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56
Simplicial gravity coupled to scalar matter
, 1993
"... A model for quantized gravity coupled to matter in the form of a single scalar field is investigated in four dimensions. For the metric degrees of freedom we employ Regge’s simplicial discretization, with the scalar field defined at the vertices of the foursimplices. We examine how the continuous p ..."
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A model for quantized gravity coupled to matter in the form of a single scalar field is investigated in four dimensions. For the metric degrees of freedom we employ Regge’s simplicial discretization, with the scalar field defined at the vertices of the foursimplices. We examine how the continuous phase transition found earlier, separating the smooth from the rough phase of quantized gravity, is influenced by the presence of scalar matter. A determination of the critical exponents seems to indicate that the effects of matter are rather small, unless the number of scalar flavors is large. Close to the critical point where the average curvature approaches zero, the coupling of matter to gravity is found to be weak. The nature of the phase diagram and the values for the critical exponents suggest that gravitational interactions increase with distance. 1.
Langevin Evolution of Disoriented Chiral Condensate MITCTP3150
, 2001
"... As the matter produced in a relativistic heavy ion collision cools through the QCD phase transition, the dynamical evolution of the chiral condensate will be driven out of thermal equilibrium. As a prelude to analyzing this evolution, and in particular as a prelude to learning how rapid the cooling ..."
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As the matter produced in a relativistic heavy ion collision cools through the QCD phase transition, the dynamical evolution of the chiral condensate will be driven out of thermal equilibrium. As a prelude to analyzing this evolution, and in particular as a prelude to learning how rapid the cooling must be in order for significant deviations from equilibrium to develop, we present a detailed analysis of the timeevolution of an idealized region of disoriented chiral condensate. We set up a Langevin field equation which can describe the evolution of these (or more realistic) linear sigma model configurations in contact with a heat bath representing the presence of other shorter wavelength degrees of freedom. We first analyze the model in equilibrium, paying particular attention to subtracting ultraviolet divergent classical terms and replacing them by their finite quantum counterparts. We use known results from lattice gauge theory and chiral perturbation theory to fix nonuniversal constants. The result is a theory which is ultraviolet cutoff independent and that reproduces quantitatively the expected equilibrium behavior of the quantum field theory of pions and σ fields over a wide range of temperatures. Finally, we estimate the viscosity η(T), which controls the dynamical timescale in the Langevin equation, by requiring that the timescale for DCC decay agrees with previous calculations. The resulting η(T) is larger than that found perturbatively. We also determine the temperature below which the classical field Langevin equation ceases to be a good model for the quantum field dynamics.
Anomalous thermal escape in Josephson systems perturbed by microwaves
, 2004
"... We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued temperature r ..."
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We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued temperature ranges both below and above the the classical to quantum crossover temperature. Switching current distributions are obtained both experimentally and numerically at temperatures both near and far above the quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with a simple anharmonic theory for Josephson resonance frequency as a function of bias current. Throughout, experimental results and direct numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement. 1
THE NONEXTENSIVE GENERALIZATION OF BOLTZMANNGIBBS STATISTICS AND ITS APPLICATIONS
, 2005
"... “I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work.” ..."
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“I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work.”
Parallelization of the twodimensional Ising Model on a Cluster of IBM RISC System/6000 Workstations
"... Using the PVM programming environment for parallel applications, we have parallelized a simulation of the twodimensional Ising Model on a cluster of IBM RISC System/6000 1 workstations connected by a Token Ring (16Mb/sec) and by Serial Optical Channels (220 Mb/sec) via a NSC 2 DX Router. The p ..."
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Using the PVM programming environment for parallel applications, we have parallelized a simulation of the twodimensional Ising Model on a cluster of IBM RISC System/6000 1 workstations connected by a Token Ring (16Mb/sec) and by Serial Optical Channels (220 Mb/sec) via a NSC 2 DX Router. The parallelization is done by dividing the lattice into sublattices, each sublattice being associated with one workstation. On each sublattice, a Metropolis algorithm using Multispin Coding techniques is used to generate new configurations. We provide numerical results concerning the number of spin updates per second, speedups, and efficiencies for various numbers of processors and lattice sizes. Keywords. Statistical Physics; Ising Model; Workstation Cluster; Geometric Parallelization. 1 Introduction The goal of Theoretical Statistical Physics is a mathematical description of thermodynamic properties (e.g. of magnetism or phase transitions) of macroscopic bodies, commercing with a description ...
PHYSICAL REVIEW D 70, 124007 (2004) Nonperturbative gravity and the spin of the lattice graviton
, 2004
"... The lattice formulation of quantum gravity provides a natural framework in which nonperturbative properties of the ground state can be studied in detail. In this paper we investigate how the lattice results relate to the continuum semiclassical expansion about smooth manifolds. As an example we give ..."
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The lattice formulation of quantum gravity provides a natural framework in which nonperturbative properties of the ground state can be studied in detail. In this paper we investigate how the lattice results relate to the continuum semiclassical expansion about smooth manifolds. As an example we give an explicit form for the lattice groundstate wave functional for semiclassical geometries. We then do a detailed comparison between the more recent predictions from the lattice regularized theory and results obtained in the continuum for the nontrivial ultraviolet fixed point of quantum gravity found using weak field and nonperturbative methods. In particular we focus on the derivative of the beta function at the fixed point and the related universal critical exponent for gravitation. Based on recently available lattice and continuum results we assess the evidence for the presence of a massless spintwo particle in the continuum limit of the strongly coupled lattice theory. Finally we compare the lattice prediction for the vacuumpolarization induced weak scale dependence of the gravitational coupling with recent calculations in the continuum, finding similar effects.
Dual description of the superconducting phase transition
, 1995
"... The dual approach to the GinzburgLandau theory of a BardeenCooperSchrieffer superconductor is reviewed. The dual theory describes a grand canonical ensemble of fluctuating closed magnetic vortices, of arbitrary length and shape, which interact with a massive vector field representing the local ma ..."
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The dual approach to the GinzburgLandau theory of a BardeenCooperSchrieffer superconductor is reviewed. The dual theory describes a grand canonical ensemble of fluctuating closed magnetic vortices, of arbitrary length and shape, which interact with a massive vector field representing the local magnetic induction. When the critical temperature is approached from below, the magnetic vortices proliferate. This is signaled by the disorder field, which describes the loop gas, developing a nonzero expectation value in the normal conducting phase. It thereby breaks a global U(1) symmetry. The ensuing Goldstone field is the magnetic scalar potential. The superconductingtonormal phase transition is studied by applying renormalization group theory to the dual formulation. In the regime of a secondorder transition, the critical exponents are given by those of a superfluid with a reversed temperature axis. I.
Microwaveinduced thermal escape in Josephson junctions
, 2008
"... We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued in a temperat ..."
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We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued in a temperature range far exceeding the classical to quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with the functional forms expected from Josephson plasma frequency dependencies on the bias current. Throughout, numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement with the experimental data. 1 The Josephson tunnel junction is an intriguing solid state physics system due to the macroscopic quantum nature of the variables describing the governing equations [1]; irradiation of junctions with microwave (ac) radiation has produced a number of significant nonlinear phenomena such as chaos and phaselocking observed both in experiments and theoretical