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Articles 691 - 707 of 707

Full-Text Articles in Physics

Symmetry Breaking In A Generalized Skyrme Model, Joseph Schechter Oct 1992

Symmetry Breaking In A Generalized Skyrme Model, Joseph Schechter

Physics

We first outline the calculations of the neutron-proton mass difference and of the axial singlet matrix element (relevant to the "proton spin" puzzle) in a generalized Skyrme model of pseudoscalars and vectors. These two calculations are, perhaps surprisingly, linked to each other and furthermore are sensitive to some fine details of symmetry breaking in the effective meson Lagrangian. This provides a motivation for us to examine these symmetry breaking terms more closely. We find a qualitatively new feature in the symmetry breaking pattern of the vector meson system and discuss its significance. (Talk at Workshop on "Baryons as Skyrme Solitons ...


Effective Hadron Dynamics: From Meson Masses To The Proton Spin Puzzle, Joseph Schechter, A Subbaraman, H. Weigel Oct 1992

Effective Hadron Dynamics: From Meson Masses To The Proton Spin Puzzle, Joseph Schechter, A Subbaraman, H. Weigel

Physics

We construct a three flavor chiral Lagrangian of pseudoscalars and vectors with special emphasis on the symmetry breaking terms. Comparing tree level two and three point functions with experiment allows us to first, fix the parameters of the model (including the light quark mass ratios) and second, to predict m(K^{*+})-m(K^{*\circ}),\, \Gamma(K^*\rightarrow K\pi) and \Gamma(\phi\rightarrow K {\overline K}). The last mentioned quantities come out reasonably well, in contrast to an ``ordinary" SU(3) treatment. For this purpose we need ``second order" symmetry breakers involving the vector fields analogous to those needed for ...


Role Of Light Vector Mesons In The Heavy Particle Chiral Lagrangian, Joseph Schechter, A. Subbaraman Sep 1992

Role Of Light Vector Mesons In The Heavy Particle Chiral Lagrangian, Joseph Schechter, A. Subbaraman

Physics

We give the general framework for adding "light" vector particles to the heavy hadron effective chiral Lagrangian. This has strong motivations both from the phenomenological and aesthetic standpoints. An application to the already observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed


The Cosmological Kibble Mechanism In The Laboratory: String Formation In Liquid Crystals, Mark Bowick, L. Chandar, Eric A. Schiff, Ajit M. Srivastava Aug 1992

The Cosmological Kibble Mechanism In The Laboratory: String Formation In Liquid Crystals, Mark Bowick, L. Chandar, Eric A. Schiff, Ajit M. Srivastava

Physics

We have observed the production of strings (disclination lines and loops) via the Kibble mechanism of domain (bubble) formation in the isotropic to nematic phase transition of a sample of uniaxial nematic liquid crystal. The probablity of string formation per bubble is measured to be $0.33 \pm 0.01$. This is in good agreement with the theoretical value $1/ \pi$ expected in two dimensions for the order parameter space $S^2/{\bf Z}_2$ of a simple uniaxial nematic liquid crystal.


Critical Behavior Of Charge Density Waves Below Threshold: Numerical And Scaling Analysis, Alan Middleton, Daniel S. Fisher Jul 1992

Critical Behavior Of Charge Density Waves Below Threshold: Numerical And Scaling Analysis, Alan Middleton, Daniel S. Fisher

Physics

The critical behavior of pinned charge density waves (CDW's) is studied as the threshold for sliding is approached. Using the Fukuyama-Lee-Rice Hamiltonian with relaxational dynamics, the polarization and linear response are calculated numerically. ... On the irreversible approach to threshold, the response due to avalanches triggered by local instabilities dominates the polarizability, which diverges in one and two dimensions. Characteristic diverging length scales are studied using finite-size scaling of the sample-to-sample variations of the threshold field in finite systems and finite-size effects in the linear polarizability and the irreversible polarization. A dominant diverging correlation length is found which controls the ...


Modification Of The Magnetic Flux-Line Interaction At A Superconductor's Surface, M. Cristina Marchetti Jul 1992

Modification Of The Magnetic Flux-Line Interaction At A Superconductor's Surface, M. Cristina Marchetti

Physics

The pair interaction between magnetic flux lines in a semi-infinite slab of an anisotropic type-II superconductor in an external field is derived in the London limit. The case where the applied field is normal to the superconductor/vacuum interface is considered. The presence of stray fields near the surface leads to an additional contribution to the repulsive interaction between flux lines that vanishes exponentially with the distance from the interface. The pair interaction is used to obtain the continuum elastic energy of a distorted semi-infinite flux-line array. The presence of the superconductor/vacuum interface yields surface contributions to the compressional ...


Numerical Study Of C>1 Matter Coupled To Quantum Gravity, Simon Catterall, John B. Kogut, Ray L. Renken Jun 1992

Numerical Study Of C>1 Matter Coupled To Quantum Gravity, Simon Catterall, John B. Kogut, Ray L. Renken

Physics

We present the results of a numerical simulation aimed at understanding the nature of the `c = 1 barrier' in two dimensional quantum gravity. We study multiple Ising models living on dynamical \phi^3 graphs and analyse the behaviour of moments of the graph loop distribution. We notice a universality at work as the average properties of typical graphs from the ensemble are determined only by the central charge. We further argue that the qualitative nature of these results can be understood from considering the effect of fluctuations about a mean field solution in the Ising sector.


Self Organization And A Dynamical Transition In Traffic Flow Models, Alan Middleton, Ofer Biham, Dov Levine Jun 1992

Self Organization And A Dynamical Transition In Traffic Flow Models, Alan Middleton, Ofer Biham, Dov Levine

Physics

A simple model that describes traffic flow in two dimensions is studied. A sharp {\it jamming transition } is found that separates between the low density dynamical phase in which all cars move at maximal speed and the high density jammed phase in which they are all stuck. Self organization effects in both phases are studied and discussed.


Three Dimensional Quantum Gravity Coupled To Ising Matter, Simon Catterall, Ray L. Renken, John B. Kogut Jun 1992

Three Dimensional Quantum Gravity Coupled To Ising Matter, Simon Catterall, Ray L. Renken, John B. Kogut

Physics

We establish the phase diagram of three--dimensional quantum gravity coupled to Ising matter. We find that in the negative curvature phase of the quantum gravity there is no disordered phase for ferromagnetic Ising matter because the coordination number of the sites diverges. In the positive curvature phase of the quantum gravity there is evidence for two spin phases with a first order transition between them.


Thermal Rounding Of The Charge Density Wave Depinning Transition, Alan Middleton May 1992

Thermal Rounding Of The Charge Density Wave Depinning Transition, Alan Middleton

Physics

The rounding of the charge density wave depinning transition by thermal noise is examined. Hops by localized modes over small barriers trigger ``avalanches'', resulting in a creep velocity much larger than that expected from comparing thermal energies with typical barriers. For a field equal to the $T=0$ depinning field, the creep velocity is predicted to have a {\em power-law} dependence on the temperature $T$; numerical computations confirm this result. The predicted order of magnitude of the thermal rounding of the depinning transition is consistent with rounding seen in experiment.


Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie Jan 1992

Empirical Relations Between Static And Dynamic Exponents For Ising Model Cluster Algorithms, Paul D. Coddington, Clive F. Baillie

Physics

We have measured the autocorrelations for the Swendsen-Wang and the Wolff cluster update algorithms for the Ising model in 2, 3 and 4 dimensions. The data for the Wolff algorithm suggest that the autocorrelations are linearly related to the specific heat, in which case the dynamic critical exponent zW int,E = α/ν. For the Swendsen-Wang algorithm, scaling the autocorrelations by the average maximum cluster size gives either a constant or a logarithm, which implies that zSW int,E = β/ν for the Ising model.


Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson Jan 1992

Translational Correlations In The Vortex Array At The Surface Of A Type-Ii Superconductor, M. Cristina Marchetti, David R. Nelson

Physics

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational ...


Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Multicriticality, Scaling Operators And Mkdv Flows For The Symmetric Unitary One Matrix Models, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics

We present a review of the Symmetric Unitary One Matrix Models. In particular we compute the scaling operators in the double scaling limit and the corresponding mKdV flows. We briefly discuss the computation of the space of solutions to the string equation as a subspace of Gr (0) \Theta Gr (0) which is invariant under the mKdV flows.


Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick Jan 1992

Unitary One Matrix Models: String Equation And Flows, Konstantinos N. Anagnostopoulos, Mark Bowick

Physics

We review the Symmetric Unitary One Matrix Models. In particular we discuss the string equation in the operator formalism, the mKdV flows and the Virasoro Constraints. We focus on the -function formalism for the flows and we describe its connection to the (big cell of the) Sato Grassmannian Gr (0) via the Plucker embedding of Gr (0) into a fermionic Fock space. Then the space of solutions to the string equation is an explicitly computable subspace of Gr (0) \Theta Gr (0) which is invariant under the flows.


The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz Jan 1991

The Solution Space Of The Unitary Matrix Model String Equation And The Sato Grassmannian, Konstantinos N. Anagnostopoulos, Mark Bowick, Albert Schwarz

Physics

The space of all solutions to the string equation of the symmetric unitary one-matrix model is determined. It is shown that the string equation is equivalent to simple conditions on points V 1 and V 2 in the big cell Gr (0) of the Sato Grassmannian Gr. This is a consequence of a well-defined continuum limit in which the string equation has the simple form [P; Q \Gamma ] = 1, with P and Q \Gamma 2 \Theta 2 matrices of differential operators. These conditions on V 1 and V 2 yield a simple system of first order differential equations whose analysis ...


Chiral Phase Transition For Su(N) Gauge Theories Via An Effective Lagrangian Approach, Joseph Schechter, Francesco Sannino Mar 1990

Chiral Phase Transition For Su(N) Gauge Theories Via An Effective Lagrangian Approach, Joseph Schechter, Francesco Sannino

Physics

We study the chiral phase transition for vector-like SU(N) gauge theories as a function of the number of quark flavors N_f by making use of an anomaly-induced effective potential. We modify an effective potential of a previous work, suggested for N_f < N, and apply it to larger values of N_f where the phase transition is expected to occur. The new effective potential depends explicitly on the full \beta-function and the anomalous dimension \gamma of the quark mass operator. By using this potential we argue that chiral symmetry is restored for \gamma <1. A perturbative computation of \gamma then leads to an estimate of the critical value N_f^c for the transition.


Eta' To Eta Pi Pi Decay As A Probe Of A Possible Lowest-Lying Scalar Nonet, Joseph Schechter, Amir H. Fariborz Feb 1990

Eta' To Eta Pi Pi Decay As A Probe Of A Possible Lowest-Lying Scalar Nonet, Joseph Schechter, Amir H. Fariborz

Physics

We study the eta' to eta pi pi decay within an effective chiral Lagrangian approach in which the lowest lying scalar meson candidates sigma(560) and kappa(900) together with the f0(980) and a0(980) are combined into a possible nonet. We show that there exists a unique choice of the free parameters of this model which, in addition to fitting the pi pi and pi K scattering amplitudes, well describes the experimental measurements for the partial decay width of eta' to eta pi pi and the energy dependence of this decay. As a by-product, we estimate the a0 ...