Vertex counting: Statistical distribution of vertices in large sets of tree diagrams

We study the problem of determining the distribution of vertices of a particular given type in the set of all Feynman tree graphs in quantum field theories. We show that in almost all cases a Gaussian distribution arises asymptotically, and we compute the mean and variance of this distribution for several theories. We show that the distribution's ”fine structure”, arising from topological sum rules, can be obtained. Received: 12 September 2002 / Published online: 24 January 2003 RID="a" ID="a" e-mail: petros@sci.kun.nl RID="b" ID="b" e-mail: kleiss@sci.kun.nl     

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     

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     

Compressible bag model and the phase structure

The phase structure of hadrons and the quark-gluon plasma is investigated by two types of equation of state of the hadrons, namely the ideal hadron gas model and the compressible bag model. It is pointed out that, while the ideal gas model produces an unrealistic extra hadron phase, the compressible bag model gives the expected and reasonable phase diagram even if the rich hadron spectrum is taken into account. Received: 22 February 2002 / Revised version: 28 June 2002 / Published online: 20 September 2002 RID="a" ID="a" e-mail: kagiyama@sci.kagoshima-u.ac.jp RID="b" ID="b" e-mail: kumamoto@cosmos01.cla.kagoshima-u.ac.jp RID="c" ID="c" e-mail: minaka@edu.kagoshima-u.ac.jp RID="d" ID="d" e-mail: nakamura@sci.kagoshima-u.ac.jp RID="e" ID="e" e-mail: ohkura@cosmos01.cla.kagoshima-u.ac.jp RID="f" ID="f" e-mail: yamaguchi@cosmos01.cla.kagoshima-u.ac.jp     

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     

Towards high-precision predictions for the MSSM Higgs sector

The status of the evaluation of the MSSM Higgs sector is reviewed. The phenomenological impact of recently obtained corrections is discussed. In particular it is shown that the upper bound on m_h within the MSSM is shifted upwards. Consequently, lower limits on obtained by confronting the upper bound as function of with the lower bound on m_h from Higgs searches are significantly weakened. Furthermore, th e region in the M_A--plane where the coupling of the lightest Higgs boson to down-type fermions is suppressed is modified. The presently not calculated higher-order corrections to the Higgs-boson mass matrix are estimated to shift the mass of the lightest Higgs boson by up to 3 GeV. Received: 12 December 2002 / Published online: 3 March 2003 RID="a" ID="a" e-mail: giuseppe.degrassi@roma3.infn.it RID="b" ID="b" e-mail: Sven.Heinemeyer@physik.uni-muenchen.de RID="c" ID="c" e-mail: hollik@mppmu.mpg.de RID="d" ID="d" e-mail: slavich@mppmu.mpg.de RID="e" ID="e" e-mail: Georg.Weiglein@durham.ac.uk     

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     

Two-photon annihilation into baryon-antibaryon pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard subprocess and form factors describing the soft transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured channels. Received: 3 July 2002 / Revised version: 7 October 2002 / Published online: 20 November 2002 RID="a" ID="a" e-mail: mdiehl@physik.rwth-aachen.de RID="b" ID="b" e-mail: kroll@physik.uni-wuppertal.de RID="c" ID="c" e-mail: cvogt@nordita.dk     

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     

A universal Regge pole model for all vector meson exclusive photoproduction by real and virtual photons

A model based on a dipole pomeron framework for exclusive vector meson photoproduction by real and virtual photons shows very good agreement with the experimental data. This model does not violate unitarity constraints and describes in a universal manner all the available data for , , , and vector meson photoproduction in the region of energies and photon virtualities . Received: 18 December 2001 / Published online: 25 October 2002 RID="a" ID="a" e-mail: martynov@bitp.kiev.ua RID="b" ID="b" e-mail: predazzi@to.infn.it RID="c" ID="c" e-mail: prokudin@to.infn.it     

On the instanton-induced portion of the nucleon strangeness II: the MIT model beyond the linearized approximation

If instantons are introduced into the MIT bag model in such a way that the bag radii are allowed to vary, the MIT bag interior can accommodate an instanton density which is by an order of magnitude larger than in the case when the radii are fixed (although it is still significantly smaller than in the non-perturbative QCD vacuum). The instanton contribution to the baryon mass shifts is also correspondingly larger. The instanton-induced part of the scalar strangeness of the nucleon MIT bag is an order of magnitude larger than found previously, within the linearized approximation. The decrease of the model radii (which is associated with the increase of the instanton density) is very favorable from the standpoint of nuclear physics. Received: 7 February 2003 / Revised version: 1 April 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: klabucar@phy.hr RID="b" ID="b" e-mail: kkumer@phy.hr RID="c" ID="c" e-mail: dmekter@rudjer.irb.hr RID="d" ID="d" e-mail: bp@phy.hr. Present address: Faculty of Civil Engineering, University of Rijeka, HR-51000 Rijeka, Croatia     

Interaction of coupled higher order nonlinear Schrödinger equation solitons

The novel inelastic collision properties of two-soliton interaction for an n-component coupled higher order nonlinear Schr?dinger equation are studied. Some interesting features of three soliton interactions, related to the integrability of the n-component coupled higher order nonlinear Schr?dinger equation are also discussed. Received 17 April 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: abhijit@iitg.ernet.in RID="b" ID="b"e-mail: sasanka@iitg.ernet.in RID="c" ID="c"e-mail: sudipta@iitg.ernet.in     

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     

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     

Antideuteron production in proton-proton and proton-nucleus collisions

The experimental data of the antideuteron production in proton-proton and proton-nucleus collisions are analyzed within a simple model based on the diagrammatic approach to the coalescence model. This model is shown to be able to reproduce most of the existing data without any additional parameter. Received: 18 April 2002 / Accepted: 30 August 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: duperray@isn.in2p3.fr RID="b" ID="b"e-mail: protasov@isn.in2p3.fr RID="c" ID="c"e-mail: avoronin@aha.ru Communicated by A. Molinari     

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     

Role of electric field polarisation in rotational transitions

The molecular dynamics of polar diatomic molecule, interacting with linearly and circularly polarised laser field is studied. Non-perturbative quasi-energy technique is used to determine the rotational field surfaces. Degeneracy in different M-levels is found to be removed in the presence of circularly polarised electromagnetic radiation. In this paper, we present the calculations exhibiting the dynamics of rotational excitation of a linear molecule and characteristic features of spectra which become observable in considered fields. Received 22 March 2002 / Received in final form 15 July 2002 Published online 6 November 2002 RID="a" ID="a"e-mail: nsinghal@physics.du.ac.in RID="b" ID="b"e-mail: vnautiyal@himalaya.du.ac.in RID="c" ID="c"e-mail: manmohan@physics.du.ac.in     

Structure and properties of confined sodium nitrite

We study the lateral and transverse diffusion of amphiphiles in two-component bilayer membranes, using a coarse-grained model for amphiphilic molecules and combined Monte Carlo-Molecular Dynamics simulations. Membrane structural properties, such as the mean thickness, are also measured. The dependence of such properties on membrane composition, inter-molecular interactions, and amphiphile stiffness is determined. In particular, we show that addition of shorter amphiphiles drives the model membrane towards a more fluid state, with increased amphiphile lateral diffusion rates. These results can be understood in the framework of a simple free-volume model. Furthermore, we observe an increase in the trans-membrane diffusion when the interaction energy of amphiphiles with their neighboring molecules is decreased. Received: 6 December 2002 / Accepted: 17 April 2003 / Published online: 27 May 2003 RID="a" ID="a"e-mail: imparato@mpikg-golm.mpg.de RID="b" ID="b"e-mail: shillcock@mpikg-golm.mpg.de RID="c" ID="c"e-mail: lipowsky@mpikg-golm.mpg.de