107 research outputs found
Non-linear Dynamics and Primordial Curvature Perturbations from Preheating
In this paper I review the theory and numerical simulations of non-linear
dynamics of preheating, a stage of dynamical instability at the end of
inflation during which homogeneous inflaton explosively decays and deposits its
energy into excitation of other matter fields. I focus on preheating in chaotic
inflation models, which proceeds via broad parametric resonance. I describe a
simple method to evaluate Floquet exponents, calculating stability diagrams of
Mathieu and Lame equations describing development of instability in
and preheating models. I discuss basic numerical methods and
issues, and present simulation results highlighting non-equilibrium
transitions, topological defect formation, late-time universality, turbulent
scaling and approach to thermalization. I explain how preheating can generate
large-scale primordial (non-Gaussian) curvature fluctuations manifest in cosmic
microwave background anisotropy and large scale structure, and discuss
potentially observable signatures of preheating.Comment: 15 pages, 10 figures; review for CQG special issu
A GPU-accelerated viewer for HEALPix maps
HEALPix by G\'orski et. al. (2005) is de-facto standard for Cosmic Microwave
Background (CMB) data storage and analysis, and is widely used in current and
upcoming CMB experiments. Almost all the datasets in Legacy Archive for
Microwave Background Data Analysis (LAMBDA) use HEALPix as a format of choice.
Visualizing the data plays important role in research, and several toolsets
were developed to do that with HEALPix maps, most notably original Fortran
facilities and Python integration with healpy.
With the current state of GPU performance, it is now possible to visualize
extremely large maps in real time on a laptop or a tablet. HEALPix Viewer
described here is developed for macOS, and takes full advantage of GPU
acceleration to handle extremely large datasets in real time. It compiles
natively on Intel and Arm64 architectures, and uses Metal framework for
high-performance GPU computations. The aim of this project is to reduce the
effort required for interactive data exploration, as well as time overhead for
producing publication-quality maps. Drag and drop integration with Keynote and
Powerpoint makes creating presentations easy.
The main codebase is written in Swift, a modern and efficient compiled
language, with high-performance computing parts delegated entirely to GPU, and
a few inserts in C interfacing to cfitsio library for I/O. Graphical user
interface is written in SwiftUI, a new declarative UI framework based on Swift.
Most common spherical projections and colormaps are supported out of the box,
and the available source code makes it easy to customize the application and to
add new features if desired.Comment: 10 pages; 7 figure
Is It Really Naked? On Cosmic Censorship in String Theory
We investigate the possibility of cosmic censorship violation in string
theory using a characteristic double-null code, which penetrates horizons and
is capable of resolving the spacetime all the way to the singularity. We
perform high-resolution numerical simulations of the evolution of negative mass
initial scalar field profiles, which were argued to provide a counterexample to
cosmic censorship conjecture for AdS-asymptotic spacetimes in five-dimensional
supergravity. In no instances formation of naked singularity is seen. Instead,
numerical evidence indicates that black holes form in the collapse. Our results
are consistent with earlier numerical studies, and explicitly show where the
`no black hole' argument breaks.Comment: 8 pages, 5 figures, 1 table; REVTeX 4.
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