1,158 research outputs found
Continuous phase transition in polydisperse hard-sphere mixture
In a previous paper (J. Zhang {\it et al.}, J. Chem. Phys. {\bf 110}, 5318
(1999)) we introduced a model for polydisperse hard sphere mixtures that is
able to adjust its particle-size distribution. Here we give the explanation of
the questions that arose in the previous description and present a consistent
theory of the phase transition in this system, based on the Percus-Yevick
equation of state. The transition is continuous, and like Bose-Einstein
condensation a macroscopic aggregate is formed due to the microscopic
interactions. A BMCSL-like treatment leads to the same conclusion with slightly
more accurate predictions.Comment: 7 pages including 5 figures in revte
Dirac Quasinormal modes of Schwarzschild black hole
The quasinormal modes (QNMs) associated with the decay of Dirac field
perturbation around a Schwarzschild black hole is investigated by using
continued fraction and Hill-determinant approaches. It is shown that the
fundamental quasinormal frequencies become evenly spaced for large angular
quantum number and the spacing is given by . The angular quantum number has the
surprising effect of increasing real part of the quasinormal frequencies, but
it almost does not affect imaginary part, especially for low overtones. In
addition, the quasinormal frequencies also become evenly spaced for large
overtone number and the spacing for imaginary part is
which is same as that of the
scalar, electromagnetic, and gravitational perturbations.Comment: 14 pages, 5 figure
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
On the Maximum Mass of Differentially Rotating Neutron Stars
We construct relativistic equilibrium models of differentially rotating
neutron stars and show that they can support significantly more mass than their
nonrotating or uniformly rotating counterparts. We dynamically evolve such
``hypermassive'' models in full general relativity and show that there do exist
configurations which are dynamically stable against radial collapse and bar
formation. Our results suggest that the remnant of binary neutron star
coalescence may be temporarily stabilized by differential rotation, leading to
delayed collapse and a delayed gravitational wave burst.Comment: 4 pages, 2 figures, uses emulateapj.sty; to appear in ApJ Letter
Quasinormal Ringing for Acoustic Black Holes at Low Temperature
We investigate a condensed matter ``black hole'' analogue, taking the
Gross-Pitaevskii (GP) equation as a starting point. The linearized GP equation
corresponds to a wave equation on a black hole background, giving quasinormal
modes under some appropriate conditions. We suggest that we can know the
detailed characters and corresponding geometrical information about the
acoustic black hole by observing quasinormal ringdown waves in the low
temperature condensed matters.Comment: 9 pages, 3 figures, PRD accepted versio
Possible direct method to determine the radius of a star from the spectrum of gravitational wave signals
We computed the spectrum of gravitational waves from a dust disk star of
radius R inspiraling into a Kerr black hole of mass M and specific angular
momentum a. We found that when R is much larger than the wave length of the
quasinormal mode, the spectrum has several peaks and the separation of peaks
is proportional to irrespective of M and a. This
suggests that the radius of the star in coalescing binary black hole - star
systems may be determined directly from the observed spectrum of gravitational
wave. This also suggests that the spectrum of the radiation may give us
important information in gravitational wave astronomy as in optical astronomy.Comment: 4 pages with 3 eps figures, revtex.sty, accepted for publication in
Phys. Rev. Let
Quasinormal ringing of Kerr black holes: The excitation factors
Distorted black holes radiate gravitational waves. In the so-called ringdown
phase radiation is emitted in a discrete set of complex quasinormal
frequencies, whose values depend only on the black hole's mass and angular
momentum. Ringdown radiation could be detectable with large signal-to-noise
ratio by the Laser Interferometer Space Antenna LISA. If more than one mode is
detected, tests of the black hole nature of the source become possible. The
detectability of different modes depends on their relative excitation, which in
turn depends on the cause of the perturbation (i.e. on the initial data). A
``universal'', initial data-independent measure of the relative mode excitation
is encoded in the poles of the Green's function that propagates small
perturbations of the geometry (``excitation factors''). We compute for the
first time the excitation factors for general-spin perturbations of Kerr black
holes. We find that for corotating modes with the excitation factors tend
to zero in the extremal limit, and that the contribution of the overtones
should be more significant when the black hole is fast rotating. We also
present the first analytical calculation of the large-damping asymptotics of
the excitation factors for static black holes, including the Schwarzschild and
Reissner-Nordstrom metrics. This is an important step to determine the
convergence properties of the quasinormal mode expansion.Comment: 33 pages, 9 figures, 7 tables, RevTeX4. v2: Two new figures and minor
changes in the presentation. Matches version in press in Phys. Rev.
Asymptotic power-law tails of massive scalar fields in Reissner-Nordstr\"{o}m background
We investigate dominant late-time tail behaviors of massive scalar fields in
nearly extreme Reissner-Nordstr\"{o}m background. It is shown that the
oscillatory tail of the scalar fields has the decay rate of at
asymptotically late times. The physical mechanism by which the asymptotic
tail yields and the relation between the field mass and the time
scale when the tail begins to dominate, are discussed in terms of resonance
backscattering due to spacetime curvature.Comment: 18 pages, 1 figure, accepted for publication in Physical Review
Asymptotic tails of massive scalar fields in a stationary axisymmetric EMDA black hole geometry
The late-time tail behavior of massive scalar fields is studied analytically
in a stationary axisymmetric EMDA black hole geometry. It is shown that the
asymptotic behavior of massive perturbations is dominated by the oscillatory
inverse power-law decaying tail at the intermediate
late times, and by the asymptotic tail at asymptotically
late times. Our result seems to suggest that the intermediate tails and the asymptotically tails
may be quite general features for evolution of massive scalar fields in any
four dimensional asymptotically flat rotating black hole backgrounds.Comment: 6 page
Superradiant instabilities of rotating black branes and strings
Black branes and strings are generally unstable against a certain sector of
gravitational perturbations. This is known as the Gregory-Laflamme instability.
It has been recently argued that there exists another general instability
affecting many rotating extended black objects. This instability is in a sense
universal, in that it is triggered by any massless field, and not just
gravitational perturbations. Here we investigate this novel mechanism in
detail. For this instability to work, two ingredients are necessary: (i) an
ergo-region, which gives rise to superradiant amplification of waves, and (ii)
``bound'' states in the effective potential governing the evolution of the
particular mode under study. We show that the black brane Kerr_4 x R^p is
unstable against this mechanism, and we present numerical results for
instability timescales for this case. On the other hand, and quite
surprisingly, black branes of the form Kerr_d x R^p are all stable against this
mechanism for d>4. This is quite an unexpected result, and it stems from the
fact that there are no stable circular orbits in higher dimensional black hole
spacetimes, or in a wave picture, that there are no bound states in the
effective potential. We also show that it is quite easy to simulate this
instability in the laboratory with acoustic black branes.Comment: 19 pages, 10 figures. v2: Enlarged discussion on the necessary
conditions for the existence of instabilit
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