577 research outputs found
Nonequilibrium Precursor Model for the Onset of Percolation in a Two-Phase System
Using a Boltzmann equation, we investigate the nonequilibrium dynamics of
nonperturbative fluctuations within the context of Ginzburg-Landau models. As
an illustration, we examine how a two-phase system initially prepared in a
homogeneous, low-temperature phase becomes populated by precursors of the
opposite phase as the temperature is increased. We compute the critical value
of the order parameter for the onset of percolation, which signals the
breakdown of the conventional dilute gas approximation.Comment: 4 pages, 4 eps figures (uses epsf), Revtex. Replaced with version in
press Physical Review
Gravitational instability of the inner static region of a Reissner-Nordstrom black hole
Reissner--Nordstr\"om black holes have two static regions:
r > \ro and 0 < r < \ri, where \ri and \ro are the inner and outer
horizon radii. The stability of the exterior static region has been established
long time ago. In this work we prove that the interior static region is
unstable under linear gravitational perturbations, by showing that field
perturbations compactly supported within this region will generically excite a
mode that grows exponentially in time. This result gives an alternative reason
to mass inflation to consider the space time extension beyond the Cauchy
horizon as physically irrelevant, and thus provides support to the strong
cosmic censorship conjecture, which is also backed by recent evidence of a
linear gravitational instability in the interior region of Kerr black holes
found by the authors. The use of intertwiners to solve for the evolution of
initial data plays a key role, and adapts without change to the case of
super-extremal \rn black holes, allowing to complete the proof of the linear
instability of this naked singularity. A particular intertwiner is found such
that the intertwined Zerilli field has a geometrical meaning -it is the first
order variation of a particular Riemann tensor invariant-. Using this,
calculations can be carried out explicitely for every harmonic number.Comment: 24 pages, 4 figures. Changes and corrections in proof using
intertwiners, also in figure
Astrophysical limits on quantum gravity motivated birefringence
We obtain observational upper bounds on a class of quantum gravity related
birefringence effects, by analyzing the presence of linear polarization in the
optical and ultraviolet spectrum of some distant sources. In the notation of
Gambini and Pullin we find .Comment: 4 pages, submitted to Phys. Rev. Let
The collision of boosted black holes: second order close limit calculations
We study the head-on collision of black holes starting from unsymmetrized,
Brill--Lindquist type data for black holes with non-vanishing initial linear
momentum. Evolution of the initial data is carried out with the ``close limit
approximation,'' in which small initial separation and momentum are assumed,
and second-order perturbation theory is used. We find agreement that is
remarkably good, and that in some ways improves with increasing momentum. This
work extends a previous study in which second order perturbation calculations
were used for momentarily stationary initial data, and another study in which
linearized perturbation theory was used for initially moving holes. In addition
to supplying answers about the collisions, the present work has revealed
several subtle points about the use of higher order perturbation theory, points
that did not arise in the previous studies. These points include issues of
normalization, and of comparison with numerical simulations, and will be
important to subsequent applications of approximation methods for collisions.Comment: 20 pages, RevTeX, 6 figures included with psfi
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