Cai

A new perturbation theory is proposed for studying finite-size effects near critical point of the $ϕ^4$ model with a one-component order parameter. The new approach is based on the techniques of generating functional and functional derivative with respect to external source field and can be used for temperatures both above and below the critical point of the

C. P. Dettmann, G. P. Morriss

The Nose Hamiltonian is adapted, leading to a derivation of the Nose-Hoover equations of motion which does not involve time transformations, and in which the degree of freedom corresponding to the external reservoir is treated on the same footing as those of the rest of the system. In this form it is possible to prove the conjugate pairing rule for Lyapunov

E. Balkovsky, G. Falkovich, V. Lebedev

We demonstrate that if the exponent $γ$ that measures non-smoothness of the velocity field is small then the isotropic zero modes of the scalar's triple correlation function have the scaling exponents proportional to $\sqrtγ$. Therefore, zero modes are subleading with respect to the forced solution that has normal scaling with the exponent $γ$.

C. S. Frenk, C. M. Baugh, S. Cole, C. G. Lacey

We review recent developments in theoretical studies of galaxy formation and evolution. In combination with new data from HST, Keck and other large telescopes, numerical and semi-analytic modelling is beginning to build up a coherent picture of galaxy formation. We summarize the current status of modelling of various galactic properties such as the structure

S. G. Djorgovski, R. R. de Carvalho, R. R. Gal, M. A. Pahre

We are conducting an effort to catalog all sources detected in the digitized POSS-II (DPOSS). This is now becoming an international collaboration including Caltech and the Observatories of Rome and Naples (project CRONA). There are also ongoing extensive CCD calibration efforts at Palomar. The resulting Palomar-Norris Sky Catalog (PNSC) is expected to contai

A. Mezzacappa, A. C. Calder, S. W. Bruenn, J. M. Blondin

We investigate neutrino-driven convection in core collapse supernovae and its ramifications for the explosion mechanism. We begin with an ``optimistic'' 15 solar mass precollapse model, which is representative of the class of stars with compact iron cores. This model is evolved through core collapse and bounce in one dimension using multigroup (neutr

Wesley N. Colley

We have measured the topology (genus) of the density distribution of large-scale structure observed in the Las Campanas Redshift Survey (LCRS). The LCRS is complete to magnitude 17.5, and contains nearly 24000 galaxies with median redshift of 30000 km/s. The large volume and large number of galaxies allows sampling of nearly 100 independent structures with w

Edward L. Wright

The FIRAS instrument on the COBE satellite has conducted an unbiased survey of the far-infrared emission from our Galaxy. The first results of this survey were reported by Wright et al. (1991), and later conclusions were reported in Bennett et al. (1994). I report the results of analyses of this spectral survey, which includes emission lines from 158 micron

Andrzej A. Zdziarski, W. Neil Johnson, Juri Poutanen, Pawel Magdziarz

We review observations and theoretical models of X-ray/gamma-ray spectra of radio-quiet Seyfert galaxies and of Galactic black-hole candidates (in the hard spectral state). The observed spectra share all their basic components: an underlying power law, a Compton-reflection component with an Fe K-alpha line, low-energy absorption by intervening cold matter, a

Luca Zampieri

Results are presented from a time-dependent, numerical investigation of super-Eddington spherical accretion onto black holes with different initial conditions. We have studied the stability of stationary solutions, the non-linear evolution of shocked models and the time-dependent accretion from an expanding medium.

Peter J. Kernan, Glenn D. Starkman, Tanmay Vachaspati

Recently Cheng, Olinto, Schramm and Truran (COST) reexamined the constraints from big bang nucleosynthesis (BBN) on the strength of primordial magnetic fields. Their bottom line agreed with that of an earlier recent paper on the subject (Kernan, Starkman and Vachaspati (KSV)), both in its final limit on the magnetic field during BBN, and in its conclusion th

Roberto Capuzzo-Dolcetta

Globular clusters can decay to the center of their mother galaxy carrying a quantity of mass sufficient to sustain the gravitational activity of a small pre-existing nucleus and to accrete it in a significant way. The AGN luminosity and lifetime depend on the characteristics of the globular cluster system and it is quite insensitive to the nucleus' initi

R. H. Sanders

Although the modified dynamics (MOND) proposed by Milgrom successfully accounts for the systematics of galaxy rotation curves and cluster dynamics without invoking dark matter, the idea remains a largely ad hoc modification of Newtonian dynamics with no basis in deeper theory. Non-standard scalar-tensor theories have been suggested as a theoretical basis for

Robert H. Cornett, Theodore P. Stecher, the UIT Science Team

A mosaic of four UIT far-UV (FUV; 1620A) images, which covers most of the SMC bar, is presented, with derived stellar and HII region photometry. The UV morphology of the SMC's Bar shows that recent star formation there has left striking features including: a) four concentrations of UV-bright stars spread from northeast to southwest at nearly equal (~30 a

D. N. Tripathy, Subodha Mishra

By making an intuitive choice for the single-particle density of a system of N self-gravitating particles, without any source for the radiation of energy, we have been able to calculate the binding energy of the system by treating these particles as fermions. Our expression for the ground state energy of the system shows a dependence of $N^{7/3}$ on the part

Ofer Lahav

We describe an Artificial Neural Network (ANN) approach to classification of galaxy images and spectra. ANNs can replicate the classification of galaxy images by a human expert to the same degree of agreement as that between two human experts, to within 2 T-type units. Similar methods are applied to classification of galaxy spectra. In particular, Principal

Martin Pohl

In this paper I investigate the $γ$-ray spectra of AGN by summing up the intensity and the power-law fit statistic of Quasars and OVV's and BL Lac's separately. The spectrum of the average AGN is softer than that of the extragalactic $γ$-ray background. It may be that BL Lac's, of which the average has a harder spectrum than Quasars, make up the

R. P. Fender, G. G. Pooley, C. R. Robinson, B. A. Harmon

We present multiwavelength observations of the superluminal jet source GRS 1915+105 in 1996 April-May, over which period a variety of phenomena, including radio QPO, strong infrared emission lines and rapid X-ray flickering and outbursts were observed.

V. V. Usov

It is suggested that the persistent X-ray emission from the soft gamma-ray repeaters is the thermal radiation of neutron stars which is enhanced by a factor of 10 or more due to the effect of a very strong magnetic field on the thermal structure of the neutron star envelope. For the thermal luminosity to be consistent with the persistent X-ray luminosity, th

Toshiyuki Fukushige, Junichiro Makino

We report on resent N-body simulations of galaxy formation performed on the GRAPE-4 (GRAvity PipE) system, a special-purpose computer for astrophysical N-body simulations. We review the astrophysical motivation, the algorithm, the actual performance, and the price per performance. The performance obtained is 332 Gflops averaged over 185 hours for a simulatio

Gilad Lifschytz, Samir D. Mathur

We calculate the potential between various configurations of membranes and gravitons in M(atrix) theory. The computed potentials agree with the short distance potentials between corresponding 2-branes and 0-brane configurations in Type IIA string theory, bound to a large number of 0-branes to account for the boost to the infinite momentum frame. We show that

Fermilab E791 Collaboration, E. M. Aitala et al

We report results of a search for CP violation in the singly Cabibbo-suppressed decays D+ -> K- K+ pi+, phi pi+, K*(892)0 K+, and pi- pi+ pi+ based on data from the charm hadroproduction experiment E791 at Fermilab. We search for a difference in the D+ and D- decay rates for each of the final states. No evidence for a difference is seen. The decay rate asymm

John J. Neumann, Boris Lavrenchuk, George Fai

Most hydrodynamical calculations used in heavy-ion physics ignore the effect of freeze-out matter carrying energy and momentum away from the expanding fluid. In a simple one-dimensional model we compare calculated energy density and velocity profiles, with and without interaction between fluid-like and freeze-out parts of the system, in order to estimate the

G. Modanese, J. Schnurer

In the weak field approximation to quantum gravity, a "local" positive cosmological term mu^2(x) corresponds to a local negative squared mass term in the Lagrangian and may thus induce instability and local pinning of the gravitational field. Such a term can be produced by the coupling to an external Bose condensate. In the functional integral, the l

J A Sellwood

I compare various popular and unpopular techniques for simulating large collisionless stellar systems. I give a quantitative comparison of the raw cpu times required for five separate codes, including tree codes and basis function expansions, which demonstrate that grid codes are most efficient for large numbers of particles. Since efficiency is only one con

E. Bergshoeff, M. de Roo, E. Eyras, B. Janssen

We give a classification of all multiple intersections of D-branes in ten dimensions and M-branes in eleven dimensions that corresponds to threshold BPS bound states. The residual supersymmetry of these composite branes is determined. By dimensional reduction composite p-branes in lower dimensions can be constructed. We emphasize in dimensions D greater or e

Oleg Teryaev, Avto Tkabladze

We calculated the color-octet contribution to the double spin asymmetry of $J/ψ$ hadroproduction with nonzero transverse momenta at fixed target energies $\sqrt{s}\simeq40$ GeV. It is shown that the color-octet contribution is dominant in the asymmetries. The expected asymmetries and statistical errors in a future option of HERA with longitudinally polarized

M. Maul, E. Stein, A. Schäfer, L. Mankiewicz

We have compared the existing experimental data on the leading power corrections to the structure functions $F_2(x,Q^2), F_3(x,Q^2)$, and $F_L(x,Q^2)$ with the IR-renormalon model predictions for higher-twist contributions. Our analysis shows that the model properly describes the x-dependence, but typically falls short by a factor 2 or 3 as far as the magnit

J. B. Rehm, G. G. Raffelt, A. Weiss

A massive long-lived tau neutrino in the MeV regime modifies the primordial light-element abundances predicted by big-bang nucleosynthesis (BBN) calculations. This effect has been used to derive limits on the tau neutrino mass. Because recently the observational situation has become somewhat confusing and, in part, intrinsically inconsistent, we reconsider t

Michael Dutsch, Gunter Scharf

The concept of perturbative gauge invariance formulated exclusively by means of asymptotic fields is generalized to massive gauge fields. Applying it to the electroweak theory leads to a complete fixing of couplings of scalar and ghost fields and of the coupling to leptons, in agreement with the standard theory. The W/Z mass ratio is also determined, as well

Diptiman Sen

We study the quantum mechanics of the derivative nonlinear Schrodinger equation which has appeared in many areas of physics and is known to be classically integrable. We find that the N-body quantum problem is exactly solvable with both bound states (with an upper bound on the particle number) and scattering states. Quantization provides an alternative way t

L. Mankiewicz, A. Saalfeld, T. Weigl

Comparing the numerically evaluated solution to the leading order GLAP equations with its analytical small-x approximation we have found that in the domain covered by a large fraction of the HERA data the analytic approximation has to be augmented by the formally non-leading term which has been usually neglected. The corrected formula fits the data much bett

G. E. Volovik

Vortex mass in Fermi superfluids and superconductors and its influence on quantum tunneling of vortices are discussed. The vortex mass is essentially enhanced due to the fermion zero modes in the core of the vortex: the bound states of the Bogoliubov qiasiparticles localized in the core. These bound states form the normal component which is nonzero even in t

Hajime Takayama, Hajime Yoshino, Koji Hukushima

Monte Carlo simulations on the SK model have been done to investigate aging processes after a rapid quench from $T=\infty$ to the spin-glass phase. The time range of simulations is taken care of so that the system does not surmount free-energy barriers between the pure states which are considered to diverge in the thermodynamic limit. We simulate time evolut

Ikaros I. Bigi

Inclusive heavy-flavour decays can be described through $1/m_Q$ expansions derived from QCD with the help of an operator product expansion. I sketch their methodology and apply them first to semileptonic B decays; $|V(cb)|$ can be extracted from $Γ_{SL}(B)$ and $\bar B \to l νD^*$ with the result: $|V(cb)|_{incl} = 0.0413 \pm 0.0016_{exp} \pm 0.002_{theor}$,

W. Lerche, P. Mayr, N. P. Warner

We study limits of four-dimensional type II Calabi-Yau compactifications with vanishing four-cycle singularities, which are dual to $\IT^2$ compactifications of the six-dimensional non-critical string with $E_8$ symmetry. We define proper subsectors of the full string theory, which can be consistently decoupled. In this way we obtain rigid effective theories

Goran Faldt, Colin Wilkin

The pp -> pp eta and pp -> pLambda K^+ reactions near threshold are dominated by the first and second S_11 resonance respectively. It is shown that a one-pion-exchange model exciting these isobars reproduces well the ratio of the production cross sections. The consequences for this and other channels are discussed.

Volker Keiner

We develop a formally covariant quark-diquark model of the nucleon. The nucleon is treated as a bound state of a constituent quark and a diquark interacting via a quark exchange. We include both scalar and axial-vector diquarks. The underlying Bethe-Salpeter equation is transformed into a pair of coupled Salpeter equations. The space- and timelike electromag

D. H. Lu, A. W. Thomas, A. G. Williams

Helicity amplitudes for the $γ^* N \to Δ$ transition are calculated using the cloudy bag model. A correction for center-of-mass motion is carried out using a modified Peierls-Thouless projection method. This reduces the magnitude of the transition amplitudes at small momentum transfer and enhances them at modest momentum transfers. Our calculation shows that

Eli Glasner, Jonathan King

For any countable group $Γ$ satisfying the ``weak Rohlin property'', and for any dynamical property, the set of $Γ$-actions with that property is either residual or meager. The class of groups with the weak Rohlin property includes each lattice $\integers^{\times{d}}$; indeed, all countable discrete amenable groups. For $Γ$ an arbitrary countable gro

Robert Myers

An irreducible open 3-manifold $W$ is {\bf R}$^2$-irreducible if every proper plane in $W$ splits off a halfspace. In this paper it is shown that if such a $W$ is the universal cover of a connected, {\bf P}$^2$-irreducible open 3-manifold $M$ with finitely generated fundamental group, then either $W$ is homeomorphic to {\bf R}$^3$ or the group is a free prod

Jae-Suk Park

Motivated by twisted N=4 supersymmetric Yang-Mills theory in 4 dimensions, a natural extension of the monad (ADHM) construction relevant to D-instantons is considered. We show that a family of Yang-Mills instantons can be constructed from D-instantons. We discuss some possible roles of reciprocity in D-brane physics. We conjecture the existence of universal

S. Kharchev, A. Mironov, A. Zhedanov

We demonstrate that the generalization of the relativistic Toda chain (RTC) is a special reduction of two-dimensional Toda Lattice hierarchy (2DTL). We also show that the RTC is gauge equivalent to the discrete AKNS hierarchy and the unitary matrix model. Relativistic Toda molecule hierarchy is also considered, along with the forced RTC. The simple approach

J. Fuchs, A. N. Schellekens, C. Schweigert

We summarize recent progress in the understanding of fixed point resolution for conformal field theories. Fixed points in both coset conformal field theories and non-diagonal modular invariants which describe simple current extensions of chiral algebras are investigated. A crucial role is played by the mathematical structures of twining characters and orbit

B. Melic, S. Meljanac

General permutation invariant statistics in the second quantized approach are considered. Simple interpolations between dual statistics are constructed. Particularly, we present a new minimal interpolation between parabosons and parafermions of any order. The connection with a simple mixing between bosons and fermions is established. The construction is exte

E. Guadagnini, L. Pilo

We consider the 3-manifold invariant I(M) which is defined by means of the Chern-Simons quantum field theory and which coincides with the Reshetikhin-Turaev invariant. We present some arguments and numerical results supporting the conjecture that, for nonvanishing I(M), the absolute value | I(M) | only depends on the fundamental group π_1 (M) of the manifold

D. K. Park, Soo-Young Lee, Jae-Rok Kahng, Sahng-Kyoon Yoo

The validity of dilute gas approximation is explored by making use of the large-sized instanton in quantum mechanical model. It is shown that the Euclidean probability amplitude derived through a dilute gas approximation not only cannot explain the result of the linear combination of atomic orbitals approximation, but also does not exhibit a proper limiting

Tohru Eguchi, Sung-Kil Yang

We discuss a new type of Landau-Ginzburg potential for the E_6 singularity of the form $W=const+(Q_1(x)+P_1(x)\sqrt{P_2(x)})/x^3$ which featured in a recent study of heterotic/typeII string duality. Here $Q_1,P_1$ and $P_2$ are polynomials of degree 15,10 and 10, respectively. We study the properties of the potential in detail and show that it gives a new an

Oliver Martin, Andreas Schäfer

We present the program summary and long write-up for SPHINX TT, a new Monte Carlo simulation for transversely polarized nucleon-nucleon scattering. The program is based on Pythia/Jetset.

Thomas G. Rizzo

We examine of the capability of the Next Linear Collider to determine the mass as well as the couplings to leptons and $b$-quarks of a new neutral gauge boson, $Z'$, below direct production threshold. By using simulated data collected at several different values of $\sqrt s$, we demonstrate how this can be done in a model-independent manner via an anonym

M. Klein-Kreisler, M. Ruiz-Altaba

We consider the possibility that the SU(2) isospin symmetry, exact in strong interactions but only approximate in nature, is in fact a quantum group. Using a doublet of q-quarks, we build the wavefuntions of pi-mesons, nucleons and Delta baryons. We redo the usual quark model computation for the magnetic moments and mass relations, and everything fits with e

Thomas D. Cohen, Xiangdong Ji

Using group theoretical methods, we enumerate possible chiral representations in which hadron interpolating currents can be classified. We give simple examples of currents in each representation, some of which are well known. The classification enables one to find relations among current vacuum correlators in a chirally and/or axial U(1) symmetric phase of Q

M. Olechowski

We present a bottom-up approach to the question of supersymmetry breaking in the MSSM. Starting with the experimentally measurable low energy supersymmetry breaking parameters which can take any values consistent with present experimental constraints, we evolve them up to an arbitrary high energy scale. Approximate analytical expressions for such an evolutio

G. Amorós, M. Neubert

We study the renormalization of operators of the type ${\bar h_{v'}} ΓG^{μν} h_v$ in the heavy-quark effective theory (HQET). We construct the combinations of such operators that are renormalized multiplicatively, and calculate their velocity-dependent anomalous dimensions at the one-loop order. We then show that the virial theorem of the HQET is not ren

W. Beenakker

A survey is given of the various gauge-invariance-related aspects that play a role when dealing with unstable gauge bosons.

W. Beenakker

A report is given on the theoretical aspects of gauge-boson production processes at LEP2 and the next linear collider (NLC). A short discussion is given on the gauge-boson-related physics issues that play a role at both coliders and on the outcome of the various LEP2/NLC studies that have taken place during the last few years. The main emphasis of this repor

Seung Woo Ham, Sun Kun Oh, Bjong Ro Kim

We search for the neutral Higgs sector of the next-to-minimal supersymmetric standard model at LEP 2. At the tree level any experimental constraints on $\tan β$ cannot be set by the Higgs search at LEP 2 with $\sqrt{s}$ = 175 GeV, whereas at LEP 2 with $\sqrt{s}$ = 192 GeV $\tan β$ can be set by an experimental constraint. Furthermore the tree level paramete

James D. Wells

The top quark may get its mass not from a fundamental scalar but a Nambu-Jona-Lasinio mechanism involving a strongly coupled gauge sector that triggers top-quark condensation. Forbidding a large hierarchy in the gap equation implies that top-quark condensation is a spectator to electroweak symmetry breaking, which must be accomplished mainly by another secto

H. Kröger

We study the geometry of propagation of relativistic fermions. We propose how to measure its quantum mechanical length. Numerical lattice results for the free propagator of Dirac-Wilson fermions yield Hausdorff dimension d_H=2 for the unit-matrix component and d_H=1 for any gamma-matrix component. A possible generalization when matter interacts with radiatio

W. Kummer, S. R. Lau

Within a first-order framework, we comprehensively examine the role played by boundary conditions in the canonical formulation of a completely general two-dimensional gravity model. Our analysis particularly elucidates the perennial themes of mass and energy. The gravity models for which our arguments are valid include theories with dynamical torsion and so-

Stephen R. Lau

Recently, Choquet-Bruhat and York and Abrahams, Anderson, Choquet-Bruhat, and York (AACY) have cast the 3+1 evolution equations of general relativity in gauge-covariant and causal ``first-order symmetric hyperbolic form,'' thereby cleanly separating physical from gauge degrees of freedom in the Cauchy problem for general relativity. A key ingredient

R. W. Tucker, C. Wang

We argue that the conjectured dark mater in the Universe may be endowed with a new kind of gravitational charge that couples to a short range gravitational interaction mediated by a massive vector field. A model is constructed that assimilates this concept into ideas of current inflationary cosmology. The model is also consistent with the observed behaviour

N. V. Prokof'ev, B. V. Svistunov, I. S. Tupitsyn

We introduce an exact Monte Carlo approach to the statistics of discrete quantum systems which does not rely on the standard fragmentation of the imaginary time, or any small parameter. The method deals with discrete objects, kinks, representing virtual transitions at different moments of time. The global statistics of kinks is reproduced by explicit local p

C. S. O'Hern, Randall D. Kamien, T. C. Lubensky, Philip Nelson

The symmetries of the DNA double helix require a new term in its linear response to stress: the coupling between twist and stretch. Recent experiments with torsionally-constrained single molecules give the first direct measurement of this important material parameter. We extract its value from a recent experiment of Strick, et al. and find rough agreement wi

Tomaso Aste, Dominique Boose, Nicolas Rivier

We investigate two and three-dimensional shell-structured-inflatable froths, which can be constructed by a recursion procedure adding successive layers of cells around a germ cell. We prove that any froth can be reduced into a system of concentric shells. There is only a restricted set of local configurations for which the recursive inflation transformation

C. Micheletti, R. B. Griffiths, J. M. Yeomans

Phase diagrams as a function of anisotropy D and magnetic field H are obtained for discommensurations and surface states for a model antiferromagnet in which $H$ is parallel to the easy axis. The surface spin-flop phase exists for all $D$. We show that there is a region where the penetration length of the surface spin-flop phase diverges. Introducing a disco

Daniel A. Stariolo

We show that for a family of problems described by non-linear diffusion equations an exact calculation of the two time correlation function gives C(t,t')=f(t-t')g(t'), t>t', exhibiting normal and anomalous diffusions, as well as aging effects, depending on the degree of non-linearity. We discuss also the form in which FDT is violated in this

Domingos Alves, J. F. Fontanari

The effects of error propagation in the reproduction of diploid organisms are studied within the populational genetics framework of the quasispecies model. The dependence of the error threshold on the dominance parameter is fully investigated. In particular, it is shown that dominance can protect the wild-type alleles from the error catastrophe. The analysis

Jean Desbois, Stéphane Ouvry, Christophe Texier

A Kubo inspired formalism is proposed to compute the longitudinal and transverse dynamical conductivities of an electron in a plane (or a gas of electrons at zero temperature) coupled to the potential vector of an external local magnetic field, with the additional coupling of the spin degree of freedom of the electron to the local magnetic field (Pauli Hamil

Pierre Le Doussal, Leticia F. Cugliandolo, Luca Peliti

We study the dynamics of a directed manifold of internal dimension D in a d-dimensional random force field. We obtain an exact solution for $d \to \infty$ and a Hartree approximation for finite d. They yield a Flory-like roughness exponent $ζ$ and a non trivial anomalous diffusion exponent $ν$ continuously dependent on the ratio $g_{T}/g_{L}$ of divergence-f

C. J. Olson, C. Reichhardt, J. Groth, Stuart B. Field

We use large-scale parallel simulations to compute the motion of superconducting magnetic vortices during avalanches triggered by small field increases. We find that experimentally observable voltage bursts correspond to pulsing vortex movement along branched channels or winding chains, and relate vortex flow images to features of statistical distributions.

T. W. B. Kibble, G. E. Volovik

In a real system the heating is nonuniform and a second-order phase transition into a broken symmetry phase occurs by propagation of the temperature front. Two parameters, the cooling rate $τ_Q$ and the velocity $v_T$ of the transition front, determine the nucleation of topological defects. Depending on the relation of these parameters two regimes are found:

Thomas Christen

It is shown that the nonequilibrium steady-state of a phase-coherent conductor can be described by a generalized thermodynamic potential based on the concept of partial densities of states. This is possible due to the fact that dissipation takes place only in the contacts for the emitted carriers. Long-range Coulomb interaction is included, and charge conser

H. Haugerud, G. Uimin, W. Selke

The oxygen deficient CuO_x planes of the high-Tc superconductors REBa_2Cu_3O_{6+x} (RE denotes a rare-earth atom or yttrium) are studied. Starting from the Emery model for the Cu-O chain fragments, an extended ASYNNNI model is proposed to describe the statistical mechanics of the CuO_x planes. The model is analysed by using Monte Carlo techniques, computing

Xiaowen Shan

Rayleigh-Bénard convection is numerically simulated in two- and three-dimensions using a recently developed two-component lattice Boltzmann equation (LBE) method. The density field of the second component, which evolves according to the advection-diffusion equation of a passive-scalar, is used to simulate the temperature field. A body force proportional to t

Raymond J. Mooney

This paper describes an experimental comparison of seven different learning algorithms on the problem of learning to disambiguate the meaning of a word from context. The algorithms tested include statistical, neural-network, decision-tree, rule-based, and case-based classification techniques. The specific problem tested involves disambiguating six senses of

N. Berglund

We study billiards in plane domains, with a perpendicular magnetic field and a potential. We give some results on periodic orbits, KAM tori and adiabatic invariants. We also prove the existence of bound states in a related scattering problem.

N. Berglund, H. Kunz

We consider the motion of a damped particle in a potential oscillating slowly between a simple and a double well. The system displays hysteresis effects which can be of periodic or chaotic type. We explain this behaviour by computing an analytic expression of a Poincar'e map.

Byung-Il Jun, T. W. Jones

We examine the formation and evolution of the density enhancement (density spike) that appears downstream of strong, cosmic-ray-modified shocks. This feature results from temporary overcompression of the flow by the combined cosmic-ray shock precursor/gas subshock. Formation of the density spike is expected whenever shock modification by cosmic-ray pressure