24,171 research outputs found
The time evolution of marginally trapped surfaces
In previous work we have shown the existence of a dynamical horizon or
marginally trapped tube (MOTT) containing a given strictly stable marginally
outer trapped surface (MOTS). In this paper we show some results on the global
behavior of MOTTs assuming the null energy condition. In particular we show
that MOTSs persist in the sense that every Cauchy surface in the future of a
given Cauchy surface containing a MOTS also must contain a MOTS. We describe a
situation where the evolving outermost MOTS must jump during the coalescence of
two seperate MOTSs. We furthermore characterize the behavior of MOTSs in the
case that the principal eigenvalue vanishes under a genericity assumption. This
leads to a regularity result for the tube of outermost MOTSs under the
genericity assumption. This tube is then smooth up to finitely many jump times.
Finally we discuss the relation of MOTSs to singularities of a space-time.Comment: 21 pages. This revision corrects some typos and contains more
detailed proofs than the original versio
Bouncing Palatini cosmologies and their perturbations
Nonsingular cosmologies are investigated in the framework of f(R) gravity
within the first order formalism. General conditions for bounces in isotropic
and homogeneous cosmology are presented. It is shown that only a quadratic
curvature correction is needed to predict a bounce in a flat or to describe
cyclic evolution in a curved dust-filled universe. Formalism for perturbations
in these models is set up. In the simplest cases, the perturbations diverge at
the turnover. Conditions to obtain smooth evolution are derived.Comment: 7 pages, 1 figure. v2: added references
Blowup of Jang's equation at outermost marginally trapped surfaces
The aim of this paper is to collect some facts about the blowup of Jang's
equation. First, we discuss how to construct solutions that blow up at an
outermost MOTS. Second, we exclude the possibility that there are extra blowup
surfaces in data sets with non-positive mean curvature. Then we investigate the
rate of convergence of the blowup to a cylinder near a strictly stable MOTS and
show exponential convergence near a strictly stable MOTS.Comment: 15 pages. This revision corrects some typo
The nonlinear development of the relativistic two-stream instability
The two-stream instability has been mooted as an explanation for a range of
astrophysical applications from GRBs and pulsar glitches to cosmology. Using
the first nonlinear numerical simulations of relativistic multi-species
hydrodynamics we show that the onset and initial growth of the instability is
very well described by linear perturbation theory. In the later stages the
linear and nonlinear description match only qualitatively, and the instability
does not saturate even in the nonlinear case by purely ideal hydrodynamic
effects.Comment: 15 pages, 9 figure
A Strong Maximum Principle for Weak Solutions of Quasi-Linear Elliptic Equations with Applications to Lorentzian and Riemannian Geometry
The strong maximum principle is proved to hold for weak (in the sense of
support functions) sub- and super-solutions to a class of quasi-linear elliptic
equations that includes the mean curvature equation for spacelike
hypersurfaces in a Lorentzian manifold. As one application a Lorentzian warped
product splitting theorem is given.Comment: 37 pages, 1 figure, ams-latex using eepi
String Effects on Fermi--Dirac Correlation Measurements
We investigate some recent measurements of Fermi--Dirac correlations by the
LEP collaborations indicating surprisingly small source radii for the
production of baryons in -annihilation at the peak. In the
hadronization models there are besides the Fermi--Dirac correlation effect also
a strong dynamical (anti-)correlation. We demonstrate that the extraction of
the pure FD effect is highly dependent on a realistic Monte Carlo event
generator, both for separation of those dynamical correlations which are not
related to Fermi--Dirac statistics, and for corrections of the data and
background subtractions. Although the model can be tuned to well reproduce
single particle distributions, there are large model-uncertainties when it
comes to correlations between identical baryons. We therefore, unfortunately,
have to conclude that it is at present not possible to make any firm conclusion
about the source radii relevant for baryon production at LEP
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