Recursive actions for scalar theories

We introduce a class of self-interacting scalar theories in which the various coupling constants obey a recursive relation. These imply a particularly simple form for the generating function of the Feynman amplitudes with vanishing external momenta, as well as for the effective potential. In addition we discuss an interesting duality inherent in these models. Specializing to the case of zero spacetime dimensions we find intriguing nullification properties for the amplitudes. Received: 19 December 2001 / Published online: 5 May 2003 RID="a" ID="a" e-mail: chrisd@sci.kun.nl RID="b" ID="b" e-mail: kleiss@sci.kun.nl RID="c" ID="c" e-mail: petros@sci.kun.nl RID="d" ID="d" e-mail: andrevh@sci.kun.nl RID="e" ID="e" e-mail: papadopo@alice.nuclear.demokritos.gr     

Singular cross sections in muon colliders

We address the problem that the cross section for the collisions of unstable particles diverges, if calculated by standard methods. This problem is considered for beams much smaller than the decay length of the unstable particle, much larger than the decay length and finally also for pancake- shaped beams. We find that in all cases this problem can be solved by taking into account the production/propagation of the unstable particle and/or the width of the incoming wave packets in momentum space. Received: 4 March 2003 / Revised version: 8 April 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: chrisd@sci.kun.nl RID="b" ID="b" e-mail: kleiss@sci.kun.nl     

A hierarchical phase space generator for QCD antenna structures

We present a ”hierarchical” strategy for phase space generation in order to efficiently map the antenna momentum structures, typically occurring in QCD amplitudes. Received: 4 April 2002 / Revised version: 6 June 2002 / Published online: 20 September 2002 RID="a" ID="a" e-mail: andrevh@inp.demokritos.gr RID="b" ID="b" e-mail: Costas.Papadopoulos@cern.ch     

On decoupling of massless modes in NCOS theories

We revisit the decoupling phenomenon of massless modes in non-commutative open string (NCOS) theories. We check the decoupling by explicit computation in (2+1) or higher dimensional NCOS theories and recapitulate the validity of the decoupling to all orders in perturbation theory. Received: 23 April 2002 / Published online: 25 October 2002 RID="a" ID="a" e-mail: hyun@phya.yonsei.ac.kr RID="b" ID="b" e-mail: sangmin@newton.skku.ac.kr RID="c" ID="c" e-mail: hshin@kias.re.kr     

Slow nucleic acid unzipping kinetics from sequence-defined barriers

Recent experiments on unzipping of RNA helix-loop structures by force have shown that ≈40-base molecules can undergo kinetic transitions between two well-defined “open” and “closed” states, on a timescale ≈1 sec [Liphardt et al., Science 297, 733-737 (2001)]. Using a simple dynamical model, we show that these phenomena result from the slow kinetics of crossing large free energy barriers which separate the open and closed conformations. The dependence of barriers on sequence along the helix, and on the size of the loop(s) is analyzed. Some DNA and RNA sequences that could show dynamics on different time scales, or three(or more)-state unzipping, are proposed. Our dynamical model is also applied to the unzipping of long (kilo-basepair) DNA molecules at constant force. Received 29 July 2002 / Received in final form 5 February 2003 Published online: 16 April 2003 RID="a" ID="a"e-mail: cocco@ldfc.u-strasbg.fr RID="b" ID="b"e-mail: jmarko@uic.edu RID="c" ID="c"e-mail: monasson@lpt.ens.fr     

Explicit model realizing parton-hadron duality

An explicit model realizing parton-hadron duality and fitting the data is suggested. Complex nonlinear Regge trajectories are important ingredients of the model. The inclusion of Δ and N^* trajectories should account for all resonances in the direct channel. The exotic trajectory is responsible for the smooth background. Received: 7 June 2002 / Accepted: 3 July 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: fiore@cs.infn.it RID="b" ID="b"e-mail: flachi@ifae.es RID="c" ID="c"e-mail: jenk@gluk.org RID="d" ID="d"e-mail: sasha@len.uzhgorod.ua RID="e" ID="e"e-mail: vladimir@cfif.ist.utl.pt Communicated by V.V. Anisovich     

Genetic Algorithms as a tool in the study of aperiodic order,with application to the case of X-Ray diffraction spectra of GaAs-AlAs multilayer heterostructures

We present the first application of Genetic Algorithms to the analysis of data from an aperiodically ordered system, high resolution X-Ray diffraction spectra from multilayer heterostructures arranged according to a deterministic or random scheme. This method paves the way to the solution of the “inverse problem”, that is the retrieval of the generating disorder from the investigation of the spectra of an unknown sample having non crystallographic, non quasi-crystallographic order. Received 18 March 2002 / Received in final form 3 July 2002 Published online 31 October 2002 RID="a" ID="a"e-mail: Evelyne.Lutton@inria.fr RID="b" ID="b"CNRS UMR 8502     

Nonlinear dynamics of dimers on periodic substrates

We study the dynamics of a dimer moving on a periodic one-dimensional substrate as a function of the initial kinetic energy at zero temperature. The aim is to describe, in a simplified picture, the microscopic dynamics of diatomic molecules on periodic surfaces, which is of importance for thin film formation and crystal growth. We find a complex behaviour, characterized by a variety of dynamical regimes, namely oscillatory, “quasi-diffusive” (chaotic) and drift motion. Parametrically resonant excitations of internal vibrations can be induced both by oscillatory and drift motion of the centre of mass. For weakly bound dimers a chaotic regime is found for a whole range of velocities between two non-chaotic phases at low and high kinetic energy. The chaotic features have been monitored by studying the Lyapunov exponents and the power spectra. Moreover, for a short-range interaction, the dimer can dissociate due to the parametric excitation of the internal motion. Received 8 July 2002 / Received in final form 15 November 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: fusco@sci.kun.nl.     

LMA solution to the solar neutrino problem and a phenomenological charged lepton mass matrix

We propose a phenomenological form of the charged lepton mass matrix which extends the idea of a ”lopsided” mass matrix found in the literature. The features of the form are that both the 2-3 and 1-3 elements of the charged lepton mass matrix are of order 1 and that the small elements have a new structure. This form leads to the interesting result that both large atmospheric and solar neutrino mixing can be accounted for by the matrix. Another interesting result of this mass matrix is that it leads to very small 1-3 mixing in the lepton sector and can suppress the branching ratio of under the present experimental limit in the supersymmetric see-saw case. Received: 3 October 2002 / Revised version: 10 November 2002 / Published online: 24 January 2003 RID="a" ID="a" e-mail: bixj@mail.tsinghua.edu.cn RID="b" ID="b" e-mail: dyb@itp.ac.cn     

Catching the PEG-induced attractive interaction between proteins

We present the experimental and theoretical background of a method to characterize the protein-protein attractive potential induced by one of the mostly used crystallizing agents in the protein-field, the poly(ethylene glycol) (PEG). This attractive interaction is commonly called, in colloid physics, the depletion interaction. Small-Angle X-ray Scattering experiments and numerical treatments based on liquid-state theories were performed on urate oxidase-PEG mixtures with two different PEGs (3350 Da and 8000 Da). A “two-component” approach was used in which the polymer-polymer, the protein-polymer and the protein-protein pair potentials were determined. The resulting effective protein-protein potential was characterized. This potential is the sum of the free-polymer protein-protein potential and of the PEG-induced depletion potential. The depletion potential was found to be hardly dependent upon the protein concentration but strongly function of the polymer size and concentration. Our results were also compared with two models, which give an analytic expression for the depletion potential. Received 29 April 2002 RID="a" ID="a"Present address: CRMC2-CNRS, Campus de Luminy, case 913, F-13288 Marseille Cedex 09, France; e-mail: vivares@crmc2.univ-mrs.fr RID="b" ID="b"e-mail: bonnete@crmc2.univ-mrs.fr RID="c" ID="c"Laboratory associated to Universities Aix-Marseille II and III.     

Hedgehog production in spatially correlated noise

The production of topological defects during a quench in a φ⁴ model is investigated. The influence of a spatially correlated noise on defect production in two and three dimensions is demonstrated. Received 28 August 2001 / Received in final form 11 February 2002 Published online 2 October 2002 RID="a" ID="a"Paper supported in part by ESF “COSLAB” Programme RID="b" ID="b"e-mail: sfdobrow@kinga.cyf-kr.edu.pl     

Deconstructing scalar QED at zero and finite temperature

We calculate the effective potential for the WLPNGB in a world with a circular latticized extra dimension. The mass of the Wilson line pseudo-Nambu-Goldstone boson (WLPNGB) is calculated from the one-loop quantum effect of scalar fields at zero and finite temperature. We show that a series expansion by the modified Bessel functions is useful to calculate the one-loop effective potentials. Received: 24 January 2003 / Published online: 14 April 2003 RID="a" ID="a" e-mail: b1834@sty.cc.yamaguchi-u.ac.jp RID="b" ID="b" e-mail: b1795@sty.cc.yamaguchi-u.ac.jp RID="c" ID="c" e-mail: shiraish@po.cc.yamaguchi-u.ac.jp     

The $-game

We propose a payoff function extending Minority Games (MG) that captures the competition between agents to make money. In contrast with previous MG, the best strategies are not always targeting the minority but are shifting opportunistically between the minority and the majority. The emergent properties of the price dynamics and of the wealth of agents are strikingly different from those found in MG. As the memory of agents is increased, we find a phase transition between a self-sustained speculative phase in which a “stubborn majority” of agents effectively collaborate to arbitrage a market-maker for their mutual benefit and a phase where the market-maker always arbitrages the agents. A subset of agents exhibit a sustained non-equilibrium risk-return profile. Received 5 June 2002 / Received in final form 21 November 2002 Published online 27 January 2003 RID="a" ID="a"e-mail: sornette@unice.fr RID="b" ID="b"CNRS UMR7536 RID="c" ID="c"CNRS UMR6622     

Coulomb interference in high-energy pp and $\bar p p$ scattering

An analysis of the Coulombic amplitude and its interference with the nuclear amplitude which is driven by the three-component pomeron is presented. It is shown that different approaches towards the evaluation of the Coulomb phase give approximately uniform results at all energies and the differences are negligible at RHIC and LHC energies. We show that the use of the amplitude which was fitted to accommodate the nucleon data only (in the region (GeV²)), combined with the Coulomb amplitude, reproduces the existing data in the Coulomb interference domain quite accurately without any adjustment of the parameters. As a consequence, we predict the differential cross section in the region of the Coulomb nucleon interference for both RHIC and LHC energies. Received: 3 June 2002 / Revised version: 27 February 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: petrov@mx.ihep.su RID="b" ID="b" e-mail: predazzi@to.infn.it RID="c" ID="c" e-mail: prokudin@to.infn.it     

World-line techniques for resumming gluon radiative corrections at the cross-section level

We employ the Polyakov world-line path-integral version of QCD to identify and resum at leading perturbative order enhanced radiative gluon contributions to the Drell-Yan type ( pair annihilation) cross-sections. We emphasize that this is the first time that world-line techniques are applied to cross-section calculations. Received: 10 June 2002 / Published online: 31 October 2002 RID="a" ID="a" e-mail: akaranik@cc.uoa.gr RID="b" ID="b" e-mail: cktorid@cc.uoa.gr RID="c" ID="c" e-mail: stefanis@tp2.ruhr-uni-bochum.de     

Probing the Majorana mass scale of right-handed neutrinos in mSUGRA

We discuss the perspectives of testing the right-handed Majorana mass scale M_R of the SUSY see-saw model in the mSUGRA framework. Lepton-flavor violating low energy processes are analyzed in recently proposed post-LEP benchmark scenarios, taking into account present uncertainties and future developments in the neutrino sector. Non-observation of in the next-generation PSI experiment will provide upper bounds on M_R of the order of GeV, while on the other hand, a positive signal for at SUPERKEKB or the LHC may determine M_R for a given mSUGRA scenario with an accuracy of a factor of 2. Received: 14 June 2002 / Revised version: 7 January 2003 / Published online: 14 April 2003 RID="a" ID="a" e-mail: deppisch@physik.uni-wuerzburg.de RID="b" ID="b" e-mail: paes@physik.uni-wuerzburg.de RID="c" ID="c" e-mail: asredelb@physik.uni-wuerzburg.de RID="d" ID="d" e-mail: rueckl@physik.uni-wuerzburg.de RID="e" ID="e" e-mail: shimizu@eken.phys.nagoya-u.ac.jp     

Modelling of magnetic effects in near-field optics

Green's dyadic technique represents a powerful tool for calculations in electrodynamics, especially in modelling optical properties of nanoscopic objects. The method does not only provide field distributions, but also maps of susceptibilities and densities of states. Whereas the formalism is well established for dielectrics and electric fields, I present here a straight forward extension to tensors of both electric and magnetic type as well as mixed ones and furthermore to the situation where objects with dielectric and magnetic permeabilities are present together. As examples, characteristic field patterns are compared for elementary dielectric and magnetic perturbations. Green's tensors calculated for a coral structure reveal that mixed susceptibilities can exhibit other symmetries than pure electric or magnetic ones. Maps of all tensor components can thus give essential clues to the interpretation of near-field images. Received 15 December 2002 Published online 20 June 2003 RID="a" ID="a"Files “maths.ps” and “tensors.ps” are only available in electronic form at http://www.edpsciences.org RID="b" ID="b"e-mail: Ursula.Schroeter@uni-konstanz.de     

How well can we reconstruct the $t\bar{t}$ system near its threshold at future ee linear colliders?

We developed a new method for the full kinematical reconstruction of the system near its threshold at future linear e ⁺ e ^- colliders. In the core of the method lies likelihood fitting which is designed to improve measurement accuracies of the kinematical variables that specify the final states resulting from decays. The improvement is demonstrated by applying this method to a Monte Carlo sample generated with various experimental effects including beamstrahlung, finite acceptance and resolution of the detector system, etc. In most cases the fit takes a broad non-Gaussian distribution of a given kinematical variable to a nearly Gaussian shape, thereby justifying phenomenological analyses based on simple Gaussian smearing of the parton-level momenta. The standard deviations of the resultant distributions of various kinematical variables are given in order to facilitate such phenomenological analyses. A possible application of the kinematical fitting method and its expected impact are also discussed. Received: 4 March 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: ikematsu@post.kek.jp RID="b" ID="b" e-mail: fujiik@jlcuxf.kek.jp RID="c" ID="c" e-mail: hioki@ias.tokushima-u.ac.jp RID="d" ID="d" e-mail: sumino@tuhep.phys.tohoku.ac.jp RID="e" ID="e" e-mail: tohrut@hiroshima-u.ac.jp     

Time-ordered perturbation theory on non-commutative spacetime II: Unitarity

We examine the unitarity issue in the recently proposed time-ordered perturbation theory on noncommutative (NC) spacetime. We show that unitarity is preserved as long as the interaction Lagrangian is explicitly hermitian. We explain why it makes sense to distinguish the hermiticity of the Lagrangian from that of the action in perturbative NC field theory and how this requirement fits in this framework. Received: 25 June 2002 / Published online: 30 August 2002 RID="a" ID="a" e-mail: liaoy@itp.uni-leipzig.de RID="b" ID="b" e-mail: sibold@itp.uni-leipzig.de