6,357 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
Second constant of motion for two-dimensional positronium in a magnetic field
Recent numerical work indicates that the classical motion of positronium in a
constant magnetic field does not exhibit chaotic behavior if the system is
confined to two dimensions. One would therefore expect this system to possess a
second constant of the motion in addition to the total energy. In this paper we
construct a generalization of the Laplace-Runge-Lenz vector and show that a
component of this vector is a constant of the motion.Comment: 4 pages, no figure
MECHANISMS OF PERSISTENT AND MASKED INFECTIONS IN TISSUE CULTURE
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75709/1/j.1749-6632.1957.tb46062.x.pd
Astrophysical neutrinos flavored with Beyond the Standard Model physics
We systematically study the allowed parameter space for the flavor
composition of astrophysical neutrinos measured at Earth, including beyond the
Standard Model theories at production, during propagation, and at detection.
One motivation is to illustrate the discrimination power of the next-generation
neutrino telescopes such as IceCube-Gen2. We identify several examples that
lead to potential deviations from the standard neutrino mixing expectation such
as significant sterile neutrino production at the source, effective operators
modifying the neutrino propagation at high energies, dark matter interactions
in neutrino propagation, or non-standard interactions in Earth matter.
IceCube-Gen2 can exclude about 90% of the allowed parameter space in these
cases, and hence will allow to efficiently test and discriminate models. More
detailed information can be obtained from additional observables such as the
energy-dependence of the effect, fraction of electron antineutrinos at the
Glashow resonance, or number of tau neutrino events.Comment: 21 pages, 9 figures, 3 tables, v2: references added, typos corrected,
conclusion unchanged, matches final version in PR
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