Studies of QCD at ${\rm e}^ + {\rm e}^-$ centre-of-mass energies between 91 and 209 GeV

The hadronic final states observed with the ALEPH detector at LEP in annihilation are analysed using 730 pb^-1 of data collected between 91 and 209 GeV in the framework of QCD. In particular event-shape variables and inclusive charged particle spectra are measured. The energy evolution of quantities derived from these measurements is compared to analytic QCD predictions. The mean charged particle multiplicity, the charged particle momentum spectrum and its peak position are compared to predictions of the modified-leading-logarithmic approximation. The strong coupling constant is determined from a fit of the QCD prediction to distributions of six event-shape variables at eight centre-of-mass energies. A study of non-perturbative power law corrections is presented.Received: 18 May 2004, Published online: 23 June 2004     

Production of spin-3 mesons in diffractive DIS

Polarized forward-backward asymmetries in the decay are calculated using the most general, model independent form of the effective Hamiltonian, including all possible forms of interactions. The dependencies of the asymmetries on new Wilson coefficients are investigated. The detectability of the asymmetries at LHC is discussed.Received: 27 December 2004, Revised: 25 January 2005, Published online: 9 March 2005PACS: 12.60.-i, 13.30.-a     

Renormalization of the neutrino mass operators in the multi-Higgs-doublet standard model

We derive the renormalization group equations (RGE) for the flavor coupling matrices of the effective dimension-five operators which yield Majorana neutrino masses in the multi-Higgs-doublet standard model; in particular, we consider the case where two different scalar doublets occur in those operators. We also write down the RGE for the scalar-potential quartic couplings and for the Yukawa couplings of that model, in the absence of quarks. As an application of the RGE, we consider two models which, based on a - interchange symmetry, predict maximal atmospheric neutrino mixing, together with U _e3 = 0, at the seesaw scale. We estimate the change of those predictions due to the evolution of the coupling matrices of the effective mass operators from the seesaw scale down to the electroweak scale. We derive an upper bound on that change, thereby finding that the radiative corrections to those predictions are in general negligible.Received: 30 September 2004, Published online: 11 January 2005PACS: 11.10.Hi, 14.60.Pq, 12.60.Fr, 11.30.Hv     

Optimizing the photoassociation of cold atoms by use of chirped laser pulses

Photoassociation of ultracold atoms induced by chirped picosecond pulses is analyzed in a non-perturbative treatment by following the wavepacket dynamics on the ground and excited surfaces. The initial state is described by a Boltzmann distribution of stationary continuum states. The chosen example is photoassociation of cesium atoms at temperature K from the continuum to bound levels in the external well of the 0 _g ^-(6s + 6p _3/2) potential. We study how the modification of the pulse characteristics (carrier frequency, duration, linear chirp rate and intensity) can enhance the number of photoassociated molecules and suggest ways of optimizing the production of stable molecules.Received: 30 June 2004, Published online: 23 November 2004PACS: 33.80.Ps Optical cooling of molecules; trapping - 33.80.-b Photon interactions with molecules - 33.90. + h Other topics in molecular properties and interactions with photons - 33.80.Gj Diffuse spectra; predissociation, photodissociation     

Inelastic $J/\psi$ and $\Upsilon$ hadroproduction

We consider the prompt hadroproduction of and the states caused by the fusion of a symmetric colour-octet state, (gg)_8s , and an additional gluon. The cross sections are calculated in leading-order perturbative QCD. We find a considerable enhancement in comparison with previous perturbative QCD predictions. Indeed, the resulting cross sections are found to be consistent with the values measured at the Tevatron and RHIC, without the need to invoke non-perturbative colour-octet type of contributions.Received: 16 October 2004, Revised: 10 November 2004, Published online: 11 January 2005     

The low-lying mass spectrum of the N = 1 SU(2) SUSY Yang-Mills theory with Wilson fermions

We analyze the low energy spectrum of bound states of the N = 1 SU(2) SUSY Yang-Mills Theory (SYM). This work continues the investigation of the non-perturbative properties of SYM by Monte Carlo simulations in the Wilson discretization with dynamical gluinos. The dynamics of the gluinos is included by the Two-Step Multi-Bosonic Algorithm (TSMB) for dynamical fermions. A new set of configurations has been generated on a lattice at and . The analysis also includes sets of configurations previously generated on a smaller ( ) lattice at and 0.1955. Guided by predictions from low energy Lagrangians, we consider spin-1/2, scalar and pseudoscalar particles. The spectrum of SYM is a challenging subject of investigation because of the extremely noisy correlators. In particular, meson-like correlators contain disconnected contributions. The larger time-extension of the lattice allows to observe two-state signals in the effective mass. Finite-volume effects are monitored by comparing results from the two lattice sizes.Received: 14 September 2004, Revised: 29 October 2004, Published online: 21 December 2004     

Hierarchical radiative masses in a supersymmetric three-family model without higgsinos

We study the scalar potential and the mass spectrum of the supersymmetric extension of a three-family model based on the local gauge group , with anomalies canceled among the three families in a non-trivial fashion. In this model the slepton multiplets play the role of the Higgs scalars and no higgsinos are required, with the consequence that the sneutrino, the selectron and six other sleptons play the role of the Goldstone bosons of the theory. By introducing an Abelian anomaly-free discrete symmetry and aligning the vacuum in a convenient way, we get a consistent mass spectrum for the scalars and for the spin 1/2 quarks and charged leptons, where only the top and charm quarks and the tau lepton acquire tree-level masses while the remaining ordinary charged fermions acquire radiative hierarchical masses.Received: 9 August 2004, Revised: 10 March 2005, Published online: 8 June 2005PACS: 12.60.Jv, 12.60.Cn, 12.15.Ff     

Neutrino dimuon production and the strangeness asymmetry of the nucleon

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and antistrange parton distributions, s(x) and . To explore the strangeness sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange multiplier method to probe the quality of the global fit as a function of [S ^-] and find -0.001 < [S ^-] < 0.004. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.Received: 15 January 2004, Revised: 23 November 2004, Published online: 15 February 2005PACS: 11.30.Hv, 12.15.-y, 13.15. + g, 12.38.-t, 13.60.Hb     

Static potentials for quarkonia at finite temperatures

We review non-perturbative static potentials commonly used in potential models for quarkonia at finite T. Potentials derived from Polyakov loop correlators are shown to be inappropriate for this purpose. The free energy is physical but has the wrong spatial decay and perturbative limit. The so-called singlet free energy is gauge dependent and unphysical. An appropriate static real time potential can be defined through a generalisation of pNRQCD to finite T. In perturbation theory, its real part reproduces the Debye-screened potential, its imaginary part accounts for Landau damping. Possibilities for its non-perturbative evaluation are discussed.     

Off equilibrium dynamics in the 3d-XY system

We investigate through Monte Carlo simulations the non-equilibrium behaviour of the three-dimensional XY-model quenched from a high temperature state to its ferromagnetic and critical phases. The two-times autocorrelation and response functions are determined in the asymptotic (scaling) regime, from which the nonequilibrium exponents and critical are extracted. The form of the scaling function is in agreement with the prediction of local scale-invariance. The so-called limit fluctuation-dissipation ratio is shown to vanish in the ordered phase and to reach a constant value around 0.43 for the critical quench.Received: 12 July 2004, Published online: 30 September 2004PACS: 75.40.Gb Dynamic properties - 05.70.Ln Non-equilibrium and irreversible thermodynamics     

Searches for neutral Higgs bosons in extended models

Searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented in this paper. Higgs boson decays into b quarks, leptons, or other Higgs bosons are considered, giving rise to four-b, four-b + jets, six-b and four- final states, as well as mixed modes with b quarks and leptons. The whole mass domain kinematically accessible at LEP in these topologies is searched. The analysed data set covers both the LEP1 and LEP2 energy ranges and exploits most of the luminosity recorded by the DELPHI experiment. No convincing evidence for a signal is found, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model-independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.Received: 26 October 2003, Revised: 1 September 2004, Published online: 28 October 2004     

Spin-gap phase in the extended t — J chain

We study the one-dimensional deformed model in terms of the continuum field theories. We found that at low doping concentration and far away from the phase separation regime, there are two phases: the Luttinger liquid and the Luther-Emery liquid, depending on or , where . Moreover, the singlet superconducting correlations are dominant in the Luther-Emery liquid.Received: 12 October 2003, Published online: 19 February 2004PACS: 71.10.Fd Lattice fermion models - 71.10.Hf Non-Fermi-liquid ground states - 74.20.Mn Non-conventional mechanisms     

Canonical local algorithms for spin systems: heat bath and Hasting’s methods

We introduce new fast canonical local algorithms for discrete and continuous spin systems. We show that for a broad selection of spin systems they compare favorably to the known ones except for the Ising 1 spins. The new procedures use discretization scheme and the necessary information have to be stored in computer memory before the simulation. The models for testing discrete spins are the Ising 1, the general Ising S or Blume-Capel model, the Potts and the clock models. The continuous spins we examine are the O(N) models, including the continuous Ising model (N = 1), the Ising model (N = 1), the XY model (N = 2), the Heisenberg model (N = 3), the Heisenberg model (N = 3), the O(4) model with applications to the SU(2) lattice gauge theory, and the general O(N) vector spins with .Received: 16 August 2004, Published online: 21 October 2004PACS: 05.70.Fh Phase transitions: general studies - 64.60.Cn Order-disorder transformations; statistical mechanics of model systems - 75.10.Hk Classical spin models - 75.10.Nr Spin-glass and other random models     

$1/2^ + uudd\bar s$ pentaquark and instanton-induced forces

The mass of the 1/2 ⁺ pentaquark is calculated within the framework of a semirelativistic effective Hamiltonian approach to QCD with instanton-induced forces, using a diquark picture. This approximation allows a correct treatment of the confinement, assumed here to be a Y-junction. With the [ud] diquark mass fitted on the -baryon, the ground-state pentaquark is found around 2.2 GeV.Received: 28 April 2004, Revised: 11 May 2004, Published online: 19 October 2004PACS: 12.39.Pn Potential models - 12.39.Ki Relativistic quark model - 14.20.-c Baryons (including antiparticles)C. Semay: FNRS Research Associate;     

3-D numerical simulation of fully-coupled particle heating in ICPTs

Numerical simulations of the trajectory and heating history of powders injected with a carrier-gas into inductively coupled plasma torches working at atmospheric pressure have been performed in the framework of a 3-D FLUENT -based model, taking into account the effects of coupling between particles and plasma. In this paper, we present a selection of the results obtained for different operating conditions of the torch and for different characteristics of the injected particles.Received: 5 January 2004, Published online: 10 February 2004PACS: 52.75.Hn Plasma torches - 52.65.-y Plasma simulation - 52.80.Pi High-frequency and RF discharges - 81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation