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## Full-Text Articles in Physics

Unitarized Pseudoscalar Meson Scattering Amplitudes In Three Flavor Linear Sigma Models, Joseph Schechter, Deirdre Black, Amir H. Fariborz, Sherif Moussa, Salah Nasri

#### Unitarized Pseudoscalar Meson Scattering Amplitudes In Three Flavor Linear Sigma Models, Joseph Schechter, Deirdre Black, Amir H. Fariborz, Sherif Moussa, Salah Nasri

*Physics*

The three flavor linear sigma model is studied as a ``toy model'' for understanding the role of possible light scalar mesons in the \pi \pi, \pi K and \pi \eta scattering channels. The approach involves computing the tree level partial wave amplitude for each channel and unitarizing by a simple K-matrix prescription which does not introduce any new parameters. If the renormalizable version of the model is used there is only one free parameter. While this highly constrained version has the right general structure to explain \pi \pi scatteirng, it is ``not quite'' right. A reasonable fit can be made ...

Phase Diagram Of Three-Dimensional Dynamical Triangulations With A Boundary, Simon Catterall, Simeon Warner, Ray Renken

#### Phase Diagram Of Three-Dimensional Dynamical Triangulations With A Boundary, Simon Catterall, Simeon Warner, Ray Renken

*Physics*

We use Monte Carlo simulation to study the phase diagram of three-dimensional dynamical triangulations with a boundary. Three phases are indentified and characterized. One of these phases is a new, boundary dominated phase; a simple argument is presented to explain its existence. First-order transitions are shown to occur along the critical lines separating phases.

Master Equation For Hydrogen Recombination On Grain Surfaces, Gianfranco Vidali, Ofer Biham, Itay Furman, Valerio Pirronello

#### Master Equation For Hydrogen Recombination On Grain Surfaces, Gianfranco Vidali, Ofer Biham, Itay Furman, Valerio Pirronello

*Physics*

Recent experimental results on the formation of molecular hydrogen on astrophysically relevant surfaces under conditions similar to those encountered in the interstellar medium provided useful quantitative information about these processes. Rate equation analysis of experiments on olivine and amorphous carbon surfaces provided the activation energy barriers for the diffusion and desorption processes relevant to hydrogen recombination on these surfaces. However, the suitability of rate equations for the simulation of hydrogen recombination on interstellar grains, where there might be very few atoms on a grain at any given time, has been questioned. To resolve this problem, we introduce a master equation ...

Exploring The Structure Of A Possible Light Scalar Nonet, Joseph Schechter, Deirdre Black, Amir H. Fariborz

#### Exploring The Structure Of A Possible Light Scalar Nonet, Joseph Schechter, Deirdre Black, Amir H. Fariborz

*Physics*

We first review the work of the Syracuse group, which uses an effective chiral Lagrangian approach, on meson-meson scattering. An illustration providing evidence for the existence of a strange scalar resonance of mass around 900 MeV is given. An attempt to fit this \kappa (900) together with a similarly obtained \sigma (560) and the well known a_0(980) and f_0(980) into a nonet pattern suggests that the underlying structure is closer to a dual quark-dual antiquark than to a quark-antiquark. A possible mechanism to explain a next higher-in mass scalar meson nonet is also discussed. This involves mixing between ...

Phase Diagram Of Four-Dimensional Dynamical Triangulations With A Boundary, Simon Catterall, Simeon Warner

#### Phase Diagram Of Four-Dimensional Dynamical Triangulations With A Boundary, Simon Catterall, Simeon Warner

*Physics*

We report on simulations of DT simplicial gravity for manifolds with the topology of the 4-disk. We find evidence for four phases in a two-dimensional parameter space. In two of these the boundary plays no dynamical role and the geometries are equivalent to those observed earlier for the sphere S^4. In another phase the boundary is maximal and the quantum geometry degenerates to a one dimensional branched polymer. In contrast we provide evidence that the fourth phase is effectively three-dimensional. We find discontinuous phase transitions at all the phase boundaries.

The Cleo Iii Ring Imaging Cherenkov Detector, Raymond Mountain, Marina Artuso, R. Ayad, A. Efimov

#### The Cleo Iii Ring Imaging Cherenkov Detector, Raymond Mountain, Marina Artuso, R. Ayad, A. Efimov

*Physics*

The CLEO detector has been upgraded to include a state of the art particle identification system, based on the Ring Imaging Cherenkov Detector (RICH) technology, in order to take data at the upgraded CESR electron positron collider. The expected performance is reviewed, as well as the preliminary results from an engineering run during the first few months of operation of the CLEO III detector.

A Lattice Path Integral For Supersymmetric Quantum Mechanics, Simon Catterall, Eric B. Gregory

#### A Lattice Path Integral For Supersymmetric Quantum Mechanics, Simon Catterall, Eric B. Gregory

*Physics*

We report on a study of the supersymmetric anharmonic oscillator computed using a euclidean lattice path integral. Our numerical work utilizes a Fourier accelerated hybrid Monte Carlo scheme to sample the path integral. Using this we are able to measure massgaps and check Ward identities to a precision of better than one percent. We work with a non-standard lattice action which we show has an {\it exact} supersymmetry for arbitrary lattice spacing in the limit of zero interaction coupling. For the interacting model we show that supersymmetry is restored in the continuum limit without fine tuning. This is contrasted with ...

Driven Vortices In Confined Geometry: The Corbino Disk, M. Cristina Marchetti

#### Driven Vortices In Confined Geometry: The Corbino Disk, M. Cristina Marchetti

*Physics*

The fabrication of artificial pinning structures allows a new generation of experiments which can probe the properties of vortex arrays by forcing them to flow in confined geometries. We discuss the theoretical analysis of such experiments in both flux liquids and flux solids, focusing on the Corbino disk geometry. In the liquid, these experiments can probe the critical behavior near a continuous liquid-glass transition. In the solid, they probe directly the onset of plasticity.

Energetics And Geometry Of Excitations In Random Systems, Alan Middleton

#### Energetics And Geometry Of Excitations In Random Systems, Alan Middleton

*Physics*

Methods for studying droplets in models with quenched disorder are critically examined. Low energy excitations in two dimensional models are investigated by finding minimal energy interior excitations and by computing the effect of bulk perturbations. The numerical data support the assumptions of compact droplets and a single exponent for droplet energy scaling. Analytic calculations show how strong corrections to power laws can result when samples and droplets are averaged over. Such corrections can explain apparent discrepancies in several previous numerical results for spin glasses

Essentials Of K-Essence, Christian Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt

#### Essentials Of K-Essence, Christian Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt

*Physics*

We recently introduced the concept of "k-essence" as a dynamical solution for explaining naturally why the universe has entered an epoch of accelerated expansion at a late stage of its evolution. The solution avoids fine-tuning of parameters and anthropic arguments. Instead, k-essence is based on the idea of a dynamical attractor solution which causes it to act as a cosmological constant only at the onset of matter-domination. Consequently, k-essence overtakes the matter density and induces cosmic acceleration at about the present epoch. In this paper, we present the basic theory of k-essence and dynamical attractors based on evolving scalar fields ...

An Improved Limit On The Rate Of The Decay K^+ -> Pi^+ Mu^+ E^-, Duncan Brown, R. Appel

#### An Improved Limit On The Rate Of The Decay K^+ -> Pi^+ Mu^+ E^-, Duncan Brown, R. Appel

*Physics*

The experiment E865 at BNL places an upper limit on the branching ratio for the decay K+ -> pi+ mu+ e- of 3.9x10^-11 (90% C.L.). Along with with other results this yields a combined upper limit on this branching ratio of 2.8x10^-11. A new upper limit on the branching ratio for pi0 -> mu+ e- of 3.8x10^-10 (90% C.L.) is also established. The experiment and analysis are described.

A Dynamical Solution To The Problem Of A Small Cosmological Constant And Late-Time Cosmic Acceleration, Christian Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt

#### A Dynamical Solution To The Problem Of A Small Cosmological Constant And Late-Time Cosmic Acceleration, Christian Armendariz-Picon, V. Mukhanov, Paul J. Steinhardt

*Physics*

Increasing evidence suggests that most of the energy density of the universe consists of a dark energy component with negative pressure, a ``cosmological constant" that causes the cosmic expansion to accelerate. In this paper, we address the puzzle of why this component comes to dominate the universe only recently rather than at some much earlier epoch. We present a class of theories based on an evolving scalar field where the explanation is based entirely on internal dynamical properties of the solutions. In the theories we consider, the dynamics causes the scalar field to lock automatically into a negative pressure state ...

Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, Alan Middleton, M. Cristina Marchetti, Thomas Prellberg

#### Viscoelastic Depinning Of Driven Systems: Mean-Field Plastic Scallops, Alan Middleton, M. Cristina Marchetti, Thomas Prellberg

*Physics*

We have investigated the mean field dynamics of an overdamped viscoelastic medium driven through quenched disorder. The model introduced incorporates coexistence of pinned and sliding degrees of freedom and can exhibit continuous elastic depinning or first order hysteretic depinning. Numerical simulations indicate mean field instabilities that correspond to macroscopic stick-slip events and lead to premature switching. The model is relevant for the dynamics of driven vortex arrays in superconductors and other extended disordered systems.

The Statistical Mechanics Of Membranes, Mark Bowick, Alex Travesset

#### The Statistical Mechanics Of Membranes, Mark Bowick, Alex Travesset

*Physics*

The fluctuations of two-dimensional extended objects membranes is a rich and exciting field with many solid results and a wide range of open issues. We review the distinct universality classes of membranes, determined by the local order, and the associated phase diagrams. After a discussion of several physical examples of membranes we turn to the physics of crystalline (or polymerized) membranes in which the individual monomers are rigidly bound. We discuss the phase diagram with particular attention to the dependence on the degree of self-avoidance and anisotropy. In each case we review and discuss analytic, numerical and experimental predictions of ...