106 research outputs found
CLUSTEREASY: A Program for Simulating Scalar Field Evolution on Parallel Computers
We describe a new, parallel programming version of the scalar field
simulation program LATTICEEASY. The new C++ program, CLUSTEREASY, can simulate
arbitrary scalar field models on distributed-memory clusters. The speed and
memory requirements scale well with the number of processors. As with the
serial version of LATTICEEASY, CLUSTEREASY can run simulations in one, two, or
three dimensions, with or without expansion of the universe, with customizable
parameters and output. The program and its full documentation are available on
the LATTICEEASY website at
http://www.science.smith.edu/departments/Physics/fstaff/gfelder/latticeeasy/.
In this paper we provide a brief overview of what CLUSTEREASY does and the ways
in which it does and doesn't differ from the serial version of LATTICEEASY.Comment: 3 pages, 1 figur
CurvedLand: An Applet for Illustrating Curved Geometry without Embedding
We have written a Java applet to illustrate the meaning of curved geometry.
The applet provides a mapping interface similar to MapQuest or Google Maps;
features include the ability to navigate through a space and place permanent
point objects and/or shapes at arbitrary positions. The underlying
two-dimensional space has a constant, positive curvature, which causes the
apparent paths and shapes of the objects in the map to appear distorted in ways
that change as you view them from different relative angles and distances.Comment: 4 page
Nonlinear Inflaton Fragmentation after Preheating
We consider the nonlinear dynamics of inflaton fragmentation during and after
preheating in the simplest model of chaotic inflation. While the earlier regime
of parametric resonant particle production and the later turbulent regime of
interacting fields evolving towards equilibrium are well identified and
understood, the short intermediate stage of violent nonlinear dynamics remains
less explored. Lattice simulations of fully nonlinear preheating dynamics show
specific features of this intermediate stage: occupation numbers of the scalar
particles are peaked, scalar fields become significantly non-gaussian and the
field dynamics become chaotic and irreversible. Visualization of the field
dynamics in configuration space reveals that nonlinear interactions generate
non-gaussian inflaton inhomogeneities with very fast growing amplitudes. The
peaks of the inflaton inhomogeneities coincide with the peaks of the scalar
field(s) produced by parametric resonance. When the inflaton peaks reach their
maxima, they stop growing and begin to expand. The subsequent dynamics is
determined by expansion and superposition of the scalar waves originating from
the peaks. Multiple wave superposition results in phase mixing and turbulent
wave dynamics. Thus, the short intermediate stage is defined by the formation,
expansion and collision of bubble-like field inhomogeneities associated with
the peaks of the original gaussian field. This process is qualitatively similar
to the bubble-like inflaton fragmentation that occurs during tachyonic
preheating after hybrid or new inflation.Comment: 9 pages, 6 fig
Inflaton Fragmentation After lambda phi^4 Inflation
We use lattice simulations to examine the detailed dynamics of inflaton
fragmentation during and after preheating in chaotic
inflation. The dynamics are qualitatively similar to preheating after inflation, involving the exponential growth and subsequent expansion
and collision of bubble-like inhomogeneities of the inflaton and other scalar
fields. During this stage fluctuations of the fields become strongly
non-Gaussian. In the quartic theory, the conformal nature of the theory allows
us to extend our simulations to much greater times than is possible for the
quadratic model. With these longer simulations we have been able to determine
the time scale on which Gaussianity is restored, which occurs after a time on
the order of a thousand inflaton oscillations.Comment: 5 pages, 5 figure
Gravitational Particle Production and the Moduli Problem
A theory of gravitational production of light scalar particles during and
after inflation is investigated. We show that in the most interesting cases
where long-wavelength fluctuations of light scalar fields can be generated
during inflation, these fluctuations rather than quantum fluctuations produced
after inflation give the dominant contribution to particle production. In such
cases a simple analytical theory of particle production can be developed.
Application of our results to the theory of quantum creation of moduli fields
demonstrates that if the moduli mass is smaller than the Hubble constant then
these fields are copiously produced during inflation. This gives rise to the
cosmological moduli problem even if there is no homogeneous component of the
classical moduli field in the universe. To avoid this version of the moduli
problem it is necessary for the Hubble constant H during the last stages of
inflation and/or the reheating temperature T_R after inflation to be extremely
small.Comment: LaTeX,7 pages, 1 figure. Minor correction
Cosmology With Negative Potentials
We investigate cosmological evolution in models where the effective potential
V(\phi) may become negative for some values of the field \phi. Phase portraits
of such theories in space of variables (\phi,\dot\phi,H) have several
qualitatively new features as compared with phase portraits in the theories
with V(\phi) > 0. Cosmological evolution in models with potentials with a
"stable" minimum at V(\phi)<0 is similar in some respects to the evolution in
models with potentials unbounded from below. Instead of reaching an AdS regime
dominated by the negative vacuum energy, the universe reaches a turning point
where its energy density vanishes, and then it contracts to a singularity with
properties that are practically independent of V(\phi). We apply our methods to
investigation of the recently proposed cyclic universe scenario. We show that
in addition to the singularity problem there are other problems that need to be
resolved in order to realize a cyclic regime in this scenario. We propose
several modifications of this scenario and conclude that the best way to
improve it is to add a usual stage of inflation after the singularity and use
that inflationary stage to generate perturbations in the standard way.Comment: 51 page, 20 figure
A Longitudinal Study of Engineering Student Performance and Retention. V. Comparisons with Traditionally-Taught Students
In a longitudinal study at North Carolina State University, a cohort of students took five chemical engineering courses taught by the same instructor in five consecutive semesters. The courses made extensive use of active and cooperative learning and a variety of other techniques designed to address a broad spectrum of learning styles. Previous reports on the study summarized the instructional methods used in the experimental course sequence, described the performance of the cohort in the introductory chemical engineering course, and examined performance and attitude differences between students from rural and urban backgrounds and between male and female students.1â4 This paper compares outcomes for the experimental cohort with outcomes for students in a traditionallyâtaught comparison group. The experimental group outperformed the comparison group on a number of measures, including retention and graduation in chemical engineering, and many more of the graduates in this group chose to pursue advanced study in the field. Since the experimental instructional model did not require small classes (the smallest of the experimental classes had 90 students) or specially equipped classrooms, it should be adaptable to any engineering curriculum at any institution
The Effects of Personality Type on Engineering Student Performance and Attitudes
The MyersâBriggs Type IndicatorÂź (MBTI) was administered to a group of 116 students taking the introductory chemical engineering course at North Carolina State University. That course and four subsequent chemical engineering courses were taught in a manner that emphasized active and cooperative learning and inductive presentation of course material. Type differences in various academic performance measures and attitudes were noted as the students progressed through the curriculum. The observations were generally consistent with the predictions of type theory, and the experimental instructional approach appeared to improve the performance of MBTI types (extraverts, sensors, and feelers) found in previous studies to be disadvantaged in the engineering curriculum. The conclusion is that the MBTI is a useful tool for helping engineering instructors and advisors to understand their students and to design instruction that can benefit all of them
Equation of state and Beginning of Thermalization After Preheating
We study the out-of-equilibrium nonlinear dynamics of fields after
post-inflationary preheating. During preheating, the energy in the homogeneous
inflaton is exponentially rapidly transfered into highly occupied
out-of-equilibrium inhomogeneous modes, which subsequently evolve towards
equilibrium. The infrared modes excited during preheating evolve towards a
saturated distribution long before thermalization completes. We compute the
equation of state during and immediately after preheating. It rapidly evolves
towards radiation domination long before the actual thermal equilibrium is
established. The exact time of this transition is a non-monotonic function of
the coupling between the inflaton and the decay products, and it varies only
very weakly (around 10^(-35) s) as this coupling changes over several orders of
magnitude. This result is applied to refine the relation between the number of
efoldings N and the physical wavelength of perturbations generated during
inflation. We also discuss the implications for the theory of modulated
perturbations from preheating. We finally argue that many questions of the
thermal history of the universe should be addressed in terms of
pre-thermalization, illustrating this point with a calculation of perturbative
production of gravitinos immediately after chaotic inflation. We also highlight
the effects of three-legs inflaton interactions on the dynamics of preheating
and thermalization in an expanding universe.Comment: 15 pages, 13 figure
BRANECODE: A Program for Simulations of Braneworld Dynamics
We describe an algorithm and a C++ implementation that we have written and
made available for calculating the fully nonlinear evolution of 5D braneworld
models with scalar fields. Bulk fields allow for the stabilization of the extra
space. However, they complicate the dynamics of the system, so that analytic
calculations (performed within an effective 4D theory) are typically only
reliable close to stabilized configurations or when the evolution of the extra
space is negligible. In the general case, a numerical study of the 5D equations
is necessary, and the algorithm and code we describe are the first ones
designed for this task. The program and its full documentation are available on
the Web at http://www.cita.utoronto.ca/~jmartin/BRANECODE/. In this paper we
provide a brief overview of what the program does and how to use it.Comment: 5 pages, 2 figure
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