Exact thermodynamic limit of short-range correlation functions of the antiferromagnetic XXZ-chain at finite temperatures

We numerically evaluate certain multiple integrals representing nearest and next-nearest neighbor correlation functions of the spin-1/2 XXZ Heisenberg infinite chain at finite temperatures.     

Delocalization of quasiparticles in quasi-two-dimensional disordered superconductors with s-wave pairing

We investigate localization behavior of quasiparticles in disordered multi-plane superconductors with s-wave pairing. By introducing disorder with random site energies, the spatial fluctuations of Bogoliubov-de Gennes pairing potential are self-consistently determined. The size dependence of rescaled localization length for a long bar is calculated by using the transfer-matrix method. From the finite-size scaling analysis we show that there exists a critical point of the disorder strength W_c which separates the extended and localized quasiparticle states in such quasi-two-dimensional systems. The associated critical behavior is studied and the relationship of the results to the number of planes is discussed.     

Quantum interference in nanotube electron waveguides

We have calculated the quantum conductance of single-walled carbon nanotube (SWNT) waveguide by using a tight binding-based Greens function approach. Our calculations show that the slow conductance oscillations as well as the fast conductance oscillations are manifestations of the intrinsic quantum interference properties of the conducting SWNTs, being independent of the defect and disorder of the SWNTs. And zigzag type tubes do not show the slow oscillations. The SWNT electron waveguide is also found to have distinctly different transport behavior depending on whether or not the length of the tube is commensurate with a (3N+1) rule, with N the number of basic carbon repeat units along the nanotube length.     

Generic two-phase coexistence in nonequilibrium systems

A beautifully simple model introduced a couple of decades ago, Tooms cellular automaton, revealed that non-equilibrium systems may exhibit generic bistability, i.e. two-phase coexistence over a finite area of the (two-dimensional) phase diagram, in violation of the equilibrium Gibbs phase rule. In this paper we analyse two interfacial models, describing more realistic situations, that share with Tooms model a phase diagram with a broad region of phase coexistence. An analysis of the interfacial models yields conditions for generic bistability in terms of physically relevant parameters that may be controlled experimentally.     

Complex grid computing

This article investigates the functional properties of complex networks used as grid computing systems. Complex networks following the Erdös-Rényi model and other models with a preferential attachment rule (with and without growth) or priority to the connection of isolated nodes are studied. Regular networks are also considered for comparison. The processing load of the parallel program executed on the grid is assigned to the nodes on demand, and the efficiency of the overall computation is quantified in terms of the parallel speedup. It is found that networks with preferential attachment allow lower computing efficiency than networks with uniform link attachment. At the same time, considering only node clusters of the same size, preferential attachment networks display better efficiencies. The regular networks, on the other hand, display a poor efficiency, due to their implied larger internode distances. A correlation is observed between the topological properties of the network, specially average cluster size, and their respective computing efficiency.     

A systematic study of neutrino mixing and <Emphasis Type="Italic">CP</Emphasis>-violationfrom lepton mass matrices with six texture zeros

We present a systematic study of 400 combinations of the charged lepton and neutrino mass matrices with six vanishing entries or texture zeros. Only 24 of them, which can be classified into a few distinct categories, are found to be compatible with current neutrino oscillation data at the level. A peculiar feature of the lepton mass matrices in each category is that they have the same phenomenological consequences. Taking account of a simple seesaw scenario for six parallel patterns of the charged lepton and Dirac neutrino mass matrices with six zeros, we show that it is possible to fit the experimental data at or below the level. In particular, the maximal atmospheric neutrino mixing can be reconciled with a strong neutrino mass hierarchy in the seesaw case. Numerical predictions are also obtained for the neutrino mass spectrum, flavor mixing angles, CP-violating phases and effective masses of the tritium beta decay and the neutrinoless double beta decay.Received: 28 September 2004, Revised: 14 October 2004, Published online: 1 December 2004PACS: 12.15.Ff, 12.10.Kt     

Transverse-momentum-ordered showers and interleaved multiple interactions

We propose a sophisticated framework for high-energy hadronic collisions, wherein different QCD physics processes are interleaved in a common sequence of falling transverse-momentum values. Thereby phase-space competition is introduced between multiple parton-parton interactions and initial-state radiation. As a first step we develop new transverse-momentum-ordered showers for initial- and final-state radiation, which should be of use also beyond the scope of the current article. These showers are then applied in the context of multiple interactions, and a few tests of the new model are presented. The article concludes with an outlook on further aspects, such as the possibility of a shower branching giving partons participating in two different interactions.Received: 26 August 2004, Revised: 14 October 2004, Published online: 11 January 2005     

Infrared regularization for spin-1 fields

We extend the method of infrared regularization to spin-1 fields. As applications, we discuss the chiral extrapolation of the rho meson mass from lattice QCD data and the pion-rho sigma term.Received: 18 November 2004, Published online: 4 February 2005PACS: 12.39.Fe, 12.38.GcWork supported in part by Deutsche Forschungsgemeinschaft through grants provided for the SFB/TR 16 Subnuclear Structure of Matter.     

Studies on chargino production and decay at a photon collider

A Monte-Carlo analysis on production and decay of supersymmetric charginos at a future photon-collider is presented. A photon collider offers the possibility of a direct branching-ratio measurement. In this study, the process has been considered for a specific mSUGRA scenario. Various backgrounds and a parameterised detector simulation have been included. Depending on the centre-of-mass energy, a statistical error for the directly measurable branching ratio BR( ) of up to 3.5% can be reached.Received: 14 March 2005, Revised: 31 May 2005, Published online: 28 June 2005G. Klämke: Now at: Institut für Theoretische Physik, Universität Karlsruhe, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe, Germany     

Strong field dual-pulse excitation of Ag<Subscript>N</Subscript>

The ionization of silver clusters exposed to pairs of intense femtosecond laser pulses strongly depends on the optical delay. Enhanced production of a certain atomic charge state z is obtained by a z-dependent delay. This may open a possible route to control the excitation process and populate specific charge states. The optimum pulse separation which maximizes the generation of highly ionized species varies by more than one order of magnitude when the mean size of the clusters increases from to . Semiclassical Vlasov simulations applied to a model system reveal the importance of the initial ionic motion in the ionization process.