42 research outputs found
Critical behavior in vacuum gravitational collapse in 4+1 dimensions
We show that the 4+1 dimensional vacuum Einstein equations admit
gravitational waves with radial symmetry. The dynamical degrees of freedom
correspond to deformations of the three-sphere orthogonal to the plane.
Gravitational collapse of such waves is studied numerically and shown to
exhibit discretely self-similar Type II critical behavior at the threshold of
black hole formation.Comment: 4 pages, 7 figure
Codimension-two critical behavior in vacuum gravitational collapse
We consider the critical behavior at the threshold of black hole formation
for the five dimensional vacuum Einstein equations satisfying the
cohomogeneity-two triaxial Bianchi IX ansatz. Exploiting a discrete symmetry
present in this model we predict the existence of a codimension-two attractor.
This prediction is confirmed numerically and the codimension-two attractor is
identified as a discretely self-similar solution with two unstable modes.Comment: 4 pages, 5 figures, typos correcte
Anomalously small wave tails in higher dimensions
We consider the late-time tails of spherical waves propagating on
even-dimensional Minkowski spacetime under the influence of a long range radial
potential. We show that in six and higher even dimensions there exist
exceptional potentials for which the tail has an anomalously small amplitude
and fast decay. Along the way we clarify and amend some confounding arguments
and statements in the literature of the subject.Comment: 13 page
On vacuum gravitational collapse in nine dimensions
We consider the vacuum gravitational collapse for cohomogeneity-two solutions
of the nine dimensional Einstein equations. Using combined numerical and
analytical methods we give evidence that within this model the
Schwarzschild-Tangherlini black hole is asymptotically stable. In addition, we
briefly discuss the critical behavior at the threshold of black hole formation.Comment: 4 pages, 4 figure
Formation of singularities for equivariant 2+1 dimensional wave maps into the two-sphere
In this paper we report on numerical studies of the Cauchy problem for
equivariant wave maps from 2+1 dimensional Minkowski spacetime into the
two-sphere. Our results provide strong evidence for the conjecture that large
energy initial data develop singularities in finite time and that singularity
formation has the universal form of adiabatic shrinking of the degree-one
harmonic map from into .Comment: 14 pages, 5 figures, final version to be published in Nonlinearit
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
Photon emission from bare quark stars
We investigate the photon emission from the electrosphere of a quark star. It
is shown that at temperatures T\sim 0.1-1 MeV the dominating mechanism is the
bremsstrahlung due to bending of electron trajectories in the mean Coulomb
field of the electrosphere. The radiated energy for this mechanism is much
larger than that for the Bethe-Heitler bremsstrahlung. The energy flux from the
mean field bremsstrahlung exceeds the one from the tunnel e^{+}e^{-} pair
creation as well. We demonstrate that the LPM suppression of the photon
emission is negligible.Comment: 35 pages, 5 figure
Two classes of nonlocal Evolution Equations related by a shared Traveling Wave Problem
We consider reaction-diffusion equations and Korteweg-de Vries-Burgers (KdVB)
equations, i.e. scalar conservation laws with diffusive-dispersive
regularization. We review the existence of traveling wave solutions for these
two classes of evolution equations. For classical equations the traveling wave
problem (TWP) for a local KdVB equation can be identified with the TWP for a
reaction-diffusion equation. In this article we study this relationship for
these two classes of evolution equations with nonlocal diffusion/dispersion.
This connection is especially useful, if the TW equation is not studied
directly, but the existence of a TWS is proven using one of the evolution
equations instead. Finally, we present three models from fluid dynamics and
discuss the TWP via its link to associated reaction-diffusion equations
Strange Star Heating Events as a Model for Giant Flares of Soft Gamma-ray Repeaters
Two giant flares were observed on 5 March 1979 and 27 August 1998 from the
soft gamma-ray repeaters SGR 0526-66 and SGR 1900+14, respectively. The
striking similarity between these remarkable bursts strongly implies a common
nature. We show that the light curves of the giant bursts may be easily
explained in the model where the burst radiation is produced by the bare quark
surface of a strange star heated, for example, by impact of a massive
comet-like object.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Letter