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Some properties of a string ; The properties of 5D gravitational flux tubes are considered. With the cross section and 5th dimension in the Planck region such tubes can be considered as stringlike objects, namely Deltastrings. A model of attachment of Deltastring to a spacetime is offered. It is shown that the attachment point is a model of an electric charge for an observer living in the spacetime. Magnetic charges are forbidden in this model. |
The Future of Tilted Bianchi Universes ; An asymptotic stability analysis of spatially homogeneous models of Bianchi type containing tilted perfect fluids is performed. Using the known attractors for the nontilted Bianchi type universes, we check whether they are stable against perturbations with respect to tilted perfect fluids. We perform the analysis for all Bianchi class B models and the Bianchi type VI0 model. In particular, we find that none of the nontilted equilibrium points are stable against tilted perfect fluids stiffer than radiation. We also indicate parts of the phase space where new tilted exact solutions might be found. |
Some Inhomogeneous Magnetized Viscous Fluid Cosmological Models with Varying ; Some cylindrically symmetric inhomogeneous viscous fluid cosmological models with electromagnetic field are obtained. To get a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. Without assumin g any it ad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor together with some p hysical aspects of the model are also discussed. |
Adiabatic decaying vacuum model for the universe ; We study a model that the entropy per particle in the universe is constant. The sources for the entropy are the particle creation and a lambda decaying term. We find exact solutions for the Einstein field equations and show the compatibilty of the model with respect to the age and the acceleration of the universe. |
SN1987A Temporal Models ; It is well known that carriers of astrophysical information are massless spinning particles. These carriers are photons, neutrinos and, expectedly, gravitons. All these particles are emitted during supernova events. Information carried by these particles characterize their sources, but such information are affected by the trajectories of the carriers. Recently, it is shown that these trajectories are spin dependent. Knowing these trajectories and the arrival times of such particles to the detectors, a spin dependent model is constructed and compared with the conventional spin independent model. |
Spacetime Foam Model of the Schwarzschild Horizon ; We consider a spacetime foam model of the Schwarzschild horizon, where the horizon consists of Planck size black holes. According to our model the entropy of the Schwarzschild black hole is proportional to the area of its event horizon. It is possible to express geometrical arguments to the effect that the constant of proportionality is, in natural units, equal to one quarter. |
Regular inflationary cosmology and gauge theories of gravitation ; Cosmological equations for homogeneous isotropic models filled by scalar fields and ultrarelativistic matter are investigated in the framework of gauge theories of gravity. Regular inflationary cosmological models of flat, closed and open type with dominating ultrarelativistic matter at a bounce are discussed. It is shown that essential part of inflationary cosmological models has bouncing character. |
World Nematic Crystal Model of Gravity Explaining the Absence of Torsion ; We attribute the gravitational interaction between sources of curvature to the world being a crystal which has undergone a quantum phase transition to a nematic phase by a condensation of dislocations. The model explains why spacetime has no observable torsion and predicts the existence of curvature sources in the form of world sheets, albeit with different highenergy properties than those of string models. |
Bulk Viscous cosmological models in Lyra geometry ; We have investigated an LRS Bianchi Type I models with bulk viscosity in the cosmological theory based on Lyra's geometry. A new class of exact solutions have been obtained by considering a timedependent displacement field for a constant value of the deceleration parameter and viscosity coefficient of bulk viscous fluid is assumed to be a power function of mass density. The physical behaviour of the models is also discussed. |
Bianchi Type I Magnetofluid Cosmological Models with Variable Cosmological Constant Revisited ; The behaviour of magnetic field in anisotropic Bianchi type I cosmological model for bulk viscous distribution is investigated. The distribution consists of an electrically neutral viscous fluid with an infinite electrical conductivity. It is assumed that the component sigma11 of shear tensor sigmaji is proportional to expansion theta and the coefficient of bulk viscosity is assumed to be a power function of mass density. Some physical and geometrical aspects of the models are also discussed in presence and also in absence of the magnetic field. |
Sufficient conditions for curvature invariants to avoid divergencies in Hyperextended Scalar Tensor theory for Bianchi models ; We look for sufficient conditions such that the scalar curvature, Ricci and Kretchmann scalars be bounded in Hyperextended Scalar Tensor theory for Bianchi models. We find classes of gravitation functions and BransDicke coupling functions such that the theories thus defined avoid the singularity. We compare our results with these found by Rama in the framework of the Generalised Scalar Tensor theory for the FLRW models. |
Causal Bulk Viscous LRS Bianchi I Models With Variable Gravitational and Cosmological Constant ; In this paper we have investigated an LRS Bianchi I anisotropic cosmological model of the universe by taking time varying G and Lambda in the presence of bulk viscous fluid source described by full causal nonequilibrium thermodynamics. We obtain a cosmological constant as a decreasing function of time and for m, n 0, the value of cosmological constant'' for this model is found to be small and positive which is supported by the results from recent supernovae observations. |
A class of nonunitary models of Newtonian gravity and its unicity ; A class of nonMarkoffian nonunitary models for Newtonian gravity is characterized as following from some rather natural hypotheses. One of such models was previously obtained as the Newtonian limit of a classically stable version of higher derivative gravity. They give rise to a mass threshold around 1011 proton masses for gravity induced localization, to a breaking of linearity and to the possible identification of thermodynamic and von Neumann entropies. |
Hawking Radiation in Trace Anomaly Free Frames ; We have used the results of renormalization of a twodimensional quantum stress tensor to develop a conformally invariant dynamical model. The model requires the consideration of those conformal frames in which there exists a correspondence between the trace anomaly and a cosmological constant. We apply this model to a two dimensionalSchwarzschild de Sitter spacetime to show that in these conformal frames one may achieve Hawking radiation without recourse to the trace anomaly . |
Information Entropy in Cosmology ; The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is identical to a fluid model of the KullbackLeibler Relative Information Entropy', expressing the distinguishability of the local inhomogeneous mass density field from its spatial average on arbitrary compact domains. We discuss the timeevolution of effective information' and explore some implications. We conjecture that the information content of the Universe measured by Relative Information Entropy of a cosmological model containing dust matter is increasing. |
Troubles with quantum anisotropic cosmological models loss of unitarity ; The anisotropic Bianchi I cosmological model coupled with perfect fluid is quantized in the minisuperspace. The perfect fluid is described by using the Schutz formalism which allows to attribute dynamical degrees of freedom to matter. It is shown that the resulting model is nonunitary. This breaks the equivalence between the manyworlds and dBB interpretations of quantum mechanics. |
The Chaplygin gas as a model for dark energy ; We review the essential features of the Chaplygin gas cosmological models and provide some examples of appearance of the Chaplygin gas equation of state in modern physics. A possible theoretical basis for the Chaplygin gas in cosmology is discussed. The relation with scalar field and tachyon cosmological models is also considered. |
Coupled oscillators as models of phantom and scalar field cosmologies ; We study a toy model for phantom cosmology recently introduced in the literature and consisting of two oscillators, one of which carries negative kinetic energy. The results are compared with the exact phase space picture obtained for similar dynamical systems describing, respectively, a massive canonical scalar field conformally coupled to the spacetime curvature, and a conformally coupled massive phantom. Finally, the dynamical system describing exactly a minimally coupled phantom is studied and compared with the toy model. |
Generalisations of the EinsteinStraus model to cylindrically symmetric settings ; We study generalisations of the EinsteinStraus model in cylindrically symmetric settings by considering the matching of a static spacetime to a nonstatic spatially homogeneous spacetime, preserving the symmetry. We find that such models possess severe restrictions, such as constancy of one of the metric coefficients in the nonstatic part. A consequence of this is that it is impossible to embed static locally cylindrically symmetric objects in reasonable spatially homogeneous cosmologies. |
Multicomponent perfect fluid with variable parameters in n Ricciflat spaces ; Ddimensional cosmological model describing the evolution of a multicomponent perfect fluid with variable barotropic parameters in n Ricciflat spaces is investigated. The equations of motion are integrated for the case, when each component possesses an isotropic pressure with respect to all spaces. Exact solutions are presented in the Kasnerlike form. Some explicit examples are given 4dimensional model with an isotropic accelerated expansion at late times and 4ddimensional model describing a compactification of extra dimensions. |
Local thermal equilibrium and ideal gas Stephani universes ; The Stephani universes that can be interpreted as an ideal gas evolving in local thermal equilibrium are determined. Five classes of thermodynamic schemes are admissible, which give rise to five classes of regular models and three classes of singular models. No Stephani universes exist representing an exact solution to a classical ideal gas one for which the internal energy is proportional to the temperature. But some Stephani universes may approximate a classical ideal gas at first order in the temperature all of them are obtained. Finally, some features about the physical behavior of the models are pointed out. |
A cosmology with variable c ; A new varyingc cosmological model constructed using two additional assumptions, which was introduced in our previous work, is briefly reviewed and the dynamic equation of the model is derived distinctly from a semiNewtonian approach. The results of this model, using a Lambda term and an extra energymomentum tensor, are considered separately. It is shown that the Universe began from a hot Big Bang and expands forever with a constant deceleration parameter regardless of its curvature. Finally, the age, the radius, and the energy content of the Universe are estimated and some discussion about the type of the geometry of the Universe is provided. |
Tilted Bianchi Type V Bulk Viscous Cosmological Models with Varying Term ; Conformally flat tilted Bianchi type V cosmological models in presence of a bulk viscous fluid and heat flow are investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density. The cosmological constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical and geometric aspects of the models are also discussed. |
Mathematical properties of cosmological models with accelerated expansion ; An introduction to solutions of the Einstein equations defining cosmological models with accelerated expansion is given. Connections between mathematical and physical issues are explored. Theorems which have been proved for solutions with positive cosmological constant or nonlinear scalar fields are reviewed. Some remarks are made on more exotic models such as the Chaplygin gas, tachyons and kessence. |
Nonsingular Spherical Models with a Variable Cosmological term ; Exact solutions of the Einstein's field equations describing a spherically symmetric cosmological model without a big bang or any other kind of singularity recently obtained by Dadhich and Patel 2000 are revisited. The matter content of the model is a shearfree perfect fluid with isotropic pressure and a radial heat flux. Three different exact solutions are obtained for both perfect fluid and fluid with bulk viscosity. It turns out that the cosmological rerm Lambdat is a decreasing function of time, which is consistent with recent observations of type Ia supernovae. |
Difficulties with Recollapsing models in Closed Isotropic Loop Quantum Cosmology ; The use of techniques from loop quantum gravity for cosmological models may solve some difficult problems in quantum cosmology. The solutions under a number of circumstances have been well studied. We will analyse the behaviour of solutions in the closed model, focusing on the behaviour of a universe containing a massless scalar field. The asymptotic behaviour of the solutions is examined, and is used to determine requirements of the initial conditions. |
Role of Modified Chaplygin Gas in Accelerated Universe ; In this paper we have considered a model of modified Chaplygin gas and its role in accelerating phase of the universe. We have assumed that the equation of state of this modified model is valid from the radiation era to LambdaCDM model. We have used recently developed statefinder parameters in characterizing different phase of the universe diagrammatically. |
On the Physical Hilbert Space of Loop Quantum Cosmology ; In this paper we present a model of Riemannian loop quantum cosmology with a selfadjoint quantum scalar constraint. The physical Hilbert space is constructed using refined algebraic quantization. When matter is included in the form of a cosmological constant, the model is exactly solvable and we show explicitly that the physical Hilbert space is separable consisting of a single physical state. We extend the model to the Lorentzian sector and discuss important implications for standard loop quantum cosmology. |
Discrete quantum gravity the Lorentz invariant weight for the BarrettCrane model ; In a recent paper 1 we have constructed the spin and tensor representations of SO4 from which the invariant weight can be derived for the BarrettCrane model in quantum gravity. By analogy with the SO4 group, we present the complexified ClebschGordan coefficients in order to construct the BiedenharnDolginov function for the SO3,1 group and the spherical function as the Lorentz invariant weight of the model. |
Quantum Cosmological Models ; We contrast the initial condition requirements of various contemporary cosmological models, including inflationary and bouncing cosmologies. Various proposals such as HartleHawking's no boundary, or Tunnelling boundary conditions are assessed on grounds of naturalness and fine tuning. Alternatively a quiescent or time machine'' state is considered. Extensions to brane models are also addressed. Further ideas about universe creation from a metauniverse are outlined. We compare the recent loop quantum cosmology of Bojowald and coworkers with these earlier proposals. A number of possible difficulties and limitations are outlined. |
Temperature Fluctuation and an Expected Limit of Hubble Parameter in the SelfConsistent Model ; The temperature gradient of microwave background radiation CMBR is calculated in the Self Consistent Model. An expected values for Hubble parameter have been presented in two different cases. In the first case the temperature is treated as a function of time only, while in the other one the temperature depends on relaxation of isotropy condition in the selfconsistent model and the assumption that the universe expands adiabatically. The COBE's or WMAP's fluctuations in temperature of CMBR may be used to predict a value for Hubble parameter. |
Observables in Extended Percolation Models of Causal Set Cosmology ; Classical sequential growth models for causal sets provide an important step towards the formulation of a quantum causal set dynamics. The covariant observables in a class of these models known as generalised percolation have been completely characterised in terms of physically welldefined stem sets'' and yield an insight into the nature of observables in quantum causal set cosmology. We discuss a recent extension of generalised percolation and show that the characterisation of covariant observables in terms of stem sets is also complete in this extension. |
Planesymmetric inhomogeneous magnetized viscous fluid universe with a variable ; The behavior of magnetic field in plane symmetric inhomogeneous cosmological models for bulk viscous distribution is investigated. The coefficient of bulk viscosity is assumed to be a power function of mass density xi xi0rhon. The values of cosmological constant for these models are found to be small and positive which are supported by the results from recent supernovae Ia observations. Some physical and geometric aspects of the models are also discussed. |
Dual Nature of the Ricci Scalar, Creation of Spinless and Spin12 Particles as Well as a New Cosmological Scenario I ; In earlier papers, it is found that the Ricci scalar behaves in dual manner i like a matter field and ii like a geometrical field. Using dual role of the Ricci scalar, inhomogeneous cosmological models are derived. The essential features of these models is capability of these to exhibit gravitational effect of compact objects also in an expanding universe. Here, production of spinless and spin12 particles are demonstrated in these models. |
Thermoinertial bouncing of a relativistic collapsing sphere A numerical model ; We present a numerical model of a collapsing radiating sphere, whose boundary surface undergoes bouncing due to a decreasing of its inertial mass density and, as expected from the equivalence principle, also of the gravitational'' force term produced by the inertial'' term of the transport equation. This model exhibits for the first time the consequences of such an effect, and shows that under physically reasonable conditions this decreasing of the gravitational term in the dynamic equation may be large enough as to revert the collapse and produce a bouncing of the boundary surface of the sphere. |
The initial conditions of the Universe and holography ; We address the initial conditions for an expanding cosmology using the holographic principle. For the case of a closed model, the old prescription of Fishler and Susskind, that uses the particle horizon to encode the bulk degrees of freedom, can be implemented for accelerated models with enough acceleration. As a bonus we have singularity free bouncing models. The bound is saturated for codimension one branes dominated universes. |
Modified Newtonian Dynamics and Induced gravity ; Modified Newtonian dynamics, a successful alternative to the cosmic dark matter model, proposes that gravitational field deviates from the Newtonian law when the field strength g is weaker than a critical value g0. We will show that the dynamics of MOND can be derived from an induced gravity model. New dynamics is shown to be compatible with the spatial deformation of scalar fields coupled to the system. Approximate solutions are shown explicitly for a simple toy model. |
Anisotropic static solutions in modelling highly compact bodies ; Einstein field equations for anisotropic spheres are solved and exact interior solutions obtained. This paper extends earlier treatments to include anisotropic models which accommodate a wider variety of physically viable energy densities. Two classes of solutions are possible. The first class contains the limiting case mupropto r2 for the energy density which arises in many astrophysical applications. In the second class the singularity at the center of the star is not present in the energy density. The models presented in this paper allow for increasing and decreasing profiles in the behavior of the energy density. |
Transition from quintessence to phantom phase in quintom model ; Assuming the Hubble parameter is a continuous and differentiable function of comoving time, we investigate necessary conditions for quintessence to phantom phase transition in quintom model. For powerlaw and exponential potential examples, we study the behavior of dynamical dark energy fields and Hubble parameter near the transition time, and show that the phantomdivideline w1 is crossed in these models. |
A lattice bosonic model as a quantum theory of gravity ; A local quantum bosonic model on a lattice is constructed whose low energy excitations are gravitons described by linearized Einstein action. Thus the bosonic model is a quantum theory of gravity, at least at the linear level. We find that the compactification and the discretization of metric tenor are crucial in obtaining a quantum theory of gravity. |
Classification of cosmological milestones ; In this paper causal geodesic completeness of FLRW cosmological models is analysed in terms of generalised power expansions of the scale factor in coordinate time. The strength of the found singularities is discussed following the usual definitions due to Tipler and Krolak. It is shown that while classical cosmological models are both timelike and lightlike geodesically incomplete, certain observationally alllowed models which have been proposed recently are lightlike geodesically complete. |
FRW Universe with Variable G and Terms ; A new class of exact solutions of Einstein's field equations with a perfect fluid source, variable gravitational coupling G and cosmological term Lambda for FRW spacetime is obtained by considering variable deceleration parameter models for the universe. The nature of the variables Gt, Lambdat and the energy density rhot have been examined for three cases i exponential ii polynomial and iii sinusoidal form. The special types of models for dust, Zel'dovich and radiating universe are also mentioned in all these cases. The behaviour of these models of the universe are also discussed in the light of recent supernovae Ia observations. |
A Simplified Mathematical Model for the Formation of Null Singularities Inside Black Holes II ; We study a simple system of two hyperbolic semilinear equations, inspired by the Einstein equations. The system, which was introduced in grqc0612136, is a model for singularity formation inside black holes. We show for a particular case of the equations that the system demonstrates a finite time blowup. The singularity that is formed is a null singularity. Then we show that in this particular case the singularity has features that are analogous to known features of models of blackhole interiors which describe the innerhorizon instability. Our simple system may provide insight into the formation of null singularities inside spinning or charged black holes. |
Hamiltonian Formulation of 5dimensional KaluzaKlein Theory ; We analyze the consistency of the ADM approach to KK model; we prove that KK reduction commute with ADM splitting. This leads to a well defined Hamiltonian; we provide the outcome. The electromagnetic constraint is derived from a geometrical one and this result enforces the physical meaning of KK model. Moreover we study the role of the extra scalar field we have in our model; classical hints from geodesic motion and cosmological solutions suggest that the scalar field can be an alternative time variable in the relational point of view. |
The Cosmology of Tetradic Theory of Gravitation ; We consider a special class of the tetrad theory of gravitation which can be considered as a viable alternative gravitational theories. We investigate cosmological models based on those theories by examining the possibility of fitting the recent astronomical measurement of supernova Ia magnitude versus shift. Our investigations result in a reasonable fit for the supernova data without introducing a cosmological constant. Thus, cosmological models based on tetradic theory of gravitation can provide alternatives to dark energy models. |
Transition from AdS universe to DS universe in the BPP model ; It can be shown that in the BPP model the smooth phase transition from the asymptotically decelerated AdS universe to the asymptotically accelerated DS universe is possible by solving the modified semiclassical equations of motion. This transition comes from noncommutative Poisson algebra, which gives the constant curvature scalars asymptotically. The decelerated expansion of the early universe is due to the negative energy density with the negative pressure induced by quantum back reaction, and the accelerated latetime universe comes from the positive energy and the negative pressure which behave like dark energy source in recent cosmological models. |
Non Commutative Bianchi type II Quantum Cosmology ; In this paper we present the noncommutative Bianchi Class A cosmological models coupled to barotropic perfect fluid. The commutative and noncommutative quantum solution to the WheelerDeWitt equation for any factor ordering, to the anisotropic Bianchi type II cosmological model are found, using a stiff fluid gamma1. In our toy model, we introduce noncommutative scale factors, is say, we consider that all minisuperspace variables rm qi does not commute, so the simplectic structure was modified. |
Search for Leptoquarks in ElectronPhoton Scattering at sqrtsee up to 209 GeV at LEP ; Searches for first generation scalar and vector leptoquarks, and for squarks in Rparity violating SUSY models with the direct decay of the squark into Standard Model particles, have been performed using ee collisions collected with the OPAL detector at LEP at ee centreofmass energies between 189 and 209 GeV. No excess of events is found over the expectation from Standard Model background processes. Limits are computed on the leptoquark couplings for different values of the branching ratio to electronquark final states. |
The LUCIAE model predictions on the light vector meson production in protonproton, protonnucleus and nucleusnucleus collisions at 158 A GeV ; The LUCIAE model predictions are compared with experimental data on light vector meson rho,omega,phi production in pp, pPb and PbPb collisions at 158 A GeV. The model reproduces the general trends of the data, but fails in describing the yield of highpT vector mesons in the central PbPb collisions. Predictions for InIn and pA A varying from Be to U collisions at 158 A GeV are also presented. |
Transverse targetspin asymmetry associated with DVCS on the proton and a resulting modeldependent constraint on the total angular momentum of quarks in the nucleon ; Results are reported on the transverse targetspin asymmetry associated with deeply virtual Compton scattering on the proton, extracted from the data accumulated by the HERMES experiment in the years 20022004. By comparing the HERMES results and theoretical predications based on a phenomenological model of generalized parton distributions, a modeldependent constraint on the total angular momentum carried by quarks in the nucleon is obtained. |
Dynamical fermion mass generation by strong gauge interaction shielded by a scalar field ; The strongly coupled lattice gauge models with confined fermion and scalar matter fields, which in a certain phase break dynamically a global chiral symmetry, are reconsidered from the point of view of the existence of heavy fermions. If these models are interpreted as describing a new strong force beyond the standard model, such heavy fermions can arise as neutral bound states of the fundamental fermion and scalar. The discussed mechanism could be considered as an alternative to the Higgs mechanism. |
U1 Lattice Gauge theory and its Dual ; The three dimensional U1 Lattice Gauge, in the weak coupling limit, is dual to a Discrete Gaussian model. We investigate this dual model and use it to calculate properties of the U1 theory. We find that, because of the nature of the dual model, its advantages are outweighed by large autocorrelation times generated when the dual system becomes disordered. |
A model for multiquark systems ; As a step towards understanding multiquark systems abundant in nature we construct a model that reproduces the binding energies of static fourquark systems. These energies have been calculated using SU2 lattice gauge theory for a set of six different geometries representative of the general case. The model is based on ground and excited state twobody potentials and multiquark interaction terms. |
Correlation functions and critical behaviour on fluctuating geometries ; We study the twopoint correlation function in the model of branched polymers and its relation to the critical behaviour of the model. We show that the correlation function has a universal scaling form in the generic phase with the only scale given by the size of the polymer. We show that the origin of the singularity of the free energy at the critical point is different from that in the standard statistical models. The transition is related to the change of the dimensionality of the system. |
The Yang Lee Edge Singularity on Feynman Diagrams ; We investigate the YangLee edge singularity on nonplanar random graphs, which we consider as the Feynman Diagrams of various d0 field theories, in order to determine the value of the edge exponent. We consider the hard dimer model on phi3 and phi4 random graphs to test the universality of the exponent with respect to coordination number, and the Ising model in an external field to test its temperature independence. The results here for generic thin'' random graphs provide an interesting counterpoint to the discussion by Staudacher of these models on planar random graphs. |
ThreeDimensional Simplicial Gravity and Degenerate Triangulations ; I define a model of threedimensional simplicial gravity using an extended ensemble of triangulations where, in addition to the usual combinatorial triangulations, I allow degenerate triangulations, i.e. triangulations with distinct simplexes defined by the same set of vertexes. I demonstrate, using numerical simulations, that allowing this type of degeneracy substantially reduces the geometric finitesize effects, especially in the crumpled phase of the model, in other respect the phase structure of the model is not affected. |
Deriving exact results for Isinglike models from the cluster variation method ; The cluster variation method CVM is an approximation technique which generalizes the mean field approximation and has been widely applied in the last decades, mainly for finding accurate phase diagrams of Isinglike lattice models. Here we discuss in which cases the CVM can yield exact results, considering i onedimensional systems and strips in which case the method reduces to the transfer matrix method, ii treelike lattices and iii the socalled disorder points of euclidean lattice models with competitive interactions in more than one dimension. |
Fat and Thin Fisher Zeroes ; We show that it is possible to determine the locus of Fisher zeroes in the thermodynamic limit for the Ising model on planar fat'' phi4 random graphs and their dual quadrangulations by matching up the real part of the high and lowtemperature branches of the expression for the free energy. Similar methods work for the meanfield model on generic, thin'' graphs. Series expansions are very easy to obtain for such random graph Ising models. |
A meron cluster solution for the sign problem of the twodimensional O3 model ; The twodimensional O3 model at a vacuum angle thetapi is investigated. This model has a severe sign problem. By a Wolff cluster algorithm an integer or halfinteger topological charge is assigned to each cluster. The meron clusters clusters with halfinteger topological charge are used to construct an improved estimator for the correlation function of two spins at thetapi. Only configurations with 0 and 2 merons contribute to this correlation function. An algorithm, that generates configurations with only 0 and 2 merons, is constructed and numerical simulations at thetapi are performed. The numerical results indicate the presence of long range correlations at thetapi. |
New algorithm of the hightemperature expansion for the Ising model in three dimensions ; New algorithm of the finite lattice method is presented to generate the hightemperature expansion series of the Ising model. It enables us to obtain much longer series in three dimensions when compared not only to the previous algorithm of the finite lattice method but also to the standard graphical method. It is applied to extend the hightemperature series of the simple cubic Ising model from beta26 to beta46 for the free energy and from beta25 to beta32 for the magnetic susceptibility. |
Higher orders of the hightemperature expansion for the Ising model in three dimensions ; The new algorithm of the finite lattice method is applied to generate the hightemperature expansion series of the simple cubic Ising model to beta50 for the free energy, to beta32 for the magnetic susceptibility and to beta29 for the second moment correlation length. The series are analyzed to give the precise value of the critical point and the critical exponents of the model. |
Teleparallel gravity on the lattice ; We consider quantum gravity model with the squared curvature action. We construct lattice discretization of the model both on hypercubic and simplicial lattices starting from its teleparallel equivalent. The resulting lattice models have the actions that are bounded from below while Einstein equations without matter appear in their classical limit. |
Vortex Proliferation and the Dual Superconductor Scenario for Confinement The 3D Compact U1 Lattice Higgs Model ; It is argued that the phase diagram of the 3D Compact U1 Lattice Higgs Model is more refined than generally thought. The confined and Higgs phases are separated by a welldefined phase boundary, marked by proliferating vortices. It is shown that the confinement mechanism at work is precisely the dual superconductor scenario. |
Accidental Approximate Generation Universality and its Possible Verification ; The universality of emutau interactions may only be an accidental approximate symmetry analogous to that of flavor SU2 and SU3. This was specifically realized by an extension of the standard model proposed in 1981. Two key predictions are that the tau lifetime should be longer and that the rho parameter measured at the Z peak should have an additional negative contribution. These are consistent with present precision electroweak measurements. A future decisive test of this model would be the discovery of new W and Z bosons with nearly degenerate masses of a few TeV. |
Discrete quarklepton symmetry need not pose a cosmological domain wall problem ; Quarks and leptons may be related to each other through a spontaneously broken discrete symmetry. Models with acceptable and interesting collider phenomenology have been constructed which incorporate this idea. However, the standard Hot Big Bang model of cosmology is generally considered to eschew spontaneously broken discrete symmetries because they often lead to the formation of unacceptably massive domain walls. We point out that there are a number of plausible quarklepton symmetric models which do not produce cosmologically troublesome domain walls. We also raise what we think are some interesting questions concerning anomalous discrete symmetries. |
HighEnergy Multiparticle Distributions and a Generalized Lattice Gas Model ; A simple lattice gas model in one dimension is constructed in which each site can be occupied by at most one particle of any one of D species. Particles interact with a randomly drawn nearest neighbor interaction. This model is capable of reproducing the factorial moments observed in highenergy scattering. In the limit D rightarrow infty, the factorial moments of the negative binomial distribution are obtained naturally. |
Neutrino Lasing in the Sun ; Applying the phenomenon of neutrino lasing in the solar interior, we show how the rate for the generic neutrino decay process nu fermion boson', can in principal be enhanced by many orders of magnitude over its normal decay rate. Such a large enhancement could be of import to neutrinodecay models invoked in response to the apparent deficit of electron neutrinos observed from the sun. The significance of this result to such models depends on the specific form of the neutrino decay, and the particle model within which it is embedded. |
Top Radiative Corrections in Nonminimal Standard Models ; We derive the oneloop effective action induced by a heavy top in models with an extended Higgs sector. We use the effective action to analyze the top corrections to the rho parameter and to the Higgsgauge boson couplings. We show that in models with rhonot1 at treelevel, one does not lose generally the bound on mt from the rho parameter. |
Scaling Laws in Hierarchical Clustering Models with Poisson Superposition ; Properties of cumulant and combinant ratios are studied for multihadron final states composed of Poisson distributed clusters. The application of these quantities to detect'' clusters is discussed. For the scaling laws which hold in hierarchical clustering models void scaling, combinant scaling a generalization is provided. It is shown that testing hierarchical models is meaningful only for phasespace volumes not larger than the characteristic correlation length introduced by Poisson superposition. Violation of the scaling laws due to QCD effects is predicted. |
Anomalous VectorBoson Couplings in Majorana Neutrino Models ; We examine the contributions of Majorana neutrinos to CPviolating WWZ and ZZZ selfcouplings, using a model in which sterile neutrinos couple to the W and Z by mixing with a fourthgeneration heavy lepton. We find that the induced form factors can be as large as 0.5. The model satisfies all phenomenological bounds in a natural way, including those due to the strong limits on the neutron and electron electric dipole moments. Anomalous CPodd couplings of this size are unlikely to be observed at LEP200, but might be detectable at NLC. |
Nambu mass hierarchies in strings ; We show that a recent proposal by Nambu to generate a hierarchy among Yukawa couplings in the standard model may be easily implemented in superstring models. In such models, two of the main ingredients of the Nambu proposal find a natural explanation minimising with respect to the Yukawas amounts to a minimisation with respect to the underlying moduli fields and a constraint on the Yukawas of the type of the Veltman condition may be attributed to the relaxation process to a phenomenologically viable string vacuum. |
Nonuniversal Soft Scalar Masses in Superstring Theories ; We study soft scalar masses comparing with gaugino masses in 4dimensional string models. In general nonuniversal soft masses are derived in orbifold models. We give conditions on modular weights to lead to the large nonuniversality in the soft scalar masses. This nonuniversality is applied to the unification of the gauge coupling constants in the minimal string model. |
Lambda1405 in the Bound State Soliton Model ; The strong and electromagnetic properties of the Lambda1405 hyperon are studied in the framework of the bound state soliton model. We explicitly evaluate the strong coupling constant gLambdaNK, the Lambda magnetic moment, mean square radii and radiative decay amplitudes. The results are shown to be in general agreement with available empirical data. A comparison with results of other models is also presented. |
Sources of CP Violation in the TwoHiggs Doublet Model ; Assuming CP violation arises solely through the Higgs potential, we develop the most general twoHiggs doublet model. There is no discrete symmetry that distinguishes the two Higgs bosons. It is assumed that an approximate global family symmetry sufficiently suppresses flavorchanging neutral scalar interactions. In addition to a CKM phase, neutral boson mixing, and superweak effects, there can be significant CP violation due to charged Higgs boson exchange. The value of epsilon'epsilon due to this last effect could be as large as in the standard model. |
HeavyNeutrino Effects on tauLepton Decays ; Minimal extensions of the Standard Model that are motivated by grand unified theories or superstring models with an E6 symmetry can naturally predict heavy neutrinos of Dirac or Majorana nature. Such heavy neutral leptons violate the de coupling theorem at the oneloop electroweak order and hence offer a unique chance for possible leptonflavour decays of the tau lepton, e.g. tau eee or tau mu mu mu, to be seen in LEP experiments. We analyze such decays in models with three and four generations. |
Physics of Strangelets ; After a brief introduction to the physics of bulk strange quark matter SQM this review focuses on the properties of low baryon number strangelets presently searched for in ultrarelativistic heavyion experiments at CERN and Brookhaven. Shellmodel calculations reveal interesting metastability properties in the experimentally accessible regime. A liquid drop model Fermigas model is shown to explain the overall behavior of the modefilling calculations, leading to a physical understanding of strangelet properties, which can be generalized to nonzero temperature and pressure. |
Yukawa Textures and Anomalies ; We augment the Minimal Supersymmetric Standard Model with a gauged familydependent U1 to reproduce Yukawa textures compatible with experiment. In the simplest model with one extra chiral electroweak singlet field, acceptable textures require this U1 to be anomalous. The cancellation of its anomalies by a generic GreenSchwarz mechanism requires sin2thetaw38 at the string scale, suggesting a superstring origin for the standard model. |
NonMinimal Higgs Sectors The Decoupling Limit and its Phenomenological Implications, ; In models with a nonminimal Higgs sector, a decoupling limit can be defined. In this limit, the masses of all the physical Higgs states are large compared to the scale of electroweak symmetry breaking except for one neutral CPeven Higgs scalar, whose properties are indistinguishable from the Higgs boson of the minimal Standard Model. The decoupling limit of the most general CPconserving twoHiggs doublet model is formulated. Detection of evidence for a nonminimal Higgs sector at future colliders in the decoupling limit may present a formidable challenge for future Higgs searches. |
Probing the Standard Model with hadronic WZ Production ; The cross section for producing WZ pairs at hadron colliders is calculated to order alphas for general C and P conserving WWZ couplings. The effects of the nexttoleadingorder corrections on the derived sensitivity limits for anomalous WWZ couplings are discussed. The prospects for observing the approximate amplitude zero, which is present in the standard model WZ helicity amplitudes, are also discussed. |
The KaonPhotoproduction Of Nucleons In The Quark Model ; In this paper, we develop a general framework to study the mesonphotoproductions of nucleons in the chiral quark model. The S and U channel resonance contributions are expressed in terms of the ChewGoldbergerLowNambu CGLN amplitudes. The kaonphotoproduction processes, gamma pto K Lambda, gamma pto K Sigma0, and gamma pto K0Sigma, are calculated. The initial results show that the quark model provides a much improved description of the reaction mechanism for the kaonphotoproductions of the nucleon with less parameters than the traditional phenomenological approaches. |
Dynamical Supersymmetry Breaking in Supergravity Theories ; In rigid supersymmetry, generic models of dynamical supersymmetry breaking contain a light Goldstone boson, called the R axion. We show that supergravity effects explicitly break the R symmetry and give mass to the R axion. For visible and renormalizable hidden sector models, the massive R axion is free from astrophysical and cosmological problems. For nonrenormalizable hidden sector models, the R axion suffers from cosmological difficulties similar to those of the moduli fields in string theory. |
BEYOND THE STANDARD MODEL WITH EFFECTIVE LAGRANGIANS ; We discuss some applications of the effective quantum field theory to the description of the physics beyond the Standard Model. We consider two different examples. In the first one we derive, at the oneloop level, an effective lagrangian for an extension of the Standard Model with a charged scalar singlet by integrating out'' the heavy scalar. In the second example we illustrate the use of general effective theories at the loop level. |
APPLICATIONS OF EFFECTIVE LAGRANGIANS ; The applications of effective lagrangians to the determination of the effects of physics beyond the Standard Model are briefly described. Emphasis is given to those effective operators which generate the largest deviations form the Standard Model; some applications are described. of the paper or other short description Talk given at Beyond the Standard Model IV, Lake Tahoe, CA, Dec. 1318, 1994 |
Chiral Effective Lagrangian Description of Bulk Nuclear Matter ; Here we point out that the fournucleon terms incorporate into lowest order nonlinear chiral effective Lagrangians the same description of bulk nuclear matter contained in the Walecka model, that is generally considered satisfactory. We find this point worth noticing because, while the Walecka model is an entirely phenomenological renormalizable model, nonlinear chiral Lagrangians have a deep basis in elementary particle physics, and, in this sense, are more fundamental. |
CP Violation and Electroweak Baryogenesis in Extensions of the Standard Model ; We develop a new and general method to calculate the effects of cp violation from extensions of the standard model on the mechanism of electroweak baryogenesis. We illustrate its applicability in the framework of twohiggs doublet models. |
Bound states of scalar bosons in extensions of the Standard Model ; We explore systematically, in a general two Higgs doublet model, the possibility, that bound systems of scalar bosons do exist. We find a wide region of parameter space in the scalar potential for which Swave bound states of Higgs bosons do indeed exist. On the contrary we show that the Minimal Supersimmetric Standard Model does not admit such bound systems. |
Constraining new interactions with leptonic tau decays ; The recent measurements of the Michel parameters in tau decays enable, for the first time, a thorough analysis of the leptonic sector. In general, in models beyond the Standard Model, these parameters will be altered through changes in the W and Z couplings, andor through interactions mediated by new gauge bosons. We perform a complete, model independent analysis of the constraints imposed by the present data on such bosonmediated interactions, and point out the existence of useful relations among the couplings. |
Spontaneous CP violation in supersymmetric models with four higgs doublets ; We consider supersymmetric extensions of the standard model with two pairs of Higgs doublets. We study the possibility that CP violation is generated spontaneously in the scalar sector via vacuum expectation values VEVs of the Higgs fields. Using a simple geometrical interpretation of the minimum conditions we prove that the minimum of the treelevel scalar potential for these models is allways real. We show that complex VEVs can appear once radiative corrections andor explicit it soft CP violating terms are added to the effective potential. |
Extended Electroweak Models and Their Tests in Future Colliders ; Some possible tests of physics beyond the Standard Model in the next generation collider experiments are considered. The main emphasis is put on the processes which may be studied in the nonconventional ee, egamma and gammagamma operation modes of the next linear collider NLC. In particular, sensitivity of the NLC for testing the gauge boson selfinteractions through the reaction egammato Wnu is investigated. High energy tests of the susy and nonsusy leftright symmetric models are analysed. |
Lepton Flavor Violation in SUSYSO10 with Predictive Yukawa Texture ; We analyze the scalar lepton mass matrices in a supersymmetric SO10 grand unified model with soft SUSY breaking terms generated at Planck scale and a GeorgiJarslkog Yukawa texture at GUT scale induced by higher dimensional operators. This model predicts lepton flavor violation. The predictive features of the GeorgiJarlskog texture are used to estimate branching ratios for the radiative decays ea rightarrow ebgamma, and we find rates that could provide an experimental test for this kind of model. |
Extensions of the Standard Model ; Rapporteur talk at the International Europhysics Conference on High Energy Physics, Brussels Belgium, July 27August 2, 1995. This talk begins with a brief general introduction to the extensions of the Standard Model, reviewing the ideology of effective field theories and its practical implications. The central part deals with candidate extensions near the Fermi scale, focusing on some phenomenological aspects of the Minimal Supersymmetric Standard Model. The final part discusses some possible lowenergy implications of further extensions near the Planck scale, namely superstring theories. |
Longitudinal Zboson pair production via gluon fusion in technicolor models ; We study the coupling of two longitudinal Zbosons to two gluons via technicolor interactions. Noticing a similarity of this process to 2 gamma rightarrow 2 pi0, we calculate the amplitude in chiral perturbation theory in onegeneration technicolor model. At the invariant mass of ZLZL above the colored pseudoGoldstone boson threshold, we find the signal in proton collisions at sqrts 14, TeV is stronger than the standard model background by an order of magnitude, and is large enough to be easily observable at LHC. The cross section for WLWL pair production is also presented. |
A Flipped SO10 GUT Model and the Fermion Mass Hierarchy ; We present a viable flipped version of the SO10 model consistent with the phenomenological requirements of having a nontrivial quark mixing matrix, natural doublettriplet splitting, and a single pair of light electroweak Higgs doublet scalar bosons. In the presence of suitable nonrenormalizable superpotential terms the model can reproduce the hierarchy observed in quark masses and mixings as well as an acceptable neutrino mass generated via the seesaw mechanism needed to explain dark matter and solar neutrino data. |
Unitarity Bounds in the Vector Condensate Model of Electroweak Interactions ; We replace the standard model scalar doublet by a doublet of vector fields and generate masses by dynamical symmetry breaking. Oblique radiative corrections are small if the new vector bosons B, B0 are heavy. In this note it is shown that the model has a low momentum scale and above Lambda simeq 2 TeV it does not respect the perturbative unitarity. From treegraph unitarity the allowed region of B B0 mass is estimated as mB geq 369 hboxGeV quad mB0 geq 410 GeV at Lambda 1 TeV. |
SUSY GUTs contributions and model independent extractions of CP phases ; We consider the origin of new phases in supersymmetric grand unification model, and show how significant new contributions arise from the gluino mediated diagram. We then present a more general model independent analysis of various modes of Bdecays suggested previously for measurement of the CKM phases and point out what they really measure. It is in principle possible to separate out all the phases. |
A Form Factor Model for Exclusive B and DDecays ; An explicit model is presented which gives the momentum transferdependent ratios of form factors of hadronic currents. For the unknown IsgurWise function and its generalization for transitions to light particles a simple phenomenological Ansatz is added. The model allows a calculation of all form factors in terms of mass parameters only. It is tested by comparison with experimental data, QCD sum rules and lattice calculations. |
Parity Violation in Bottom Quark Pair Production at Polarized Hadron Colliders ; Parity violation induced by the chromoanapole form factor of the bottom quark, generated from weak corrections, is studied in polarized hadron collisions. The forwardbackward asymmetry in the bottom quark pair production at polarized pp and pbarp colliders is evaluated in the Standard Model and in a Two Higgs Doublet Model to examine the effects of parity violation. In the models studied, promising results are found for polarized pbarp colliders. |
Electroweak baryogenesis and the Minimal Supersymmetric Standard Model ; In principle, the baryon asymmetry of the Universe can be generated at the electroweak phase transition but the experimental lower limit on the Higgs mass seems to rule out a Standard Model scenario. However, it has been shown recently that in the Minimal Supersymmetric Standard Model, the electroweak phase transition can be a strong enough first order one for baryogenesis if the mass of one top squark is close to or smaller than the top mass. |
Coupling Gravity and the Standard Model a Conformal Approach ; In 1992 Professor Ryszard Rcaczka started to work on formulation of a version of the Standard Model conformally coupled with gravity. Being his student I had got the honour to participate in those researches. The conformally invariant HiggsFree Model was the result of our investigations. Ryszard Rcaczka passed away on 26 August 1996. I present here a short memorial survey of our results. |
The phenomenology of neutral heavy leptons ; Naturally small neutrino masses can arise in some grand unified models. The mechanism of neutrino mass generation in these models typically requires the existence of neutral heavy leptons. We study the lowenergy phenomenology of these new fermions. Concentrating on loop corrections due to neutral heavy leptons, we examine how the flavourconserving leptonic decays of the Z boson, universality breaking in these decays, and the W boson mass depend on the mass and mixings of the neutral heavy leptons. Working within the framework of a superstringinspired SU2L x U1Y model, we show that these flavourconserving processes have some virtues over the traditionally considered flavourviolating decays. |