573 research outputs found
Gravitational Collapse in One Dimension
We simulate the evolution of one-dimensional gravitating collisionless
systems from non- equilibrium initial conditions, similar to the conditions
that lead to the formation of dark- matter halos in three dimensions. As in the
case of 3D halo formation we find that initially cold, nearly homogeneous
particle distributions collapse to approach a final equilibrium state with a
universal density profile. At small radii, this attractor exhibits a power-law
behavior in density, {\rho}(x) \propto |x|^(-{\gamma}_crit), {\gamma}_crit
\simeq 0.47, slightly but significantly shallower than the value {\gamma} = 1/2
suggested previously. This state develops from the initial conditions through a
process of phase mixing and violent relaxation. This process preserves the
energy ranks of particles. By warming the initial conditions, we illustrate a
cross-over from this power-law final state to a final state containing a
homogeneous core. We further show that inhomogeneous but cold power-law initial
conditions, with initial exponent {\gamma}_i > {\gamma}_crit, do not evolve
toward the attractor but reach a final state that retains their original
power-law behavior in the interior of the profile, indicating a bifurcation in
the final state as a function of the initial exponent. Our results rely on a
high-fidelity event-driven simulation technique.Comment: 14 Pages, 13 Figures. Submitted to MNRA
Sparticle Spectrum and Dark Matter in M-Theory
The phenomenological implications of the eleven dimensional limit of
-theory (strongly coupled ) are investigated. In particular
we calculate the supersymmetric spectrum subject to constraints of correct
electroweak symmetry breaking and the requirement that the lighest
supersymmetric particle provides the dark matter of the universe. The -soft
term associated with the generation of a term in the superpotential is
calculated and its phenomenology is discussed.Comment: LaTeX file 15 pages,1 figure adde
Elastic Waves Scattering from Corrugated Metal Interfaces
This is a study of elastic waves diffracted by corrugated metallic surfaces. The corrugations consist of triangular grooves with variable parameters. The results of the narrow band experiments show significant diffraction patterns depending on angle and frequency. In addition, a continuous schlieren system is used to visualize the diffracted orders. Measurements were also carried out using a broadband pulse echo system. The behavior of the received spectra is characteristic of the surface profile. Both front and back surfaces have been investigated
Nonexistence theorems for traversable wormholes
Gauss-Bonnet formula is used to derive a new and simple theorem of
nonexistence of vacuum static nonsingular lorentzian wormholes. We also derive
simple proofs for the nonexistence of lorentzian wormhole solutions for some
classes of static matter such as, for instance, real scalar fields with a
generic potential obeying and massless fermions fields
Prompt Beta Spectroscopy as a Diagnostic for Mix in Ignited NIF Capsules
The National Ignition Facility (NIF) technology is designed to drive
deuterium-tritium (DT) internal confinement fusion (ICF) targets to ignition
using indirect radiation from laser beam energy captured in a hohlraum.
Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix
between the DT fue l and the ablator shell material are of fundamental physical
interest and can affect the performance characteristics of the capsule. In this
Letter we describe new radiochemical diagnostics for mix processes in ICF
capsules with plastic or Be (0.9%Cu) ablator shells. Reactions of high-energy
tritons with shell material produce high-energy -emitters.
We show that mix between the DT fuel and the shell material enhances
high-energy prompt beta emission from these reactions by more than an order of
magnitude over that expected in the absence of mix
Detecting an Invisibly Decaying Higgs Boson at a Hadron Supercollider
We demonstrate that an invisibly decaying Higgs boson with Standard Model
coupling strength to top--anti-top can be detected at the LHC for masses up to
about 250 GeV.Comment: 7 pages, requires phyzzx.tex and tables.tex, revised to convert
results from SSC to LHC and include additional top quark mass cases, full
postscript file including embedded figure available via anonymous ftp at
ucdhep.ucdavis.edu as [anonymous.gunion]hinvisible_revised.ps, preprint
UCD-93-2
Using the acoustic peak to measure cosmological parameters
Recent measurements of the cosmic microwave background radiation by the
Boomerang experiment indicate that the universe is spatially flat. Here some
simple back-of-the-envelope calculations are used to explain their result. The
main result is a simple formula for the angular scale of the acoustic peak in
terms of the standard cosmological parameters:
l=193*[1+3(1-Omega_0)/5+(1-h)/5+Omega_Lambda/35].Comment: 4 pages, 1 figure, Explanations have been clarifie
The Inflationary Perturbation Spectrum
Motivated by the prospect of testing inflation from precision cosmic
microwave background observations, we present analytic results for scalar and
tensor perturbations in single-field inflation models based on the application
of uniform approximations. This technique is systematically improvable,
possesses controlled error bounds, and does not rely on assuming the slow-roll
parameters to be constant. We provide closed-form expressions for the power
spectra and the corresponding scalar and tensor spectral indices.Comment: 4 pages, 1 figur
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