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Full-Text Articles in Physics

From Twisted Supersymmetry To Orbifold Lattices, Simon Catterall Dec 2007

From Twisted Supersymmetry To Orbifold Lattices, Simon Catterall

Physics

We show how to derive the supersymmetric orbifold lattices of Cohen et al. \cite{Cohen:2003xe,Cohen:2003qw} and Kaplan et al. \cite{Kaplan:2005ta} by direct discretization of an appropriate twisted supersymmetric Yang-Mills theory. We examine in detail the four supercharge two dimensional theory and the theory with sixteen supercharges in four dimensions. The continuum limit of the latter theory is the well known Marcus twist of {\cal N}=4 Yang-Mills. The lattice models are gauge invariant and possess one exact supersymmetry at non-zero lattice spacing.


Preheating In Derivatively-Coupled Inflation Models, Christian Armendariz-Picon, Mark Trodden, Eric J. West Nov 2007

Preheating In Derivatively-Coupled Inflation Models, Christian Armendariz-Picon, Mark Trodden, Eric J. West

Physics

We study preheating in theories where the inflaton couples derivatively to scalar and gauge fields. Such couplings may dominate in natural models of inflation, in which the flatness of the inflaton potential is related to an approximate shift symmetry of the inflaton. We compare our results with previously studied models with non-derivative couplings. For sufficiently heavy scalar matter, parametric resonance is ineffective in reheating the universe, because the couplings of the inflaton to matter are very weak. If scalar matter fields are light, derivative couplings lead to a mild long-wavelength instability that drives matter fields to non-zero expectation values. In ...


Matching Kasteleyn Cities For Spin Glass Ground States, Alan Middleton, Creighton K. Thomas Nov 2007

Matching Kasteleyn Cities For Spin Glass Ground States, Alan Middleton, Creighton K. Thomas

Physics

As spin glass materials have extremely slow dynamics, devious numerical methods are needed to study low-temperature states. A simple and fast optimization version of the classical Kasteleyn treatment of the Ising model is described and applied to two-dimensional Ising spin glasses. The algorithm combines the Pfaffian and matching approaches to directly strip droplet excitations from an excited state. Extended ground states in Ising spin glasses on a torus, which are optimized over all boundary conditions, are used to compute precise values for ground state energy densities.


Scalar Mesons From An Effective Lagrangian Approach, Joseph Schechter, Amir H. Fariborz, Renata Jora Nov 2007

Scalar Mesons From An Effective Lagrangian Approach, Joseph Schechter, Amir H. Fariborz, Renata Jora

Physics

A brief discussion of the recent interest in light scalar mesons motivates the study of a generalized linear sigma model. In an SU(3) flavor invariant version of the model there is a prediction that the the lighter scalars have sizeable "four quark" content. It is further predicted that one of the singlet scalars should be exceptionally light. Due to the presence of scalar mesons, the model gives "controlled" corrections to the current algebra formula for threshold pion pion scattering. These corections act in the direction to improve agreement with current experiments.


Vacancy Localization In The Square Dimer Model, Mark Bowick, J. Bouttier, Emmanuel Guitter, Monwhea Jeng Oct 2007

Vacancy Localization In The Square Dimer Model, Mark Bowick, J. Bouttier, Emmanuel Guitter, Monwhea Jeng

Physics

We study the classical dimer model on a square lattice with a single vacancy by developing a graph-theoretic classification of the set of all configurations which extends the spanning tree formulation of close-packed dimers. With this formalism, we can address the question of the possible motion of the vacancy induced by dimer slidings. We find a probability 57/4-10Sqrt[2] for the vacancy to be strictly jammed in an infinite system. More generally, the size distribution of the domain accessible to the vacancy is characterized by a power law decay with exponent 9/8. On a finite system, the probability ...


Asymmetric Weak-Pinning Superconducting Channels: Vortex Ratchets, Britton Plourde, T. W. Heitmann, C. Song, M. P. Defeo, Kang Yu Oct 2007

Asymmetric Weak-Pinning Superconducting Channels: Vortex Ratchets, Britton Plourde, T. W. Heitmann, C. Song, M. P. Defeo, Kang Yu

Physics

The controlled motion of objects through narrow channels is important in many fields. We have fabricated asymmetric weak-pinning channels in a superconducting thin-film strip for controlling the dynamics of vortices. The lack of pinning allows the vortices to move through the channels with the dominant interaction determined by the shape of the channel walls. We present measurements of vortex dynamics in the channels and compare these with similar measurements on a set of uniform-width channels. While the uniform-width channels exhibit a symmetric response for both directions through the channel, the vortex motion through the asymmetric channels is quite different, with ...


Gauge-Gravity Duality -- Super Yang Mills Quantum Mechanics, Simon Catterall, Toby Wiseman Sep 2007

Gauge-Gravity Duality -- Super Yang Mills Quantum Mechanics, Simon Catterall, Toby Wiseman

Physics

We describe the conjectured holographic duality between Yang-Mills quantum mechanics and type IIa string theory. This duality allows us to use lattice Monte Carlo simulations to probe the physics of the gravitational theory - for example, at low energies it provides a computation of black hole entropy in terms of a sum over microstates of the dual gauge theory. Numerical results are presented of the 4 supercharge theory at finite temperature.


Bubble Raft Model For A Paraboloidal Crystal, Mark Bowick, Luca Giomi, Homin Shin, Creighton K. Thomas Sep 2007

Bubble Raft Model For A Paraboloidal Crystal, Mark Bowick, Luca Giomi, Homin Shin, Creighton K. Thomas

Physics

We investigate crystalline order on a two-dimensional paraboloid of revolution by assembling a single layer of millimeter-sized soap bubbles on the surface of a rotating liquid, thus extending the classic work of Bragg and Nye on planar soap bubble rafts. Topological constraints require crystalline configurations to contain a certain minimum number of topological defects such as disclinations or grain boundary scars whose structure is analyzed as a function of the aspect ratio of the paraboloid. We find the defect structure to agree with theoretical predictions and propose a mechanism for scar nucleation in the presence of large Gaussian curvature.


Formation Of Molecular Hydrogen On Amorphous Silicate Surfaces, Gianfranco Vidali, Ling Li, E. Congiu, S. Swords Sep 2007

Formation Of Molecular Hydrogen On Amorphous Silicate Surfaces, Gianfranco Vidali, Ling Li, E. Congiu, S. Swords

Physics

Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H_2 formation in diffuse interstellar clouds.


Low Energy Scattering With A Nontrivial Pion, Joseph Schechter, Amir H. Fariborz, Renata Jora Aug 2007

Low Energy Scattering With A Nontrivial Pion, Joseph Schechter, Amir H. Fariborz, Renata Jora

Physics

An earlier calculation in a generalized linear sigma model showed that the well-known current algebra formula for low energy pion pion scattering held even though the massless Nambu Goldstone pion contained a small admixture of a two-quark two-antiquark field. Here we turn on the pion mass and note that the current algebra formula no longer holds exactly. We discuss this small deviation and also study the effects of an SU(3) symmetric quark mass type term on the masses and mixings of the eight SU(3) multiplets in the model. We calculate the s wave scattering lengths, including the beyond ...


Persistence And Memory In Patchwork Dynamics For Glassy Models, Alan Middleton, Creighton K. Thomas, Olivia L. White Aug 2007

Persistence And Memory In Patchwork Dynamics For Glassy Models, Alan Middleton, Creighton K. Thomas, Olivia L. White

Physics

Slow dynamics in disordered materials prohibits direct simulation of their rich nonequilibrium behavior at large scales. "Patchwork dynamics" is introduced to mimic relaxation over a very broad range of time scales by equilibrating or optimizing directly on successive length scales. This dynamics is used to study coarsening and to replicate memory effects for spin glasses and random ferromagnets. It is also used to find, with high confidence, exact ground states in large or toroidal samples.


The Yale Lar Tpc, Mitchell Soderberg, A. Curioni, Bonnie T. Fleming Aug 2007

The Yale Lar Tpc, Mitchell Soderberg, A. Curioni, Bonnie T. Fleming

Physics

In this paper we give a concise description of a liquid argon time projection chamber (LAr TPC) developed at Yale, and present results from its first calibration run with cosmic rays.


Interstitial Fractionalization And Spherical Crystallography, Mark Bowick, David R. Nelson, Homin Shin Jul 2007

Interstitial Fractionalization And Spherical Crystallography, Mark Bowick, David R. Nelson, Homin Shin

Physics

Finding the ground states of identical particles packed on spheres has relevance for stabilizing emulsions and a venerable history in the literature of theoretical physics and mathematics. Theory and experiment have confirmed that defects such as disclinations and dislocations are an intrinsic part of the ground state. Here we discuss the remarkable behavior of vacancies and interstitials in spherical crystals. The strain fields of isolated disclinations forced in by the spherical topology literally rip interstitials and vacancies apart, typically into dislocation fragments that combine with the disclinations to create small grain boundary scars. The fractionation is often into three charge-neutral ...


Two Chiral Nonet Model With Massless Quarks, Joseph Schechter, Amir H. Fariborz, Renata Jora Jul 2007

Two Chiral Nonet Model With Massless Quarks, Joseph Schechter, Amir H. Fariborz, Renata Jora

Physics

We present a detailed study of a linear sigma model containing one chiral nonet transforming under U(1)_A as a quark-antiquark composite and another chiral nonet transforming as a diquark-anti diquark composite (or, equivalently from a symmetry point of view, as a two meson molecule). The model provides an intuitive explanation of a current puzzle in low energy QCD: Recent work has suggested the existence of a lighter than 1 GeV nonet of scalar mesons which behave like four quark composites. On the other hand, the validity of a spontaneously broken chiral symmetric description would suggest that these states ...


Towards Lattice Simulation Of The Gauge Theory Duals To Black Holes And Hot Strings, Simon Catterall, Toby Wiseman Jun 2007

Towards Lattice Simulation Of The Gauge Theory Duals To Black Holes And Hot Strings, Simon Catterall, Toby Wiseman

Physics

A generalization of the AdS/CFT conjecture postulates a duality between IIA string theory and 16 supercharge Yang-Mills quantum mechanics in the large N 't Hooft limit. At low temperatures string theory describes black holes, whose thermodynamics may hence be studied using the dual quantum mechanics. This quantum mechanics is strongly coupled which motivates the use of lattice techniques. We argue that, contrary to expectation, the theory when discretized naively will nevertheless recover continuum supersymmetry as the lattice spacing is sent to zero. We test these ideas by studying the 4 supercharge version of this Yang-Mills quantum mechanics in the ...


Exact Relativistic Beta Decay Endpoint Spectrum, Joseph Schechter, S. S. Masood Jun 2007

Exact Relativistic Beta Decay Endpoint Spectrum, Joseph Schechter, S. S. Masood

Physics

The exact relativistic form for the beta decay endpoint spectrum is derived and presented in a simple factorized form. We show that our exact formula can be well approximated to yield the endpoint form used in the fit method of the KATRIN collaboration. We also discuss the three neutrino case and how information from neutrino oscillation experiments may be useful in analyzing future beta decay endpoint experiments.


Cosmological Moduli Dynamics, Scott Watson, Brian Greene, Simon Judes, Amanda Weltman Jun 2007

Cosmological Moduli Dynamics, Scott Watson, Brian Greene, Simon Judes, Amanda Weltman

Physics

Low energy effective actions arising from string theory typically contain many scalar fields, some with a very complicated potential and others with no potential at all. The evolution of these scalars is of great interest. Their late time values have a direct impact on low energy observables, while their early universe dynamics can potentially source inflation or adversely affect big bang nucleosynthesis. Recently, classical and quantum methods for fixing the values of these scalars have been introduced. The purpose of this work is to explore moduli dynamics in light of these stabilization mechanisms. In particular, we explore a truncated low ...


Baryons And Mesons With Beauty, Goldstein R. Gary, Kameshwar C. Wali May 2007

Baryons And Mesons With Beauty, Goldstein R. Gary, Kameshwar C. Wali

Physics

Recent experimental findings of several mesons and baryons with "beauty" and "charm" as flavors remind us of the days when strangeness was discovered, and how its inclusion led to SU(3)-flavor symmetry with enormous success in the classification of the "proliferated" states into SU(3) multiplets. One of the key elements was the successful application of the first order perturbation in symmetry breaking, albeit what then appeared to be huge mass differences, and the prediction of new states that were confirmed by experiments. In this note, we venture into the past and, applying the same techniques, predict some new ...


Creating Statistically Anisotropic And Inhomogeneous Perturbations, Christian Armendariz-Picon May 2007

Creating Statistically Anisotropic And Inhomogeneous Perturbations, Christian Armendariz-Picon

Physics

In almost all structure formation models, primordial perturbations are created within a homogeneous and isotropic universe, like the one we observe. Because their ensemble averages inherit the symmetries of the spacetime in which they are seeded, cosmological perturbations then happen to be statistically isotropic and homogeneous. Certain anomalies in the cosmic microwave background on the other hand suggest that perturbations do not satisfy these statistical properties, thereby challenging perhaps our understanding of structure formation. In this article we relax this tension. We show that if the universe contains an appropriate triad of scalar fields with spatially constant but non-zero gradients ...


Two Or Four: A Hint From Scalar Mesons In Radiative Phi Decays?, Joseph Schechter, Deirdre Black, Masayasu Harada May 2007

Two Or Four: A Hint From Scalar Mesons In Radiative Phi Decays?, Joseph Schechter, Deirdre Black, Masayasu Harada

Physics

In this write-up, we summarize our recent analysis of radiative decays involving light scalar mesons. Our analysis using the vector meson dominance model at tree level indicates that it may be difficult to distinguish qq\bar{q}\bar{q} picture and q\bar{q} picture for the light scalar nonet. Our result on the process of \phi \to \pi^0 \eta \gamma shows that the derivative-type f_0 K\bar{K} interaction reproduces experimental data below 950 GeV well, but gives a poor fit above 950 GeV, i.e., in the energy region around the mass of a_0(980), but that ...


Long-Range Coupling And Scalable Architecture For Superconducting Flux Qubits, Britton Plourde, Austin G. Fowler Apr 2007

Long-Range Coupling And Scalable Architecture For Superconducting Flux Qubits, Britton Plourde, Austin G. Fowler

Physics

Constructing a fault-tolerant quantum computer is a daunting task. Given any design, it is possible to determine the maximum error rate of each type of component that can be tolerated while still permitting arbitrarily large-scale quantum computation. It is an underappreciated fact that including an appropriately designed mechanism enabling long-range qubit coupling or transport substantially increases the maximum tolerable error rates of all components. With this thought in mind, we take the superconducting flux qubit coupling mechanism described in PRB 70, 140501 (2004) and extend it to allow approximately 500 MHz coupling of square flux qubits, 50 um a side ...


Molecular Hydrogen Formation On Amorphous Silicates Under Interstellar Conditions, Gianfranco Vidali, Hagai B. Perets, Ling Li, S. Swords, E. Congiu Apr 2007

Molecular Hydrogen Formation On Amorphous Silicates Under Interstellar Conditions, Gianfranco Vidali, Hagai B. Perets, Ling Li, S. Swords, E. Congiu

Physics

Experimental results on the formation of molecular hydrogen on amorphous silicate surfaces are presented for the first time and analyzed using a rate equation model. The energy barriers for the relevant diffusion and desorption processes are obtained. They turn out to be significantly higher than those obtained earlier for polycrystalline silicates, demonstrating the importance of grain morphology. Using these barriers we evaluate the efficiency of molecular hydrogen formation on amorphous silicate grains under interstellar conditions. It is found that unlike polycrystalline silicates, amorphous silicate grains are efficient catalysts of H_{2} formation within a temperature range which is relevant to ...


Alternative Large Nc Schemes And Chiral Dynamics, Joseph Schechter, Francesco Sannino Apr 2007

Alternative Large Nc Schemes And Chiral Dynamics, Joseph Schechter, Francesco Sannino

Physics

We compare the dependences on the number of colors of the leading pion pion scattering amplitudes using the single index quark field and two index quark fields. These are seen to have different relationships to the scattering amplitudes suggested by chiral dynamics which can explain the long puzzling pion pion s wave scattering up to about 1 GeV. This may be interesting for getting a better understanding of the large Nc approach as well as for application to recently proposed technicolor models.


On The Restoration Of Supersymmetry In Twisted Two-Dimensional Lattice Yang-Mills Theory, Simon Catterall Mar 2007

On The Restoration Of Supersymmetry In Twisted Two-Dimensional Lattice Yang-Mills Theory, Simon Catterall

Physics

We study a discretization of {\cal N}=2 super Yang-Mills theory which possesses a single exact supersymmetry at non-zero lattice spacing. This supersymmetry arises after a reformulation of the theory in terms of {\it twisted} fields. In this paper we derive the action of the other twisted supersymmetries on the component fields and study, using Monte Carlo simulation, a series of corresponding Ward identities. Our results for SU(2) and SU(3) support a restoration of these additional supersymmetries without fine tuning in the infinite volume continuum limit. Additionally we present evidence supporting a restoration of (twisted) rotational invariance in ...


Dynamics And Instabilities Of Defects In Two-Dimensional Crystals On Curved Backgrounds, Mark Bowick, Homin Shin, Alex Travesset Mar 2007

Dynamics And Instabilities Of Defects In Two-Dimensional Crystals On Curved Backgrounds, Mark Bowick, Homin Shin, Alex Travesset

Physics

Point defects are ubiquitous in two dimensional crystals and play a fundamental role in determining their mechanical and thermodynamical properties. When crystals are formed on a curved background, finite length grain boundaries (scars) are generally needed to stabilize the crystal. We provide a continuum elasticity analysis of defect dynamics in curved crystals. By exploiting the fact that any point defect can be obtained as an appropriate combination of disclinations, we provide an analytical determination of the elastic spring constants of dislocations within scars and compare them with existing experimental measurements from optical microscopy. We further show that vacancies and interstitials ...


Hydrodynamic And Rheology Of Active Polar Filaments, Tanniemola B. Liverpool, M. Cristina Marchetti Mar 2007

Hydrodynamic And Rheology Of Active Polar Filaments, Tanniemola B. Liverpool, M. Cristina Marchetti

Physics

The cytoskeleton provides eukaryotic cells with mechanical support and helps them perform their biological functions. It is a network of semiflexible polar protein filaments and many accessory proteins that bind to these filaments, regulate their assembly, link them to organelles and continuously remodel the network. Here we review recent theoretical work that aims to describe the cytoskeleton as a polar continuum driven out of equilibrium by internal chemical reactions. This work uses methods from soft condensed matter physics and has led to the formulation of a general framework for the description of the structure and rheology of active suspension of ...


Minimal Walking On The Lattice, Simon Catterall, Francesco Sannino Mar 2007

Minimal Walking On The Lattice, Simon Catterall, Francesco Sannino

Physics

We provide the first evidence of a walking dynamics for two color lattice Yang-Mills theory with two Dirac flavors in the symmetric representation of the gauge group.


Crystalline Order On Riemannian Manifolds With Variable Gaussian Curvature And Boundary, Mark Bowick, Luca Giomi Feb 2007

Crystalline Order On Riemannian Manifolds With Variable Gaussian Curvature And Boundary, Mark Bowick, Luca Giomi

Physics

We investigate the zero temperature structure of a crystalline monolayer constrained to lie on a two-dimensional Riemannian manifold with variable Gaussian curvature and boundary. A full analytical treatment is presented for the case of a paraboloid of revolution. Using the geometrical theory of topological defects in a continuum elastic background we find that the presence of a variable Gaussian curvature, combined with the additional constraint of a boundary, gives rise to a rich variety of phenomena beyond that known for spherical crystals. We also provide a numerical analysis of a system of classical particles interacting via a Coulomb potential on ...


Living On A Ds Brane: Effects Of Kk Modes On Inflation, Scott Watson, Claudia De Rham Feb 2007

Living On A Ds Brane: Effects Of Kk Modes On Inflation, Scott Watson, Claudia De Rham

Physics

We develop a formalism to study non-local higher-dimensional effects in braneworld scenarios from a four-dimensional effective theory point of view and check it against the well-known Garriga-Tanaka result in the appropriate limit. We then use this formalism to study the spectrum of density perturbations during inflation as seen from the lower-dimensional effective theory. In particular, we find that the gravitational potential is greatly enhanced at short wavelengths. The consequences to the curvature perturbations are nonetheless very weak and will lead to no characteristic signatures on the power spectrum.


Irrational Mode Locking In Quasiperiodic Systems, Alan Middleton, Creighton K. Thomas Feb 2007

Irrational Mode Locking In Quasiperiodic Systems, Alan Middleton, Creighton K. Thomas

Physics

A model for ac-driven systems, based on the Tang-Wiesenfeld-Bak-Coppersmith-Littlewood automaton for an elastic medium, exhibits mode-locked steps with frequencies that are irrational multiples of the drive frequency, when the pinning is spatially quasiperiodic. Detailed numerical evidence is presented for the large-system-size convergence of such a mode-locked step. The irrational mode locking is stable to small thermal noise and weak disorder. Continuous time models with irrational mode locking and possible experimental realizations are discussed.