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Partially Asymmetric Simple Exclusion Model in the Presence of an Impurity on a Ring ; We study a generalized twospecies model on a ring. The original model 1 describes ordinary particles hopping exclusively in one direction in the presence of an impurity. The impurity hops with a rate different from that of ordinary particles and can be overtaken by them. Here we let the ordinary particles hop also backward with the rate q. Using Matrix Product Ansatz MPA, we obtain the relevant quadratic algebra. A finite dimensional representation of this algebra enables us to compute the stationary bulk density of the ordinary particles, as well as the speed of impurity on a set of special surfaces of the parameter space. We will obtain the phase structure of this model in the accessible region and show how the phase structure of the original model is modified. In the infinitevolume limit this model presents a shock in one of its phases.

FiniteSize Scaling in Twodimensional Continuum Percolation Models ; We test the universal finitesize scaling of the cluster mass order parameter in twodimensional 2D isotropic and directed continuum percolation models below the percolation threshold by computer simulations. We found that the simulation data in the 2D continuum models obey the same scaling expression of mass M to sample size L as generally accepted for isotropic lattice problems, but with a positive sign of the slope in the lnln plot of M versus L. Another interesting aspect of the finitesize 2D models is also suggested by plotting the normalized mass in 2D continuum and lattice bond percolation models, versus an effective percolation parameter, independently of the system structure i.e. lattice or continuum and of the possible directions allowed for percolation i.e. isotropic or directed in regions close to the percolation thresholds. Our study is the first attempt to map the scaling behaviour of the mass for both lattice and continuum model systems into one curve.

Temperature scaling, glassiness and stationarity in the BakSneppen model ; We show that the emergence of criticality in the locallydefined BakSneppen model corresponds to separation over a hierarchy of timescales. Near to the critical point the model obeys scaling relations, with exponents which we derive numerically for a onedimensional system. We further describe how the model can be related to the glass model of Bouchaud em J. Phys. I France bf 2, 1705 1992, and we use this insight to comment on the usual assumption of stationarity in the BakSneppen model. Finally, we propose a general definition of selforganised criticality which is in partial agreement with other recent definitions.

Slow dynamics of Ising models with energy barriers ; Using Monte Carlo simulations we study the dynamics of threedimensional Ising models with nearest, nextnearest, and fourspin plaquette interactions. During coarsening, such models develop growing energy barriers, which leads to very slow dynamics at low temperature. As already reported, the model with only the plaquette interaction exhibits some of the features characteristic of ordinary glasses strong metastability of the supercooled liquid, a weak increase of the characteristic length under cooling, stretchedexponential relaxation and aging. The addition of twospin interactions, in general, destroys such behaviour the liquid phase loses metastability and the slowdynamics regime terminates well below the melting transition, which is presumably related with a certain cornerrounding transition. However, for a particular choice of interaction constants, when the ground state is strongly degenerate, our simulations suggest that the slowdynamics regime extends up to the melting transition. The analysis of these models leads us to the conjecture that in the fourspin Ising model domain walls lose their tension at the glassy transition and that they are basically tensionless in the glassy phase.

Modelling fluctuations of financial time series from cascade process to stochastic volatility model ; In this paper, we provide a simple, generic'' interpretation of multifractal scaling laws and multiplicative cascade process paradigms in terms of volatility correlations. We show that in this context 1f power spectra, as observed recently by Bonanno et al., naturally emerge. We then propose a simple solvable stochastic volatility'' model for return fluctuations. This model is able to reproduce most of recent empirical findings concerning financial time series no correlation between price variations, longrange volatility correlations and multifractal statistics. Moreover, its extension to a multivariate context, in order to model portfolio behavior, is very natural. Comparisons to real data and other models proposed elsewhere are provided.

Adjusting the melting point of a model system via GibbsDuhem integration application to a model of Aluminum ; Model interaction potentials for real materials are generally optimized with respect to only those experimental properties that are easily evaluated as mechanical averages e.g., elastic constants at T0 K, static lattice energies and liquid structure. For such potentials, agreement with experiment for the nonmechanical properties, such as the melting point, is not guaranteed and such values can deviate significantly from experiment. We present a method for reparameterizing any model interaction potential of a real material to adjust its melting temperature to a value that is closer to its experimental melting temperature. This is done without significantly affecting the mechanical properties for which the potential was modeled. This method is an application of GibbsDuhem integration D. Kofke, Mol. Phys.78, 1331 1993. As a test we apply the method to an embedded atom model of aluminum J. Mei and J.W. Davenport, Phys. Rev. B 46, 21 1992 for which the melting temperature for the thermodynamic limit is 826.4 1.3K somewhat below the experimental value of 933K. After reparameterization, the melting temperature of the modified potential is found to be 931.5K 1.5K.

Symmetry effects and equivalences in lattice models of hydrophobic interaction ; We establish the equivalence of a recently introduced discrete model of the hydrophobic interaction, as well as its extension to continuous state variables, with the Ising model in a magnetic field with temperaturedependent strength. In order to capture the effect of symmetries of the solvent particles we introduce a generalized multistate model. We solve this model which is not of the Ising type exactly in one dimension. Our findings suggest that a small increase in symmetry decreases the amplitude of the solventmediated part of the potential of mean force between solute particles and enhances the solubility in a very simple fashion. High symmetry decreases also the range of the attractive potential. This weakening of the hydrophobic effect observed in the model is in agreement with the notion that the effect is entropic in origin.

WWW and Internet models from 1955 till our days and the popularity is attractive'' principle ; We note that the model discussed in the communication of S. Bornholdt and H. Ebel World Wide Web scaling exponent from Simon's 1955 model, condmat0008465 is the particular case of the model considered and solved exactly in our paper, condmat0004434. These models may be used for estimation of the order of the deviation of the scaling exponent from 2 both for the distributions of incoming links and links coming out from nodes but not for the obtaining some specific values of the exponents from the WWW growth data. We emphasize that, unlike the statement of Bornholdt and Ebel, both the network under consideration and the model of Barab'asi and Albert provide quite equal possibilities for individual growth. There is no great difference between them in this respect. The resulting distributions for individual nodes and arising scaling relations have been obtained in our paper, condmat0004434. We discuss briefly the modern state of art in the physics of the evolving networks and the great role of the general principle em popularity is attractive in the selforganization of complex communications networks, in physics of nonequilibrium phenomena, and in Nature.

On the nature of the stock market Simulations and experiments ; In this dissertation two simple models of stock exchange are developed and simulated numerically. The first is characterized by centralized trading with a market maker. Unfortunately, this model is unable to generate realistic market dynamics. The second model discards the requirement of centralized trading. Under variation of the control parameter the model exhibits two phase transitions both a first and a secondorder critical. The decentralized model is able to capture many of the interesting properties observed in empirical markets. Significantly, these properties only emerge when the parameters are tuned such that the model spans the critical point. This suggests that real markets may operate at or near a critical point, but is unable to explain why this should be. One of the main points of the thesis is that these empirical phenomena are not present in the stochastic driving force, but emerge endogenously from interactions between agents.

Introducing Protein Folding Using Simple Models ; We discuss recent theoretical developments in the study of simple lattice models of proteins. Such models are designed to understand general features of protein structures and mechanism of folding. Among the topics covered are i the use of lattice models to understand the selection of the limited set of viable protein folds; ii the relationship between structure and sequence spaces; iii the application of lattice models for studying folding mechanisms topological frustration, kinetic partitioning mechanism. Classification of folding scenarios based on the intrinsic thermodynamic properties of a sequence namely, the collapse and folding transition temperatures is outlined. A brief discussion of random heteropolymer model is also presented.

Connecting polymers to the quantum Hall plateau transition ; A mapping is developed between the quantum Hall plateau transition and twodimensional selfinteracting lattice polymers. This mapping is exact in the classical percolation limit of the plateau transition, and diffusive behavior at the critical energy is shown to be related to the critical exponents of a class of chiral polymers at the thetapoint. The exact critical exponents of the chiral polymer model on the honeycomb lattice are found, verifying that this model is in the same universality class as a previously solved model of polymers on the Manhattan lattice. The mapping is obtained by averaging analytically over the local random potentials in a previously studied lattice model for the classical plateau transition. This average generates a weight on chiral polymers associated with the classical localization length exponent nu 43. We discuss the differences between the classical and quantum transitions in the context of polymer models and use numerical results on highermoment scaling laws at the quantum transition to constrain possible polymer descriptions. Some properties of the polymer models are verified by transfer matrix and Monte Carlo studies.

Exact ground state of one and twodimensional frustrated quantum spin systems ; We outline the recent results on the ground state for a class of one and twodimensional frustrated quantum spin models with competing ferroF and antiferromagnetic AF interactions. Frustrated spin systems are known to have many interesting properties due to large quantum fluctuations. As a result of these fluctuations usual meanfield approach gives quite crude if not false description of these systems. Therefore, exactly solvable models are very instructive at investigations of such systems. The exact ground state wave function of proposed models has a structure of the valencebond state VBS type. One of the 1D model describes the transition line between the F and AF phase. The exact singlet ground state on this line has a doublespiral ordering. Using different approximation methods we study the magnetization curve in the AF phase. The second considered set of the 1D and 2D models has an exact nondegenerate ground state with exponentially decaying spin correlations. We also proposed the 1D and 2D electronic models with exact ground state represented in terms of singlet bond functions which are the generalization of the RVB functions including ionic states.

Competition of Branches ; We consider a general model of branch competition that automatically leads to a critical branching configuration. This model is inspired by the 4eta expansion of the dielectric breakdown model DBM, but the mechanism of arriving at the critical point may be of relevance to other branching systems as well, such as fractures. The exact solution of this model clarifies the direct renormalization procedure used for the DBM, and demonstrates nonperturbatively the existence of additional irrelevant operators with complex scaling dimensions leading to discrete scale invariance. The anomalous exponents are shown to depend upon the details of branch interaction; we contrast with the branched growth model BGM in which these exponents are universal to lowest order in 1nu, and show that the BGM includes an inherent branch interaction different from that found in the DBM. We consider stationary and nonstationary regimes, corresponding to different growth geometries in the dielectricbreakdown model.

Electronic Properties of the Effective SingletTriplet Model ; In present work the effective singlettriplet model for CuO2layer on the grounds of multiband pd model of strongly correlated electrons is obtained. The resulting Hamiltonian has a form of generalized singlettriplet tt'J model for ptype superconductors and form of usual tt'J model for ntype superconductors. In the mean field approximation in Xoperator representation we derived equations for Gorkov type Green functions. The symmetry classification of the superconducting order parameter in case of tetragonal lattice resulted in dx2y2 and dxytypes of singlet pairing for both p and ntype superconductors while stype singlet pairing don't take place. Also normal paramagnetic phase of effective singlettriplet model was investigated and dispersion over Brillouin zone, density of states and evolution of Fermi level with doping were obtained.

Thermodynamics of pseudospinelectron model in mean field approximation ; The mean field type approach based on the selfconsistent consideration of an effective field created by electron transfer is developed for a description of thermodynamics of the Hubbard type models with an infinitely large onsite repulsion. This procedure, formulated by Izyumov et al, is an extension of the recently proposed generalized random phase approximationGRPA. Within this approach, the thermodynamic properties of the twosublattice pseudospinelectron model the Hubbard model with local anharmonicity are studied. Such a model can be used for a description of dielectric properties of YBaCuOtype superconductors along caxis; pseudospins represent anharmonic motions of apical oxygens O4. It is shown that there are either phase transitions in the model with jumps of the mean values of a pseudospin and of electron concentration in the muconst regime or the phase separation in the nconst regime. The phase transitions or phase separation are caused by pseudospinpseudospin interaction as well as by electron transfer the latter results in appearing of effective interaction between pseudospins. The possibility of the ferroelectric type ordering of pseudospins is investigated.

An exactly solvable random satisfiability problem ; We introduce a new model for the generation of random satisfiability problems. It is an extension of the hyperSAT model of RicciTersenghi, Weigt and Zecchina, which is a variant of the famous KSAT model it is extended to qstate variables and relates to a different choice of the statistical ensemble. The model has an exactly solvable statistic the critical exponents and scaling functions of the SATUNSAT transition are calculable at zero temperature, with no need of replicas, also with exact finitesize corrections. We also introduce an exact duality of the model, and show an analogy of thermodynamic properties with the Random Energy Model of disordered spin systems theory. Relations with ErrorCorrecting Codes are also discussed.

On the Prospects of Chaos Aware Traffic Modeling ; In this paper the chaotic properties of the TCP congestion avoidance mechanism are investigated. The analysis focuses on the origin of the complex behavior appearing in deterministic TCPIP networks. From the traffic modeling point of view the understanding of the mechanism generating chaos is essential, since present models are unable to cope with this phenomena. Using the basic tools of chaos theory in our study, the main characteristics of chaotic dynamics are revealed. The dynamics of packet loss events is studied by a simple symbolic description. The cellular structure of the phase space of congestion windows is shown. This implies periodic behavior for large time scales. Chaotic behavior in short time scales and periodicity for larger times makes it necessary to develop models that account for both. Thus a simple model that describes the congestion window dynamics according to fluid equations, but handles the packet loss events separately is introduced. This model can reproduce the basic features observed in realistic packet level simulations.

Monte Carlo Studies of ThreeDimensional BondDiluted Ferromagnets ; In this report we give an overview on recent results obtained from extensive Monte Carlo MC computer simulations of the 3D 2state Ising and 4state Potts models with bonddilution. The motivation to study the 4state Potts model derives from the fact that, in the pure case, this model is known to exhibit a fairly strong firstorder transition, such that a disorderinduced softening to a secondorder transition would give clear support of the theoretical expectations. Modeling the disorder by bonddilution enables in the Ising case a test of the expected universality with respect to the type of disorder. Furthermore, for both models this choice facilitates a quantitative comparison with recent hightemperature series expansions for general randombond qstate Potts models.

Ferromagnetism in the Hubbard model A constructive approach ; It is believed that strong ferromagnetic orders in some solids are generated by subtle interplay between quantum manybody effects and spinindependent Coulomb interactions between electrons. Here we describe our rigorous and constructive approach to ferromagnetism in the Hubbard model, which is a standard idealized model for strongly interacting electrons in a solid. We introduce a class of Hubbard models in any dimensions which are nonsingular in the sense that both the Coulomb interaction and the density of states at the Fermi level are finite. We then prove that the ground states of the models exhibit saturated ferromagnetism, i.e., have maximum total spins. Combined with our earlier results, the present work provides nonsingular models of itinerant electrons with only spinindependent interactions where low energy behaviors are proved to be that of a healthy'' ferromagnetic insulator.

First Order Phase Transition in a ReactionDiffusion Model With Open Boundary The YangLee Theory Approach ; A coagulationdecoagulation model is introduced on a chain of length L with open boundary. The model consists of one species of particles which diffuse, coagulate and decoagulate preferentially in the leftward direction. They are also injected and extracted from the left boundary with different rates. We will show that on a specific plane in the space of parameters, the steady state weights can be calculated exactly using a matrix product method. The model exhibits a firstorder phase transition between a lowdensity and a highdensity phase. The density profile of the particles in each phase is obtained both analytically and using the Monte Carlo Simulation. The twopoint densitydensity correlation function in each phase has also been calculated. By applying the YangLee theory we can predict the same phase diagram for the model. This model is further evidence for the applicability of the YangLee theory in the nonequilibrium statistical mechanics context.

Scaling and Commonality in Anomalous Fluctuation Statistics in Models for Turbulence and Ferromagnetism ; Recently, Portelli et al 2003 have seminumerically obtained a functional form of the probability distribution of fluctuations in the total energy flow in a model for fluid turbulence. This follows earlier work suggesting that fluctuations in the total magnetization in the 2D XY model for a ferromagnet also follow this distribution. Here, starting from the scaling ansatz that is the basis of the turbulence model we analytically derive the functional form of this distribution and find its single control parameter that depends upon the scaling exponents and system size of the model. Our analysis allows us to identify this explicitly with that of the XY model, and suggest a possible generalization.

Fluctuationdissipation relations in trap models ; Trap models are intuitively appealing and often solvable models of glassy dynamics. In particular, they have been used to study aging and the resulting outofequilibrium fluctuationdissipation relations between correlations and response functions. In this note I show briefly that one such relation, first given by Bouchaud and Dean, is valid for a general class of meanfield trap models it relies only on the way a perturbation affects the transition rates, but is independent of the distribution of trap depths and the form of the unperturbed transition rates, and holds for all observables that are uncorrelated with the energy. The model with Glauber dynamics and an exponential distribution of trap depths, as considered by Barrat and Mezard, does not fall into this class if the perturbation is introduced in the standard way by shifting all trap energies. I show that a similar relation between response and correlation nevertheless holds for the outofequilibrium dynamics at low temperatures. The results point to intriguing parallels between trap models with energetic and entropic barriers.

Spinlattice models inhomogeneity and diffusion ; In spinlattice models with order parameter conserved, we generalize the idea of spin diffusion incorporating a variety factors as possible driving forces, including the external field and the temperature. The Kawasaki dynamics in the Gaussian model and the onedimensional Ising model are studied. The Gaussian model is rigorously treated and the critical exponent gamma 1 is obtained. The competition of the internal and the external inhomogeneities may lead to interesting and rich dynamic behavior. The diffusion induced by the inhomogeneity of the magnetization itself is believed to vanish near the critical point, meanwhile the nonvanishing diffusion induced by the inhomogeneity of the environment may be coupled to the spin configuration and weakened by thermal noise. Several interesting examples are visualized, and the concept of local hysteresis is proposed in this spinconserved dynamics. A dynamic phase transition is observed in the onedimensional Ising model subject to an electromagnetic wave.

Nontrivial fixed point in a twofold orbitally degenerate Anderson impurity model ; We study the phase diagram of a twofold orbitally degenerate Anderson impurity model which presents a nontrivial fixed point similar to the twoimpurity Kondo model one. Remarkably, this fixed point is more robust than the latter one, since it can only be destabilized by orbital or gauge symmetry breaking. The impurity model is interesting per se, but here our interest is rather in the possibility that it might be representative of the behavior of a stronglycorrelated lattice model close to a Mott transition. We argue that this lattice model should unavoidably encounter the nontrivial fixed point just before the Mott transition and react to its instability by spontaneous generation of an orbital, spinorbital or superconducting order parameter.

Stripes and the Cu13BEC model ; The Cu13BEC model of hightemperature superconductivity was previously shown to account for many of the principal thermodynamic and electronic properties of the superconducting cuprates. Here I show that this model is also able to account for many of the key characteristics of the coupled CDW and SDW orders in these compounds. These include the general coexistence of metallic parallel stripes with superconductivity, the wellknown linear relationship between the incommensurability of the SDWinduced IC magnetic peaks and the dopant concentration, as well as the saturation of this incommensurabilty at a value of about 18 for doping greater than 18. The model also provides a natural explanation for the celebrated 18anomaly in LSCO and LBCO. It is also able to account for the severe suppression of the superconductivity in LNSCO at all doping levels and for the variations in the properties of LBSCO, at a fixed hole doping of 18, as its crystal structure is changed. Furthermore, the Cu13BEC model is also consistent with many of the characteristics of the SDW orders in Y123. Most importantly, scanning tunneling microscopy results on Bi2212 appear to provide a direct validation of the CDW order predicted by the model.

Modeling DNA Structure, Elasticity and Deformations at the Basepair Level ; We present a generic model for DNA at the basepair level. We use a variant of the GayBerne potential to represent the stacking energy between neighboring basepairs. The sugarphosphate backbones are taken into account by semirigid harmonic springs with a nonzero spring length. The competition of these two interactions and the introduction of a simple geometrical constraint leads to a stacked righthanded BDNAlike conformation. The mapping of the presented model to the MarkoSiggia and the StackofPlates model enables us to optimize the free model parameters so as to reproduce the experimentally known observables such as persistence lengths, mean and mean squared basepair step parameters. For the optimized model parameters we measured the critical force where the transition from B to SDNA occurs to be approximately 140pN. We observe an overstretched SDNA conformation with highly inclined bases that partially preserves the stacking of successive basepairs.

The qcomponent static model modeling social networks ; We generalize the static model by assigning a qcomponent weight on each vertex. We first choose a component mu among the q components at random and a pair of vertices is linked with a color mu according to their weights of the component mu as in the static model. A 1f fraction of the entire edges is connected following this way. The remaining fraction f is added with q1th color as in the static model but using the maximum weights among the q components each individual has. This model is motivated by social networks. It exhibits similar topological features to real social networks in that i the degree distribution has a highly skewed form, ii the diameter is as small as and iii the assortativity coefficient r is as positive and large as those in real social networks with r reaching a maximum around f approx 0.2.

Geometrical vs. FortuinKasteleyn Clusters in the TwoDimensional qState Potts Model ; The tricritical behavior of the twodimensional qstate Potts model with vacancies for 1leq q leq4 is argued to be encoded in the fractal structure of the geometrical spin clusters of the pure model. The close connection between the critical properties of the pure model and the tricritical properties of the diluted model is shown to be reflected in an intimate relation between FortuinKasteleyn and geometrical clusters The same transformation mapping the two critical regimes onto each other also maps the two cluster types onto each other. The map conserves the central charge, so that both cluster types are in the same universality class. The geometrical picture is supported by a Monte Carlo simulation of the hightemperature representation of the Ising model q2. In this new numerical approach, closed graph configurations are generated by means of a Metropolis update algorithm, involving single plaquettes.

An extended Hubbard model with ring exchange a route to a nonAbelian topological phase ; We propose an extended Hubbard model on a 2D Kagome lattice with an additional ringexchange term. The particles can be either bosons or spinless fermions . At a special filling fraction of 16 the model is analyzed in the lowest nonvanishing order of perturbation theory. Such undoped'' model is closely related to the Quantum Dimer Model. We show how to arrive at an exactly soluble point whose ground state manifold is the extensively degenerate disotopy space'', a necessary precondition for for a certain type of nonAbelian topological order. Near the special'' values, d 2 cos pik2, this space is expected to collapse to a stable topological phase with anyonic excitations closely related to SU2 ChernSimons theory at level k.

Effects of the Screening Breakdown in the DiffusionLimited Aggregation Model ; Several models based on the diffusionlimited aggregation DLA model were proposed and their scaling properties explored by computational and theoretical approaches. In this paper, we consider a new extension of the onlattice DLA model in which the unitary random steps are replaced by random flights of fixed length. This procedure reduces the screening for particle penetration present in the original DLA model and, consequently, generates new pattern classes. The patterns have DLAlike scaling properties at small length of the random flights. However, as the flight size increases, the patterns are initially round and compact but become fractal for sufficiently large clusters. Their radius of gyration and number of particles at the cluster surface scale asymptotically as in the original DLA model. The transition between compact and fractal patterns is characterized by wavelength selection, and 1k noise was observed far from the transition.

Rate equation approach for correlations in growing network models ; We propose a rate equation approach to compute two vertex correlations in scalefree growing network models based in the preferential attachment mechanism. The formalism, based on previous work of Szab'o textitet al. Phys. Rev. E textbf67 056102 2002 for the clustering spectrum, measuring three vertex correlations, is based on a rate equation in the continuous degree and time approximation for the average degree of the nearest neighbors of vertices of degree k, with an appropriate boundary condition. We study the properties of both two and three vertex correlations for linear preferential attachment models, and also for a model yielding a large clustering coefficient. The expressions obtained are checked by means of extensive numerical simulations. The rate equation proposed can be generalized to more sophisticated growing network models, and also extended to deal with related correlation measures. As an example, we consider the case of a recently proposed model of weighted networks, for which we are able to compute a weighted two vertex correlation function, taking into account the strength of the interactions between connected vertices.

The Spot Model for randompacking dynamics ; The diffusion and flow of amorphous materials, such as glasses and granular materials, has resisted a simple microscopic description, analogous to defect theories for crystals. Early models were based on either gaslike inelastic collisions or crystallike vacancy diffusion, but here we propose a cooperative mechanism for dense randompacking dynamics, based on diffusing spots'' of interstitial free volume. Simulations with the Spot Model can efficiently generate realistic flowing packings, and yet the model is simple enough for mathematical analysis. Starting from a nonlocal stochastic differential equation, we derive continuum equations for tracer diffusion, given the dynamics of free volume spots. Throughout the paper, we apply the model to granular drainage in a silo, and we also briefly discuss glassy relaxation. We conclude by discussing the prospects of spotbased multiscale modeling and simulation of amorphous materials.

Quantum phase transitions in the FermiBose Hubbard model ; We propose a multiband FermiBose Hubbard model with onsite fermionboson conversion and general filling factor in three dimensions. Such a Hamiltonian models an atomic Fermi gas trapped in a lattice potential and subject to a Feshbach resonance. We solve this model in the two state approximation for paired fermions at zero temperature. The problem then maps onto a coupled Heisenberg spin model. In the limit of large positive and negative detuning, the quantum phase transitions in the Bose Hubbard and PairedFermi Hubbard models are correctly reproduced. Near resonance, the Mott states are given by a superposition of the pairedfermion and boson fields and the Mottsuperfluid borders go through an avoided crossing in the phase diagram.

Evolving Model of Weighted Networks Inspired by Scientific Collaboration Networks ; Inspired by scientific collaboration networks, especially our empirical analysis of the network of econophysicists, an evolutionary model for weighted networks is proposed. Both degreedriven and weightdriven models are considered. Compared with the BA model and other evolving models with preferential attachment, there are two significant generalizations. First, besides the new vertex added in at every time step, old vertices can also attempt to build up new links, or to reconnect the existing links. The reconnection between both newold and oldold nodes are recorded and the connecting times on every link is converted into the weight of the link. This provides a natural way for the evolution of edge weight. Second, besides degree and the weight of vertices, a pathrelated local information is also used as a reference in the preferential attachment. The pathrelated preferential attachment mechanism significantly increases the clustering coefficient of the network. The model shows the scalefree phenomena in degree and weight distribution. It also gives well qualitatively consistent behavior with the empirical results.

Condensation and Lasing of Microcavity Polaritons Comparison between two Models ; Condensation of microcavity polaritons and the substantial influence of pairbreaking disorder and decoherence leading to a laser regime has been recently considered using two different models a model for direct two band excitons in a disordered quantum well coupled to light and a model where the cavity mode couples instead to a medium of localised excitons, represented by twolevel oscillators in the presence of dephasing processes. Even if complementary from the point of view of assumptions, the models share most of the main conclusions and show similar phase diagrams. The issue whether excitons are propagating or localised seems secondary for the polariton condensation and the way in which pairbreaking disorder and decoherence processes influence the condensation and drive the microcavity into a lasing regime is, within the approximations used in each model, generic. The reasons for the similarities between the two physical situations are analysed and explained.

Thermodynamic anomalies in a lattice model of water Solvation properties ; We investigate a latticefluid model of water, defined on a 3dimensional bodycentered cubic lattice. Model molecules possess a tetrahedral symmetry, with four equivalent bonding arms. The model is similar to the one proposed by Roberts and Debenedetti J. Chem. Phys. 105, 658 1996, simplified by removing distinction between donors and acceptors. We focus on solvation properties, mainly as far as an ideally inert hydrophobic solute is concerned. As in our previous analysis, devoted to neat water J. Chem. Phys. 121, 11856 2004, we make use of a generalized first order approximation on a tetrahedral cluster. We show that the model exhibits quite a coherent picture of water thermodynamics, reproducing qualitatively several anomalous properties observed both in pure water and in solutions of hydrophobic solutes. As far as supercooled liquid water is concerned, the model is consistent with the second critical point scenario.

Critical behavior in a nonlocal interface model ; The Raise and Peel model is a recently proposed onedimensional statistical model describing a fluctuating interface. The evolution of the model follows from the competition between adsorption and desorption processes. The model is nonlocal due to the possible occurrence of avalanches. At a special ratio of the adsorptiondesorption rates the model is integrable and many rigorous results are known. Off the critical point, the phase diagram and scaling properties are not known. In this paper, we search for indications of phase transition studying the gap in the spectrum of the nonhermitian generator of the stochastic interface evolution. We present results for the gap obtained from exact diagonalization and from Monte Carlo estimates derived from temporal correlations of various observables.

From exotic phases to microscopic Hamiltonians ; We report recent analytical progress in the quest for spin models realising exotic phases. We focus on the question of reverseengineering' a local, SU2 invariant S12 Hamiltonian to exhibit phases predicted on the basis of effective models, such as largeN or quantum dimer models. This aim is to provide a pointofprinciple demonstration of the possibility of constructing such microscopic lattice Hamiltonians, as well as to complement and guide numerical and experimental approaches to the same question. In particular, we demonstrate how to utilise peturbed Klein Hamiltonians to generate effective quantum dimer models. These models use local multispin interactions and, to obtain a controlled theory, a decoration procedure involving the insertion of MajumdarGhosh chainlets on the bonds of the lattice. The phases we thus realise include deconfined resonating valence bond liquids, a devil's staircase of interleaved phases which exhibits Cantor deconfinement, as well as a threedimensional U1 liquid phase exhibiting photonic excitations.

Collective Effects in Models for Interacting Molecular Motors and MotorMicrotubule Mixtures ; Three problems in the statistical mechanics of models for an assembly of molecular motors interacting with cytoskeletal filaments are reviewed. First, a description of the hydrodynamical behaviour of densitydensity correlations in fluctuating ratchet models for interacting molecular motors is outlined. Numerical evidence indicates that the scaling properties of dynamical behavior in such models belong to the KPZ universality class. Second, the generalization of such models to include boundary injection and removal of motors is provided. In common with known results for the asymmetric exclusion processes, simulations indicate that such models exhibit sharp boundary driven phase transitions in the thermodynamic limit. In the third part of this paper, recent progress towards a continuum description of pattern formation in mixtures of motors and microtubules is described, and a nonequilibrium phasediagram'' for such systems discussed.

Dynamics of active membranes with internal noise ; We study the timedependent height fluctuations of an active membrane containing energydissipating pumps that drive the membrane out of equilibrium. Unlike previous investigations based on models that neglect either curvature couplings or random fluctuations in pump activities, our formulation explores two new models that take both of these effects into account. In the first model, the magnitude of the nonequilibrium forces generated by the pumps is allowed to fluctuate temporally. In the second model, the pumps are allowed to switch between on and off states. We compute the mean squared displacement of a membrane point for both models, and show that they exhibit distinct dynamical behaviors from previous models, and in particular, a superdiffusive regime specifically arising from the shot noise.

Exact Solutions for Network Rewiring Models ; Evolving networks with a constant number of edges may be modelled using a rewiring process. These models are used to describe many realworld processes including the evolution of cultural artifacts such as family names, the evolution of gene variations, and the popularity of strategies in simple econophysics models such as the minority game. The model is closely related to Urn models used for glasses, quantum gravity and wealth distributions. The full mean field equation for the degree distribution is found and its exact solution and generating solution are given.

Fluctuationdissipation relations in plaquette spin systems with multistage relaxation ; We study aging dynamics in two nondisordered spin models with multispin interactions, following a sudden quench to low temperature. The models are relevant to the physics of supercooled liquids. Their low temperature dynamics resemble those of kinetically constrained models, and obey dynamical scaling, controlled by zerotemperature critical points. Dynamics in both models are thermally activated, resulting in multistage relaxation towards equilibrium. We study several twotime correlation and response functions. We find that equilibrium fluctuationdissipation relations are generically not satisfied during the aging regime, but deviations from them are well described by fluctuationdissipation ratios, as found numerically in supercooled liquids. These ratios are purely dynamic objects, containing information about the nature of relaxation in the models. They are nonuniversal, and can even be negative as a result of activated dynamics. Thus, effective temperatures are not welldefined in these models.

Mean Escape Time in a System with Stochastic Volatility ; We study the mean escape time in a market model with stochastic volatility. The process followed by the volatility is the Cox Ingersoll and Ross process which is widely used to model stock price fluctuations. The market model can be considered as a generalization of the Heston model, where the geometric Brownian motion is replaced by a random walk in the presence of a cubic nonlinearity. We investigate the statistical properties of the escape time of the returns, from a given interval, as a function of the three parameters of the model. We find that the noise can have a stabilizing effect on the system, as long as the global noise is not too high with respect to the effective potential barrier experienced by a fictitious Brownian particle. We compare the probability density function of the return escape times of the model with those obtained from real market data. We find that they fit very well.

Dynamic firstorder phase transition in kinetically constrained models of glasses ; We show that the dynamics of kinetically constrained models of glass formers takes place at a firstorder coexistence line between active and inactive dynamical phases. We prove this by computing the largedeviation functions of suitable spacetime observables, such as the number of configuration changes in a trajectory. We present analytic results for dynamic facilitated models in a meanfield approximation, and numerical results for the FredricksonAndersen model, the East model, and constrained lattice gases, in various dimensions. This dynamical firstorder transition is generic in kinetically constrained models, and we expect it to be present in systems with fully jammed states.

Scattering approach to impurity thermodynamics ; Recently the authors developed a scattering approach that allows for a complete description of the steadystate physics of quantumimpurities in and out of equilibrium. Quantum impurities are described using scattering eigenstates defined ab initio on the open, infinite line with asymptotic boundary conditions imposed by the leads. The scattering states on the open line are constructed for integrable quantumimpurity models by means of a significant generalization of the BetheAnsatz which we call the Scattering BetheAnsatz SBA. The purpose of the paper is to present in detail the scattering approach to quantumimpurity models and the SBA and show that they reproduce wellknown thermodynamic results for several widely studied models the Resonance Level model, Interacting Resonance Level model and the Kondo model. Though the SBA is more complex than the traditional Thermodynamic Bethe Ansatz TBA when applied to thermodynamical questions, the scattering approach SBA allows access to an array of new questions that cannot be addressed otherwise, ranging from scattering of electrons off magnetic impurities to nonequilibrium dynamics.

Push vs. Pull in WebBased Network Management ; In this paper, we show how Web technologies can be used effectively to i address some of the deficiencies of traditional IP network management platforms, and ii render these expensive platforms redundant. We build on the concept of embedded management application, proposed by Wellens and Auerbach, and present two models of network management application designs that rely on Web technologies. First, the pull model is based on the requestresponse paradigm. It is typically used to perform data polling. Several commercial management platforms already use Web technologies that rely on this model to provide for ad hoc management; we demonstrate how to extend this to regular management. Second, the push model is a novel approach which relies on the publishsubscribedistribute paradigm. It is better suited to regular management than the pull model, and allows administrators to conserve network bandwidth as well as CPU time on the management station. It can be seen as a generalization of the paradigm commonly used for notification delivery. Finally, we introduce the concept of the collapsed network management platform, where these two models coexist.

A Family of Simplified Geometric Distortion Models for Camera Calibration ; The commonly used radial distortion model for camera calibration is in fact an assumption or a restriction. In practice, camera distortion could happen in a general geometrical manner that is not limited to the radial sense. This paper proposes a simplified geometrical distortion modeling method by using two different radial distortion functions in the two image axes. A family of simplified geometric distortion models is proposed, which are either simple polynomials or the rational functions of polynomials. Analytical geometric undistortion is possible using two of the distortion functions discussed in this paper and their performance can be improved by applying a piecewise fitting idea. Our experimental results show that the geometrical distortion models always perform better than their radial distortion counterparts. Furthermore, the proposed geometric modeling method is more appropriate for cameras whose distortion is not perfectly radially symmetric around the center of distortion.

Dynamic Modelling and Adaptive Traction Control for Mobile Robots ; Mobile robots have received a great deal of research in recent years. A significant amount of research has been published in many aspects related to mobile robots. Most of the research is devoted to design and develop some control techniques for robot motion and path planning. A large number of researchers have used kinematic models to develop motion control strategy for mobile robots. Their argument and assumption that these models are valid if the robot has low speed, low acceleration and light load. However, dynamic modelling of mobile robots is very important as they are designed to travel at higher speed and perform heavy duty work. This paper presents and discusses a new approach to develop a dynamic model and control strategy for wheeled mobile robot which I modelled as a rigid body that roles on two wheels and a castor. The motion control strategy consists of two levels. The first level is dealing with the dynamic of the system and denoted as Low level controller. The second level is developed to take care of path planning and trajectory generation.

Removing Propagation Redundant Constraints in Redundant Modeling ; A widely adopted approach to solving constraint satisfaction problems combines systematic tree search with various degrees of constraint propagation for pruning the search space. One common technique to improve the execution efficiency is to add redundant constraints, which are constraints logically implied by others in the problem model. However, some redundant constraints are propagation redundant and hence do not contribute additional propagation information to the constraint solver. Redundant constraints arise naturally in the process of redundant modeling where two models of the same problem are connected and combined through channeling constraints. In this paper, we give general theorems for proving propagation redundancy of one constraint with respect to channeling constraints and constraints in the other model. We illustrate, on problems from CSPlib httpwww.csplib.org, how detecting and removing propagation redundant constraints in redundant modeling can significantly speed up constraint solving.

Model Checking Probabilistic Pushdown Automata ; We consider the model checking problem for probabilistic pushdown automata pPDA and properties expressible in various probabilistic logics. We start with properties that can be formulated as instances of a generalized random walk problem. We prove that both qualitative and quantitative model checking for this class of properties and pPDA is decidable. Then we show that model checking for the qualitative fragment of the logic PCTL and pPDA is also decidable. Moreover, we develop an errortolerant model checking algorithm for PCTL and the subclass of stateless pPDA. Finally, we consider the class of omegaregular properties and show that both qualitative and quantitative model checking for pPDA is decidable.

A Formal ArchitectureCentric ModelDriven Approach for the Automatic Generation of Grid Applications ; This paper discusses the concept of modeldriven software engineering applied to the Grid application domain. As an extension to this concept, the approach described here, attempts to combine both formal architecturecentric and modeldriven paradigms. It is a commonly recognized statement that Grid systems have seldom been designed using formal techniques although from past experience such techniques have shown advantages. This paper advocates a formal engineering approach to Grid system developments in an effort to contribute to the rigorous development of Grids software architectures. This approach addresses quality of service and crossplatform developments by applying the modeldriven paradigm to a formal architecturecentric engineering method. This combination benefits from a formal semantic description power in addition to modelbased transformations. The result of such a novel combined concept promotes the reuse of design models and facilitates developments in Grid computing.

The computational power of population protocols ; We consider the model of population protocols introduced by Angluin et al., in which anonymous finitestate agents stably compute a predicate of the multiset of their inputs via twoway interactions in the allpairs family of communication networks. We prove that all predicates stably computable in this model and certain generalizations of it are semilinear, answering a central open question about the power of the model. Removing the assumption of twoway interaction, we also consider several variants of the model in which agents communicate by anonymous messagepassing where the recipient of each message is chosen by an adversary and the sender is not identified to the recipient. These oneway models are distinguished by whether messages are delivered immediately or after a delay, whether a sender can record that it has sent a message, and whether a recipient can queue incoming messages, refusing to accept new messages until it has had a chance to send out messages of its own. We characterize the classes of predicates stably computable in each of these oneway models using natural subclasses of the semilinear predicates.

Hamiltonian Formulation of Bianchi Cosmological Models in Quadratic Theories of Gravity ; We use Boulware's Hamiltonian formalism of quadratic gravity theories in order to analyze the classical behaviour of Bianchi cosmological models for a Lagrangian density containing quadratic terms in the curvature. For this purpose we define a canonical transformation which leads to a clear distinction between two main variants of the quadratic theory, namely the Rsquared or conformal Lagrangian densities. In this paper we restrict the study to the first variant. For Bianchi type I and IX models we give the explicit forms of the superHamiltonian constraint, of the ADM Hamiltonian density and of the corresponding canonical equations. In the case of a pure Rsquared theory we solve these equations analytically for Bianchi I model. For Bianchi type IX model, we reduce the firstorder equations of the Hamiltonian system to three coupled secondorder equations for the true physical degrees of freedom. This discussion is extended to isotropic FLRW models.

On compatibility of the KaluzaKlein approach with the COBE experiment ; Contributions of primordial gravitational waves to the largeangularscale anisotropies of the cosmic microwave background radiation in multidimensional cosmological models KaluzaKlein models are studied. We derive limits on free parameters of the models using results of the COBE experiment and other astrophysical data. It is shown that in principle there is a room for KaluzaKlein models as possible candidates for the description of the Early Universe. However, the obtained limits are very restrictive. Assuming that the anisotropies are mostly due to gravitational waves, none of the concrete models, analyzed in the article, satisfy them. On the other hand, if the contribution of gravitational waves is very small then a string inspired model is not ruled out.

Galactic periodicity and the oscillating G model ; We consider the model involving the oscillation of the effective gravitational constant that has been put forward in an attempt to reconcile the observed periodicity in the galaxy number distribution with the standard cosmological models. This model involves a highly nonlinear dynamics which we analyze numerically. We carry out a detailed study of the bound that nucleosynthesis imposes on this model. The analysis shows that for any assumed value for Omega the total energy density one can fix the value of Omegarm bar the baryonic energy density in such a way as to accommodate the observational constraints coming from the 4rm He primordial abundance. In particular, if we impose the inflationary value Omega1 the resulting baryonic energy density turns out to be Omegarm barsim 0.021. This result lies in the very narrow range 0.016 leq Omegarm bar leq 0.026 allowed by the observed values of the primordial abundances of the other light elements. The remaining fraction of Omega corresponds to dark matter represented by a scalar field.

Gravitation Theory with Propagating Torsion ; We present a review of some recent models of gravitation theory with propagating torsion based on the use of a torsiondilaton field and propose one more model of this type which promises to be more realistic. A proper universal selfconsistent minimal action principle yields the properties of this model and predicts the interactions of torsiondilaton field with the real matter. The new model may be compatible with the string models with dilaton field and gives a novel interpretation of the dilaton as a part of the spacetime torsion. A relation with some recent models of dilatonic gravity is also possible.

Spin Foam Perturbation Theory ; We study perturbation theory for spin foam models on triangulated manifolds. Starting with any model of this sort, we consider an arbitrary perturbation of the vertex amplitudes, and write the evolution operators of the perturbed model as convergent power series in the coupling constant governing the perturbation. The terms in the power series can be efficiently computed when the unperturbed model is a topological quantum field theory. Moreover, in this case we can explicitly sum the whole power series in the limit where the number of topdimensional simplices goes to infinity while the coupling constant is suitably renormalized. This dilute gas limit' gives spin foam models that are triangulationindependent but not topological quantum field theories. However, we show that models of this sort are rather trivial except in dimension 2.

Closed cosmologies with a perfect fluid and a scalar field ; Closed, spatially homogeneous cosmological models with a perfect fluid and a scalar field with exponential potential are investigated, using dynamical systems methods. First, we consider the closed FriedmannRobertsonWalker models, discussing the global dynamics in detail. Next, we investigate KantowskiSachs models, for which the future and past attractors are determined. The global asymptotic behaviour of both the FriedmannRobertsonWalker and the KantowskiSachs models is that they either expand from an initial singularity, reach a maximum expansion and thereafter recollapse to a final singularity for all values of the potential parameter kappa, or else they expand forever towards a flat powerlaw inflationary solution when kappa22. As an illustration of the intermediate dynamical behaviour of the KantowskiSachs models, we examine the cases of no barotropic fluid, and of a massless scalar field in detail. We also briefly discuss Bianchi type IX models.

On the rmode spectrum of relativistic stars Inclusion of the radiation reaction ; We consider both mode calculations and time evolutions of axial rmodes for relativistic uniformly rotating nonbarotropic neutron stars, using the slowrotation formalism, in which rotational corrections are considered up to linear order in the angular velocity Omega. We study various stellar models, such as uniform density models, polytropic models with different polytropic indices n, and some models based on realistic equations of state. For weakly relativistic uniform density models, and polytropes with small values of n, we can recover the growth times predicted from Newtonian theory when standard multipole formulae for the gravitational radiation are used. However, for more compact models, we find that relativistic linear perturbation theory predicts a weakening of the instability compared to the Newtonian results. When turning to polytropic equations of state, we find that for certain ranges of the polytropic index n, the rmode disappears, and instead of a growth, the time evolutions show a rapid decay of the amplitude. This is clearly at variance with the Newtonian predictions. It is, however, fully consistent with our previous results obtained in the lowfrequency approximation.

A spin foam model for pure gauge theory coupled to quantum gravity ; We propose a spin foam model for pure gauge fields coupled to Riemannian quantum gravity in four dimensions. The model is formulated for the triangulation of a fourmanifold which is given merely combinatorially. The Riemannian BarrettCrane model provides the gravity sector of our model and dynamically assigns geometric data to the given combinatorial triangulation. The gauge theory sector is a lattice gauge theory living on the same triangulation and obtains from the gravity sector the geometric information which is required to calculate the YangMills action. The model is designed so that one obtains a continuum approximation of the gauge theory sector at an effective level, similarly to the continuum limit of lattice gauge theory, when the typical length scale of gravity is much smaller than the YangMills scale.

Irreversible Processes in a Universe modelled as a mixture of a Chaplygin gas and radiation ; The evolution of a Universe modelled as a mixture of a Chaplygin gas and radiation is determined by taking into account irreversible processes. This mixture could interpolate periods of a radiation dominated, a matter dominated and a cosmological constant dominated Universe. The results of a Universe modelled by this mixture are compared with the results of a mixture whose constituents are radiation and quintessence. Among other results it is shown that a for both models there exists a period of a past deceleration with a present acceleration; b the slope of the acceleration of the Universe modelled as a mixture of a Chaplygin gas with radiation is more pronounced than that modelled as a mixture of quintessence and radiation; c the energy density of the Chaplygin gas tends to a constant value at earlier times than the energy density of quintessence does; d the energy density of radiation for both mixtures coincide and decay more rapidly than the energy densities of the Chaplygin gas and of quintessence.

SO1,1 dark energy model and the universe transition ; We suggest a scalar model of dark energy with the SO1,1 symmetry. The model may be reformulated in terms of a real scalar field Phi and the scale factor a so that the Lagrangian may be decomposed as that of the real quintessence model plus the negative coupling energy term of Phi to a. The existence of the coupling term Lc leads to a wider range of wPhi and overcomes the problem of negative kinetic energy in the phantom universe model. We propose a powerlaw expansion model of univese with timedependent power, which can describe the phantom universe and the universe transition from ordinary acceleration to super acceleration.

Phenomenology of braneworld cosmological models ; We present a brief review of braneworld models models in which our observable Universe with its standard matter fields is assumed as localized on a domain wall threebrane in a higher dimensional surrounding bulk spacetime. Models of this type arise naturally in Mtheory and have been intensively studied during the last years. We pay particular attention to the covariant projection approach, the Cardassian scenario, to induced gravity models, selftuning models and the Ekpyrotic scenario. A brief discussion is given of their basic properties and their connection with conventional FRW cosmology.

On the equation of state of a flat FRW model filled with a bulk viscous fluid ; In this paper, we study the equation of state admissible for a flat FRW models filled with a bulk viscous fluid by using the Lie group method. It is founded that the model admits scaling symmetries iff the bulk viscous parameter gamma 12. In this case, it is found that the main quantities follow a power law solution and in particular the bulk viscous pressure Pi has the same order of magnitude as the energy density rho , in such a way that it is possible to formulate the equation of state Pi varkappa rho , where varkappa in mathbbR i.e. is a negative numerical constant. If we assume such relationship we find again that the model is scale invariant iff gamma 12. We conclude that the model accepts a scaling symmetry iff gamma 12 and that for this value of the viscous parameter, Pi varkappa rho , but the hypothesis Pi varkappa rho does not imply gamma 12, and that the model is scale invariant.

Statefinder diagnosis in a nonflat universe and the holographic model of dark energy ; In this paper, we study the holographic dark energy model in nonflat universe from the statefinder viewpoint. We plot the evolutionary trajectories of the holographic dark energy model for different values of the parameter c as well as for different contributions of spatial curvature, in the statefinder parameterplanes. The statefinder diagrams characterize the properties of the holographic dark energy and show the discrimination between this scenario and other dark energy models. As we show, the contributions of the spatial curvature in the model can be diagnosed out explicitly by the statefinder diagrams. Furthermore, we also investigate the holographic dark energy model in the ww' plane, which can provide us with a useful dynamical diagnosis complement to the statefinder geometrical diagnosis.

Loop quantum cosmology and the k 1 RW model ; The loop quantization of the negatively curved k1 RW model poses several technical challenges. We show that the issues can be overcome and a successful quantization is possible that extends the results of the k0,1 models in a natural fashion. We discuss the resulting dynamics and show that for a universe consisting of a massless scalar field, a bounce is predicted in the backward evolution in accordance with the results of the k0,1 models. We also show that the model predicts a vacuum repulsion in the high curvature regime that would lead to a bounce even for matter with vanishing energy density. We finally comment on the inverse volume modifications of loop quantum cosmology and show that, as in the k0 model, the modifications depend sensitively on the introduction of a length scale which a priori is independent of the curvature scale or a matter energy scale.

Psi2S pi pi Jpsi Decay Distributions ; Using a sample of 3.8 M psi2S events accumulated with the BES detector, the process psi2S pi pi Jpsi is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some Dwave, as well as Swave. On the other hand, the Jpsipi pi relative angular momentum is consistent with being pure Swave. The decay distributions have been fit to heavy quarkonium models, including the NovikovShifman model. This model, which is written in terms of the parameter kappa, predicts that Dwave should be present. We determine kappa 0.183 0.002 0.003 based on the joint dipion mass cos theta distribution. The fraction of Dwave as a function of the dipion mass is found to decrease with increasing dipion mass, in agreement with the model. We have also fit the MannelYan model, another model that allows Dwave.

Study of the Asymptotic Freedom of 2D Yukawa Models on the Lattice ; We investigate on the lattice the Yukawa models in 2 dimensions with Z2 and U1 symmetries. These models reduce to the usual and chiral GrossNeveu models, respectively, when the kinetic and the selfcoupling terms of the scalar field are turned off. The numerical data and mean field arguments suggest that, at least for some range of the scalar field hopping parameter, fermion mass is dynamically generated for arbitrarily weak Yukawa coupling. The models are asymptotically free in this coupling, like the GrossNeveu models, even when the scalar quartic selfcoupling is strong.

QCD Sum Rules on the Lattice ; We study the work of Leinweber by applying the Continuum Model of QCD Sum Rules QCDSR to the analysis of quenched lattice correlation functions. We expand upon his work in several areas and find that, while the QCDSR Continuum Model very adequately fits lattice data, it does so only for nonphysical values of its parameters. The nonrelativistic model is found to predict essentially the same form for the correlation functions as the QCDSR Continuum Model but without the latter's restrictions. By fitting lattice data to a general form which includes the nonrelativistic quark model as a special case, we confirm it as the model of choice.

When Are Radiative Corrections Important in the Minimal Supersymmetric Model ; Precision electroweak measurements at LEP currently check the validity of the Standard Model to about one part in a thousand. Any successful model of physics beyond the Standard Model must be consistent with these observations. The impact of radiative corrections on the Minimal Supersymmetric Model MSSM is considered. The influence of supersymmetric particles on precision electroweak measurements is generally negligible since radiative corrections mediated by supersymmetric particles are suppressed by a factor of order mZ2Mrm SUSY2 where Mrm SUSY is the scale characterizing the scale of supersymmetric particle masses. However, there are a few pertinent exceptions. For example, the radiative corrections to the rare decay bto sgamma from charged Higgs and supersymmetric particle exchange can be of the same order as the Standard Model contribution. Large radiative corrections also lead to modifications of MSSM treelevel natural relations. The largest corrections of this type occur in the MSSM Higgs sector and are enhanced by powers of the top quark mass. The consequences of the radiatively corrected MSSM Higgs sector are briefly discussed.

Realistic Superstring Models ; I discuss the construction of realistic superstring standardlike models in the four dimensional free fermionic formulation. I discuss the massless spectrum of the superstring standardlike models and the texture of fermion mass matrices. These models suggest an explanation for the top quark mass hierarchy. At the cubic level of the superpotential only the top quark get a mass term. The lighter quarks and leptons obtain their mass terms from nonrenormalizable terms that are suppressed relative to the cubic order term. A numerical estimate yielded mtsim175180GeV. The suppression of the lightest generation masses results from the horizontal symmetries in the superstring models. The problems of neutrino masses, gauge coupling unification and hierarchical SUSY breaking are discussed. I argue that the realistic features of these models are due to the underlying Z2times Z2 orbifold, with standard embedding, at the free fermionic point in toroidal compactification space.

SU3 StringFlip Potential Models and Nuclear Matter ; For over 50 years attempts have been made to explain the properties of nuclear matter in terms of constituent nucleons with very little success. Here we will investigate one class of many possible models, stringflip potential models, in which fluxtubes are connected between quarks in a gasplasma to give a minimal overall field configuration. A general overview of the current status of these models, along with some of our recently finished work, shall be given. It shall be shown that these models seem promising in that they do get most of the bulk properties of nuclear matter correct with the exception of nuclear binding. Finally we will conclude with a brief discussion on ways to improve the stringflip potential models in an attempt to obtain nuclear binding currently we are investigating short range onegluon exchange effects some preliminary results shall be mentioned.

CP Violation and the Baryonic Asymmetry of the Universe ; The physics of electroweak baryogenesis is described with the aim of making the essentials clear to nonexperts. Several models for the source of the necessary CP violation are discussed CKM phases as in the minimal standard model, general two higgs doublet models, the supersymmetric standard model, Z condensates, and the singlet majoron model. In a more technical section, a strategy is introduced for consistently treating quark dynamics in the neighborhood of the bubble wall, where both local and nonlocal interactions are important. This provides a method for deciding whether gluonic corrections wash out the elecroweak contribution to the baryonic asymmetry in the minimal standard model.

A Dynamical LeftRight Symmetry Breaking Model ; Leftright symmetry breaking in a model with composite Higgs scalars is discussed. It is assumed that the lowenergy degrees of freedom are just fermions and gauge bosons and that the Higgs bosons are generated dynamically through a set of gauge and parityinvariant 4fermion operators. It is shown that in a model with composite bidoublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the righthanded scale the tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale muR propagates down and eventually causes the EW symmetry breaking at the scale muEWsim 100 GeV. The model exhibits a number of low and intermediate mass Higgs bosons with certain relations between their masses. In particular, the SU2L Higgs doublet chiL is a pseudoGoldstone boson of the accidental approximate SU4 symmetry of the Higgs potential and therefore is expected to be relatively light.

A Supersymmetric SO10 Model with Inflation and Cosmic Strings ; We have built a supersymmetric SO10 model consistent with cosmological observations. The model gives rise to a false vacuum hybrid inflationary scenario which solves the monopole problem. We argue that this type of inflationary scenario is generic in supersymmetric SO10 model, and arises naturally from the theory. Neither any external field nor any external symmetry has to be added. It can just be a consequence of the theory. In our specific model, at the end of inflation, cosmic strings form. The properties of the strings are presented. The cosmic background radiation anisotropies induced by the inflationary perturbations and the cosmic strings are estimated. The model produces a stable lightest superparticle and a very light lefthanded neutrino which may serve as the cold and hot dark matter. The properties of a mixed cosmic stringinflationary large scale structure formation scenario are discussed.

Heavy Quark Solitons in the NambuJonaLasinio Model ; The NambuJonaLasinio model NJL is extended to incorporate heavy quark spinsymmetry. In this model baryons containing one heavy quark are analyzed as boundstates of light baryons, represented as chiral solitons, and mesons containing one heavy quark. From related studies in Skyrme type models, the groundstate heavy baryon is known to arise for the heavy meson in a Pwave configuration. In the limit of an infinitely large quark mass the heavy meson wavefunction is sharply peaked at the center of the chiral soliton. Therefore the bound state equation reduces to an eigenvalue problem for the coefficients of the operators contained in the most general Pwave it ansatz for the heavy meson. Within the NJL model a novel feature arises from the coupling of the heavy meson to the various light quark states. In this respect conceptual differences to Skyrme model calculations are discovered The strongest bound state is given by a heavy meson configuration which is completely decoupled from the grand spin zero channel of the light quarks.

Electroweak Baryogenesis in a Supersymmetric Model ; In the electroweak phase transition there arises the problem of baryon number washout by sphaleron transitions, which can be avoided if the phase transition is strongly enough first order. The phase transition in the Standard Model or in the Minimal Supersymmetric Standard Model seems to be too weak to suppress the sphaleron transitions sufficiently. We report here on an investigation of the Next to Minimal Supersymmetric Standard Model, NMSSM, which contains a Higgs singlet N in addition to the two Higgs doublets of the minimal SUSY model. This next to minimal model has the helpful new feature that the Higgs potential contains a tree level trilinear field term. We consider the most general form of the Higgs potential without imposing a discrete symmetry; in particular we allow the presence of a muterm in the superpotential. We find that electroweak baryon preservation is compatible with the NMSSM.

Family Structure from Periodic Solutions of an Improved Gap Equation ; Fermion mass models usually contain a horizontal symmetry and therefore fail to predict the exponential mass spectrum of the Standard Model in a natural way. In dynamical symmetry breaking there are different concepts to introduce a fermion mass spectrum, which automatically has the desired hierarchy. In constructing a specific model we show that in some modified gap equations periodic solutions with several fermion poles appear. The stability of these excitations and the application of this toy model are discussed. The mass ratios turn out to be approximately epi and e2pi. Thus the model explains the large ratios of fermion masses between successive generations in the Standard Model without introducing large or small numbers by hand.

Generalized messengers of supersymmetry breaking and the sparticle mass spectrum ; We investigate the sparticle spectrum in models of gaugemediated supersymmetry breaking. In these models, supersymmetry is spontaneously broken at an energy scale only a few orders of magnitude above the electroweak scale. The breakdown of supersymmetry is communicated to the standard model particles and their superpartners by messenger fields through their ordinary gauge interactions. We study the effects of a messenger sector in which the supersymmetryviolating Fterm contributions to messenger scalar masses are comparable to the supersymmetrypreserving ones. We also argue that it is not particularly natural to restrict attention to models in which the messenger fields lie in complete SU5 GUT multiplets, and we identify a much larger class of viable models. Remarkably, however, we find that the superpartner mass parameters in these models are still subject to many significant contraints.

Polarization Measurements and TViolation in Exclusive Semileptonic B Decays ; We provide a general analysis of time reversal invariance violation in the exclusive semileptonic B decays B to D l nu and B to D l nu. Measurements of the lepton and D polarizations can be used to search for and identify nonstandard model sources of T violation. Upper limits are placed on the Todd polarization observables in both the supersymmetric Rparity conserving and Rparity breaking theories, as well as in some nonsupersymmetric extensions of the standard model, including multiHiggsdoublet models, leptoquark models, and leftright symmetric models. It is noted that many of these models allow for large Tviolating polarization effects which could be within the reach of the planned B factories.

Beyond the Standard Model ; These lectures constitute a short course in Beyond the Standard Model' for students of experimental particle physics. I discuss the general ideas which guide the construction of models of physics beyond the Standard Model. The central principle, the one which most directly motivates the search for new physics, is the search for the mechanism of the spontaneous symmetry breaking observed in the theory of weak interactions. To illustrate models of weakinteraction symmetry breaking, I give a detailed discussion of the idea of supersymmetry and that of new strong interactions at the TeV energy scale. I discuss experiments that will probe the details of these models at future pp and ee colliders. Lectures presented at the 1996 European School of HighEnergy Physics.

A lowenergy compatible SU4type Model for Vector Leptoquarks of Mass 1 TeV ; The Standard Model is extended by a SU2L singlet of vector leptoquarks. An additional SU4 gauge symmetry between righthanded up quarks and righthanded leptons is introduced to render the model renormalizable. The arrangement is made in such a way that no conflict with low energy restrictions is encountered. The SU2L singlet mediates interactions between the righthanded leptons and up type quarks for which only moderate low energy restrictions MLQgLQ few hundred GeV exist. We cancel the anomalies of the model and furthermore argue that the inequality gLQ gQCD is a general feature of consistent vector leptoquark models. Although our model is not relevant for HERA, it is interesting per se as a description of leptoquarks of mass 1 TeV consistent with all lowenergy requirements.

The Anomalous Chromomagnetic Dipole Moment of the Top Quark ; We calculate the one loop corrections to the chromomagnetic dipole moment of the top quark in the framework of the Standard Model, the two Higgs doublet model and the Minimal Supersymmetric Standard Model. In the Standard Model we consider the QCD and the electroweak corrections generated by gluon and Higgs boson exchanges, respectively. In the Minimal Supersymmetric Standard Model, we calculate the SUSY QCD corrections, including the mixing effects between the stop coming from the left and righthanded sectors. We obtain that the Standard Model contribution is of the order of 0.004 delta kappagt 0.001, and the values for diferents scenarios are of the order of 0.001 delta kappagt 0.01.

Dynamical ElectroWeak Symmetry Breaking with a Standard Model Limit ; We argue that a Standard Model decoupling limit is generically the necessary ingredient which makes scenarios of electroweak symmetry breaking viable. This applies especially also to models of dynamical electroweak symmetry breaking. Additional requirements are only that the mass predictions of a given model e.g. predictions or theoretical limits on the Higgs or top mass are consistent with existing data. We discuss the necessary ingredients for dynamical symmetry breaking and present a dynamically broken leftrightsymmetric model as an example. The model exhibits such a decoupling limit, is phenomenologically viable and leads to interesting mass predictions and relations which are further examined.

Models of Electroweak Symmetry Breaking ; Discovering the dynamics responsible for electroweak symmetry breaking is the outstanding question facing particle physics today, and the answer will be found in the next decade. In these lectures I discuss the range of models which have been proposed to explain electroweak symmetry breaking. I begin with an overview of Higgs models, with emphasis on the naturalnesshierarchy and triviality problems, and then consider general lessons which can be drawn about the symmetry breaking sector in arbitrary scalar models. Subsequently, I discuss the symmetry breaking sector in supersymmetric models and then consider models of dynamical electroweak symmetry breaking. I conclude with a brief review of the open questions.

Getting the Supersymmetric Unification Scale from Quantum Confinement with Chiral Symmetry Breaking ; Two models which generate the supersymmetric Grand Unification Scale from the strong dynamics of an additional gauge group are presented. The particle content is chosen such that this group confines with chiral symmetry breaking. Fields that are usually introduced to break the Grand Unified group appear instead as composite degrees of freedom and can acquire vacuum expectation values due to the confining dynamics. The models implement known solutions to the doublettriplet splitting problem. The SO10 model only requires one higher dimensional representation, an adjoint. The dangerous coloured Higgsinomediated proton decay operator is naturally suppressed in this model to a phenomenologically interesting level. Neither model requires the presence of gauge singlets. Both models are only technically natural.

Exclusive B pi e e and B rho e e ; We investigate the exclusive B pi e e and B rho e e decays in framework of the general two Higgs doublet model model III, in which an extra phase angle in the chargedHiggs fermion coupling, i.e., a new source for CP violation exists. The CP violation for both decays are calculated and it is observed that the CP violating asymmetry in model III differs significantly than the one predicted by the standard model and model II which is a special case of model III. Furthermore, it is shown that the zero value of forward backward asymmetry AFB is shifted when compared with the SM value, which can also serve as the efficiency tool for establishing new physics.

Microwave background anisotropies in quasiopen inflation ; Quasiopenness seems to be generic to multifield models of singlebubble open inflation. Instead of producing infinite open universes, these models actually produce an ensemble of very large but finite inflating islands. In this paper we study the possible constraints from CMB anisotropies on existing models of open inflation. The effect of supercurvature anisotropies combined with the quasiopenness of the inflating regions make some models incompatible with observations, and severely reduces the parameter space of others. Supernatural open inflation and the uncoupled twofield model seem to be ruled out due to these constraints for values of Omega0lesssim0.98. Others, such as the open hybrid inflation model with suitable parameters for the slow roll potential can be made compatible with observations.

Experimental Signatures of Fermiophobic Higgs bosons ; The most general Two Higgs Doublet Model potential without explicit CP violation depends on 10 real independent parameters. Excluding spontaneous CP violation results in two 7 parameter models. Although both models give rise to 5 scalar particles and 2 mixing angles, the resulting phenomenology of the scalar sectors is different. If flavour changing neutral currents at tree level are to be avoided, one has, in both cases, four alternative ways of introducing the fermion couplings. In one of these models the mixing angle of the CP even sector can be chosen in such a way that the fermion couplings to the lightest scalar Higgs boson vanishes. At the same time it is possible to suppress the fermion couplings to the charged and pseudoscalar Higgs bosons by appropriately choosing the mixing angle of the CP odd sector. We investigate the phenomenology of both models in the fermiophobic limit and present the different branching ratios for the decays of the scalar particles. We use the present experimental results from the LEP collider to constrain the models.

Tests of the leftright electroweak model at linear collider ; The leftright model is a gauge theory of electroweak interactions based on the gauge symmetry SU2R . The main motivations for this model are that it gives an explanation for the parity violation of weak interactions, provides a mechanism seesaw for generating neutrino masses, and has BL as a gauge symmetry. The quarklepton symmetry in weak interactions is also maintained in this theory. The model has many predictions one can directly test at a TeVscale linear collider. We will consider here two processes e,e q, q, barQ, barQ and e,e mu, nu, q, barQ testing the lepton flavour violation predicted by the model. We will also discuss constraints on supersymmetric versions of the model.

Experimental signature of a fermiophobic Higgs boson ; The most general Two Higgs Doublet Model potential without explicit CP violation depends on 10 real independent parameters . Excluding spontaneous CP violation results in two 7 parameter models. Although both models give rise to 5 scalar particles and 2 mixing angles, the resulting phenomenology of the scalar sectors is different. If flavour changing neutral currents at tree level are to be avoided, one has four alternative ways of introducing the fermion couplings in both cases. In one of these models the mixing angle of the CP even sector can be chosen in such a way that the fermion couplings to the lightest scalar Higgs boson vanishes. At the same time it is possible to suppress the fermion couplings to the charged and pseudoscalar Higgs boson by appropriately choosing the mixing angle of the CP odd sector. We investigate the phenomenology of both models in the fermiophobic limit and present the different branching ratios for the decays of the scalar particles. We use the present experimental results from the LEP collider to constrain the models.

Electroweak Symmetry Breaking by Strong Supersymmetric Dynamics at the TeV Scale ; We construct models in which electroweak symmetry is spontaneously broken by supersymmetric strong dynamics at the TeV scale. The order parameter is a composite of scalars, and the longitudinal components of the W and Z are stronglycoupled bound states of scalars. The usual phenomenological problems of dynamical electroweak symmetry breaking are absent the sign of the S parameter unconstrained in strongly interacting SUSY theories, and fermion masses are generated without flavorchanging neutral currents or large corrections to the rho parameter. The lightest neutral Higgs scalar can be heavier than MZ without radiative corrections from standardmodel fields. All the mass scales in the model can be naturally related in lowscale models of supersymmetry breaking. The mu problem can also be solved naturally, and the model can incorporate perturbative unification of standardmodel gauge couplings with intermediate thresholds.

TwoBrane Models and BBN ; We obtain a class of solutions for the AdS5 twobrane models by imposing the observed value of cosmological constant and Newton coupling constant on the visible brane. When all terms up to the first order of matter density are included, the cosmological evolution on the observable brane depends on the equation of state of the matter and consequently when the pressure exists, the cosmology of these models deviates from FLRW cosmology. We show that it is possible to choose the matter equation of state on the hidden brane to neutralize its contribution on the cosmological evolution of the visible brane. We compare the prediction of these models for primordial it 4He yield with observations. In standard BBN with nnulight 3 this brane model is ruled out. If in addition to 3 SM neutrinos there is one light sterile neutrino, this model reconciles the observed it 4He yield with a high Omegab sim 0.033 h2 suggested by BOOMERANG and MAXIMA experiments.

Evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model ; The general features of the evolution of the Yukawa coupling constants and seesaw operators in the universal seesaw model with det MF0 are investigated. Especially, it is checked whether the model causes bursts of Yukawa coupling constants, because in the model not only the magnitude of the Yukawa coupling constant YLu33 in the upquark sector but also that of YLd33 in the downquark sector is of the order of one, i.e., YLu33 sim YLd33 sim 1. The requirement that the model should be calculable perturbatively puts some constraints on the values of the intermediate mass scales and tanbeta in the SUSY model.

Leptogenesis in a Realistic Supersymmetric Model of Inflation with a Low Reheat Temperature ; We discuss leptogenesis in a realistic supersymmetric model of inflation with a low reheat temperature 110 GeV. The lepton asymmetry is generated by a decaying right handed sneutrino, which is produced after inflation during preheating. The inflationary model is based on a simple variant of the NexttoMinimal Supersymmetric Standard model NMSSM which solves the mu problem, called phiNMSSM, where the additional singlet phi plays the role of the inflaton in hybrid or inverted hybrid type models. The model is invariant under an approximate PecceiQuinn symmetry which also solves the strong CP problem, and leads to an invisible axion with interesting cosmological consequences. We show how the baryon number of the universe and the nature of cold dark matter are determined by the same parameters controlling the strong CP problem, the mu problem and the neutrino masses and mixing angles.

Direct CP asymmetry of b s gamma and b d gamma in models beyond the Standard Model ; We study the direct CP asymmetry of the decays b s gamma and b d gamma in the context of two models i a supersymmetric SUSY model with unconstrained SUSY phases, and ii a model with a single generation of vector quarks. In both the above models we show that b d gamma can sizeably influence the combined asymmetry i.e. that of a sample containing both b s gamma and b d gamma, and in case ii may in fact be the dominant contribution.

The Effective Lagrangian in the RandallSundrum Model and Electroweak Physics ; We consider the twobrane RandallSundrum RS model with bulk gauge fields. We carefully match the bulk theory to a 4D lowenergy effective Lagrangian. In addition to the fourfermion operators induced by KK exchange we find that large negative S and T parameters are induced in the effective theory. This is a treelevel effect and is a consequence of the shapes of the W and Z wave functions in the bulk. Such effects are generic in extra dimensional theories where the standard model SM gauge bosons have nonuniform wave functions along the extra dimension. The corrections to precision electroweak observables in the RS model are mostly dominated by S. We fit the parameters of the RS model to the experimental data and find somewhat stronger bounds than previously obtained; however, the standard model bound on the Higgs mass from precision measurements can only be slightly relaxed in this theory.

Electroweak Limits on NonUniversal Z' Bosons ; Many types of physics beyond the standard model include an extended electroweak gauge group. If these extensions are associated with flavor symmetry breaking, the gauge interactions will not be flavoruniversal. In this note we update the bounds placed by electroweak data on the existence of flavor nonuniversal extensions to the standard model in the context of topcolor assisted technicolor TC2, noncommuting extended technicolor NCETC, and the ununified standard model UUM. In the first two cases the extended gauge interactions couple to the third generation fermions differently than to the light fermions, while in the ununified standard model the gauge interactions couple differently to quarks and leptons. The extra SU2 triplet of gauge bosons in NCETC and UUM models must be heavier than about 3 TeV, while the extra Z boson in TC2 models must be heavier than about 1 TeV.

U1 masses in intersecting Dbrane SMlike models ; For recently constructed classes of D6brane models, yielding the Standard Model fermion spectrum and gauge symmetry, we compute lower bounds on the masses of new U1 fields that such models predict in addition to the hypercharge U1Y. In models with extra dimensions, generic uncertainties due to unknown values of the compactification radii of the extra dimensions affect the value of the string scale and thus the predictive power of such models. Using rho parameter and ZU1 mixingangle constraints we show how to avoid such uncertainties, to provide lower mass bounds for the additional U1 fields. These are in the region above 750 GeV for mixing angles less than 1.5 times 103 and as low as 550 GeV for mixing angles of 3times 103.

Tests for Cosmological Evolution of a Brane Universe Model ; The relativistic Friedmann Lemaitre cosmology model FLCM is very sucessful to describe the evolution history of the Universe from the First three Minutes. Any alternative model should be consistent with the FLCM explanations to the later stage evolutions of the Universe at certain points. An noncompact extra dimension model was recently proposed by Randall and Sundrum. Binetruy et al. obtained the modified Friedmann equation, in which the energy density of the brane appears quadratically in contrast with the linear behavior of the standard Friedmann equation. We investigate kinds of classical cosmological effects of the new models and get a general solution of the cosmic evolution for this extended model, with more detail discussions of the brane tension parameter on these cosmological tests.